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Institute
Born cross sections for the processes e+eβ β ΟΞ· and e+eβ β ΟΟ0 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+eβ β ΟΞ· cross sections, a resonance with a mass of (2176 Β± 24 Β± 3) MeV/c2 and a width of (89 Β± 50 Β± 5) MeV is observed with a significance of 6.2Ο. Its properties are consistent with the Ο(2170). In the e+eβ β ΟΟ0 cross sections, a resonance denoted Y (2040) is observed with a significance of more than 10Ο. Its mass and width are determined to be (2034 Β± 13 Β± 9) MeV/c2 and (234 Β± 30 Β± 25) MeV, respectively, where the first uncertainties are statistical and the second ones are systematic.
There has recently been a dramatic renewal of interest in hadron spectroscopy and charm physics. This renaissance has been driven in part by the discovery of a plethora of charmonium-like XYZ states at BESIII and B factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related X(1835) meson state at BESIII, as well as the threshold measurements of charm mesons and charm baryons.
We present a detailed survey of the important topics in tau-charm physics and hadron physics that can be further explored at BESIII during the remaining operation period of BEPCII. This survey will help in the optimization of the data-taking plan over the coming years, and provides physics motivation for the possible upgrade of BEPCII to higher luminosity.
Using 16 energy points of e+eβ annihilation data collected in the vicinity of the J/Ο resonance with the BESIII detector and with a total integrated luminosity of around 100 pbβ1, we study the relative phase between the strong and electromagnetic amplitudes of J/Ο decays. The relative phase between J/Ο electromagnetic decay and the continuum process (e+eβ annihilation without the J/Ο resonance) is confirmed to be zero by studying the cross section lineshape of ΞΌ+ΞΌβ production. The relative phase between J/Ο strong and electromagnetic decays is then measured to be (84.9 Β± 3.6)β¦ or (β84.7 Β± 3.1)β¦ for the 2(Ο+Οβ)Ο0 final state by investigating the interference pattern between the J/Ο decay and the continuum process. This is the first measurement of the relative phase between J/Ο 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 Ξ·Ο+Οβ with Ξ· β Ο+ΟβΟ0, which provides additional information about the phase between the J/Ο electromagnetic decay amplitude and the continuum process. Additionally, the branching fraction of J/Ο β 2(Ο+Οβ)Ο0 is measured to be (4.73 Β± 0.44)% or (4.85 Β± 0.45)%, and the branching fraction of J/Ο β Ξ·Ο+Οβ is measured to be (3.78 Β± 0.68) Γ 10β4. 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.
In particle collider experiments, elementary particle interactions with large momentum transfer produce quarks and gluons (known as partons) whose evolution is governed by the strong force, as described by the theory of quantum chromodynamics (QCD). These partons subsequently emit further partons in a process that can be described as a parton shower which culminates in the formation of detectable hadrons. Studying the pattern of the parton shower is one of the key experimental tools for testing QCD. This pattern is expected to depend on the mass of the initiating parton, through a phenomenon known as the dead-cone effect, which predicts a suppression of the gluon spectrum emitted by a heavy quark of mass mQ and energy E, within a cone of angular size mQ/E around the emitter. Previously, a direct observation of the dead-cone effect in QCD had not been possible, owing to the challenge of reconstructing the cascading quarks and gluons from the experimentally accessible hadrons. We report the direct observation of the QCD dead cone by using new iterative declustering techniques to reconstruct the parton shower of charm quarks. This result confirms a fundamental feature of QCD. Furthermore, the measurement of a dead-cone angle constitutes a direct experimental observation of the non-zero mass of the charm quark, which is a fundamental constant in the standard model of particle physics.
At particle collider experiments, elementary particle interactions with large momentum transfer produce quarks and gluons (known as partons) whose evolution is governed by the strong force, as described by the theory of quantum chromodynamics (QCD). The vacuum is not transparent to the partons and induces gluon radiation and quark pair production in a process that can be described as a parton shower. Studying the pattern of the parton shower is one of the key experimental tools in understanding the properties of QCD. This pattern is expected to depend on the mass of the initiating parton, through a phenomenon known as the dead-cone effect, which predicts a suppression of the gluon spectrum emitted by a heavy quark of mass m and energy E, within a cone of angular size m/E around the emitter. A direct observation of the dead-cone effect in QCD has not been possible until now, due to the challenge of reconstructing the cascading quarks and gluons from the experimentally accessible bound hadronic states. We report the first direct observation of the QCD dead-cone by using new iterative declustering techniques to reconstruct the parton shower of charm quarks. This result confirms a fundamental feature of QCD, which is derived more generally from its origin as a gauge quantum field theory. Furthermore, the measurement of a dead-cone angle constitutes a direct experimental observation of the non-zero mass of the charm quark, which is a fundamental constant in the standard model of particle physics.
We report the first measurement of the absolute branching fraction for Ξ+cβΞΞΌ+Ξ½ΞΌ. This measurement is based on a sample of e+eβ annihilation data at a center-of-mass energy of sβ=4.6 GeV collected with the BESIII detector at the BEPCII storage rings. The sample corresponds to an integrated luminosity of 567 pbβ1. The branching fraction is determined to be B(Ξ+cβΞΞΌ+Ξ½ΞΌ)=(3.49Β±0.46(stat)Β±0.27(syst))%. In addition, we calculate the ratio B(Ξ+cβΞΞΌ+Ξ½ΞΌ)/B(Ξ+cβΞe+Ξ½e) to be 0.96Β±0.16(stat)Β±0.04(syst).
Measurements of the branching fractions for D+βKS0KS0K+, KS0KS0Ο+ and D0βKS0KS0, KS0KS0KS0
(2016)
By analyzing 2.93 fbβ1 of data taken at the Ο(3770) resonance peak with the BESIII detector, we measure the branching fractions for the hadronic decays D+ β K0S K0S K +, D+ β K0S K0SΟ+, D0 β K0S K0S and D0 β K0S K0S K0S . They are determined to be B(D+ β K0S K0S K +) = (2.54 Β± 0.05stat. Β± 0.12sys.) Γ 10β3, B(D+ β K0S K0SΟ+) = (2.70 Β± 0.05stat. Β± 0.12sys.) Γ 10β3, B(D0 β K0S K0S ) = (1.67 Β± 0.11stat. Β± 0.11sys.) Γ 10β4 and B(D0 β K0S K0S K0S ) = (7.21 Β± 0.33stat. Β± 0.44sys.) Γ 10β4, 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 Ξ+cβΞ£βΟ+Ο+Ο0, based on data obtained in e+eβ annihilations with an integrated luminosity of 567~pbβ1 at sβ=4.6~GeV. The data were collected with the BESIII detector at the BEPCII storage rings. The absolute branching fraction B(Ξ+cβΞ£βΟ+Ο+Ο0) is determined to be (2.11Β±0.33(stat.)Β±0.14(syst.))%. In addition, an improved measurement of B(Ξ+cβΞ£βΟ+Ο+) is determined as (1.81Β±0.17(stat.)Β±0.09(syst.))%.
The decays of Οc2βK+KβΟ0, KSKΒ±Οβ and Ο+ΟβΟ0 are studied with the Ο(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of Οc2βKβKΒ―Β―Β―Β―Β―, Οc2βaΒ±2(1320)Οβ/a02(1320)Ο0 and Οc2βΟ(770)Β±Οβ are measured. Here KβKΒ―Β―Β―Β―Β― denotes both KβΒ±Kβ and Kβ0KΒ―Β―Β―Β―Β―0+c.c., and Kβ denotes the resonances Kβ(892), Kβ2(1430) and Kβ3(1780). The observations indicate a strong violation of the helicity selection rule in Οc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of Οc2βKβ(892)KΒ―Β―Β―Β―Β― are more than 10 times larger than the upper limit of Οc2βΟ(770)Β±Οβ, which is so far the first direct observation of a significant U-spin symmetry breaking effect in charmonium decays.
We report the first measurements of absolute branching fractions for the W -exchange-only processes + c β 0K + and + c β (1530)0K + with the double-tag technique, by analyzing an e+eβ collision data sample, that corresponds to an integrated luminosity of 567 pbβ1 collected at a center-of-mass energy of 4.6 GeV by the BESIII detector. The branching fractions are measured to be B(+c β 0K +) = (5.90 Β± 0.86 Β± 0.39) Γ 10β3 and B(+c β (1530)0K +) = (5.02 Β± 0.99 Β± 0.31) Γ 10β3, where the first uncertainties are statistical and the second systematic. Our results are more precise than the previous relative measurements.
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+eβ β ΟΟΟ and e+eβ β ΟΟΟ. The Born cross sections are measured and the ratio of the cross sections Ο(e+eβ β ΟΟΟ)/Ο(e+eβ β ΟΟΟ) is estimated to be 1.75 Β± 0.22 Β± 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.
The Born cross sections of the e+eβ β +Β― β and e+eβ β βΒ― + 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 β 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 Β± form factors require more theoretical discussions for the hyperons.
Using a data sample of 448.1 Γ 106 Ο(3686) events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay Ο(3686) β Ξ· e+eβ, with significances of 7.0Ο and 6.3Ο when reconstructing the Ξ· meson via its decay modes Ξ· β Ξ³Ο+Οβ and Ξ· β Ο+ΟβΞ· (Ξ· β Ξ³Ξ³ ), respectively. The weighted average branching fraction is determined to be B(Ο(3686) β Ξ· e+eβ) = (1.90 Β± 0.25 Β± 0.11) Γ 10β6, where the first uncertainty is statistical and the second systematic.
Based on e+eβ 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+eβ β ppΒ―Ο0 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+eβ β Y (4260) β ppΒ―Ο0 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)βppΒ―Ο0) B(Y (4260)βΟ+Οβ J/Ο) at the 90% C.L. is determined to be 0.02%.
The decays of Οc2βK+KβΟ0, KSKΒ±Οβ and Ο+ΟβΟ0 are studied with the Ο(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of Οc2βKβKΒ―Β―Β―Β―Β―, Οc2βaΒ±2(1320)Οβ/a02(1320)Ο0 and Οc2βΟ(770)Β±Οβ are measured. Here KβKΒ―Β―Β―Β―Β― denotes both KβΒ±Kβ and Kβ0KΒ―Β―Β―Β―Β―0+c.c., and Kβ denotes the resonances Kβ(892), Kβ2(1430) and Kβ3(1780). The observations indicate a strong violation of the helicity selection rule in Οc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of Οc2βKβ(892)KΒ―Β―Β―Β―Β― are more than 20 times larger than that of Οc2βΟ(770)Β±Οβ, which implies the effects are largely due to U-spin symmetry breaking, rather than just isospin symmetry breaking in charmonium decays.
The decays of Οc2βK+KβΟ0, KSKΒ±Οβ and Ο+ΟβΟ0 are studied with the Ο(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of Οc2βKβKΒ―Β―Β―Β―Β―, Οc2βaΒ±2(1320)Οβ/a02(1320)Ο0 and Οc2βΟ(770)Β±Οβ are measured. Here KβKΒ―Β―Β―Β―Β― denotes both KβΒ±Kβ and Kβ0KΒ―Β―Β―Β―Β―0+c.c., and Kβ denotes the resonances Kβ(892), Kβ2(1430) and Kβ3(1780). The observations indicate a strong violation of the helicity selection rule in Οc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of Οc2βKβ(892)KΒ―Β―Β―Β―Β― are more than 20 times larger than that of Οc2βΟ(770)Β±Οβ, which implies the effects are largely due to U-spin symmetry breaking, rather than just isospin symmetry breaking in charmonium decays.
We extract the e+eβ βΟ+Οβ 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 fbβ1 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 |FΟ|2 as well as the contribution of the measured cross section to the leading-order hadronic vacuum polarization contribution to (gβ2)ΞΌ. We find this value to be aΟΟ,LO ΞΌ (600β900 MeV) = (368.2 Β±2.5statΒ±3.3sys) Β·10β10, which is between the corresponding values using the BaBar or KLOE data.
The decays of Οc2βK+KβΟ0, KSKΒ±Οβ and Ο+ΟβΟ0 are studied with the Ο(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of Οc2βKβKΒ―Β―Β―Β―Β―, Οc2βaΒ±2(1320)Οβ/a02(1320)Ο0 and Οc2βΟ(770)Β±Οβ are measured. Here KβKΒ―Β―Β―Β―Β― denotes both KβΒ±Kβ and Kβ0KΒ―Β―Β―Β―Β―0+c.c., and Kβ denotes the resonances Kβ(892), Kβ2(1430) and Kβ3(1780). The observations indicate a strong violation of the helicity selection rule in Οc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of Οc2βKβ(892)KΒ―Β―Β―Β―Β― are more than 10 times larger than the upper limit of Οc2βΟ(770)Β±Οβ, which is so far the first direct observation of a significant U-spin symmetry breaking effect in charmonium decays.
Using an π+β’πβ collision data sample of 2.93ββfbβ1 collected at a center-of-mass energy of 3.773 GeV by the BESIII detector at BEPCII, we report the observation of π·0βπ0β’(980)ββ’π+β’ππ and evidence for π·+βπ0β’(980)0β’π+β’ππ with significances of 6.4β’π and 2.9β’π, respectively. The absolute branching fractions are determined to be β¬β‘(π·0βπ0β’(980)ββ’π+β’ππ)Γβ¬β‘(π0β’(980)ββπβ’πβ) = [1.3β’3+0.33β0.29β’(stat)Β±0.09β’(syst)]Γ10β4 and β¬β‘(π·+βπ0β’(980)0β’π+β’ππ)Γβ¬β‘(π0β’(980)0βπβ’π0)=[1.6β’6+0.81
β0.66β’(stat)Β±0.11β’(syst)]Γ10β4. This is the first time the π0β‘(980) meson has been measured in a π·0 semileptonic decay, which would open one more interesting page in the investigation of the nature of the puzzling π0β‘(980) states.
The cross section of the process e+eββK+Kβ is measured at a number of center-of-mass energies sβ from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of M=2239.2Β±7.1Β±11.3~and a width of Ξ=139.8Β±12.3Β±20.6 MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the time-like electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.