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Institute
We report the first observation of the semimuonic decay 𝐷+→𝜔𝜇+𝜈𝜇 using an 𝑒+𝑒− collision data sample corresponding to an integrated luminosity of 2.93 fb−1 collected with the BESIII detector at a center-of-mass energy of 3.773 GeV. The absolute branching fraction of the 𝐷+→𝜔𝜇+𝜈𝜇 decay is measured to be ℬ𝐷+→𝜔𝜇+𝜈𝜇=(17.7±1.8stat±1.1syst)×10−4. Its ratio with the world average value of the branching fraction of the 𝐷+→𝜔𝑒+𝜈𝑒 decay probes lepton flavor universality and it is determined to be ℬ𝐷+→𝜔𝜇+𝜈𝜇/ℬPDG 𝐷+→𝜔𝑒+𝜈𝑒=1.05±0.14, in agreement with the standard model expectation within one standard deviation.
Cross sections of the process 𝑒+𝑒−→𝜋0𝜋0𝐽/𝜓 at center-of-mass energies between 3.808 and 4.600 GeV are measured with high precision by using 12.4 fb−1 of data samples collected with the BESIII detector operating at the BEPCII collider facility. A fit to the measured energy-dependent cross sections confirms the existence of the charmoniumlike state 𝑌(4220). The mass and width of the 𝑌(4220) are determined to be (4220.4±2.4±2.3) MeV/𝑐2 and (46.2±4.7±2.1) MeV, respectively, where the first uncertainties are statistical and the second systematic. The mass and width are consistent with those measured in the process 𝑒+𝑒−→𝜋+𝜋−𝐽/𝜓. The neutral charmonium-like state 𝑍𝑐(3900)0 is observed prominently in the 𝜋0𝐽/𝜓 invariant-mass spectrum, and, for the first time, an amplitude analysis is performed to study its properties. The spin-parity of 𝑍𝑐(3900)0 is determined to be 𝐽𝑃=1+, and the pole position is (3893.1±2.2±3.0)−𝑖(22.2±2.6±7.0) MeV/𝑐2, which is consistent with previous studies of electrically charged 𝑍𝑐(3900)±. In addition, cross sections of 𝑒+𝑒− → 𝜋0𝑍𝑐(3900)0 → 𝜋0𝜋0𝐽/𝜓 are extracted, and the corresponding line shape is found to agree with that of the 𝑌(4220).
We report an amplitude analysis and branching fraction measurement of D+s→K+K−π+ decay using a data sample of 3.19 fb−1 recorded with BESIII detector at a center-of-mass energy of 4.178 GeV.
We perform a model-independent partial wave analysis in the low K+K− mass region to determine the K+K− S-wave lineshape, followed by an amplitude analysis of our very pure high-statistics sample.
The amplitude analysis provides an accurate determination of the detection efficiency allowing us to measure the branching fraction B(D+s→K+K−π+)=(5.47±0.08stat±0.13sys)%.
We report on the first search for ¯Λ−Λ oscillations in the decay 𝐽/𝜓→𝑝𝐾−¯Λ+c.c. by analyzing 1.31×109 𝐽/𝜓 events accumulated with the BESIII detector at the BEPCII collider. The 𝐽/𝜓 events are produced using 𝑒+𝑒− collisions at a center of mass energy √𝑠=3.097 GeV. No evidence for hyperon oscillations is observed. The upper limit for the oscillation rate of ¯Λ to Λ hyperons is determined to be 𝒫(Λ)=[ℬ(𝐽/𝜓→𝑝𝐾−Λ+c.c.)/ℬ(𝐽/𝜓→𝑝𝐾−¯Λ+c.c.)]<4.4×10−6 corresponding to an oscillation parameter 𝛿𝑚Λ¯Λ of less than 3.8×10−18 GeV at the 90% confidence level.
Using 2.93 fb−1 of 𝑒+𝑒− collision data taken at a center-of-mass energy of 3.773 GeV by the BESIII detector at the BEPCII, we measure the branching fractions of the singly Cabibbo-suppressed decays 𝐷→𝜔𝜋𝜋 to be ℬ(𝐷0→𝜔𝜋+𝜋−)=(1.33±0.16±0.12)×10−3 and ℬ(𝐷+→𝜔𝜋+𝜋0)=(3.87±0.83±0.25)×10−3, where the first uncertainties are statistical and the second ones systematic. The statistical significances are 12.9𝜎 and 7.7𝜎, respectively. The precision of ℬ(𝐷0→𝜔𝜋+𝜋−) is improved by a factor of 2.1 over prior measurements, and ℬ(𝐷+→𝜔𝜋+𝜋0) is measured for the first time. No significant signal for 𝐷0→𝜔𝜋0𝜋0 is observed, and the upper limit on the branching fraction is ℬ(𝐷0→𝜔𝜋0𝜋0)<1.10×10−3 at the 90% confidence level. The branching fractions of 𝐷→𝜂𝜋𝜋 are also measured and consistent with existing results.
Using 2.93 fb−1 of 𝑒+𝑒− annihilation data collected at a center-of-mass energy √𝑠=3.773 GeV with the BESIII detector operating at the BEPCII collider, we search for the semileptonic 𝐷0(+) decays into a 𝑏1(1235)−(0) axial-vector meson for the first time. No significant signal is observed for either charge combination. The upper limits on the product branching fractions are ℬ𝐷0→𝑏1(1235)−𝑒+𝜈𝑒·ℬ𝑏1(1235) −→ 𝜔𝜋−<1.12×10−4 and ℬ𝐷+→𝑏1(1235)0𝑒+𝜈𝑒·ℬ𝑏1(1235)0→𝜔𝜋0<1.75×10−4 at the 90% confidence level.
The Born cross sections and effective form factors for process 𝑒+𝑒−→Ξ−¯Ξ+ are measured at eight center-of-mass energies between 2.644 and 3.080 GeV, using a total integrated luminosity of 363.9 pb−1 𝑒+𝑒− collision data collected with the BESIII detector at BEPCII. After performing a fit to the Born cross section of 𝑒+𝑒−→Ξ−¯Ξ+, no significant threshold effect is observed.
We report a study of the processes of e+e−→K+(D−sD∗0+D∗−sD0) based on e+e− annihilation samples collected with the BESIII detector operating at BEPCII at five center-of-mass energies ranging from 4.628 to 4.698 GeV with a total integrated luminosity of 3.7 fb−1. An excess over the known contributions of the conventional charmed mesons is observed near the D−sD∗0 and D∗−sD0 mass thresholds in the K+ recoil-mass spectrum for events collected at s√=4.681 GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5+1.8−2.6±2.1) MeV/c2 and (12.8+5.3−4.4±3.0) MeV, respectively. The first uncertainties are statistical and the second are systematic. The significance of the resonance hypothesis is estimated to be 5.3 σ over the pure contributions from the conventional charmed mesons. This is the first candidate of the charged hidden-charm tetraquark with strangeness, decaying into D−sD∗0 and D∗−sD0. However, the genuine properties of the excess need further exploration with more statistics.
The Born cross sections for the process e+e−→η′π+π− at different center-of-mass energies between 2.00 and 3.08~GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of 6.3σ and a mass and width of M=(2108±46±25)~MeV/c2 and Γ=(138±36±30)~MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in e+e−→η′π+π− and BESIII in e+e−→ωπ0 within two standard deviations.
Observation of a near-threshold structure in the K⁺ recoil-mass spectra in e⁺e⁻ → K⁺(Dₛ⁻D*⁰+Dₛ*⁻D⁰)
(2021)
We report a study of the processes of 𝑒+𝑒−→𝐾+𝐷−𝑠𝐷*0 and 𝐾+𝐷*−𝑠𝐷0 based on 𝑒+𝑒− annihilation samples collected with the BESIII detector operating at BEPCII at five center-of-mass energies ranging from 4.628 to 4.698 GeV with a total integrated luminosity of 3.7 fb−1. An excess of events over the known contributions of the conventional charmed mesons is observed near the 𝐷−𝑠𝐷*0 and 𝐷*−𝑠𝐷0 mass thresholds in the 𝐾+ recoil-mass spectrum for events collected at √𝑠=4.681 GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5+1.8
−2.6±2.1) MeV/𝑐2 and (12.8+5.3−4.4±3.0) MeV, respectively. The first uncertainties are statistical and the second are systematic. The significance of the resonance hypothesis is estimated to be 5.3 𝜎 over the contributions only from the conventional charmed mesons. This is the first candidate for a charged hidden-charm tetraquark with strangeness, decaying into 𝐷−𝑠𝐷*0 and 𝐷*−𝑠𝐷0. However, the properties of the excess need further exploration with more statistics.
The Born cross sections for the process e+e−→η′π+π− at different center-of-mass energies between 2.00 and 3.08 GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of 6.3σ and a mass and width of M=(2111±43±25)~MeV/c2 and Γ=(135±34±30)~MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in e+e−→η′π+π− and BESIII in e+e−→ωπ0 within two standard deviations.
We report a study of the processes of e+e−→K+(D−sD∗0+D∗−sD0) based on e+e− annihilation samples collected with the BESIII detector operating at BEPCII at five center-of-mass energies ranging from 4.628 to 4.698 GeV with a total integrated luminosity of 3.7 fb−1. An excess over the known contributions of the conventional charmed mesons is observed near the D−sD∗0 and D∗−sD0 mass thresholds in the K+ recoil-mass spectrum for events collected at s√=4.681 GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5+1.8−2.6±2.1) MeV/c2 and (12.8+5.3−4.4±3.0) MeV, respectively. The first uncertainties are statistical and the second are systematic. The significance of the resonance hypothesis is estimated to be 5.3 σ over the contributions only from the conventional charmed mesons. This is the first candidate of the charged hidden-charm tetraquark with strangeness, decaying into D−sD∗0 and D∗−sD0. However, the properties of the excess need further exploration with more statistics.
he Born cross sections for the process 𝑒+𝑒−→𝜂′𝜋+𝜋− at different center-of-mass energies between 2.00 and 3.08 GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of 6.3𝜎 and a mass and width of 𝑀=(2111±43±25) MeV/𝑐2 and Γ=(135±34±30) MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in 𝑒+𝑒−→𝜂′𝜋+𝜋− and BESIII in 𝑒+𝑒−→𝜔𝜋0 within two standard deviations.
The Born cross sections for the process e+e−→η′π+π− at different center-of-mass energies between 2.00 and 3.08~GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of 6.3σ and a mass and width of M=(2108±46±25)~MeV/c2 and Γ=(138±36±30)~MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in e+e−→η′π+π− and BESIII in e+e−→ωπ0 within two standard deviations.
We report a measurement of the observed cross sections of e+ e− → J/ψX based on 3.21 fb − 1 of data accumulated at energies from 3.645 to 3.891 GeV with the BESIII detector operated at the BEPCII collider. In analysis of the cross sections, we measured the decay branching fractions of B(ψ(3686) → J/ψX) = (64.4 ± 0.6 ± 1.6)% and B(ψ(3770) → J/ψX) = (0.5 ± 0.2 ± 0.1)% for the first time. The energy-dependent line shape of these cross sections cannot be well described by two Breit-Wigner (BW) amplitudes of the expected decays ψ (3686) → J/ψX and ψ(3770) → J/ψX. Instead, it can be better described with one more BW amplitude of the decay R(3760)→ J/ψX. Under this assumption, we extracted the R (3760) mass M R (3760 ) = 3766.2 ± 3.8 ± 0.4 MeV/c2, total width Γ tot R ( 3760 ) = 22.2 ± 5.9 ± 1.4 MeV, and product of leptonic width and decay branching fraction
ΓeeR(3760) B[R(3760) → J/ψX] = (79.4 ± 85.5 ± 11.7) eV. The significance of the R(3760) is 5.3σ. The first uncertainties of these measured quantities are from fits to the cross sections and second systematic.
Relative fractions and phases of the intermediate decays are determined. With the detection efficiency estimated by the results of the amplitude analysis, the branching fraction of Dþ s → K−Kþπþπ0 decay is measured to be ð5.42 0.10stat 0.17systÞ%.
In Ref. [1] the BESIII collaboration published a cross section measurement of the process e+e− → π+π− in the energy range between 600 and 900 MeV. In this corrigendum, we report a corrected evaluation of the statistical errors in terms of a fully propagated covariance matrix. The correction also yields a reduced statistical uncertainty for the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon, which now reads as aππ,LO μ (600 − 900 MeV) = (368.2 ± 1.5stat ± 3.3syst) × 10−10. The central values of the cross section measurement and of aππ,LO μ , as well as the systematic uncertainties remain unchanged.
By analyzing 2.93 fb−1 of data taken at the ψ(3770) resonance peak with the BESIII detector, we measure the branching fractions for the hadronic decays D+ → K0S K0S K +, D+ → K0S K0Sπ+, D0 → K0S K0S and D0 → K0S K0S K0S . They are determined to be B(D+ → K0S K0S K +) = (2.54 ± 0.05stat. ± 0.12sys.) × 10−3, B(D+ → K0S K0Sπ+) = (2.70 ± 0.05stat. ± 0.12sys.) × 10−3, B(D0 → K0S K0S ) = (1.67 ± 0.11stat. ± 0.11sys.) × 10−4 and B(D0 → K0S K0S K0S ) = (7.21 ± 0.33stat. ± 0.44sys.) × 10−4, where the second one is measured for the first time and the others are measured with significantly improved precision over the previous measurements.
We report the first observation of the decay Λ+c→Σ−π+π+π0, based on data obtained in e+e− annihilations with an integrated luminosity of 567~pb−1 at s√=4.6~GeV. The data were collected with the BESIII detector at the BEPCII storage rings. The absolute branching fraction B(Λ+c→Σ−π+π+π0) is determined to be (2.11±0.33(stat.)±0.14(syst.))%. In addition, an improved measurement of B(Λ+c→Σ−π+π+) is determined as (1.81±0.17(stat.)±0.09(syst.))%.
Measurements of cross section of e⁺e⁻ → pp¯π⁰ at center-of-mass energies between 4.008 and 4.600 GeV
(2017)
Based on e+e− annihilation data samples collected with the BESIII detector at the BEPCII collider at 13 center-of-mass energies from 4.008 to 4.600 GeV, measurements of the Born cross section of e+e− → pp¯π0 are performed. No significant resonant structure is observed in the measured energy dependence of the cross section. The upper limit on the Born cross section of e+e− → Y (4260) → pp¯π0 at the 90% C.L. is determined to be 0.01 pb. The upper limit on the ratio of the branching fractions B(Y (4260)→pp¯π0) B(Y (4260)→π+π− J/ψ) at the 90% C.L. is determined to be 0.02%.
We report cumulants of the proton multiplicity distribution from dedicated fixed-target Au+Au collisions at 3.0 GeV, measured by the STAR experiment in the kinematic acceptance of rapidity (y) and transverse momentum (pT) within −0.5<y<0 and 0.4<pT<2.0 GeV/c. In the most central 0--5\% collisions, a proton cumulant ratio is measured to be C4/C2=−0.85±0.09 (stat.)±0.82 (syst.), which is less than unity, the Poisson baseline. The hadronic transport UrQMD model reproduces our C4/C2 in the measured acceptance. Compared to higher energy results and the transport model calculations, the suppression in C4/C2 is consistent with fluctuations driven by baryon number conservation and indicates an energy regime dominated by hadronic interactions. These data imply that the QCD critical region, if created in heavy-ion collisions, could only exist at energies higher than 3\,GeV.
We report cumulants of the proton multiplicity distribution from dedicated fixed-target Au+Au collisions at 3.0 GeV, measured by the STAR experiment in the kinematic acceptance of rapidity (y) and transverse momentum (pT) within −0.5<y<0 and 0.4<pT<2.0 GeV/c. In the most central 0--5\% collisions, a proton cumulant ratio is measured to be C4/C2=−0.85±0.09 (stat.)±0.82 (syst.), which is less than unity, the Poisson baseline. The hadronic transport UrQMD model reproduces our C4/C2 in the measured acceptance. Compared to higher energy results and the transport model calculations, the suppression in C4/C2 is consistent with fluctuations driven by baryon number conservation and indicates an energy regime dominated by hadronic interactions. These data imply that the QCD critical region, if created in heavy-ion collisions, could only exist at energies higher than 3\,GeV.
We report cumulants of the proton multiplicity distribution from dedicated fixed-target Au+Au collisions at sNN−−−√ = 3.0 GeV, measured by the STAR experiment in the kinematic acceptance of rapidity (y) and transverse momentum (pT) within −0.5<y<0 and 0.4<pT<2.0 GeV/c. In the most central 0--5\% collisions, a proton cumulant ratio is measured to be C4/C2=−0.85±0.09 (stat.)±0.82 (syst.), which is less than unity, the Poisson baseline. The hadronic transport UrQMD model reproduces our C4/C2 in the measured acceptance. Compared to higher energy results and the transport model calculations, the suppression in C4/C2 is consistent with fluctuations driven by baryon number conservation and indicates an energy regime dominated by hadronic interactions. These data imply that the QCD critical region, if created in heavy-ion collisions, could only exist at energies higher than 3\,GeV.
Using a data sample of e+e− collision data corresponding to an integrated luminosity of 2.93 fb−1 collected with the BESIII detector at a center-of-mass energy of s=3.773GeV, we search for the singly Cabibbo-suppressed decays D0→π0π0π0, π0π0η, π0ηη and ηηη using the double tag method. The absolute branching fractions are measured to be B(D0→π0π0π0)=(2.0±0.4±0.3)×10−4, B(D0→π0π0η)=(3.8±1.1±0.7)×10−4 and B(D0→π0ηη)=(7.3±1.6±1.5)×10−4 with the statistical significances of 4.8σ, 3.8σ and 5.5σ, respectively, where the first uncertainties are statistical and the second ones systematic. No significant signal of D0→ηηη is found, and the upper limit on its decay branching fraction is set to be B(D0→ηηη)<1.3×10−4 at the 90% confidence level.
We study the decays of J/ψ and ψ(3686) to the final states Σ(1385)0Σ¯(1385)0 and Ξ0Ξ¯0 based on a single baryon tag method using data samples of (1310.6±7.0)×106 J/ψ and (447.9±2.9)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider. The decays to Σ(1385)0Σ¯(1385)0 are observed for the first time. The measured branching fractions of J/ψ and ψ(3686)→Ξ0Ξ¯0 are in good agreement with, and much more precise, than the previously published results. The angular parameters for these decays are also measured for the first time. The measured angular decay parameter for J/ψ→Σ(1385)0Σ¯(1385)0, α=−0.64±0.03±0.10, is found to be negative, different to the other decay processes in this measurement. In addition, the "12\% rule" and isospin symmetry in the J/ψ and ψ(3686)→ΞΞ¯ and Σ(1385)Σ¯(1385) systems are tested.
Using 16 energy points of e+e− annihilation data collected in the vicinity of the J/ψ resonance with the BESIII detector and with a total integrated luminosity of around 100 pb−1, we study the relative phase between the strong and electromagnetic amplitudes of J/ψ decays. The relative phase between J/ψ electromagnetic decay and the continuum process (e+e− annihilation without the J/ψ resonance) is confirmed to be zero by studying the cross section lineshape of μ+μ− production. The relative phase between J/ψ strong and electromagnetic decays is then measured to be (84.9 ± 3.6)◦ or (−84.7 ± 3.1)◦ for the 2(π+π−)π0 final state by investigating the interference pattern between the J/ψ decay and the continuum process. This is the first measurement of the relative phase between J/ψ strong and electromagnetic decays into a multihadron final state using the lineshape of the production cross section. We also study the production lineshape of the multihadron final state ηπ+π− with η → π+π−π0, which provides additional information about the phase between the J/ψ electromagnetic decay amplitude and the continuum process. Additionally, the branching fraction of J/ψ → 2(π+π−)π0 is measured to be (4.73 ± 0.44)% or (4.85 ± 0.45)%, and the branching fraction of J/ψ → ηπ+π− is measured to be (3.78 ± 0.68) × 10−4. Both of them are consistent with the world average values. The quoted uncertainties include both statistical and systematic uncertainties, which are mainly caused by the low statistics.
We report the first measurement of the absolute branching fraction for Λ+c→Λμ+νμ. This measurement is based on a sample of e+e− annihilation data at a center-of-mass energy of s√=4.6 GeV collected with the BESIII detector at the BEPCII storage rings. The sample corresponds to an integrated luminosity of 567 pb−1. The branching fraction is determined to be B(Λ+c→Λμ+νμ)=(3.49±0.46(stat)±0.27(syst))%. In addition, we calculate the ratio B(Λ+c→Λμ+νμ)/B(Λ+c→Λe+νe) to be 0.96±0.16(stat)±0.04(syst).
Using data samples collected with the BESIII detector at the BEPCII collider at six center-of-mass energies between 4.008 and 4.600 GeV, we observe the processes e+e− → φφω and e+e− → φφφ. The Born cross sections are measured and the ratio of the cross sections σ(e+e− → φφω)/σ(e+e− → φφφ) is estimated to be 1.75 ± 0.22 ± 0.19 averaged over six energy points, where the first uncertainty is statistical and the second is systematic. The results represent first measurements of these interactions.
We report the first measurements of absolute branching fractions for the W -exchange-only processes + c → 0K + and + c → (1530)0K + with the double-tag technique, by analyzing an e+e− collision data sample, that corresponds to an integrated luminosity of 567 pb−1 collected at a center-of-mass energy of 4.6 GeV by the BESIII detector. The branching fractions are measured to be B(+c → 0K +) = (5.90 ± 0.86 ± 0.39) × 10−3 and B(+c → (1530)0K +) = (5.02 ± 0.99 ± 0.31) × 10−3, where the first uncertainties are statistical and the second systematic. Our results are more precise than the previous relative measurements.
Using a data sample of 448.1 × 106 ψ(3686) events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay ψ(3686) → η e+e−, with significances of 7.0σ and 6.3σ when reconstructing the η meson via its decay modes η → γπ+π− and η → π+π−η (η → γγ ), respectively. The weighted average branching fraction is determined to be B(ψ(3686) → η e+e−) = (1.90 ± 0.25 ± 0.11) × 10−6, where the first uncertainty is statistical and the second systematic.
Measurement of branching fractions for D meson decaying into ϕ meson and a pseudoscalar meson
(2019)
The four decay modes D0 → φπ0, D0 → φη, D+ → φπ+, and D+ → φK + are studied by using a data sample taken at the centre-of-mass energy √s = 3.773 GeV with the BESIII detector, corresponding to an integrated luminosity of 2.93 fb−1. The branching fractions of the first three decay modes are measured to be B(D0 → φπ0) = (1.168 ± 0.028 ± 0.028) × 10−3, B(D0 → φη) = (1.81 ± 0.46 ± 0.06) × 10−4, and B(D+ → φπ+) = (5.70 ± 0.05 ± 0.13) × 10−3, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the upper limit of the branching fraction for D+ → φK+ is given to be 2.1 × 10−5 at the 90% confidence level. The ratio of B(D0 → φπ0) to B(D+ → φπ+) is calculated to be (20.49 ± 0.50 ± 0.45)%, which is consistent with the theoretical prediction based on isospin symmetry between these two decay modes.
Measurement of the e+e−→π+π− cross section between 600 and 900 MeV using initial state radiation
(2016)
We extract the e+e− →π+π− cross section in the energy range between 600 and 900 MeV, exploiting the method of initial state radiation. A data set with an integrated luminosity of 2.93 fb−1 taken at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider is used. The cross section is measured with a systematic uncertainty of 0.9%. We extract the pion form factor |Fπ|2 as well as the contribution of the measured cross section to the leading-order hadronic vacuum polarization contribution to (g−2)μ. We find this value to be aππ,LO μ (600–900 MeV) = (368.2 ±2.5stat±3.3sys) ·10−10, which is between the corresponding values using the BaBar or KLOE data.
In high-energy heavy-ion collisions, partonic collectivity is evidenced by the constituent quark number scaling of elliptic flow anisotropy for identified hadrons. A breaking of this scaling and dominance of baryonic interactions is found for identified hadron collective flow measurements in √sNN = 3 GeV Au+Au collisions. In this paper, we report measurements of the first- and second-order azimuthal anisotropic parameters, v1 and v2, of light nuclei (d, t, 3He, 4He) produced in √sNN = 3 GeV Au+Au collisions at the STAR experiment. An atomic mass number scaling is found in the measured v1 slopes of light nuclei at mid-rapidity. For the measured v2 magnitude, a strong rapidity dependence is observed. Unlike v2 at higher collision energies, the v2 values at mid-rapidity for all light nuclei are negative and no scaling is observed with the atomic mass number. Calculations by the Jet AA Microscopic Transport Model (JAM), with baryonic mean-field plus nucleon coalescence, are in good agreement with our observations, implying baryonic interactions dominate the collective dynamics in 3 GeV Au+Au collisions at RHIC.
The electromagnetic process is studied with the initial-state-radiation technique using 7.5 fb−1 of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/ using the invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.
Measurement of cold nuclear matter effects for inclusive J/ψ in p+Au collisions at √sNN = 200 GeV
(2022)
Measurement by the STAR experiment at RHIC of the cold nuclear matter (CNM) effects experienced by inclusive J/ψ at mid-rapidity in 0-100% p+Au collisions at √sNN = 200 GeV is presented. Such effects are quantified utilizing the nuclear modification factor, RpAu, obtained by taking a ratio of J/ψ yield in p+Au collisions to that in p+p collisions scaled by the number of binary nucleon-nucleon collisions. The differential J/ψ yield in both p+p and p+Au collisions is measured through the dimuon decay channel, taking advantage of the trigger capability provided by the Muon Telescope Detector in the RHIC 2015 run. Consequently, the J/ψ RpAu is derived within the transverse momentum (pT) range of 0 to 10 GeV/c. A suppression of approximately 30% is observed for pT < 2 GeV/c, while J/ψ RpAu becomes compatible with unity for pT greater than 3 GeV/c, indicating the J/ψ yield is minimally affected by the CNM effects at high pT. Comparison to a similar measurement from 0-20% central Au+Au collisions reveals that the observed strong J/ψ suppression above 3 GeV/c is mostly due to the hot medium effects, providing strong evidence for the formation of the quark-gluon plasma in these collisions. Several model calculations show qualitative agreement with the measured J/ψ RpAu, while their agreement with the J/ψ yields in p+p and p+Au collisions is worse.
We report on the measurements of directed flow v1 and elliptic flow v2 for hadrons (π±, K ±, K0 S , p, φ, Λ and ) from Au+Au collisions at √sN N = 3 GeV and v2 for (π±, K ±, p and p) at 27 and 54.4 GeV with the STAR experiment. While at the two higher energy midcentral collisions the numberof-constituent-quark (NCQ) scaling holds, at 3 GeV the v2 at midrapidity is negative for all hadrons and the NCQ scaling is absent. In addition, the v1 slopes at midrapidity for almost all observed hadrons are found to be positive, implying dominant repulsive baryonic interactions. The features of negative v2 and positive v1 slope at 3 GeV can be reproduced with a baryonic mean-field in transport model calculations. These results imply that the medium in such collisions is likely characterized by baryonic interactions.
Born cross sections for the processes e+e− → ωη and e+e− → ωπ0 have been determined for centerof-mass energies between 2.00 and 3.08 GeV with the BESIII detector at the BEPCII collider. The results obtained in this work are consistent with previous measurements but with improved precision. Two resonant structures are observed. In the e+e− → ωη cross sections, a resonance with a mass of (2176 ± 24 ± 3) MeV/c2 and a width of (89 ± 50 ± 5) MeV is observed with a significance of 6.2σ. Its properties are consistent with the φ(2170). In the e+e− → ωπ0 cross sections, a resonance denoted Y (2040) is observed with a significance of more than 10σ. Its mass and width are determined to be (2034 ± 13 ± 9) MeV/c2 and (234 ± 30 ± 25) MeV, respectively, where the first uncertainties are statistical and the second ones are systematic.
A linearly polarized photon can be quantized from the Lorentz-boosted electromagnetic field of a nucleus traveling at ultrarelativistic speed. When two relativistic heavy nuclei pass one another at a distance of a few nuclear radii, the photon from one nucleus may interact through a virtual quark-antiquark pair with gluons from the other nucleus, forming a short-lived vector meson (e.g., ρ0). In this experiment, the polarization was used in diffractive photoproduction to observe a unique spin interference pattern in the angular distribution of ρ0 → π+π− decays. The observed interference is a result of an overlap of two wave functions at a distance an order of magnitude larger than the ρ0 travel distance within its lifetime. The strong-interaction nuclear radii were extracted from these diffractive interactions and found to be 6.53 ± 0.06 fm (197Au) and 7.29 ± 0.08 fm (238U), larger than the nuclear charge radii. The observable is demonstrated to be sensitive to the nuclear geometry and quantum interference of nonidentical particles. Polarized photon-gluon fusion reveals quantum wave interference of non-identical particles and shape of high-energy nuclei.
The Born cross sections of the e+e− → +¯ − and e+e− → −¯ + processes are determined for centerof-mass energy from 2.3864 to 3.0200 GeV with the BESIII detector. The cross section lineshapes can be described properly by a pQCD function and the resulting ratio of effective form factors for the + and − is consistent with 3. In addition, ratios of the + electric and magnetic form factors, |GE /GM |, are obtained at three center-of-mass energies through an analysis of the angular distributions. These measurements, which are studied for the first time in the off-resonance region, provide precision experimental input for understanding baryonic structure. The observed new features of the ± form factors require more theoretical discussions for the hyperons.
In high-energy heavy-ion collisions, partonic collectivity is evidenced by the constituent quark number scaling of elliptic flow anisotropy for identified hadrons. A breaking of this scaling and dominance of baryonic interactions is found for identified hadron collective flow measurements in sNN−−−√ = 3 GeV Au+Au collisions. In this paper, we report measurements of the first-order and second-order azimuthal anisotropic parameters, v1 and v2, of light nuclei (d, t, 3He, 4He) produced in sNN−−−√ = 3 GeV Au+Au collisions at the STAR experiment. An atomic mass number scaling is found in the measured v1 slopes of light nuclei at mid-rapidity. For the measured v2 magnitude, a strong rapidity dependence is observed. Unlike v2 at higher collision energies, the v2 values at mid-rapidity for all light nuclei are negative and no scaling is observed with the atomic mass number. Calculations by the Jet AA Microscopic Transport Model (JAM), with baryonic mean-field plus nucleon coalescence, are in good agreement with our observations, implying baryonic interactions dominate the collective dynamics in 3 GeV Au+Au collisions at RHIC.
In high-energy heavy-ion collisions, partonic collectivity is evidenced by the constituent quark number scaling of elliptic flow anisotropy for identified hadrons. A breaking of this scaling and dominance of baryonic interactions is found for identified hadron collective flow measurements in sNN−−−√ = 3 GeV Au+Au collisions. In this paper, we report measurements of the first- and second-order azimuthal anisotropic parameters, v1 and v2, of light nuclei (d, t, 3He, 4He) produced in sNN−−−√ = 3 GeV Au+Au collisions at the STAR experiment. An atomic mass number scaling is found in the measured v1 slopes of light nuclei at mid-rapidity. For the measured v2 magnitude, a strong rapidity dependence is observed. Unlike v2 at higher collision energies, the v2 values at mid-rapidity for all light nuclei are negative and no scaling is observed with the atomic mass number. Calculations by the Jet AA Microscopic Transport Model (JAM), with baryonic mean-field plus nucleon coalescence, are in good agreement with our observations, implying baryonic interactions dominate the collective dynamics in 3 GeV Au+Au collisions at RHIC.
Using 5.9 pb−1 of e+e− annihilation data collected at center-of-mass energies from 3.640 to 3.701 GeV with the BESIII detector at the BEPCII Collider, we measure the observed cross sections of e+e−→K0SX (where X=anything). From a fit to these observed cross sections with the sum of continuum and ψ(3686) and J/ψ Breit-Wigner functions and considering initial state radiation and the BEPCII beam energy spread, we obtain for the first time the inclusive decay branching fraction B(ψ(3686)→K0SX)=(16.04±0.29±0.90)%, where the first uncertainty is statistical and the second is systematic.
The STAR Collaboration reports measurements of the transverse single-spin asymmetry (TSSA) of inclusive 𝜋0 at center-of-mass energies (√𝑠) of 200 GeV and 500 GeV in transversely polarized proton-proton collisions in the pseudo-rapidity region 2.7 to 4.0. The results at the two different energies show a continuous increase of the TSSA with Feynman-𝑥, and, when compared to previous measurements, no dependence on √𝑠 from 19.4 GeV to 500 GeV is found. To investigate the underlying physics leading to this large TSSA, different topologies have been studied. 𝜋0 with no nearby particles tend to have a higher TSSA than inclusive 𝜋0. The TSSA for inclusive electromagnetic jets, sensitive to the Sivers effect in the initial state, is substantially smaller, but shows the same behavior as the inclusive 𝜋0 asymmetry as a function of Feynman-𝑥. To investigate final-state effects, the Collins asymmetry of 𝜋0 inside electromagnetic jets has been measured. The Collins asymmetry is analyzed for its dependence on the 𝜋0 momentum transverse to the jet thrust axis and its dependence on the fraction of jet energy carried by the 𝜋0. The asymmetry was found to be small in each case for both center-of-mass energies. All the measurements are compared to QCD-based theoretical calculations for transverse-momentum-dependent parton distribution functions and fragmentation functions. Some discrepancies are found, which indicates new mechanisms might be involved.
Measurement of inclusive charged-particle jet production in Au+Au collisions at √sNN = 200 GeV
(2021)
The STAR Collaboration at the Relativistic Heavy Ion Collider reports the first measurement of inclusive jet production in peripheral and central Au+Au collisions at sNN−−−−√=200 GeV. Jets are reconstructed with the anti-kT algorithm using charged tracks with pseudorapidity |η|<1.0 and transverse momentum 0.2<pchT,jet<30 GeV/c, with jet resolution parameter R=0.2, 0.3, and 0.4. The large background yield uncorrelated with the jet signal is observed to be dominated by statistical phase space, consistent with a previous coincidence measurement. This background is suppressed by requiring a high-transverse-momentum (high-pT) leading hadron in accepted jet candidates. The bias imposed by this requirement is assessed, and the pT region in which the bias is small is identified. Inclusive charged-particle jet distributions are reported in peripheral and central Au+Au collisions for 5<pchT,jet<25 GeV/c and 5<pchT,jet<30 GeV/c, respectively. The charged-particle jet inclusive yield is suppressed for central Au+Au collisions, compared to both the peripheral Au+Au yield from this measurement and to the pp yield calculated using the PYTHIA event generator. The magnitude of the suppression is consistent with that of inclusive hadron production at high pT, and that of semi-inclusive recoil jet yield when expressed in terms of energy loss due to medium-induced energy transport. Comparison of inclusive charged-particle jet yields for different values of R exhibits no significant evidence for medium-induced broadening of the transverse jet profile for R<0.4 in central Au+Au collisions. The measured distributions are consistent with theoretical model calculations that incorporate jet quenching.
Measurement of inclusive J/ψ polarization in p + p collisions at √s=200 GeV by the STAR experiment
(2020)
We report on new measurements of inclusive 𝐽/𝜓 polarization at midrapidity in 𝑝+𝑝 collisions at √𝑠=200 GeV by the STAR experiment at the Relativistic Heavy Ion Collider. The polarization parameters, 𝜆𝜃, 𝜆𝜙, and 𝜆𝜃𝜙, are measured as a function of transverse momentum (𝑝T) in both the helicity and Collins-Soper (CS) reference frames within 𝑝T<10 GeV/𝑐. Except for 𝜆𝜃 in the CS frame at the highest measured 𝑝T, all three polarization parameters are consistent with 0 in both reference frames without any strong 𝑝T dependence. Several model calculations are compared with data, and the one using the Color Glass Condensate effective field theory coupled with nonrelativistic QCD gives the best overall description of the experimental results, even though other models cannot be ruled out due to experimental uncertainties.
We report on the measurement of the Central Exclusive Production of charged particle pairs h+h− (h = π, K, p) with the STAR detector at RHIC in proton-proton collisions at √s = 200 GeV. The charged particle pairs produced in the reaction pp → p′ + h+h− + p′ are reconstructed from the tracks in the central detector and identified using the specific energy loss and the time of flight method, while the forward-scattered protons are measured in the Roman Pot system. Exclusivity of the event is guaranteed by requiring the transverse momentum balance of all four final-state particles. Differential cross sections are measured as functions of observables related to the central hadronic final state and to the forward-scattered protons. They are measured in a fiducial region corresponding to the acceptance of the STAR detector and determined by the central particles’ transverse momenta and pseudorapidities as well as by the forward-scattered protons’ momenta. This fiducial region roughly corresponds to the square of the four-momentum transfers at the proton vertices in the range 0.04 GeV2 < −t1, −t2 < 0.2 GeV2, invariant masses of the charged particle pairs up to a few GeV and pseudorapidities of the centrally-produced hadrons in the range |η| < 0.7. The measured cross sections are compared to phenomenological predictions based on the Double Pomeron Exchange (DPE) model. Structures observed in the mass spectra of π+π− and K+K− pairs are consistent with the DPE model, while angular distributions of pions suggest a dominant spin-0 contribution to π+π− production. For π+π− production, the fiducial cross section is extrapolated to the Lorentz-invariant region, which allows decomposition of the invariant mass spectrum into continuum and resonant contributions. The extrapolated cross section is well described by the continuum production and at least three resonances, the f0(980), f2(1270) and f0(1500), with a possible small contribution from the f0(1370). Fits to the extrapolated differential cross section as a function of t1 and t2 enable extraction of the exponential slope parameters in several bins of the invariant mass of π+π− pairs. These parameters are sensitive to the size of the interaction region.
Measurement of inclusive charged-particle jet production in Au + Au collisions at √sNN=200 GeV
(2020)
The STAR Collaboration at the Relativistic Heavy Ion Collider reports the first measurement of inclusive jet production in peripheral and central Au+Au collisions at √𝑠𝑁𝑁=200 GeV. Jets are reconstructed with the anti-𝑘𝑇 algorithm using charged tracks with pseudorapidity |𝜂|<1.0 and transverse momentum 0.2<𝑝ch
𝑇,jet<30 GeV/𝑐, with jet resolution parameter 𝑅=0.2, 0.3, and 0.4. The large background yield uncorrelated with the jet signal is observed to be dominated by statistical phase space, consistent with a previous coincidence measurement. This background is suppressed by requiring a high-transverse-momentum (high-𝑝𝑇) leading hadron in accepted jet candidates. The bias imposed by this requirement is assessed, and the 𝑝𝑇 region in which the bias is small is identified. Inclusive charged-particle jet distributions are reported in peripheral and central Au+Au collisions for 5<𝑝ch
𝑇,jet<25 GeV/𝑐 and 5<𝑝ch
𝑇,jet<30 GeV/𝑐, respectively. The charged-particle jet inclusive yield is suppressed for central Au+Au collisions, compared to both the peripheral Au+Au yield from this measurement and to the 𝑝𝑝 yield calculated using the PYTHIA event generator. The magnitude of the suppression is consistent with that of inclusive hadron production at high 𝑝𝑇 and that of semi-inclusive recoil jet yield when expressed in terms of energy loss due to medium-induced energy transport. Comparison of inclusive charged-particle jet yields for different values of 𝑅 exhibits no significant evidence for medium-induced broadening of the transverse jet profile for 𝑅 <0.4 in central Au+Au collisions. The measured distributions are consistent with theoretical model calculations that incorporate jet quenching.
Two-particle correlations on transverse rapidity in Au+Au collisions at √sNN = 200 GeV at STAR
(2022)
Two-particle correlation measurements projected onto two-dimensional, transverse rapidity coordinates (yT1,yT2), allow access to dynamical properties of the QCD medium produced in relativistic heavy-ion collisions that angular correlation measurements are not sensitive to. We report non-identified charged-particle correlations for Au + Au minimum-bias collisions at sNN−−−√ = 200 GeV taken by the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). Correlations are presented as 2D functions of transverse rapidity for like-sign, unlike-sign and all charged-particle pairs, as well as for particle pairs whose relative azimuthal angles lie on the near-side, the away-side, or at all relative azimuth. The correlations are constructed using charged particles with transverse momentum pT≥0.15 GeV/c, pseudorapidity from −1 to 1, and azimuthal angles from −π to π. The significant correlation structures that are observed evolve smoothly with collision centrality. The major correlation features include a saddle shape plus a broad peak with maximum near yT≈3, corresponding to pT≈ 1.5 GeV/c. The broad peak is observed in both like- and unlike-sign charge combinations and in near- and away-side relative azimuthal angles. The all-charge, all-azimuth correlation measurements are compared with the theoretical predictions of {\sc hijing} and {\sc epos}. The results indicate that the correlations for peripheral to mid-central collisions can be approximately described as a superposition of nucleon + nucleon collisions with minimal effects from the QCD medium. Strong medium effects are indicated in mid- to most-central collisions.
We report a new measurement of the production cross section for inclusive electrons from open heavy-flavor hadron decays as a function of transverse momentum (pT) at mid-rapidity (|y|< 0.7) in p+p collisions at s√=200 GeV. The result is presented for 2.5 <pT< 10 GeV/c with an improved precision above 6 GeV/c with respect to the previous measurements, providing more constraints on perturbative QCD calculations. Moreover, this measurement also provides a high-precision reference for measurements of nuclear modification factors for inclusive electrons from open-charm and -bottom hadron decays in heavy-ion collisions.
We report a new measurement of the production cross section for inclusive electrons from open heavy-flavor hadron decays as a function of transverse momentum (pT) at mid-rapidity (|y|< 0.7) in p+p collisions at s√=200 GeV. The result is presented for 2.5 <pT< 10 GeV/c with an improved precision at high pT with respect to the previous measurements, and thus provides a better constraint on perturbative QCD calculations. Moreover, this measurement also provides a high-precision reference for measurements of nuclear modification factors for inclusive electrons from open-charm and -bottom hadron decays in heavy-ion collisions.