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By analyzing e+eā annihilation data with an integrated luminosity of 2.93 fbā1 collected at the center-of-mass energy sā= 3.773 GeV with the BESIII detector, we present the first absolute measurements of the branching fractions of twenty Cabibbo-suppressed hadronic D0(+) decays involving multiple pions. The largest four branching fractions obtained are B(D0āĻ+ĻāĻ0) = >(1.343Ā±0.013statĀ±0.016syst)%, B(D0āĻ+Ļā2Ļ0) = (0.998Ā±0.019statĀ±0.024syst)%, B(D+ā2Ļ+ĻāĻ0)
(1.174Ā±0.021statĀ±0.021syst)%, and B(D+ā2Ļ+Ļā2Ļ0) = (1.074Ā±0.040statĀ±0.030syst)%. The CP asymmetries for the six decays with highest event yields are also determined.
Using a sample of (448.1Ā±2.9)Ć106āšā”(3686) decays collected with the BESIII detector at BEPCII, we report an observation of Īā transverse polarization with a significance of 7.3ā¢š in the decay šā”(3686)āĪāā¢ ĀÆĪ+ (ĪāāĪā¢šā, ĀÆĪ+āĀÆĪā¢š+, Īāšā¢šā, ĀÆĪāĀÆšā¢š+). The relative phase of the electric and magnetic form factors is determined to be Īā¢Ī¦=(0.667Ā±0.111Ā±0.058)āārad. This is the first measurement of the relative phase for a šā”(3686) decay into a pair of Īāā¢ĀÆĪ+ hyperons. The Īā decay parameters (š¼Īā, šĪā) and their conjugates (š¼ĀÆĪ+, šĀÆĪ+), the angular-distribution parameter š¼š, and the strong-phase difference šæšāšæš for Īā¢šā scattering are measured to be consistent with previous BESIII results.
From December 2019 to June 2021, the BESIII experiment collected about 5.85 fbā1 of data at center-of-mass energies between 4.61 GeV and 4.95 GeV. This is the highest collision energy BEPCII has reached so far. The accumulated e+eā annihilation data samples are useful for studying charmonium(-like) states and charmed-hadron decays. By adopting a novel method of analyzing the production of Ī+cĪĀÆāc pairs in e+eā annihilation, the center-of-mass energies are measured with a precision of ā¼0.6 MeV. Integrated luminosities are measured with a precision of better than 1\% by analyzing the events of large-angle Bhabha scattering. These measurements provide important inputs to the analyses based on these data samples.
The production cross section of inclusive isolated photons has been measured by the ALICE experiment at the CERN LHC in pp collisions at centre-of-momentum energy of sā=13 TeV collected during the LHC Run 2 data-taking period. The measurement is performed by combining the measurements of the electromagnetic calorimeter EMCal and the central tracking detectors ITS and TPC, covering a pseudorapidity range of |Ī·Ī³|<0.67 and a transverse momentum range of 7<pĪ³T<200 GeV/c. The result extends to lower pĪ³T and xĪ³T=2pĪ³T/sā ranges, the lowest xĪ³T of any isolated photon measurements to date, extending significantly those measured by the ATLAS and CMS experiments towards lower pĪ³T at the same collision energy with a small overlap between the measurements. The measurement is compared with next-to-leading order perturbative QCD calculations and the results from the ATLAS and CMS experiments as well as with measurements at other collision energies. The measurement and theory prediction are in agreement with each other within the experimental and theoretical uncertainties.
Alternating acquisition of background and sample spectra is often employed in conventional Fourier-transform infrared spectroscopy or ultravioletāvisible spectroscopy for accurate background subtraction. For example, for solvent background correction, typically a spectrum of a cuvette with solvent is measured and subtracted from a spectrum of a cuvette with solvent and solute. Ultrafast spectroscopies, though, come with many peculiarities that make the collection of well-matched, subtractable background and sample spectra challenging. Here, we present a demountable split-sample cell in combination with a modified Lissajous scanner to overcome these challenges. It allows for quasi-simultaneous measurements of background and sample spectra, mitigating the effects of drifts of the setup and maintaining the beam and sample geometry when swapping between background and sample measurements. The cell is moving between subsequent laser shots to refresh the excited sample volume. With less than 45 Ī¼l of solution for 150 Ī¼m optical thickness, sample usage is economical. Cell assembly is a key step and covered in an illustrated protocol.
Using about 23āāfā¢bā1 of data collected with the BESIII detector operating at the BEPCII storage ring, a precise measurement of the š+ā¢šāāš+ā¢šāā¢š½/š Born cross section is performed at center-of-mass energies from 3.7730 to 4.7008 GeV. Two structures, identified as the šā”(4220) and the šā”(4320) states, are observed in the energy-dependent cross section with a significance larger than 10ā¢š. The masses and widths of the two structures are determined to be (š,Ī)=(4221.4Ā±1.5Ā±2.0āāMeV/š2,41.8Ā±2.9Ā±2.7āāMeV) and (š,Ī)=(4298Ā±12Ā±26āāMeV/š2,127Ā±17Ā±10āāMeV), respectively. A small enhancement around 4.5 GeV with a significance about 3ā¢š, compatible with the šā”(4415), might also indicate the presence of an additional resonance in the spectrum. The inclusion of this additional contribution in the fit to the cross section affects the resonance parameters of the šā”(4320) state.
The hadronic decay ššā”(2ā¢š)ā3ā¢(š+ā¢šā) is observed with a statistical significance of 9.3 standard deviations using (448.1Ā±2.9)Ć106āāšā”(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of ššā”(2ā¢š) are (3643.4Ā±2.3ā(stat)Ā±4.4ā(syst))āāMeV/š2 and (19.8Ā±3.9ā(stat)Ā±3.1ā(syst))āāMeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction ā¬ā”[šā”(3686)āš¾ā¢ššā”(2ā¢š)]Ćā¬ā”[ššā”(2ā¢š)ā3ā¢(š+ā¢šā)] is measured to be (9.2Ā±1.0ā(stat)Ā±1.2ā(syst))Ć10ā6. Using ā¬ā”[šā”(3686)āš¾ā¢ššā”(2ā¢š)]=(7.ā¢0+3.4ā2.5)Ć10ā4, we obtain ā¬ā”[ššā”(2ā¢š)ā3ā¢(š+ā¢šā)]=(1.31Ā±0.15ā(stat)Ā±0.17ā(syst) (+0.64ā0.47)ā(extr))Ć10ā2, where the third uncertainty is from ā¬ā”[šā”(3686)āš¾ā¢ššā”(2ā¢š)]. We also measure the ššā¢š½ā3ā¢(š+ā¢šā) (š½=0, 1, 2) decays via šā²āš¾ā¢ššā¢š½ transitions. The branching fractions are ā¬ā”[ššā¢0ā3ā¢(š+ā¢šā)]=(2.080Ā±0.006ā(stat)Ā±0.068ā(syst))Ć10ā2, ā¬ā”[ššā¢1ā3ā¢(š+ā¢šā)]=(1.092Ā±0.004ā(stat)Ā±0.035ā(syst))Ć10ā2, and ā¬ā”[ššā¢2ā3ā¢(š+ā¢šā)]=(1.565Ā±0.005ā(stat)Ā±0.048ā(syst))Ć10ā2.
The hadronic decay Ī·c(2S)ā3(Ļ+Ļā) is observed with a statistical significance of 9.3 standard deviations using (448.1Ā±2.9)Ć106 Ļ(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of Ī·c(2S) are (3643.4Ā±2.3(stat.)Ā±4.4(syst.)) MeV/c2 and (19.8Ā±3.9(stat.)Ā±3.1(syst.)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction B[Ļ(3686)āĪ³Ī·c(2S)]ĆB[Ī·c(2S)ā3(Ļ+Ļā)] is measured to be (9.2Ā±1.0(stat.)Ā±0.9(syst.))Ć10ā6. Using B[Ļ(3686)āĪ³Ī·c(2S)]=(7.0+3.4ā2.5)Ć10ā4, we obtain B[Ī·c(2S)ā3(Ļ+Ļā)]=(1.31Ā±0.15(stat.)Ā±0.13(syst.)(+0.64ā0.47)(extr))Ć10ā2, where the third uncertainty is from B[Ļ(3686)āĪ³Ī·c(2S)]. We also measure the ĻcJā3(Ļ+Ļā) (J=0,1,2) decays via Ļ(3686)āĪ³ĻcJ transitions. The branching fractions are B[Ļc0ā3(Ļ+Ļā)]=(2.080Ā±0.006(stat.)Ā±0.068(syst.))Ć10ā2, B[Ļc1ā3(Ļ+Ļā)]=(1.092Ā±0.004(stat.)Ā±0.035(syst.))Ć10ā2, and B[Ļc2ā3(Ļ+Ļā)]=(1.565Ā±0.005(stat.)Ā±0.048(syst.))Ć10ā2.
The hadronic decay Ī·c(2S)ā3(Ļ+Ļā) is observed with a statistical significance of 9.3 standard deviations using (448.1Ā±2.9)Ć106 Ļ(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of Ī·c(2S) are (3643.4Ā±2.3(stat.)Ā±4.4(syst.)) MeV/c2 and (19.8Ā±3.9(stat.)Ā±3.1(syst.)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction B[Ļ(3686) ā Ī³Ī·c(2S)]ĆB[Ī·c(2S)ā3(Ļ+Ļā)] is measured to be (9.2Ā±1.0(stat.)Ā±0.9(syst.))Ć10ā6. Using B[Ļ(3686)āĪ³Ī·c(2S)]=(7.0+3.4ā2.5)Ć10ā4, we obtain B[Ī·c(2S)ā3(Ļ+Ļā)]=(1.31Ā±0.15(stat.)Ā±0.13(syst.)(+0.64ā0.47)(extr))Ć10ā2, where the third uncertainty is from B[Ļ(3686)āĪ³Ī·c(2S)]. We also measure the ĻcJā3(Ļ+Ļā) (J=0,1,2) decays via Ļ(3686)āĪ³ĻcJ transitions. The branching fractions are B[Ļc0ā3(Ļ+Ļā)]=(2.080Ā±0.006(stat.)Ā±0.068(syst.))Ć10ā2, B[Ļc1ā3(Ļ+Ļā)]=(1.092Ā±0.004(stat.)Ā±0.035(syst.))Ć10ā2, and B[Ļc2ā3(Ļ+Ļā)]=(1.565Ā±0.005(stat.)Ā±0.048(syst.))Ć10ā2.
The absolute branching fraction of the decay Īc(2625)+āĪ+cĻ+Ļā is measured for the first time to be (50.7Ā±5.0stat.Ā±4.9syst.)% with 368.48 pbā1 of e+eā collision data collected by the BESIII detector at the center-of-mass energies of sā=4.918 and 4.950 GeV. This result is lower than the naive prediction of 67\%, obtained from isospin symmetry, by more than 2Ļ, thereby indicating that the novel mechanism referred to as the \textit{threshold effect}, proposed for the strong decays of Īc(2595)+, also applies to Īc(2625)+. This measurement is necessary to obtain the coupling constants for the transitions between s-wave and p-wave charmed baryons in heavy hadron chiral perturbation theory. In addition, we search for the decay Īc(2595)+āĪ+cĻ+Ļā. No significant signal is observed, and the upper limit on its branching fraction is determined to be 80.8\% at the 90\% confidence level.
Using a sample of (10.09 Ā± 0.04) Ć 109 J/Ļ decays collected with the BESIII detector, partial wave analyses of the decay J/Ļ ā Ī³K0SK0SĻ0 are performed within the K0SK0SĻ0 invariant mass region below 1.6 GeV/c2. The covariant tensor amplitude method is used in both mass independent and mass dependent approaches. Both analysis approaches exhibit dominant pseudoscalar and axial vector components, and show good consistency for the other individual components. Furthermore, the mass dependent analysis reveals that the K0SK0 SĻ0 invariant mass spectrum for the pseudoscalar component can be well described with two isoscalar resonant states using relativistic Breit-Wigner model, i.e., the Ī·(1405) with a mass of 1391.7Ā±0.7+11.3 ā0.3 MeV/c 2 and a width of 60.8Ā±1.2+5.5 ā12.0 MeV, and the Ī·(1475) with a mass of 1507.6Ā±1.6+15.5ā32.2 MeV/c2 and a width of 115.8Ā±2.4 +14.8 ā10.9 MeV. The first and second uncertainties are statistical and systematic, respectively. Alternate models for the pseudoscalar component are also tested, but the description of the K0SK0SĻ0invariant mass spectrum deteriorates significantly.
We report a measurement of the cross section for the process e+eāāĻ+ĻāJ/Ļ around the X(3872) mass in search for the direct formation of e+eāāX(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)āĻ+ĻāJ/Ļ is determined to be ĪeeĆB(X(3872)āĻ+ĻāJ/Ļ)<7.5Ć10ā3eV at 90% confidence level under an assumption of total width of 1.19Ā±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)āĻ+ĻāJ/Ļ), an upper limit on the electronic width Īee of X(3872) is obtained to be <0.32eV at the 90% confidence level.
A measurement of the CP-even fraction of the decay D0āĻ+ĻāĻ+Ļā is performed with a quantum-correlated Ļ(3770)āDDĀÆ data sample collected by the BESIII experiment, corresponding to an integrated luminosity of 2.93 fbā1. Using a combination of CP eigenstates, DāĻ+ĻāĻ0 and DāK0S,LĻ+Ļā as tagging modes, the CP-even fraction is measured to be F4Ļ+=0.735Ā±0.015Ā±0.005, where the first uncertainty is statistical and the second is systematic. This is the most precise determination of this quantity to date. It provides valuable model-independent input for the measurement of the CKM angle Ī³ with BĀ±āDKĀ± decays, and for time-dependent studies of CP violation and mixing in the D0-DĀÆ0 system.
A measurement of the š¶ā¢š-even fraction of the decay š·0āš+ā¢šāā¢š+ā¢šā is performed with a quantum-correlated šā”(3770)āš·ā¢ĀÆš· data sample collected by the BESIII experiment, corresponding to an integrated luminosity of 2.93āāfbā1. Using a combination of š¶ā¢š eigenstates, š·āš+ā¢šāā¢š0 and š·āš¾0š,šæā¢š+ā¢šā as tagging modes, the š¶ā¢š-even fraction is measured to be š¹4ā¢š+=0.735Ā±0.015Ā±0.005, where the first uncertainty is statistical and the second is systematic. This is the most precise determination of this quantity to date. It provides valuable model-independent input for the measurement of the angle š¾ of the Cabibbo-Kobayashi-Maskawa matrix with šµĀ±āš·ā¢š¾Ā± decays, and for time-dependent studies of š¶ā¢š violation and mixing in the š·0āĀÆš·0 system.
Using a data sample of (448.1Ā±2.9)Ć106āāšā”(3686) decays collected at an š+ā¢šā center-of-mass energy of 3.686 GeV by the BESIII detector at Beijing Electron Positron Collider II, we report an observation of the hindered electromagnetic Dalitz decay šā”(3686)āš+ā¢šāā¢šš with a significance of 7.9ā¢š. The branching fraction is determined to be ā¬ā”(šā”(3686)āš+ā¢šāā¢šš)=(3.77Ā±0.4ā¢0statĀ±0.1ā¢8syst)Ć10ā5, agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the šā”(3686) and the šš, which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of šš decays.
We use lattice QCD to investigate the spectrum of the ĀÆšĀÆšā¢š¢ā¢š four-quark system with quantum numbers š¼ā”(š½š)=0ā¢(1+). We use five different gauge-link ensembles with 2+1 flavors of domain-wall fermions, including one at the physical pion mass, and treat the heavy ĀÆš quark within the framework of lattice nonrelativistic QCD. Our work improves upon previous similar computations by considering in addition to local four-quark interpolators also nonlocal two-meson interpolators and by performing a LĆ¼scher analysis to extrapolate our results to infinite volume. We obtain a binding energy of (ā128Ā±24Ā±10)āāMeV, corresponding to the mass (10476Ā±24Ā±10)āāMeV, which confirms the existence of a ĀÆšā¢ĀÆšā¢š¢ā¢š tetraquark that is stable with respect to the strong and electromagnetic interactions.
We present our recent results on antiheavy-antiheavy-light-light tetraquark systems using lattice QCD. Our study of the bĀÆbĀÆus four-quark system with quantum numbers JP=1+ and the bĀÆcĀÆud four-quark systems with I(JP)=0(0+) and I(JP)=0(1+) utilizes scattering operators at the sink to improve the extraction of the low-lying energy levels. We found a bound state for bĀÆbĀÆus with Ebind,bĀÆbĀÆus=(ā86Ā±22Ā±10)MeV, but no indication for a bound state in both bĀÆcĀÆud channels. Moreover, we show preliminary results for bĀÆbĀÆud with I(JP)=0(1+), where we used scattering operators both at the sink and the source. We found a bound state and determined its infinite-volume binding energy with a scattering analysis, resulting in Ebind,bĀÆbĀÆud=(ā103Ā±8)MeV.
The rare decay šā²āš+ā¢šāā¢š+ā¢šā is studied using a sample of 1.3Ć109āāš½/š events collected with the BESIII detector at BEPCII in 2009 and 2012. The branching fraction is measured with improved precision to be (2.42Ā±0.0ā¢5statĀ±0.0ā¢8syst)Ć10ā3. Due to the inclusion of new data, this result supersedes the last BESIII result on this branching fraction. In addition, the š¶ā¢š-violating asymmetry in the angle between the decay planes of the š+ā¢šā-pair and the š+ā¢šā-pair is investigated. A measurable value would indicate physics beyond the standard model; the result is šš¶ā¢š=(2.9Ā±3.ā¢7statĀ±1.ā¢1syst)%, which is consistent with the standard model expectation of no š¶ā¢š-violation. The precision is comparable to the asymmetry measurement in the š¾0šæāš+ā¢šāā¢š+ā¢šā decay where the observed (14Ā±2)% effect is driven by a standard model mechanism.
Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider, we search for the process š+ā¢šāāššā¢šā¢š+ā¢šā. The search is performed using five large datasets recorded at center-of-mass energies of 4.23, 4.26, 4.36, 4.42, and 4.60 GeV. The šš meson is reconstructed in 16 exclusive decay modes. No signal is observed in the šš mass region at any center-of-mass energy. The upper limits on the reaction cross sections are determined to be 6.2, 10.8, 27.6, 22.6 and 23.7 pb at the 90% confidence level at the center-of-mass energies listed above.
Using a sample of 1.31Ć109āāš½/š events collected with the BESIII detector, we perform a study of š½/šāš¾ā¢šā¢šā¢šā² to search for the šā”(2370) and šš in the šā¢šā¢šā² invariant mass distribution. No significant signal for the šā”(2370) is observed, and we set an upper limit for the product branching fraction of ā¬(š½/šāš¾ā¢šā”(2370)Ā·ā¬ā”(šā”(2370)āšā¢šā¢šā²)<9.2Ć10ā6 at the 90% confidence level. A clear šš signal is observed for the first time, yielding a product branching fraction of ā¬ā”(š½/šāš¾ā¢šš)Ā·ā¬ā”(ššāšā¢šā¢šā²)=(4.86Ā±0.62ā¢(stat)Ā±0.45ā¢(sys))Ć10ā5.
Using (1310.6Ā±7.0)Ć106 š½/š events acquired with the BESIII detector at the BEPCII storage rings, the decay šā²āš+ā¢šāā¢š+ā¢šā is observed for the first time with a significance of 8ā¢š via the process š½/šāš¾ā¢šā². We measure the branching fraction of šā²āš+ā¢šāā¢š+ā¢šā to be ā¬ā”(šā²āš+ā¢šāā¢š+ā¢šā)=(1.97Ā±0.33ā¢(stat)Ā±0.19ā¢(syst))Ć10ā5, where the first and second uncertainties are statistical and systematic, respectively
he Born cross sections for the process š+ā¢šāāšā²ā¢š+ā¢šā 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 6.3ā¢š and a mass and width of š=(2111Ā±43Ā±25)āāMeV/š2 and Ī=(135Ā±34Ā±30)āāMeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in š+ā¢šāāšā²ā¢š+ā¢šā and BESIII in š+ā¢šāāšā¢š0 within two standard deviations.
The Born cross sections for the process e+eāāĪ·ā²Ļ+Ļā 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 6.3Ļ and a mass and width of M=(2111Ā±43Ā±25)~MeV/c2 and Ī=(135Ā±34Ā±30)~MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in e+eāāĪ·ā²Ļ+Ļā and BESIII in e+eāāĻĻ0 within two standard deviations.
The Born cross sections for the process e+eāāĪ·ā²Ļ+Ļā 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 6.3Ļ and a mass and width of M=(2108Ā±46Ā±25)~MeV/c2 and Ī=(138Ā±36Ā±30)~MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in e+eāāĪ·ā²Ļ+Ļā and BESIII in e+eāāĻĻ0 within two standard deviations.
The Born cross sections for the process e+eāāĪ·ā²Ļ+Ļā 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 6.3Ļ and a mass and width of M=(2108Ā±46Ā±25)~MeV/c2 and Ī=(138Ā±36Ā±30)~MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in e+eāāĪ·ā²Ļ+Ļā and BESIII in e+eāāĻĻ0 within two standard deviations.
We report a study of the processes of e+eāāK+(DāsDā0+DāāsD0) based on e+eā 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 fbā1. An excess over the known contributions of the conventional charmed mesons is observed near the DāsDā0 and DāāsD0 mass thresholds in the K+ recoil-mass spectrum for events collected at sā=4.681 GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5+1.8ā2.6Ā±2.1) MeV/c2 and (12.8+5.3ā4.4Ā±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 Ļ over the contributions only from the conventional charmed mesons. This is the first candidate of the charged hidden-charm tetraquark with strangeness, decaying into DāsDā0 and DāāsD0. However, the properties of the excess need further exploration with more statistics.
We report a study of the processes of e+eāāK+(DāsDā0+DāāsD0) based on e+eā 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 fbā1. An excess over the known contributions of the conventional charmed mesons is observed near the DāsDā0 and DāāsD0 mass thresholds in the K+ recoil-mass spectrum for events collected at sā=4.681 GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5+1.8ā2.6Ā±2.1) MeV/c2 and (12.8+5.3ā4.4Ā±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 Ļ over the pure contributions from the conventional charmed mesons. This is the first candidate of the charged hidden-charm tetraquark with strangeness, decaying into DāsDā0 and DāāsD0. However, the genuine properties of the excess need further exploration with more statistics.
We report a study of the processes of š+ā¢šāāš¾+ā¢š·āš ā¢š·*0 and š¾+ā¢š·*āš ā¢š·0 based on š+ā¢šā 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 3.7āāfbā1. An excess of events over the known contributions of the conventional charmed mesons is observed near the š·āš ā¢š·*0 and š·*āš ā¢š·0 mass thresholds in the š¾+ recoil-mass spectrum for events collected at āš =4.681āāGeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5+1.8
ā2.6Ā±2.1)āāMeV/š2 and (12.8+5.3ā4.4Ā±3.0)āāMeV, respectively. The first uncertainties are statistical and the second are systematic. The significance of the resonance hypothesis is estimated to be 5.3āāš over the contributions only from the conventional charmed mesons. This is the first candidate for a charged hidden-charm tetraquark with strangeness, decaying into š·āš ā¢š·*0 and š·*āš ā¢š·0. However, the properties of the excess need further exploration with more statistics.
In this work we investigate the existence of bound states for doubly heavy tetraquark systems QĀÆQĀÆā²qqā² in a full lattice-QCD computation, where heavy bottom quarks are treated in the framework of non-relativistic QCD. We focus on three systems with quark content bĀÆbĀÆud, bĀÆbĀÆus and bĀÆcĀÆud. We show evidence for the existence of bĀÆbĀÆud and bĀÆbĀÆus bound states, while no binding appears to be present for bĀÆcĀÆud. For the bound four-quark states we also discuss the importance of various creation operators and give an estimate of the meson-meson and diquark-antidiquark percentages.
In this work we investigate the existence of bound states for doubly heavy tetraquark systems QĀÆQĀÆā²qqā² in a full lattice-QCD computation, where heavy bottom quarks are treated in the framework of non-relativistic QCD. We focus on three systems with quark content bĀÆbĀÆud, bĀÆbĀÆus and bĀÆcĀÆud. We show evidence for the existence of bĀÆbĀÆud and bĀÆbĀÆus bound states, while no binding appears to be present for bĀÆcĀÆud. For the bound four-quark states we also discuss the importance of various creation operators and give an estimate of the meson-meson and diquark-antidiquark percentages.
This thesis is concerned with the investigation of static and dynamic properties of quantum Heisenberg paramagnets in the absence of a magnetic field and therefore for vanishing magnetization. For this purpose a new formulation of the spin functional renormalization group (SFRG) is employed. The first manifestations of the SFRG were developed by Krieg and Kopietz, motivated by the FRG approach to ordinary field theories and the older works of Vaks, Larkin and Pikin on diagrammatic methods for spin operators.
The main idea is to study quantum spin systems by considering the evolution of correlation functions under a continuous deformation of the interaction between magnetic moments, starting from a solvable limit. This leads to nonperturbative results for quantities like the spin-spin correlation function. After a basic introduction to the phenomena and concomitant problems discussed in this thesis, a detailed description of the SFRG method in its initial formulation is given in the second chapter. We start with the generating functional of connected imaginary-time spin-correlation functions GĪ [h], for which an exact flow equation is derived. A particular issue, already pointed out by Krieg and Kopietz, arises here, namely the singular non-interacting limit of its subtracted Legendre transform ĪĪ [m]. As a consequence the initial condition of that functional does not have a proper series expansion in powers of m. This prevents us from working directly within a pure one-particle irreducible (1-PI) parametrization of the correlation functions, as is often done in the context of field theories. Thus motivated, we develop a workaround explicitly tailored to paramagnets, which provides us with a functional that has a well-behaved Legendre transform. The new approach is based on a different treatment of fluctuations at zero and finite frequencies, analogous to a previous hybrid formulation for the symmetry-broken phase. Certain properties, considered to be highly relevant for isotropic paramagnets, as well as previous observations, already made in the study of simpler spin systems like the Ising model, serve as additional justifications for choosing this construction.
In the third chapter our new method is assessed by calculating the dynamic susceptibility G(k, iĻ) and thus the dynamic structure factor S(k, Ļ) in the symmetric phase. For this purpose an approximate integral equation for the dynamic polarization function Ī Ģ(k, iĻ) was derived. This equation results from a truncation of the hierarchy of flow equations and contains static quantities, that are assumed to be known from another source. Our first application is the high-temperature limit T ā ā in d ā¤ 3 dimensions. Salient features, believed to be part of the spin dynamics in isotropic Heisenberg magnets are also exhibited by our solution, like (anomalous) diffusion in a suitable hydrodynamic limit. Moreover we obtain the same order of magnitude for the diffusion coefficient D as in experiments and other theoretical calculations. Other aspects do not entirely agree with previous approaches.
Afterwards we continue by investigating systems close to the critical point Tc. Dynamic scaling forms for Ī Ģ(k, iĻ) and S(k, Ļ), which, like spin diffusion, are postulated on the basis of quite general physical arguments, are reproduced. Agreement of the line-shapes 2with neutron scattering experiments at T = Tc is found to be satisfying, with deviations for Ļ ā 0, that may be attributed to the simplicity of the approximation, like at infinite temperature.
Finally, we focus our attention on the thermodynamic properties of isotropic Heisenberg paramagnets by calculating the static susceptibility G(k). For this purpose we employ simple truncation schemes of the flow equations for the static self-energy Ī£Ī (k) and four-spin vertex ĪĪ , together with a basic ansatz for the dynamic polarization Ī Ģ(k, iĻ) in quantum systems. As a result we obtain transition temperatures Tc of three-dimensional nonfrustrated magnets within an accuracy of 5 percent compared to established benchmark values from Quantum Monte Carlo and high temperature expansion series. We conclude this chapter by giving an outlook on the application of our method to frustrated systems, which may require a combined non-trivial calculation of static and dynamic properties.
Using a data sample of (1310.6Ā±7.0)Ć106āāš½/š events taken with the BESIII detector at the center-of-mass energy of 3.097 GeV, we search for the first time for the lepton number violating decay Ī£āāšā¢šāā¢šā and the rare inclusive decay Ī£āāĪ£+ā¢š, where š denotes any possible particle combination. The Ī£ā candidates are tagged in š½/šāĀÆĪ£ā¢(1385)+ā¢Ī£ā decays. No signal candidates are found, and the upper limits on the branching fractions at the 90% confidence level are determined to be ā¬ā”(Ī£āāšā¢šāā¢šā)<6.7Ć10ā5 and ā¬ā”(Ī£āāĪ£+ā¢š)<1.2Ć10ā4.
Using 10.1 Ć 109 J/Ļ events produced by the Beijing Electron Positron Collider (BEPCII) at a center-of-mass energy ās = 3.097 GeV and collected with the BESIII detector, we present a search for the rare semi-leptonic decay J/Ļ ā Dāe+Ī½e + c.c. No excess of signal above background is observed, and an upper limit on the branching fraction B(J/Ļ ā Dāe +Ī½e + c.c.) < 7.1 Ć 10ā8 is obtained at 90% confidence level. This is an improvement of more than two orders of magnitude over the previous best limit.
Amplitude analysis and branching-fraction measurement of DāāŗāāāKāā°Kā»ĻāŗĻāŗ
(2021)
Using 6.32āāfbā1 of š+ā¢šā collision data collected by the BESIII detector at the center-of-mass energies between 4.178 and 4.226 GeV, an amplitude analysis of the š·+š āš¾0šā¢š¾āā¢š+ā¢š+ decays is performed for the first time to determine the intermediate-resonant contributions. The dominant component is the š·+š āš¾*ā¢(892)+ā¢ĀÆš¾*ā¢(892)0 decay with a fraction of (40.6Ā±2.ā¢9statĀ±4.ā¢9sys)%. Our results of the amplitude analysis are used to obtain a more precise measurement of the branching fraction of the š·+š āš¾0šā¢š¾āā¢š+ā¢š+ decay, which is determined to be (1.46Ā±0.0ā¢5statĀ±0.0ā¢5sys)%.
Using a total of 5.25 fbā1 of e+eā collision data with center-of-mass energies from 4.236 to 4.600 GeV, we report the first observation of the process e+eā ā Ī·Ļ(2S) with a statistical significance of 4.9 standard deviations. The data sets were collected by the BESIII detector operating at the BEPCII storage ring. We measure the yield of events integrated over center-of-mass energies and also present the energy dependence of the measured cross section.
The decays D ā KāĻ+Ļ+Ļā and D ā KāĻ+Ļ 0 are studied in a sample of quantum-correlated DDĀÆ pairs produced through the process e+eā ā Ļ(3770) ā DDĀÆ, exploiting a data set collected by the BESIII experiment that corresponds to an integrated luminosity of 2.93 fbā1 . Here D indicates a quantum superposition of a D0 and a DĀÆ 0 meson. By reconstructing one neutral charm meson in a signal decay, and the other in the same or a different final state, observables are measured that contain information on the coherence factors and average strong-phase differences of each of the signal modes. These parameters are critical inputs in the measurement of the angle Ī³ of the Unitarity Triangle in Bā ā DKā decays at the LHCb and Belle II experiments. The coherence factors are determined to be RK3Ļ = 0.52+0.12ā0.10 and RKĻĻ0 = 0.78 Ā± 0.04, with values for the average strong-phase differences that are Ī“ K3Ļ D = (167+31ā19)ā¦ and Ī“KĻĻ0D = (196+14ā15ā¦ , where the uncertainties include both statistical and systematic contributions. The analysis is re-performed in four bins of the phase-space of the D ā KāĻ+Ļ+Ļā to yield results that will allow for a more sensitive measurement of Ī³ with this mode, to which the BESIII inputs will contribute an uncertainty of around 6ā¦.
We report new measurements of the branching fraction ā¬ā”(š·+š āā+ā¢š), where ā+ is either š+ or š+ā”(āš+ā¢ĀÆšš), based on 6.32āāfbā1 of electron-positron annihilation data collected by the BESIII experiment at six center-of-mass energy points between 4.178 and 4.226 GeV. Simultaneously floating the š·+š āš+ā¢šš and š·+š āš+ā¢šš components yields ā¬ā”(š·+š āš+ā¢šš)=(5.21Ā±0.25Ā±0.17)Ć10ā2, ā¬ā”(š·+š āš+ā¢šš)=(5.35Ā±0.13Ā±0.16)Ć10ā3, and the ratio of decay widths š
=Īā”(š·+š āš+ā¢šš)Īā”(š·+š āš+ā¢šš)=9.7ā¢3+0.61ā0.58Ā±0.36, where the first uncertainties are statistical and the second systematic. No evidence of š¶ā¢š asymmetry is observed in the decay rates š·Ā±š āšĀ±ā¢šš and š·Ā±š āšĀ±ā¢šš: š“š¶ā¢šā”(šĀ±ā¢š)=(ā1.2Ā±2.5Ā±1.0)% and š“š¶ā¢šā”(šĀ±ā¢š)=(+2.9Ā±4.8Ā±1.0)%. Constraining our measurement to the Standard Model expectation of lepton universality (š
=9.75), we find the more precise results ā¬ā”(š·+š āš+ā¢šš)=(5.22Ā±0.10Ā±0.14)Ć10ā2 and š“š¶ā¢šā”(šĀ±ā¢šš)=(ā0.1Ā±1.9Ā±1.0)%. Combining our results with inputs external to our analysis, we determine the šāĀÆš quark mixing matrix element, š·+š decay constant, and ratio of the decay constants to be |ššā¢š |=0.973Ā±0.009Ā±0.014, šš·+š =249.9Ā±2.4Ā±3.5āāMeV, and šš·+š /šš·+=1.232Ā±0.035, respectively.
Using 2.93 fbā1 of e+eā collision data taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, the observation of the D0āK1(1270)āe+Ī½e semileptonic decay is presented. The statistical significance of the decay D0āK1(1270)āe+Ī½e is greater than 10Ļ. The branching fraction of D0āK1(1270)āe+Ī½e is measured to be (1.09Ā±0.13+0.09ā0.16Ā±0.12)Ć10ā3. Here, the first uncertainty is statistical, the second is systematic, and the third originates from the assumed branching fraction of K1(1270)āāKāĻ+Ļā. The fraction of longitudinal polarization in D0āK1(1270)āe+Ī½e is determined for the first time to be 0.50Ā±0.19statĀ±0.08syst.
Using 2.93 fbā1 of e+eā collision data taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, the observation of the D0āK1(1270)āe+Ī½e semileptonic decay is presented. The statistical significance of the decay D0āK1(1270)āe+Ī½e is greater than 10Ļ. The branching fraction of D0āK1(1270)āe+Ī½e is measured to be (1.09Ā±0.13+0.09ā0.13Ā±0.12)Ć10ā3. Here, the first uncertainty is statistical, the second is systematic, and the third originates from the assumed branching fraction of K1(1270)āāKāĻ+Ļā.
Measurement of branching fractions for D meson decaying into Ļ meson and a pseudoscalar meson
(2019)
The four decay modes D0 ā ĻĻ0, D0 ā ĻĪ·, D+ ā ĻĻ+, and D+ ā ĻK + are studied by using a data sample taken at the centre-of-mass energy ās = 3.773 GeV with the BESIII detector, corresponding to an integrated luminosity of 2.93 fbā1. The branching fractions of the first three decay modes are measured to be B(D0 ā ĻĻ0) = (1.168 Ā± 0.028 Ā± 0.028) Ć 10ā3, B(D0 ā ĻĪ·) = (1.81 Ā± 0.46 Ā± 0.06) Ć 10ā4, and B(D+ ā ĻĻ+) = (5.70 Ā± 0.05 Ā± 0.13) Ć 10ā3, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the upper limit of the branching fraction for D+ ā ĻK+ is given to be 2.1 Ć 10ā5 at the 90% confidence level. The ratio of B(D0 ā ĻĻ0) to B(D+ ā ĻĻ+) is calculated to be (20.49 Ā± 0.50 Ā± 0.45)%, which is consistent with the theoretical prediction based on isospin symmetry between these two decay modes.
Search for heavy Majorana neutrino in lepton number violating decays of DāāāKĻeāŗeāŗ
(2019)
Using a data sample with an integrated luminosity of 2.93āāfbā1 taken at the center-of-mass energy of 3.773 GeV, we search for the Majorana neutrino (šš) in the lepton number violating decays š·āš¾ā¢šā¢š+ā¢š+. No significant signal is observed, and the upper limits on the branching fraction at the 90% confidence level are set to be ā¬ā”(š·0āš¾āā¢šāā¢š+ā¢š+)<2.8Ć10ā6, ā¬ā”(š·+āš¾0šā¢šāā¢š+ā¢š+)<3.3Ć10ā6 and ā¬ā”(š·+āš¾āā¢š0ā¢š+ā¢š+)<8.5Ć10ā6. The Majorana neutrino is searched for with different mass assumptions ranging from 0.25 to 1.0āāGeV/š2 in the decays š·0āš¾āā¢š+ā¢šš,ššāšāā¢š+ and š·+āš¾0šā¢š+ā¢šš,ššāšāā¢š+, and the upper limits on the branching fraction at the 90% confidence level are at the level of 10ā7ā¼10ā6, depending on the mass of the Majorana neutrino. The constraints on the mixing matrix element |ššā¢šš|2 are also evaluated.
We study the electromagnetic Dalitz decay š½/šāš+ā¢šāā¢š and search for dielectron decays of a dark gauge boson (š¾ā²) in š½/šāš¾ā²ā¢š with the two š decay modes šāš¾ā¢š¾ and šāš+ā¢šāā¢š0 using (1310.6Ā±7.0)Ć106āāš½/š events collected with the BESIII detector. The branching fraction of š½/šāš+ā¢šāā¢š is measured to be (1.43Ā±0.04ā¢(stat)Ā±0.06ā¢(syst))Ć10ā5, with a precision that is improved by a factor of 1.5 over the previous BESIII measurement. The corresponding dielectron invariant mass dependent modulus square of the transition form factor is explored for the first time, and the pole mass is determined to be Ī=2.84Ā±0.11ā¢(stat)Ā±0.08ā¢(syst)āāGeV/š2. We find no evidence of š¾ā² production and set 90% confidence level upper limits on the product branching fraction ā¬ā”(š½/šāš¾ā²ā¢š)Ćā¬ā”(š¾ā²āš+ā¢šā) as well as the kinetic mixing strength between the standard model photon and š¾ā² in the mass range of 0.01ā¤šš¾ā²ā¤2.4āāGeV/š2.
By analyzing (448.1Ā±2.9)Ć106āāšā”(3686) events collected with the BESIII detector operating at the BEPCII collider, the decays of ššā¢š½āĪā¢
ĀÆĪā¢š (š½=0, 1, and 2) are observed for the first time with statistical significances of 13.9ā¢š, 6.7ā¢š, and 8.2ā¢š, respectively. The product branching fractions of šā”(3686)āš¾ā¢ššā¢š½ and ššā¢š½āĪā¢ĀÆĪā¢š are measured. Dividing by the world averages of the branching fractions of šā”(3686)āš¾ā¢ššā¢š½, the branching fractions of ššā¢š½āĪā¢ĀÆĪā¢š decays are determined to be (2.31Ā±0.30Ā±0.21)Ć10ā4, (5.86Ā±1.38Ā±0.68)Ć10ā5, and (1.05Ā±0.21Ā±0.15)Ć10ā4 for š½=0, 1 and 2, respectively, where the first uncertainties are statistical and the second systematic.
Using e+eā annihilation data sets collected with the BESIII detector, we measure the cross sections of the processes e+eāāe+eā and e+eāāĪ¼+Ī¼ā at fifteen center-of-mass energy points in the vicinity of the J/Ļ resonance. By a simultaneous fit to the measured, center-of-mass energy dependent cross sections of the two processes, the combined quantities ĪeeĪee/Ītot and ĪeeĪĪ¼Ī¼/Ītot are determined to be (0.346Ā±0.009) and (0.335Ā±0.006) keV, respectively, where Īee, ĪĪ¼Ī¼, and Ītot are the electronic, muonic, and total decay widths of the J/Ļ resonance, respectively. Using the resultant ĪeeĪĪ¼Ī¼/Ītot and ĪeeĪee/Ītot, the ratio Īee/ĪĪ¼Ī¼ is calculated to be 1.031Ā±0.015, which is consistent with the expectation of lepton universality within about two standard deviations. Assuming lepton universality and using the branching fraction of the J/Ļ leptonic decay measured by BESIII in 2013, Ītot and Īll are determined to be (93.0Ā±2.1) and (5.56Ā±0.11) keV, respectively, where Īll is the average leptonic decay width of the J/Ļ resonance.
Ten hadronic final states of the āš decays are investigated via the process šā”(3686)āš0ā¢āš, using a data sample of (448.1Ā±2.9)Ć106āāšā”(3686) events collected with the BESIII detector. The decay channel āšāš¾+ā¢š¾āā¢š+ā¢šāā¢š0 is observed for the first time and has a measured significance of 6.0ā¢š. The corresponding branching fraction is determined to be ā¬ā”(āšāš¾+ā¢š¾āā¢š+ā¢šāā¢š0)=(3.3Ā±0.6Ā±0.6)Ć10ā3 (where the uncertainties are statistical and systematic, respectively). Evidence for the decays āšāš+ā¢šāā¢š0ā¢š and āšāš¾0šā¢š¾Ā±ā¢šāā¢š+ā¢šā is found with a significance of 3.6ā¢š and 3.8ā¢š, respectively. The corresponding branching fractions (and upper limits) are obtained to be ā¬ā”(āšāš+ā¢šāā¢š0ā¢š)=(7.2Ā±1.8Ā±1.3)Ć10ā3 (<1.8Ć10ā2) and ā¬ā”(āšāš¾0šā¢š¾Ā±ā¢šāā¢š+ā¢šā)=(2.8Ā±0.9Ā±0.5)Ć10ā3 (<4.7Ć10ā3). Upper limits on the branching fractions for the final states āšāš¾+ā¢š¾āā¢š0, š¾+ā¢š¾āā¢š, š¾+ā¢š¾āā¢š+ā¢šāā¢š, 2ā¢(š¾+ā¢š¾ā)ā¢š0, š¾+ā¢š¾āā¢š0ā¢š, š¾0šā¢š¾Ā±ā¢šā, and šā¢ĀÆšā¢š0ā¢š0 are determined at a confidence level of 90%.
Using a dedicated data sample taken in 2018 on the J/Ļ peak, we perform a detailed study of the trigger efficiencies of the BESIII detector. The efficiencies are determined from three representative physics processes, namely Bhabha scattering, dimuon production and generic hadronic events with charged particles. The combined efficiency of all active triggers approaches 100% in most cases, with uncertainties small enough not to affect most physics analyses.
Born cross sections for the processes e+eā ā ĻĪ· and e+eā ā ĻĻ0 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+eā ā ĻĪ· cross sections, a resonance with a mass of (2176 Ā± 24 Ā± 3) MeV/c2 and a width of (89 Ā± 50 Ā± 5) MeV is observed with a significance of 6.2Ļ. Its properties are consistent with the Ļ(2170). In the e+eā ā ĻĻ0 cross sections, a resonance denoted Y (2040) is observed with a significance of more than 10Ļ. Its mass and width are determined to be (2034 Ā± 13 Ā± 9) MeV/c2 and (234 Ā± 30 Ā± 25) MeV, respectively, where the first uncertainties are statistical and the second ones are systematic.
The Born cross sections of the e+eā ā +ĀÆ ā and e+eā ā āĀÆ + 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 ā 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 Ā± form factors require more theoretical discussions for the hyperons.