The discovery of the Higgs boson with its mass around 125 GeV by the ATLAS and CMS Collaborations marked the beginning of a new era in high energy physics.The Higgs boson will be the subject of extensive studies of th...The discovery of the Higgs boson with its mass around 125 GeV by the ATLAS and CMS Collaborations marked the beginning of a new era in high energy physics.The Higgs boson will be the subject of extensive studies of the ongoing LHC program.At the same time,lepton collider based Higgs factories have been proposed as a possible next step beyond the LHC,with its main goal to precisely measure the properties of the Higgs boson and probe potential new physics associated with the Higgs boson.The Circular Electron Positron Collider(CEPC)is one of such proposed Higgs factories.The CEPC is an e^+e^- circular collider proposed by and to be hosted in China.Located in a tunnel of approximately 100 km in circumference,it will operate at a center-of-mass energy of 240 GeV as the Higgs factory.In this paper,we present the first estimates on the precision of the Higgs boson property measurements achievable at the CEPC and discuss implications of these measurements.展开更多
Based on 58 million J/ψ events collected by the BESⅡ detector at the BEPC, J/ψ→ΛΛ π＋π- is observed for the first time. The branching fraction is measured to be Br（J/ψ→ΛΛ π＋π-）=（4.30±0.13±0...Based on 58 million J/ψ events collected by the BESⅡ detector at the BEPC, J/ψ→ΛΛ π＋π- is observed for the first time. The branching fraction is measured to be Br（J/ψ→ΛΛ π＋π-）=（4.30±0.13±0.99）×10-3, excluding the decays to intermediate states, namely J/ψ→Ξ-Ξ＋, J/ψ→Σ（1385）-Σ（1385）＋, and J/ψ→Σ（1385）＋Σ（1385）-. The branching fractions for these intermediate resonance channels are measured to be：Br（J/ψ→Ξ-Ξ＋）=（0.90±0.03±0.18）×10-3, Br（J/ψ→Σ（1385）-Σ（1385）＋）=（1.23±0.07±0.30）×10-3,and Br（J/ψ→Σ（1385）＋Σ（1385）-）=（1.50±0.08±0.38）×10-3, respectively. The angular distribution is of the form dN/d（cosθ）α（1＋αcos2θ） with α=（0.35±0.29±0.06） for J/ψ→Ξ-Ξ＋, α=（-0.54±0.22±0.10） for J/ψ→Σ（1385）-Σ（1385）＋, and α=（-0.35±0.29±0.06） for J/ψ→Σ（1385）＋Σ（1385）-.展开更多
The decay ψ（2S）→Ω-Ω＋ is analyzed using 14×106 ψ（2S） events recorded by the Beijing Spectrometer Ⅱ （BESⅡ） at the Beijing Electron Positron Collider （BEPC）. Based upon events with no missing charged...The decay ψ（2S）→Ω-Ω＋ is analyzed using 14×106 ψ（2S） events recorded by the Beijing Spectrometer Ⅱ （BESⅡ） at the Beijing Electron Positron Collider （BEPC）. Based upon events with no missing charged tracks and a satisfactory four-constraint kinematic t, we determine the upper limit for the branching fraction of ψ（2S）→Ω-Ω＋ to be 1.5×104 at a 90% confidence level. By including events with one missing charged track, we are able to report the first evidence of an Ω＋ signal with a statistical signi cance of 3.1｜σ. The branching fraction of ψ（2S）Ω＋ is determined to be （4.80±1.56（stat）±1.30（sys））105.展开更多
We investigate fermionic dark matter interactions with standard model particles from an additional U(1)X gauge symmetry,assuming kinetic mixing between the U(1)X and U(1)Y gauge fields as well as a nonzero U(1)X charg...We investigate fermionic dark matter interactions with standard model particles from an additional U(1)X gauge symmetry,assuming kinetic mixing between the U(1)X and U(1)Y gauge fields as well as a nonzero U(1)X charge of the Higgs doublet.To ensure gauge-invariant Yukawa interactions and the cancellation of gauge anomalies,standard model fermions are assigned Y-sequential U(1)X charges proportional to the Higgs charge.Although the Higgs charge should be small owing to collider constraints,it is useful to decrease the effective cross section of dark matter scattering off nucleons by two orders of magnitude to easily evade direct detection bounds.After performing numerical scans in the parameter space,we find that the introduction of the Higgs charge can also enhance the dark matter relic density by at least two orders of magnitude.In the case where the resonance effect is important for dark matter freeze-out,when the observed relic density and direct detection constraints are tangled,the Higgs charge can expand physical windows to some extent by relieving the tension between the relic density and direct detection.展开更多
We study the sensitivity of constraining the model independent HZZ coupling based on the effective theory up to dimension-6 operators at a future Higgs factory. Using the current conceptual design parameters of the Ci...We study the sensitivity of constraining the model independent HZZ coupling based on the effective theory up to dimension-6 operators at a future Higgs factory. Using the current conceptual design parameters of the Circular Electron Positron Collider, we give the experimental limits for the model independent operators given by the total Higgsstrahlung cross-section and the angular distribution of Z boson decays. In particular, we give the very small sensitivity limit for the CP violation parameter g, which will be a clear window to test the Standard Model and look for new physics signals.展开更多
基金Supported by the National Key Program for S&T Researh and Development(2016YFA0400400)CAS Center for Excellence in Particle Physics+12 种基金Yifang Wang’s Science Studio of the Ten Thousand Talents Projectthe CAS/SAFEA International Partnership Program for Creative Research Teams(H751S018S5)IHEP Innovation Grant(Y4545170Y2)Key Research Program of Frontier Sciences,CAS(XQYZDY-SSW-SLH002)Chinese Academy of Science Special Grant for Large Scientific Project(113111KYSB20170005)the National Natural Science Foundation of China(11675202)the Hundred Talent Programs of Chinese Academy of Science(Y3515540U1)the National 1000 Talents Program of ChinaFermi Research Alliance,LLC(DE-AC02-07CH11359)the NSF(PHY1620074)by the Maryland Center for Fundamental Physics(MCFP)Tsinghua University Initiative Scientific Research Programthe Beijing Municipal Science and Technology Commission project(Z181100004218003)
文摘The discovery of the Higgs boson with its mass around 125 GeV by the ATLAS and CMS Collaborations marked the beginning of a new era in high energy physics.The Higgs boson will be the subject of extensive studies of the ongoing LHC program.At the same time,lepton collider based Higgs factories have been proposed as a possible next step beyond the LHC,with its main goal to precisely measure the properties of the Higgs boson and probe potential new physics associated with the Higgs boson.The Circular Electron Positron Collider(CEPC)is one of such proposed Higgs factories.The CEPC is an e^+e^- circular collider proposed by and to be hosted in China.Located in a tunnel of approximately 100 km in circumference,it will operate at a center-of-mass energy of 240 GeV as the Higgs factory.In this paper,we present the first estimates on the precision of the Higgs boson property measurements achievable at the CEPC and discuss implications of these measurements.
基金Supported by National Natural Science Foundation of China(10491300,10225524,10225525,10425523,10625524,10521003,10821063,10825524)Chinese Academy of Sciences(KJ95T-03)+3 种基金100Talents Program of CAS(U-11,U-24,U-25)Knowledge Innovation Project of CAS(U-602,U-34)(IHEP)National Natural Science Foundation of China(10775077,10225522)(Tsinghua University)Department of Energy(DE-FG02-04ER41291)(U.Hawaii)
文摘Based on 58 million J/ψ events collected by the BESⅡ detector at the BEPC, J/ψ→ΛΛ π＋π- is observed for the first time. The branching fraction is measured to be Br（J/ψ→ΛΛ π＋π-）=（4.30±0.13±0.99）×10-3, excluding the decays to intermediate states, namely J/ψ→Ξ-Ξ＋, J/ψ→Σ（1385）-Σ（1385）＋, and J/ψ→Σ（1385）＋Σ（1385）-. The branching fractions for these intermediate resonance channels are measured to be：Br（J/ψ→Ξ-Ξ＋）=（0.90±0.03±0.18）×10-3, Br（J/ψ→Σ（1385）-Σ（1385）＋）=（1.23±0.07±0.30）×10-3,and Br（J/ψ→Σ（1385）＋Σ（1385）-）=（1.50±0.08±0.38）×10-3, respectively. The angular distribution is of the form dN/d（cosθ）α（1＋αcos2θ） with α=（0.35±0.29±0.06） for J/ψ→Ξ-Ξ＋, α=（-0.54±0.22±0.10） for J/ψ→Σ（1385）-Σ（1385）＋, and α=（-0.35±0.29±0.06） for J/ψ→Σ（1385）＋Σ（1385）-.
基金Supported by National Natural Science Foundation of China （10491300, 10225524, 10225525, 10425523, 10625524, 10521003, 10821063, 10825524）, Chinese Academy of Sciences （KJ 95T-03）, 100 Talents Program of CAS （U-11, U-24, U-25）, Knowledge Innovation Project of CAS （U-602, U-34 （IHEP））, National Natural Science Foundation of China （10775077, 10225522） （Tsinghua University）, and Department of Energy （DE-FG02-04ER41291） （U. Hawaii）
文摘The decay ψ（2S）→Ω-Ω＋ is analyzed using 14×106 ψ（2S） events recorded by the Beijing Spectrometer Ⅱ （BESⅡ） at the Beijing Electron Positron Collider （BEPC）. Based upon events with no missing charged tracks and a satisfactory four-constraint kinematic t, we determine the upper limit for the branching fraction of ψ（2S）→Ω-Ω＋ to be 1.5×104 at a 90% confidence level. By including events with one missing charged track, we are able to report the first evidence of an Ω＋ signal with a statistical signi cance of 3.1｜σ. The branching fraction of ψ（2S）Ω＋ is determined to be （4.80±1.56（stat）±1.30（sys））105.
基金Supported by the National Natural Science Foundation of China(12135014)。
文摘We investigate fermionic dark matter interactions with standard model particles from an additional U(1)X gauge symmetry,assuming kinetic mixing between the U(1)X and U(1)Y gauge fields as well as a nonzero U(1)X charge of the Higgs doublet.To ensure gauge-invariant Yukawa interactions and the cancellation of gauge anomalies,standard model fermions are assigned Y-sequential U(1)X charges proportional to the Higgs charge.Although the Higgs charge should be small owing to collider constraints,it is useful to decrease the effective cross section of dark matter scattering off nucleons by two orders of magnitude to easily evade direct detection bounds.After performing numerical scans in the parameter space,we find that the introduction of the Higgs charge can also enhance the dark matter relic density by at least two orders of magnitude.In the case where the resonance effect is important for dark matter freeze-out,when the observed relic density and direct detection constraints are tangled,the Higgs charge can expand physical windows to some extent by relieving the tension between the relic density and direct detection.
基金supported in part by National Natural Science Foundation of China under Grant No.11521505 and 11621131001
文摘We study the sensitivity of constraining the model independent HZZ coupling based on the effective theory up to dimension-6 operators at a future Higgs factory. Using the current conceptual design parameters of the Circular Electron Positron Collider, we give the experimental limits for the model independent operators given by the total Higgsstrahlung cross-section and the angular distribution of Z boson decays. In particular, we give the very small sensitivity limit for the CP violation parameter g, which will be a clear window to test the Standard Model and look for new physics signals.
