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Using a data sample of (1.0087±0.0044)×1010 J/ψ decay events collected with the BESIII detector at the center-of-mass energy of s√=3.097 GeV, we present a search for the hyperon semileptonic decay Ξ0→Σ−e+νe which violates the ΔS=ΔQ rule. No significant signal is observed, and the upper limit on the branching fraction B(Ξ0→Σ−e+νe) is determined to be 1.6×10−4 at the 90% confidence level. This result improves the previous upper limit result by about one order of magnitude.
Using a data sample of (1.0087±0.0044)×1010 J/ψ decay events collected with the BESIII detector at the center-of-mass energy of s√=3.097 GeV, we present a search for the hyperon semileptonic decay Ξ0→Σ−e+νe which violates the ΔS=ΔQ rule. No significant signal is observed, and the upper limit on the branching fraction B(Ξ0→Σ−e+νe) is determined to be 1.6×10−4 at the 90% confidence level. This result improves the previous upper limit result by about one order of magnitude.
A search for a massless dark photon 𝛾′ is conducted using 4.5 fb−1 of 𝑒+𝑒− collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. No significant signal is observed, and the upper limit on the branching fraction ℬ(Λ+𝑐→𝑝𝛾′) is determined to be 8.0×10−5 at 90% confidence level.
A search for a massless dark photon γ′ is conducted using 4.5 fb−1 of e+e− collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. No significant signal is observed, and the upper limit on the branching fraction B(Λ+c→pγ′) is determined to be 8.0×10−5 at 90% confidence level.
A search for a massless dark photon γ′ is conducted using 4.5 fb−1 of e+e− collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. No significant signal is observed, and the upper limit on the branching fraction B(Λ+c→pγ′) is determined to be 8.0×10−5 at 90% confidence level.
Measurement of the absolute branching fraction of the singly Cabibbo suppressed decay Λc⁺ → pη′
(2022)
The singly Cabibbo suppressed decay Λ+𝑐→𝑝𝜂′ is measured using 4.5 fb−1 of 𝑒+𝑒− collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. Evidence for Λ+𝑐→𝑝𝜂′ with a statistical significance of 3.6𝜎 is reported with a double-tag approach. The Λ+𝑐→𝑝𝜂′ absolute branching fraction is determined to be (5.62+2.46−2.04±0.26)×10−4, where the first and second uncertainties are statistical and systematic, respectively. Our result is consistent with the branching fraction obtained by the Belle collaboration within the uncertainty of 1𝜎.
Measurement of the absolute branching fraction of the singly Cabibbo suppressed decay Λc⁺ → pη′
(2022)
The singly Cabibbo suppressed decay Λ+c→pη′ is measured using 4.5 fb−1 of e+e− collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. Evidence for Λ+c→pη′ with a statistical significance of 3.6σ is reported with a double-tag approach. The Λ+c→pη′ absolute branching fraction is determined to be (5.62+2.46−2.04±0.26)×10−4, where the first and second uncertainties are statistical and systematic, respectively. Our result is consistent with the branching fraction obtained by the Belle collaboration within the uncertainty of 1σ.
Measurement of the absolute branching fraction of the singly Cabibbo suppressed decay Λc⁺ → pη′
(2022)
The singly Cabibbo suppressed decay Λ+c→pη′ is measured using 4.5 fb−1 of e+e− collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. Evidence for Λ+c→pη′ with a statistical significance of 3.6σ is reported with a double-tag approach. The Λ+c→pη′ absolute branching fraction is determined to be (5.62+2.46−2.04±0.26)×10−4, where the first and second uncertainties are statistical and systematic, respectively. Our result is consistent with the branching fraction obtained by the Belle collaboration within the uncertainty of 1σ.
Using data samples with an integrated luminosity of 6.4~fb−1 collected by the BESIII detector operating at the BEPCII storage ring, the process of e+e−→γϕJ/ψ is studied. The processes of e+e−→ϕχc1,c2, χc1,c2→γJ/ψ are observed with a significance of more than 10σ. The s√-dependent cross section of e+e−→ϕχc1,c2 is measured between 4.600 and 4.951~GeV, and evidence of a resonance structure is found for the first time in the ϕχc2 process. We also search for the processes of e+e−→γX(4140), γX(4274) and γX(4500) via the γϕJ/ψ final state, but no obvious structures are found. The upper limits on the production cross section times the branching fraction for these processes at the 90% confidence level are reported.
Using a data sample corresponding to an integrated luminosity of 11.3 fb−1 collected at center-of-mass energies from 4.23 to 4.70 GeV with the BESIII detector, we observe the process e+e− → π0π0ψ2(3823) for the first time with a statistical significance of 6.0 standard deviations. The ratio of average cross sections for e+e− → π0π0ψ2(3823) and π+π−ψ2(3823) is determined to be R = σ[e+e− → π0π0ψ2(3823)] σ[e+e−→π+π−ψ2(3823)] = 0.57 ± 0.14 ± 0.05, which is consistent with expectations from isospin symmetry. Here and below, the first uncertainties are statistical and the second are systematic. The mass of the ψ2(3823) is measured to be M[ψ2(3823)] = 3824.5±2.4±1.0 MeV/c2. Due to the limited data sample, an upper limit of 18.8 MeV at 90% confidence level is set on the intrinsic width of ψ2(3823).
Using (448.1 ± 2.9) × 106 ψ(3686) events collected with the BESIII detector at the BEPCII collider, the decay ψ(3686) → Σ⁻Σ‾⁺ is observed for the first time with a branching fraction of (2.82 ± 0.04stat. ± 0.08syst.) × 10−4, and the angular parameter αΣ− is measured to be 0.96 ± 0.09stat. ± 0.03syst..
Using a data set of electron-positron collisions corresponding to an integrated luminosity of 2.93 fb−1 taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, a search for the baryon (B) and lepton (L) number violating decays D±→n(n¯)e± is performed. No signal is observed and the upper limits on the branching fractions at the 90% confidence level are set to be 1.43×10−5 for the decays D+(−)→n¯(n)e+(−) with Δ|B−L|=0, and 2.91×10−5 for the decays D+(−)→n(n¯)e+(−) with Δ|B−L|=2 , where Δ|B−L| denotes the change in the difference between baryon and lepton numbers.
Using 15.6 fb−1 of e+e− collision data collected at twenty-four center-of-mass energies from 4.0 to 4.6 GeV with the BESIII detector, the helicity amplitudes of the process e+e− → π+π−ω are analyzed for the first time. Born cross section measurements of two-body intermediate resonance states with statistical significance greater than 5σ are presented, such as f0(500), f0(980), f2(1270), f0(1370), b1(1235)±, and ρ(1450)±. In addition, evidence of a resonance state in e+e− → π+π−ω production is found. The mass of this state obtained by line shape fitting is about 4.2 GeV/c2, which is consistent with the production of ψ(4160) or Y(4220).
Using a data set of electron-positron collisions corresponding to an integrated luminosity of 2.93 fb−1 taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, a search for the baryon (B) and lepton (L) number violating decays D±→n(n¯)e± is performed. No signal is observed and the upper limits on the branching fractions at the 90% confidence level are set to be 1.43×10−5 for the decays D+(−)→n¯(n)e+(−) with Δ|B−L|=0, and 2.91×10−5 for the decays D+(−)→n(n¯)e+(−) with Δ|B−L|=2 , where Δ|B−L| denotes the change in the difference between baryon and lepton numbers.
Using a sample of 4.3×105 η′→ηπ0π0 events selected from the ten billion J/ψ event dataset collected with the BESIII detector, we study the decay η′→ηπ0π0 within the framework of nonrelativistic effective field theory. Evidence for a structure at π+π− mass threshold is observed in the invariant mass spectrum of π0π0 with a statistical significance of around 3.5σ, which is consistent with the cusp effect as predicted by the nonrelativistic effective field theory. After introducing the amplitude for describing the cusp effect, the ππ scattering length combination a0−a2 is determined to be 0.226±0.060stat±0.013syst, which is in good agreement with theoretical calculation of 0.2644±0.0051.
Using a sample of 4.3×105 η′→ηπ0π0 events selected from the ten billion J/ψ event dataset collected with the BESIII detector, we study the decay η′→ηπ0π0 within the framework of nonrelativistic effective field theory. Evidence for a structure at π+π− mass threshold is observed in the invariant mass spectrum of π0π0 with a statistical significance of around 3.5σ, which is consistent with the cusp effect as predicted by the nonrelativistic effective field theory. After introducing the amplitude for describing the cusp effect, the ππ scattering length combination a0−a2 is determined to be 0.226±0.060stat±0.013syst, which is in good agreement with theoretical calculation of 0.2644±0.0051.
Using a sample of 4.3×105 η′→ηπ0π0 events selected from the 10 billion J/ψ event data set collected with the BESIII detector, we study the decay η′→ηπ0π0 within the framework of non-relativistic effective field theory. Evidence for a structure at π+π− mass threshold is observed in the invariant mass spectrum of π0π0 with a statistical significance of around 3.5σ, which is consistent with the cusp effect as predicted by the non-relativistic effective field theory. After introducing the amplitude for describing the cusp effect, the ππ scattering length combination a0−a2 is determined to be 0.226±0.060stat.±0.012syst., which is in good agreement with theoretical calculation of 0.2644±0.0051.
Based on e+e− collision samples corresponding to an integrated luminosity of 4.4 fb−1 collected with the BESIII detector at center-of-mass energies between 4.6GeV and 4.7GeV, a partial wave analysis of the charmed baryon hadronic decay Λ+c→Λπ+π0 is performed, and the decays Λ+c→Λρ(770)+ and Λ+c→Σ(1385)π are studied for the first time. Making use of the world-average branching fraction B(Λ+c→Λπ+π0), their branching fractions are determined to be B(Λ+c→Λρ(770)+)=B(Λ+c→Σ(1385)+π0)=B(Λ+c→Σ(1385)0π+)=(4.06±0.30±0.35±0.23)×10−2,(5.86±0.49±0.52±0.35)×10−3,(6.47±0.59±0.66±0.38)×10−3, where the first uncertainties are statistical, the second are systematic, and the third are from the uncertainties of the branching fractions B(Λ+c→Λπ+π0) and B(Σ(1385)→Λπ). In addition, %according to amplitudes determined from the partial wave analysis, the decay asymmetry parameters are measured to be αΛρ(770)+=−0.763±0.053±0.039, αΣ(1385)+π0=−0.917±0.069±0.046, and αΣ(1385)0π+=−0.789±0.098±0.056.
Using a data set of electron-positron collisions corresponding to an integrated luminosity of 2.93 fb−1 taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, a search for the baryon (B) and lepton (L) number violating decays D±→n(n¯)e± is performed. No signal is observed and the upper limits on the branching fractions at the 90% confidence level are set to be 1.43×10−5 for the decays D+(−)→n¯(n)e+(−) with Δ|B−L|=0, and 2.91×10−5 for the decays D+(−)→n(n¯)e+(−) with Δ|B−L|=2 , where Δ|B−L| denotes the change in the difference between baryon and lepton numbers.
Using 15.6 fb−1 of e+e− collision data collected at twenty-four center-of-mass energies from 4.0 to 4.6 GeV with the BESIII detector, the helicity amplitudes of the process e+e−→π+π−ω are analyzed for the first time. Born cross section measurements of two-body intermediate resonance states with statistical significance greater than 5σ are presented, such as f0(500), f0(980), f2(1270), f0(1370), b1(1235)±, and ρ(1450)±. In addition, evidence of a resonance state in e+e−→π+π−ω production is found. The mass of this state obtained by line shape fitting is about 4.2 GeV/c2, which is consistent with the production of ψ(4160) or Y(4220).
The singly Cabibbo-suppressed decay D+s → K+π+π−π0 is observed by using a data set corresponding to an integrated luminosity of 6.32 fb−1 recorded by the BESIII detector at the centre-of-mass energies between 4.178 and 4.226 GeV. The first amplitude analysis of D+s → K+π+π−π0 reveals the sub-structures in this decay and determines the fractions and relative phases of different intermediate processes. The dominant intermediate process is D+s → K∗0ρ+, with a fit fraction of (40.5 ± 2.8stat. ± 1.5syst.)%. With the detection efficiency based on our amplitude analysis, the absolute branching fraction forD+s → K+π+π−π0 is measured to be (9.75 ± 0.54stat. ± 0.17syst.) × 10−3.
Improved measurement of the branching fractions of the inclusive decays D⁺ → Kₛ⁰X and D⁰ → Kₛ⁰X
(2023)
By analyzing 2.93 fb−1 of e+e− collision data taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, the branching fractions of the inclusive decays D+→K0SX and D0→K0SX are measured to be (32.78±0.13±0.27)% and (20.54±0.12±0.18)%, respectively, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world averages of previous measurements, but with improved precision.
Using data samples collected with the BESIII detector operating at the BEPCII storage ring, the cross section of the inclusive process e+e−→η+X, normalized by the total cross section of e+e−→hadrons, is measured at eight center-of-mass energy points from 2.0000 GeV to 3.6710 GeV. These are the first measurements with momentum dependence in this energy region. Our measurement shows a significant discrepancy from calculations with the existing fragmentation functions. To address this discrepancy, a new QCD analysis is performed at the next-to-next-to-leading order with hadron mass corrections and higher twist effects, which can explain both the established high-energy data and our measurements reasonably well.
Using (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector, we perform the first search for the weak baryonic decay ψ(3686)→Λ+cΣ¯−+c.c.. The analysis procedure is optimized using a blinded method. No significant signal is observed, and the upper limit on the branching fraction (B) of ψ(3686)→Λ+cΣ¯−+c.c. is set to be 1.4×10−5 at the 90\% confidence level.
Using (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector, we perform the first search for the weak baryonic decay ψ(3686)→Λ+cΣ¯−+c.c.. The analysis procedure is optimized using a blinded method. No significant signal is observed, and the upper limit on the branching fraction (B) of ψ(3686)→Λ+cΣ¯−+c.c. is set to be 1.4×10−5 at the 90\% confidence level.
Using (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector, we perform the first search for the weak baryonic decay ψ(3686)→Λ+cΣ¯−+c.c.. The analysis procedure is optimized using a blinded method. No significant signal is observed, and the upper limit on the branching fraction (B) of ψ(3686)→Λ+cΣ¯−+c.c. is set to be 1.4×10−5 at the 90\% confidence level.
Based on 7.33 fb−1 of e+e− collision data taken at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, we measure the branching fraction of D∗+s→D+sπ0 relative to that of D∗+s→D+sγ to be (6.16±0.43±0.19)%. The first uncertainty is statistical and the second one is systematic. By using the world average value of the branching fraction of D∗+s→D+se+e−, we determine the branching fractions of D∗+s→D+sγ and D∗+s→D+sπ0 to be (93.57±0.44±0.19)% and (5.76±0.44±0.19)%, respectively.
Using an 𝑒+𝑒− collision data sample with a total integrated luminosity of 3.19 fb−1 collected with the BESIII detector at a center-of-mass energy of 4.178 GeV, the branching fraction of the inclusive decay of the 𝐷+𝑠 meson to final states including at least three charged pions is measured for the first time to be ℬ(𝐷+𝑠→𝜋+𝜋+𝜋−𝑋)=(32.81±0.35stat±0.63syst)%. In this measurement the charged pions from 𝐾0𝑆 meson decays are excluded. The partial branching fractions of 𝐷+𝑠→𝜋+𝜋+𝜋−𝑋 are also measured as a function of the 𝜋+𝜋+𝜋− invariant mass.
We report a search for a dark photon using 14.9~fb−1 of e+e− annihilation data taken at center-of-mass energies from 4.13 to 4.60~GeV with the BESIII detector operated at the BEPCII storage ring. The dark photon is assumed to be produced in the radiative annihilation process of e+e− and to predominantly decay into light dark matter particles, which escape from the detector undetected. The mass range from 1.5 to 2.9~GeV is scanned for the dark photon candidate, and no significant signal is observed. The mass dependent upper limits at the 90% confidence level on the coupling strength parameter ϵ for a dark photon coupling with an ordinary photon vary between 1.6×10−3 and 5.7×10−3.
Based on a sample of 4.4 fb−1 of e+e− annihilation data collected in the energy region between 4.6 GeV and 4.7 GeV with the BESIII detector at BEPCII, two singly Cabibbo-suppressed decays Λ+c→Σ0K+ and Λ+c→Σ+K0S are studied. The ratio of the branching fraction B(Λ+c→Σ0K+) relative to B(Λ+c→Σ0π+) is measured to be 0.0361±0.0073(stat.)±0.0005(syst.), and the ratio of B(Λ+c→Σ+K0S) relative to B(Λ+c→Σ+π+π−) is measured to be 0.0106±0.0031(stat.)±0.0004(syst.). After taking the world-average branching fractions of the reference decay channels, the branching fractions B(Λ+c→Σ0K+) and B(Λ+c→Σ+K0S) are determined to be (4.7±0.9(stat.)±0.1(syst.)±0.3(ref.))×10−4 and (4.8±1.4(stat.)±0.2(syst.)±0.3(ref.))×10−4, respectively. The branching fraction of the Λ+c→Σ+K0S decay is measured for the first time.
The study of the Cabibbo-favored semileptonic decay Λ+𝑐→Λ𝑒+𝜈𝑒 is reported using a 4.5 fb−1 data sample of 𝑒+𝑒− annihilations collected at center-of-mass energies ranging from 4.600 GeV to 4.699 GeV with the BESIII detector at the BEPCII collider. The branching fraction of the decay is measured to be ℬ(Λ+𝑐→Λ𝑒+𝜈𝑒)=(3.56±0.11stat±0.07syst)%, which is the most precise measurement to date. Furthermore, we perform an investigation of the internal dynamics in Λ+𝑐→Λ𝑒+𝜈𝑒. We provide the first direct comparisons of the differential decay rate and form factors with those predicted from lattice quantum chromodynamics (LQCD) calculations. Combining the measured branching fraction with a 𝑞2-integrated rate predicted by LQCD, we determine 𝑉𝑐𝑠|=0.936±0.017ℬ±0.024LQCD±0.007𝜏Λ𝑐.
Using 4.5 fb−1 of e+e− annihilation data samples collected at the center-of-mass energies ranging from 4.600~GeV to 4.699~GeV with the BESIII detector at the BEPCII collider, a first study of the semileptonic decays Λ+c→pK−e+νe, Λ+c→Λ(1520)e+νe and Λ+c→Λ(1405)e+νe is performed. The Λ+c→pK−e+νe decay is observed with a significance of 8.2σ and the branching fraction is measured to be B(Λ+c→pK−e+νe)=(0.88±0.17stat.±0.07syst.)×10−3. We also report evidence of Λ+c→Λ(1520)e+νe and Λ+c→Λ(1405)e+νe with significances of 3.3σ and 3.2σ, respectively, and measure B(Λ+c→Λ(1520)e+νe)=(1.02±0.52stat.±0.11syst.)×10−3 and B(Λ+c→Λ(1405)[→pK−]e+νe)=(0.42±0.19stat.±0.04syst.)×10−3. Combining these with the inclusive semileptonic Λ+c branching fraction measured by BESIII, the relative fraction is determined to be [B(Λ+c→pK−e+νe)/B(Λ+c→Xe+νe)]=(2.1±0.4stat.±0.2syst.)%, which provides a clear confirmation that semileptonic Λ+c decays are not saturated by the Λℓ+νℓ final state.
The Cabibbo-allowed weak radiative decay Λ+c→Σ+γ has been searched for in a sample of Λ+cΛ¯−c pairs produced in e+e− annihilations, corresponding to an integrated luminosity of 4.5fb−1 collected with the BESIII detector at center-of-mass energies between 4.60 and 4.70 GeV. No excess of signal above background is observed, and we set an upper limit on the branching fraction of this decay to be B(Λ+c→Σ+γ)<4.4×10−4 at a confidence level of 90\%, which is in agreement with Standard Model expectations.
Cross sections for the process e+e−→K0SK0SJ/ψ at center-of-mass energies from 4.128 to 4.950 GeV are measured using data samples with a total integrated luminosity of 21.2 fb−1 collected by the BESIII detector operating at the BEPCII storage ring. The Y(4230) state is observed in the energy dependence of the e+e−→K0SK0SJ/ψ cross section for the first time with a statistical significance of 26.0σ. In addition, an enhancement around 4.710 GeV, called the Y(4710), is seen with a statistical significance of 4.2σ. There is no clear structure around 4.484 GeV. Using a fit with a coherent sum of three Breit-Wigner functions, we determine the mass and width of the Y(4230) state to be 4226.9±6.6±21.9 MeV/c2 and 71.7±16.2±31.4 MeV, respectively, and the mass and width of the Y(4710) state to be 4704.0±52.3±69.5 MeV/c2 and 183.2±114.0±90.8 MeV, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the average Born cross section ratio of e+e−→K0SK0SJ/ψ to e+e−→K+K−J/ψ is measured to be 0.388+0.035−0.028±0.016, or 0.426+0.038−0.031±0.018 if three-body phase space is considered.
The Cabibbo-allowed weak radiative decay Λ+c→Σ+γ has been searched for in a sample of Λ+cΛ¯−c pairs produced in e+e− annihilations, corresponding to an integrated luminosity of 4.5fb−1 collected with the BESIII detector at center-of-mass energies between 4.60 and 4.70 GeV. No excess of signal above background is observed, and we set an upper limit on the branching fraction of this decay to be B(Λ+c→Σ+γ)<4.4×10−4 at a confidence level of 90\%, which is in agreement with Standard Model expectations.
The Cabibbo-allowed weak radiative decay Λ+c→Σ+γ has been searched for in a sample of Λ+cΛ¯−c pairs produced in e+e− annihilations, corresponding to an integrated luminosity of 4.5fb−1 collected with the BESIII detector at center-of-mass energies between 4.60 and 4.70 GeV. No excess of signal above background is observed, and we set an upper limit on the branching fraction of this decay to be B(Λ+c→Σ+γ)<4.4×10−4 at a confidence level of 90\%, which is in agreement with Standard Model expectations.
Cross sections for the process e+e−→K0SK0SJ/ψ at center-of-mass energies from 4.128 to 4.950 GeV are measured using data samples with a total integrated luminosity of 21.2 fb−1 collected by the BESIII detector operating at the BEPCII storage ring. The Y(4230) state is observed in the energy dependence of the e+e−→K0SK0SJ/ψ cross section for the first time with a statistical significance of 26.0σ. In addition, an enhancement around 4.710 GeV, called the Y(4710), is seen with a statistical significance of 4.2σ. There is no clear structure around 4.484 GeV. Using a fit with a coherent sum of three Breit-Wigner functions, we determine the mass and width of the Y(4230) state to be 4226.9±6.6±21.9 MeV/c2 and 71.7±16.2±31.4 MeV, respectively, and the mass and width of the Y(4710) state to be 4704.0±52.3±69.5 MeV/c2 and 183.2±114.0±90.8 MeV, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the average Born cross section ratio of e+e−→K0SK0SJ/ψ to e+e−→K+K−J/ψ is measured to be 0.388+0.035−0.028±0.016, or 0.426+0.038−0.031±0.018 if three-body phase space is considered.
Using 7.33 fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies between 4.128 and 4.226~GeV, we observe for the first time the decay D±s→ωπ±η with a statistical significance of 7.6σ. The measured branching fraction of this decay is (0.54±0.12±0.04)%, where the first uncertainty is statistical and the second is systematic.
We report a measurement of the cross section for the process e+e−→π+π−J/ψ around the X(3872) mass in search for the direct formation of e+e−→X(3872) through the two-photon fusion process. No enhancement of the cross section is observed at the X(3872) peak and an upper limit on the product of electronic width and branching fraction of X(3872)→π+π−J/ψ is determined to be Γee×B(X(3872)→π+π−J/ψ)<7.5×10−3eV at 90% confidence level under an assumption of total width of 1.19±0.21 MeV. This is an improvement of a factor of about 17 compared to the previous limit. Furthermore, using the latest result of B(X(3872)→π+π−J/ψ), an upper limit on the electronic width Γee of X(3872) is obtained to be <0.32eV at the 90% confidence level.
Improved measurement of the branching fractions of the inclusive decays D⁺ → Kₛ⁰X and D⁰ → Kₛ⁰X
(2023)
By analyzing 2.93 fb−1 of 𝑒+𝑒− collision data taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, the branching fractions of the inclusive decays 𝐷+→𝐾0 𝑆𝑋 and 𝐷0→𝐾0 𝑆𝑋 are measured to be (33.11±0.13±0.36)% and (20.75±0.12±0.20)%, respectively, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world averages of previous measurements, but with much improved precision.
Cross sections for the process e+e−→K0SK0SJ/ψ at center-of-mass energies from 4.128 to 4.950 GeV are measured using data samples with a total integrated luminosity of 21.2 fb−1 collected by the BESIII detector operating at the BEPCII storage ring. The Y(4230) state is observed in the energy dependence of the e+e−→K0SK0SJ/ψ cross section for the first time with a statistical significance of 26.0σ. In addition, an enhancement around 4.710 GeV, called the Y(4710), is seen with a statistical significance of 4.2σ. There is no clear structure around 4.484 GeV. Using a fit with a coherent sum of three Breit-Wigner functions, we determine the mass and width of the Y(4230) state to be 4226.9±6.6±21.9 MeV/c2 and 71.7±16.2±31.4 MeV, respectively, and the mass and width of the Y(4710) state to be 4704.0±52.3±69.5 MeV/c2 and 183.2±114.0±90.8 MeV, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the average Born cross section ratio of e+e−→K0SK0SJ/ψ to e+e−→K+K−J/ψ is measured to be 0.388+0.035−0.028±0.016, or 0.426+0.038−0.031±0.018 if three-body phase space is considered.
Using 4.5fb−1 of e+e− annihilation data samples collected at center-of-mass energies ranging from 4.600 to 4.698 GeV with the BESIII detector at the BEPCII collider, we measured the absolute branching fraction for the inclusive semileptonic decay Λ+c→Xe+νe, where X refers to any possible particle system. The branching fraction of the decay is determined to be B(Λ+c→Xe+νe)=(4.06±0.10stat.±0.09syst.)%. Our result improves the precision of previous measurement of B(Λ+c→Xe+νe) by more than threefold. Using the known Λ+c lifetime and the charge-averaged semileptonic decay width of nonstrange charmed mesons, we measure the ratio of inclusive semileptonic decay widths Γ(Λ+c→Xe+νe)/Γ¯(D→Xe+νe)=1.28±0.05, where statistical and systematic uncertainties are combined.
Based on 7.33 fb−1 of e+e− collision data taken at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, we measure the branching fraction of D∗+s→D+sπ0 relative to that of D∗+s→D+sγ to be (6.16±0.43±0.19)%. The first uncertainty is statistical and the second one is systematic. By using the world average value of the branching fraction of D∗+s→D+se+e−, we determine the branching fractions of D∗+s→D+sγ and D∗+s→D+sπ0 to be (93.57±0.44±0.19)% and (5.76±0.44±0.19)%, respectively.
Based on 7.33 fb−1 of e+e− collision data taken at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, we measure the branching fraction of D∗+s→D+sπ0 relative to that of D∗+s→D+sγ to be (6.16±0.43±0.19)%. The first uncertainty is statistical and the second one is systematic. By using the world average value of the branching fraction of D∗+s→D+se+e−, we determine the branching fractions of D∗+s→D+sγ and D∗+s→D+sπ0 to be (93.57±0.44±0.19)% and (5.76±0.44±0.19)%, respectively.
Using a data sample of (1.0087±0.0044)×1010 𝐽/𝜓 decay events collected with the BESIII detector at the center-of-mass energy of √𝑠=3.097 GeV, we present a search for the hyperon semileptonic decay Ξ0→Σ−𝑒+𝜈𝑒 which violates the Δ𝑆=Δ𝑄 rule. No significant signal is observed, and the upper limit on the branching fraction ℬ(Ξ0→Σ−𝑒+𝜈𝑒) is determined to be 1.6×10−4 at the 90% confidence level. This result improves the previous upper limit result by about one order of magnitude.
One individual referable to Calliopiidae G.O. Sars, 1893 was collected from a chemically reduced habitat, the hydrothermal vent systems in Okinawa Trough, and was identified as a new genus and species belonging to this family after a morphological examination. A formal description of this new species and a discussion of the relationship of the new genus within Calliopiidae are presented.
The formation of secondary particles in the atmosphere accounts for more than half of global cloud condensation nuclei. Experiments at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined the importance of ions for new particle formation, but quantifying their effect in the atmosphere remains challenging. By using a novel instrument setup consisting of two nano-particle counters, one of them equipped with an ion filter, we were able to further investigate the ion-related mechanisms of new particle formation. In autumn 2015, we carried out experiments at CLOUD on four systems of different chemical compositions involving monoterpenes, sulfuric acid, nitrogen oxides, and ammonia. We measured the influence of ions on the nucleation rates under precisely controlled and atmospherically relevant conditions. Our results indicate that ions enhance the nucleation process when the charge is necessary to stabilize newly formed clusters, i.e. in conditions where neutral clusters are unstable. For charged clusters that were formed by ion-induced nucleation, we were able to measure, for the first time, their progressive neutralization due to recombination with oppositely charged ions. A large fraction of the clusters carried a charge at 1.2 nm diameter. However, depending on particle growth rates and ion concentrations, charged clusters were largely neutralized by ion–ion recombination before they grew to 2.2 nm. At this size, more than 90 % of particles were neutral. In other words, particles may originate from ion-induced nucleation, although they are neutral upon detection at diameters larger than 2.2 nm. Observations at Hyytiälä, Finland, showed lower ion concentrations and a lower contribution of ion-induced nucleation than measured at CLOUD under similar conditions. Although this can be partly explained by the observation that ion-induced fractions decrease towards lower ion concentrations, further investigations are needed to resolve the origin of the discrepancy.
Nucleation and growth of aerosol particles from atmospheric vapors constitutes a major source of global cloud condensation nuclei (CCN). The fraction of newly formed particles that reaches CCN sizes is highly sensitive to particle growth rates, especially for particle sizes <10 nm, where coagulation losses to larger aerosol particles are greatest. Recent results show that some oxidation products from biogenic volatile organic compounds are major contributors to particle formation and initial growth. However, whether oxidized organics contribute to particle growth over the broad span of tropospheric temperatures remains an open question, and quantitative mass balance for organic growth has yet to be demonstrated at any temperature. Here, in experiments performed under atmospheric conditions in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN), we show that rapid growth of organic particles occurs over the range from −25 ∘C to 25 ∘C. The lower extent of autoxidation at reduced temperatures is compensated by the decreased volatility of all oxidized molecules. This is confirmed by particle-phase composition measurements, showing enhanced uptake of relatively less oxygenated products at cold temperatures. We can reproduce the measured growth rates using an aerosol growth model based entirely on the experimentally measured gas-phase spectra of oxidized organic molecules obtained from two complementary mass spectrometers. We show that the growth rates are sensitive to particle curvature, explaining widespread atmospheric observations that particle growth rates increase in the single-digit-nanometer size range. Our results demonstrate that organic vapors can contribute to particle growth over a wide range of tropospheric temperatures from molecular cluster sizes onward.
Members of the ATP‐binding cassette (ABC) transporter superfamily translocate a broad spectrum of chemically diverse substrates. While their eponymous ATP‐binding cassette in the nucleotide‐binding domains (NBDs) is highly conserved, their transmembrane domains (TMDs) forming the translocation pathway exhibit distinct folds and topologies, suggesting that during evolution the ancient motor domains were combined with different transmembrane mechanical systems to orchestrate a variety of cellular processes. In recent years, it has become increasingly evident that the distinct TMD folds are best suited to categorize the multitude of ABC transporters. We therefore propose a new ABC transporter classification that is based on structural homology in the TMDs:
Nontarget screening exhibits a seasonal cycle of PM2.5 organic aerosol composition in Beijing
(2022)
The molecular composition of atmospheric particulate matter (PM) in the urban environment is complex, and it remains a challenge to identify its sources and formation pathways. Here, we report the seasonal variation of the molecular composition of organic aerosols (OA), based on 172 PM2.5 filter samples collected in Beijing, China, from February 2018 to March 2019. We applied a hierarchical cluster analysis (HCA) on a large nontarget-screening data set and found a strong seasonal difference in the OA chemical composition. Molecular fingerprints of the major compound clusters exhibit a unique molecular pattern in the Van Krevelen-space. We found that summer OA in Beijing features a higher degree of oxidation and a higher proportion of organosulfates (OSs) in comparison to OA during wintertime, which exhibits a high contribution from (nitro-)aromatic compounds. OSs appeared with a high intensity in summer-haze conditions, indicating the importance of anthropogenic enhancement of secondary OA in summer Beijing. Furthermore, we quantified the contribution of the four main compound clusters to total OA using surrogate standards. With this approach, we are able to explain a small fraction of the OA (∼11–14%) monitored by the Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM). However, we observe a strong correlation between the sum of the quantified clusters and OA measured by the ToF-ACSM, indicating that the identified clusters represent the major variability of OA seasonal cycles. This study highlights the potential of using nontarget screening in combination with HCA for gaining a better understanding of the molecular composition and the origin of OA in the urban environment.
Cloud microphysical processes involving the ice phase in tropospheric clouds are among the major uncertainties in cloud formation, weather and General Circulation Models (GCMs). The simultaneous detection of aerosol particles, liquid droplets, and ice crystals, especially in the small cloud-particle size range below 50 µm, remains challenging in mixed phase, often unstable ice-water phase environments. The Cloud Aerosol Spectrometer with Polarisation (CASPOL) is an airborne instrument that has the ability to detect such small cloud particles and measure their effects on the backscatter polarisation state. Here we operate the versatile Cosmics-Leaving- OUtdoor-Droplets (CLOUD) chamber facility at the European Organisation for Nuclear Research (CERN) to produce controlled mixed phase and other clouds by adiabatic expansions in an ultraclean environment, and use the CASPOL to discriminate between different aerosols, water and ice particles. In this paper, optical property measurements of mixed phase clouds and viscous Secondary Organic Aerosol (SOA) are presented. We report observations of significant liquid – viscous SOA particle polarisation transitions under dry conditions using CASPOL. Cluster analysis techniques were subsequently used to classify different types of particles according to their polarisation ratios during phase transition. A classification map is presented for water droplets, organic aerosol (e.g., SOA and oxalic acid), crystalline substances such as ammonium sulphate, and volcanic ash. Finally, we discuss the benefits and limitations of this classi- fication approach for atmospherically relevant concentration and mixtures with respect to the CLOUD 8–9 campaigns and its potential contribution to Tropical Troposphere Layer (TTL) analysis.
The growth of aerosol due to the aqueous phase oxidation of sulfur dioxide by ozone was measured in laboratory-generated clouds created in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). Experiments were performed at 10 and −10 °C, on acidic (sulfuric acid) and on partially to fully neutralised (ammonium sulfate) seed aerosol. Clouds were generated by performing an adiabatic expansion – pressurising the chamber to 220 hPa above atmospheric pressure, and then rapidly releasing the excess pressure, resulting in a cooling, condensation of water on the aerosol and a cloud lifetime of approximately 6 min. A model was developed to compare the observed aerosol growth with that predicted using oxidation rate constants previously measured in bulk solutions. The model captured the measured aerosol growth very well for experiments performed at 10 and −10 °C, indicating that, in contrast to some previous studies, the oxidation rates of SO2 in a dispersed aqueous system can be well represented by using accepted rate constants, based on bulk measurements. To the best of our knowledge, these are the first laboratory-based measurements of aqueous phase oxidation in a dispersed, super-cooled population of droplets. The measurements are therefore important in confirming that the extrapolation of currently accepted reaction rate constants to temperatures below 0 °C is correct.
The growth of aerosol due to the aqueous phase oxidation of sulfur dioxide by ozone was measured in laboratory-generated clouds created in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). Experiments were performed at 10 and −10 °C, on acidic (sulfuric acid) and on partially to fully neutralised (ammonium sulfate) seed aerosol. Clouds were generated by performing an adiabatic expansion – pressurising the chamber to 220 hPa above atmospheric pressure, and then rapidly releasing the excess pressure, resulting in a cooling, condensation of water on the aerosol and a cloud lifetime of approximately 6 min. A model was developed to compare the observed aerosol growth with that predicted using oxidation rate constants previously measured in bulk solutions. The model captured the measured aerosol growth very well for experiments performed at 10 and −10 °C, indicating that, in contrast to some previous studies, the oxidation rates of SO2 in a dispersed aqueous system can be well represented by using accepted rate constants, based on bulk measurements. To the best of our knowledge, these are the first laboratory-based measurements of aqueous phase oxidation in a dispersed, super-cooled population of droplets. The measurements are therefore important in confirming that the extrapolation of currently accepted reaction rate constants to temperatures below 0 °C is correct.
Cloud microphysical processes involving the ice phase in tropospheric clouds are among the major uncertainties in cloud formation, weather, and general circulation models. The detection of aerosol particles, liquid droplets, and ice crystals, especially in the small cloud particle-size range below 50 μm, remains challenging in mixed phase, often unstable environments. The Cloud Aerosol Spectrometer with Polarization (CASPOL) is an airborne instrument that has the ability to detect such small cloud particles and measure the variability in polarization state of their backscattered light. Here we operate the versatile Cosmics Leaving OUtdoor Droplets (CLOUD) chamber facility at the European Organization for Nuclear Research (CERN) to produce controlled mixed phase and other clouds by adiabatic expansions in an ultraclean environment, and use the CASPOL to discriminate between different aerosols, water, and ice particles. In this paper, optical property measurements of mixed-phase clouds and viscous secondary organic aerosol (SOA) are presented. We report observations of significant liquid–viscous SOA particle polarization transitions under dry conditions using CASPOL. Cluster analysis techniques were subsequently used to classify different types of particles according to their polarization ratios during phase transition. A classification map is presented for water droplets, organic aerosol (e.g., SOA and oxalic acid), crystalline substances such as ammonium sulfate, and volcanic ash. Finally, we discuss the benefits and limitations of this classification approach for atmospherically relevant concentrations and mixtures with respect to the CLOUD 8–9 campaigns and its potential contribution to tropical troposphere layer analysis.
There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate deposition ice nucleation and thus influence cirrus cloud properties. However, experimental ice nucleation studies of biogenic SOA are scarce. Here, we investigated the ice nucleation ability of viscous SOA particles.
The SOA particles were produced from the ozone initiated oxidation of α-pinene in an aerosol chamber at temperatures in the range from −38 to −10 ◦C at 5–15 % relative humidity with respect to water to ensure their formation in a highly viscous phase state, i.e. semi-solid or glassy. The ice nucleation ability of SOA particles with different sizes was investigated with a new continuous flow diffusion chamber. For the first time, we observed heterogeneous ice nucleation of viscous α-pinene SOA in the deposition mode for ice saturation ratios between 1.3 and 1.4 significantly below the homogeneous freezing limit. The maximum frozen fractions found at temperatures between −36.5 and −38.3 °C ranged from 6 to 20 % and did not depend on the particle surface area. Global modelling of monoterpene SOA particles suggests that viscous biogenic SOA particles are indeed present in regions where cirrus cloud formation takes place. Hence, they could make up an important contribution to the global ice nuclei (IN) budget.
Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood1. Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours2. It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere3,4, and that ions have a relatively minor role5. Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded6,7. Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of α-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.
About half of present-day cloud condensation nuclei originate from atmospheric nucleation, frequently appearing as a burst of new particles near midday1. Atmospheric observations show that the growth rate of new particles often accelerates when the diameter of the particles is between one and ten nanometres2,3. In this critical size range, new particles are most likely to be lost by coagulation with pre-existing particles4, thereby failing to form new cloud condensation nuclei that are typically 50 to 100 nanometres across. Sulfuric acid vapour is often involved in nucleation but is too scarce to explain most subsequent growth5,6, leaving organic vapours as the most plausible alternative, at least in the planetary boundary layer7,8,9,10. Although recent studies11,12,13 predict that low-volatility organic vapours contribute during initial growth, direct evidence has been lacking. The accelerating growth may result from increased photolytic production of condensable organic species in the afternoon2, and the presence of a possible Kelvin (curvature) effect, which inhibits organic vapour condensation on the smallest particles (the nano-Köhler theory)2,14, has so far remained ambiguous. Here we present experiments performed in a large chamber under atmospheric conditions that investigate the role of organic vapours in the initial growth of nucleated organic particles in the absence of inorganic acids and bases such as sulfuric acid or ammonia and amines, respectively. Using data from the same set of experiments, it has been shown15 that organic vapours alone can drive nucleation. We focus on the growth of nucleated particles and find that the organic vapours that drive initial growth have extremely low volatilities (saturation concentration less than 10−4.5 micrograms per cubic metre). As the particles increase in size and the Kelvin barrier falls, subsequent growth is primarily due to more abundant organic vapours of slightly higher volatility (saturation concentrations of 10−4.5 to 10−0.5 micrograms per cubic metre). We present a particle growth model that quantitatively reproduces our measurements. Furthermore, we implement a parameterization of the first steps of growth in a global aerosol model and find that concentrations of atmospheric cloud concentration nuclei can change substantially in response, that is, by up to 50 per cent in comparison with previously assumed growth rate parameterizations.
Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the CLOUD experiment at CERN, we deployed a new in-situ optical method to detect the viscosity of α-pinene SOA particles and measured their transition from the amorphous viscous to liquid state. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical liquid particles during deliquescence. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to spherical shape was observed as the RH was increased to between 35 % at −10 ◦C and 80 % at −38 ◦C, confirming previous calculations of the viscosity transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.
Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of α-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35 % at −10 °C and 80 % at −38 °C, confirming previous calculations of the viscosity-transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.
There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate heterogeneous ice nucleation and thus influence cloud properties. However, experimental ice nucleation studies of biogenic SOA are scarce. Here, we investigated the ice nucleation ability of viscous SOA particles.
The SOA particles were produced from the ozone initiated oxidation of α-pinene in an aerosol chamber at temperatures in the range from −38 to −10 °C at 5–15 % relative humidity with respect to water to ensure their formation in a highly viscous phase state, i.e. semi-solid or glassy. The ice nucleation ability of SOA particles with different sizes was investigated with a new continuous flow diffusion chamber. For the first time, we observed heterogeneous ice nucleation of viscous α-pinene SOA for ice saturation ratios between 1.3 and 1.4 significantly below the homogeneous freezing limit. The maximum frozen fractions found at temperatures between −39.0 and −37.2 °C ranged from 6 to 20 % and did not depend on the particle surface area. Global modelling of monoterpene SOA particles suggests that viscous biogenic SOA particles are indeed present in regions where cirrus cloud formation takes place. Hence, they could make up an important contribution to the global ice nucleating particle budget.