NLO QCD corrections to B_c(B_c~*) production around the Z pole at an e~+e~- collider

The production of B_c and B_c~* mesons at a Z-factory(an e~+e~- collider operating at energies around the Z pole) is calculated up to the next-to-leading order(NLO) QCD accuracy. The results show that the dependence of the total cross sections on the renormalization scale μ is suppressed by the corrections, and the NLO corrections enhance the total cross sections of B_c by 52%and of B_c~* by 33% when the renormalization scale is taken at μ = 2 mb. To observe the various behaviors of the production of the mesons B_c and B_c~*, such as the differential cross section vs. the out-going angle, the forward-backward asymmetry, and the distribution vs. the energy fraction z up to NLO QCD accuracy as well as the relevant K-factor(NLO to LO) for the production,are calculated, and it is pointed out that some of the observables obtained in the present work may be used as a specific precision test of the standard model.     

Probing new physics in dimension-8 neutral gauge couplings at e~+e~- colliders

Neutral triple gauge couplings(nTGCs)are absent in the standard model effective theory up to dimension-6 operators,but could arise from dimension-8 effective operators.In this work,we study the pure gauge operators of dimension-8 that contribute to nTGCs and are independent of the dimension-8 operator involving the Higgs doublet.We show that the pure gauge operators generate both ZγZ^*and Zγγ^*vertices with rapid energy dependence∝E^5,which can be probed sensitively via the reaction e^+e^-→Zγ.We demonstrate that measuring the nTGCs via the reaction e^+e^-→Zγfollowed by Z→qq decays can probe the new physics scales of dimension-8 pure gauge operators up to the range(1-5)TeV at the CEPC,FCC-ee and ILC colliders with s~(1/2)=(0.25-1)TeV,and up to the range(10-16)TeV at CLIC with s~(1/2)=(3-5)TeV,assuming in each case an integrated luminosity of 5 ab~(-1).We compare these sensitivities with the corresponding probes of the dimension-8 nTGC operators involving Higgs doublets and the dimension-8 fermionic contact operators that contribute to the e^+e^-Zγvertex.     

Exotic decays of the 125 GeV Higgs boson at future e~+e~- colliders

The discovery of unexpected properties of the Higgs boson would offer an intriguing opportunity to shed light on some of the most profound puzzles in particle physics. Beyond Standard Model(BSM) decays of the Higgs boson could reveal new physics in a direct manner. Future electron-positron lepton colliders operating as Higgs factories, including CEPC, FCC-ee and ILC, with the advantages of a clean collider environment and large statistics,could greatly enhance sensitivity in searching for these BSM decays. In this work, we perform a general study of Higgs exotic decays at future e~+e~-lepton colliders, focusing on the Higgs decays with hadronic final states and/or missing energy, which are very challenging for the High-Luminosity program of the Large Hadron Collider(HL-LHC).We show that with simple selection cuts,O(10~(-3)-10~(-5)) limits on the Higgs exotic decay branching fractions can be achieved using the leptonic decaying spectator Z boson in the associated production mode e~+e~-→ZH. We further discuss the interplay between detector performance and Higgs exotic decays, and other possibilities of exotic decays.Our work is a first step in a comprehensive study of Higgs exotic decays at future lepton colliders, which is a key area of Higgs physics that deserves further investigation.     

Hidden-charm Pentaquark Production at e~+e~- Colliders

We study one possible production mechanism for the hidden-charm pentaquark via a color-octet cc pair fragmentation in e~+e~-collision.The pentaquark production at B factory energy is dominated by e~+e~-→ccg→P_c+X,while at Z~0pole energy,there are several partonic processes playing significant role.Our results show that it is possible to search for the direct pentaquark production signal at e~+e~-colliders,which is important to understand the properties of pentaquark.     

Derived Born cross sections of e~+e~- annihilation into open charm mesons from CLEO-c measurements

The exclusive Born cross sections of the production of D~0, D~+ and D_s~+ smesons in e~+e~- annihilation at 13 energy points between 3.970 and 4.260 Ge V are obtained by applying corrections for initial state radiation and vacuum polarization to the observed cross sections measured by the CLEO-c experiment. Both the statistical and the systematic uncertainties for the obtained Born cross sections are estimated.     

Charmed baryon decay asymmetry in e~+e~- annihilation

We propose to measure the decay asymmetry parameters in the hadronic weak decays of singly charmed baryons, such as Λ_c~+ →Λπ~+, Σ~0π~+, pK_0, Ξ0c →Ξ-π+and ?0c →?-π+. The joint angular formulae for these processes are presented, and are used to extract the asymmetry parameters in e+e-annihilation data. Base on the currentΛ+c data set collected at BESIII, we estimate the experimental sensitivities to measure the parameters αΛπ+forΛ+c →Λπ+, αΣ+π0for Λ+c →Σ+π0and αΣ0π+for Λ+c →Σ0π+.     

An exclusive event generator for e~+ e~- scan experiments

An exclusive event generator is designed for e+e-scan experiments,including initial state radiation effects up to the second order correction.The generator is coded within the framework of BesEvtGen.There are seventy hadronic decay modes available,with effective center-of-mass energy coverage from the two pion mass threshold up to about 6 GeV.The accuracy achieved for the initial state radiation correction reaches the level achieved by the KKMC generator.The uncertainty associated with the calculation of the correction factor to the initial state radiation is dominated by the measurements of the energy-dependent Born cross section.     

FRAGMENTATION FUNCTIONS IN e~+e~-,ep AND pp COLLISIONS

<正>Revised August 2013 by 0.Biebel(Ludwig-Maximilians-Universitat.Munich,Germany),D.de Florian(Dep.de Fisica.FCEyN-UBA,Buenos Aires,Argentina),D.Milstead(Fysikum,Stockholms Universitet.Sweden),and A.Vogt(Dep.of Mathematical Sciences,University of Liverpool.UK).20.1.Introduction to fragmentation The term'fragmentation functions'is widely used for two conceptually different(albeit related)sets of functions describing final-state single particle energy distributions in hard scattering processes(see Refs.[1,2]for introductory reviews,and Refs.[3,4]for summaries of experimental and theoretical research in this field).The first are cross-section observables such as the functions F_T,L,A(x,s)in semi-inclusive e~+e~-annihilation at center-of-mass(CM)energy s~(1/2)via an intermediate photon or 2-boson,e~+e~-→γ/Z→h+X,given by     

Physics cross sections and event generation of e~+e~- annihilations at the CEPC

The cross sections of the Higgs production and the corresponding backgrounds of e~+e~- annihilations at the CEPC(Circular Electron and Positron Collider) are calculated by a Monte-Carlo method, and the beamstrahlung effect at the CEPC is carefully investigated. The numerical results and the expected number of events for the CEPC are provided.     

A method for measuring D~* electromagnetic form factors in e~+e~- annihilation

We describe a method for measuring the electromagnetic form factors of the D~* meson at time-like momentum transfer in e~+e~-annihilation.This is to study the joint angular distribution of the e~+e~-→γ~*→D~*+D~*-,D~*~+→D~0π~+,and D~*-→D~0π-processes.The magnitudes and relative phases of the charge,magnetic and quadrupole form factors can be determined.The method can also be applied to other vector particles.     

Uncertainty of the beam energy measurement in the e~+e~- collision using Compton backscattering

The beam energy is measured in the e+e-collision by using Compton backscattering. The uncertainty of this measurement process is studied by virtue of analytical formulas, and the special effects of variant energy spread and energy drift on the systematic uncertainty estimation are also studied with the Monte Carlo sampling technique. These quantitative conclusions are especially important for understanding the uncertainty of the beam energy measurement system.     

Energy dependence of non-linear dynamical features in e^＋e^- collisions

A study of the d.ynamical fluctuation properties at various c.m.energies in e~ e~- collisions is performed using the Monte Carlo method.The results suggest that,after the normalized factorial moments of 3-dimensional phase space are analyzed using an isotropical phase space partition,the NFM describing non- linear dynamical properties show a power-law scaling,i.e.,the dynamical fluctuations in higher dimensional phase space are isotropic.For c.m.energies s~(1/2)≤80 GeV,the scaling exponentsφ_q increase rapidly with the c.m.energy and for c.m.energies s~(1/2)>80 GeV,theφ_q gradually saturate.     

Production of charmonium（like）states in e^＋e^- interactions

We present a search for new charmonium like states in e~ e~- annihilation using the initial-state radiation and the process e~ e~-→J/ψD~(*)~(*).The analyses are based on a huge data sample recorded near theγ(4S)resonance with the Belle detector at the KEKB e~ e~- asymmetric-energy collider.     

CP violation in two-body hadronic decays of B_c mesons

Using the next-to-leading-order low-energy effective Hamiltonian, the CP asymmetries for -meson decays into meson pairs are calculated in the spectator approximation. We do not compute the hadronic matrix elements directly; instead, we use the amplitude ratios to estimate the CP asymmetries. This is quite different from previous treatments in the literature. The values of the momentum squared carried by the virtual particles in timelike penguin diagrams are also carefully discussed. From our calculated results, the best decay modes to observe CP violation in decays would be , , , , and , each of them needs about of events in experiment. Received: 17 December 1998 / Published online: 30 June 1999     

Complementary studies on N~* from e~+e~-, pp and pp(-) collisions

Complementary to the conventional experimental studies on N~* from πN and γ(~*)N reactions, the e~+e~-, pp and pp collisions can give novel insights into these N~* resonances. While the e~+e~- collisions through production and decay of vector charmonium ψ provide a nice isospin filter for a simultaneously study of N~*, △~*, Λ~*, ∑* and Ξ~*, the pp collisions should be the best place for producing those △~(*++) with large coupling to p+p though pp→n△~(*++) reaction, and the pp(-) collisions should be the best place for looking for those N~* with large coupling to σN.     

Searching for a neutral top-Higgs in association with top-quark pairs at an e~+e~- collider in the TC2 model

We investigate the associated production of the neutral top-Higgs h_t⁰ with a pair of top-quarks in the context of the topcolor-assisted technicolor (TC2) model at the future e⁺e^- Linear Colliders (LC) i.e. e⁺e^- → tt h_t⁰. We calculate the production rate and present the distributions of the transverse momenta of top-Higgs and top-quarks. The results show that the total cross section is typically of the order of 1.0-7.5 fb in the energy range between 1000 GeV and 2000 GeV of the LC for the whole top-Higgs mass region of interest. It should be distinctly possible that hundreds or even thousands of h_t⁰ signals can be produced per year at the LC given the luminosity L=500 fb^-1.     

Production of a heavy quarkonium with a photon or via ISR at Z peak in e~+e~- collider

Considering the possibility to build an e + e-collider at the energies around Z-boson resonance with a luminosity so high as L ∝ 10 34 cm-2 s-1 (even higher) and the abilities of a modern synthesis detector,we systematically calculate the exclusive two body processes of the heavy quarkonium production: e + eannihilates into a heavy quarkonium and a photon,involving the initial state radiation (i.e.ISR) cases,at the energies around the Z-boson resonance.Since the couplings of Z-boson to quarks contain an axial vector term as well as a vector one,a charmonium such as J/ψ or η c or h c or χ cJ ···,or a bottomonium such as Υ or η b or h b or χ bJ ···,associating with a photon,may be produced respectively via Z-boson annihilation.If we call such a collider with so high luminosity and running around the Z-boson resonance as a Z-factory,then our results obtained here indicate that experimental studies of the various heavy quarkona (their ground and excited states) via the two-body processes at a Z-factory have outstanding advantages,especially,the production of the possible states with quantum numbers J PC = 1-via ISR.