arXiv subjects

Chao-Hsi Chang

Publications and source records attributed to Chao-Hsi Chang.

At least 55 records · Page 3Linked to original sources

arXiv2015

BCVEGPY2.2: A Newly Upgraded Version for Hadronic Production of the Meson $B_c$ and Its Excited States

A newly upgraded version of the BCVEGPY, a generator for hadronic production of the meson $B_c$ and its excited states, is available. In comparison with the previous one [C.H. Chang, J.X. Wang and X.G. Wu, Comput. Phys. Commun. {\bf 175}, 624 (2006)], the new version is to apply an improved hit-and-miss technology to generating the un-weighted events much more efficiently under various simulation environments. The codes for production of $2S$-wave $B_c$ states are also given here.

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arXiv2015

Suggestion for measuring the weak dipole moment of $τ$ lepton at Z-factory

Three new observables for Z-factory to measure the weak dipole moment of $τ$ lepton ($d_w^τ$) are proposed. As those observables employed at LEP-I, the new observables depend on the real and imaginary parts of $d_w^τ$ linearly, thus we calculate the slopes, i.e. the linear coefficients of the dependence, precisely and find that the obtained slopes are much lager than those employed at LEP-I. It means that the signal for the weak dipole moment $d_w^τ$ may be enhanced quite a lot, if one employs the new observables. Being superior to those at LEP-I, we recommend measuring the weak dipole moment $d_w^τ$ in terms of the new observables if re-analyzing the data of LEP-I or doing the measurement at a possible Z-factory in the near future.

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arXiv2014

Spontaneous R-parity violation in the minimal gauged $(B-L)$ supersymmetry with a $125\;{\rm GeV}$ Higgs

We precisely derive the mass squared matrices for charged and neutral (CP-odd and CP-even) Higgs, as well as the mass matrices for neutrino-neutralino and charged lepton-chargino in the minimal R-parity violating supersymmetry with local $U(1)_{B-L}$ symmetry. In the framework the nonzero TeV scale vacuum expectations of right-handed sneutrinos induce the heavy mass of neutral $U(1)_{B-L}$ gauge boson, and result in relatively large mixing between the lightest CP-even Higgs and three generation right-handed sneutrinos when we include the one-loop corrections to the scalar potential. We numerically show that there is parameter space of the considered model to accommodate experimental data on the newly ones of Higgs signal from LHC and experimental observations on the neutrino oscillation simultaneously.

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arXiv2014

Neutrino Production via $e^-e^+$ Collision at $Z$-boson Peak

The production of the three normal neutrinos via $e^-e+$ collision at $Z$-boson peak (neutrino production in a Z-factory) is investigated thoroughly. The differences of $ν_e$-pair production from $ν_μ$-pair and $ν_τ$-pair production are presented in various aspects. Namely the total cross sections, relevant differential cross sections and the forward-backward asymmetry etc for these neutrinos are presented in terms of figures as well as numerical tables. The restriction on the room for the mixing of the three species of light neutrinos with possible externals (heavy neutral leptons and/or stereos) from refined measurements of the invisible width of $Z$-boson is discussed.

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arXiv2012

The $B_c$ Decays to $P$-wave Charmonium by Improved Bethe-Salpeter Approach

We re-calculate the exclusive semileptonic and nonleptonic decays of $B_c$ meson to a $P$-wave charmonium in terms of the improved Bethe-Salpeter (B-S) approach, which is developed recently. Here the widths for the exclusive semileptonic and nonleptonic decays, the form factors, and the charged lepton spectrums for the semileptonic decays are precisely calculated. To test the concerned approach by comparing with experimental measurements when the experimental data are available, and to have comparisons with the other approaches the results obtained by the approach and those by some approaches else as well as the original B-S approach, which appeared in literature, are comparatively presented and discussed.

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arXiv2010

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 ${\cal L} \propto 10^{34}cm^{-2}s^{-1}$ (even higher) and the abilities of a modern synthesis detector, we systematically calculate the exclusive two body processes: $e^+e^-$ annihilates into a heavy quarkonium and a photon (initiate state radiation i.e. ISR is involved), at the energies around the $Z$-boson resonance. Since the couplings of $Z$-boson to quarks contain axial vector as well as vector, so here the produced heavy quarkonium may stand for a charmonium such as ${J/ψ,η_c,h_c,χ_{cJ}}\cdots$ and a bottomonium such as ${Υ,η_b,h_b,χ_{bJ}}\cdots$ respectively. 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 at a $Z$-factory about the various heavy quarkona (their ground and excited states) via the two-body processes, especially, the production of the bound states with quantum number $J^{PC}=1^{--}$ via ISR, have outstanding advantages.

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arXiv2010

Spectrum for Heavy Quankonia and Mixture of the Relevant Wave Functions within the Framework of Bethe-Salpeter Equation

Considering the fact that some excited states of the heavy quarkonia (charmonium and bottomonium) still missing in experimental observations and potential applications of the relevant wave functions of the bound states, we re-analyze the spectrum and the relevant wave functions of the heavy quarkonia within the framework of Bethe-Salpeter (B.S.) equation with a proper QCD-inspired kernel. Such a kernel for the heavy quarkonia, relating to potential of non-relativistic quark model, is instantaneous, so we call the corresponding B.S. equation as BS-In equation throughout the paper. Particularly, a new way to solve the B.S. equation, which is different from the traditional ones, is proposed here, and with it not only the known spectrum for the heavy quarkonia is re-generated, but also an important issue is brought in, i.e., the obtained solutions of the equation `automatically' include the 'fine', 'hyperfine' splittings and the wave function mixture, such as $S-D$ wave mixing in $J^{PC}=1^{--}$ states, $P-F$ wave mixing in $J^{PC}=2^{++}$ states for charmonium and bottomonium etc. It is pointed out that the best place to test the wave mixture probably is at $Z$-factory ($e^+e^-$ collider running at $Z$-boson pole with extremely high luminosity).

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arXiv2010

The magnetic dipole transitions in the $(c\bar{b})$ binding system

The magnetic dipole transitions between the vector mesons $B_c^*$ and their relevant pseudoscalar mesons $B_c$ ($B_c$, $B_c^*$, $B_c(2S)$, $B_c^*(2S)$, $B_c(3S)$ and $B_c^*(3S)$ etc, the binding states of $(c\bar{b})$ system) of the $B_c$ family are interesting. To see the `hyperfine' splitting due to spin-spin interaction is an important topic for understanding the spin-spin interaction and the spectrum of the the $(c\bar{b})$ binding system. The knowledge about the magnetic dipole transitions is also very useful for identifying the vector boson $B_c^*$ mesons experimentally, whose masses are just slightly above the masses of their relevant pseudoscalar mesons $B_c$ accordingly. Considering the possibility to observe the vector mesons via the transitions at $Z^0$ factory and the potentially usages of the theoretical estimate on the transitions, we fucus our efforts on calculating the magnetic dipole transitions, i.e. precisely to calculate the rates for the transitions such as decays $B_c^*\to B_cγ$ and $B_c^*\to B_c e^+e^-$, and particularly work in the Behte-Salpeter framework. In the estimate, as a typical example, we carefully investigate the dependance of the rate $Γ(B_c^*\to B_cγ)$ on the mass difference $ΔM=M_{B_c^*}-M_{B_c}$ as well.

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arXiv2009

GENXICC2.0: An Upgraded Version of the Generator for Hadronic Production of Double Heavy Baryons $Ξ_{cc}$, $Ξ_{bc}$ and $Ξ_{bb}$

An upgraded (second) version of the package GENXICC ({\bf A Generator for Hadronic Production of the Double Heavy Baryons $Ξ_{cc}$, $Ξ_{bc}$ and $Ξ_{bb}$ by C.H. Chang, J.X. Wang and X.G. Wu,} [its first version: in Comput. Phys. Commun. {\bf 177} (2007) 467-478]) is presented. Users, with this version being implemented in PYTHIA and a GNU C compiler, may simulate full events of the production in various experimental environments conveniently. In comparison with the previous version, in order to implement it in PYTHIA properly, a subprogram for the fragmentation of the produced double heavy diquark to the relevant baryon is complemented and the interphase of the generator to PYTHIA is changed accordingly. In the subprogram, with explanation, certain necessary assumptions (approximations) are made so as to conserve the momenta and the QCD `color' flow for the fragmentation.

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arXiv2009

J/ψpolarization in photo-production up-to the next-to-leading order of QCD

We investigate the J/psi polarization in photoproduction at the Hadron Electron Ring Accelerator(HERA) up to the next-to-leading order of QCD. The results show that the transverse momentum p_t and energy fraction z distributions of J/psi production do not agree with the observed ones very well. The theoretical uncertainties for the z distributions of the J/psi polarization parameters with respect to various choices of the renormalization and factorization scales are too large to give an accurate prediction. The uncertainties for the p_t distributions of these parameters are small when p_t>3GeV and the obtained p_t distributions can not describe the experimental data even in this region.

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arXiv2009

Hadronic production of $B^{(*)}_s$ at TEVATRON and LHC

We study the hadronic production of $B_s$ and $B_s^*$ mesons within the fixed-flavor-number scheme, in which the dominant gluon-gluon fusion mechanism is dealt with by using the complete $α_s^4$ approach. Main theoretical uncertainties for $B_s$ and $B_s^*$ production at TEVATRON and LHC are presented. It is found that when $m_s$ increases by steps of 0.1 GeV, the integrated cross section of $B^{(*)}_s$ decreases by $80%-100%$, when $m_b$ increases by steps of 0.1 GeV, it changes to be $\sim 10%$. While the uncertainties caused by the parton distribution function and the factorization scale varies within the region of 1/5 to 1/3. Considering possible kinematic cut on the transverse momentum and the rapidity cut for the detectors at TEVATRON and LHC, we also make estimations on the $B_s$ and $B_s^*$ production with various kinematic cuts.

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arXiv2008

Further insights into the "$ρπ$ puzzle"

Based on a systematic investigation of $J/ψ(ψ^\prime)\to VP$, where $V$ and $P$ stand for light vector and pseudoscalar mesons, we identify the role played by the electromagnetic (EM) transitions and intermediate meson loop transitions, which are essential ingredients for understanding the $J/ψ$ and $ψ^\prime$ couplings to $VP$. We show that on the one hand, the EM transitions have relatively larger interferences in $ψ^\prime\to ρπ$ and $K^*\bar{K}+c.c.$ as explicitly shown by vector meson dominance (VMD). On the other hand, the strong decay of $ψ^\prime$ receives relatively larger destructive interferences from the intermediate meson loop transitions. By identifying these mechanisms in an overall study of $J/ψ(ψ^\prime)\to VP$, we provide a coherent understanding of the so-called "$ρπ$ puzzle".

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arXiv2008

Decays of $J/ψ$ and $ψ^\prime$ into vector and pseudoscalar meson and the pseudoscalar glueball-$q\bar{q}$ mixing

We introduce a parametrization scheme for $J/ψ(ψ^\prime)\to VP$ where the effects of SU(3) flavor symmetry breaking and doubly OZI-rule violation (DOZI) can be parametrized by certain parameters with explicit physical interpretations. This scheme can be used to clarify the glueball-$q\bar{q}$ mixing within the pseudoscalar mesons. We also include the contributions from the electromagnetic (EM) decays of $J/ψ$ and $ψ^\prime$ via $J/ψ(ψ^\prime)\to γ^*\to VP$. Via study of the isospin violated channels, such as $J/ψ(ψ^\prime)\to ρη$, $ρη^\prime$, $ωπ^0$ and $ϕπ^0$, reasonable constraints on the EM decay contributions are obtained. With the up-to-date experimental data for $J/ψ(ψ^\prime)\to VP$, $J/ψ(ψ^\prime)\to γP$ and $P\to γγ$, etc, we arrive at a consistent description of the mentioned processes with a minimal set of parameters. As a consequence, we find that there exists an overall suppression of the $ψ^\prime\to 3g$ form factors, which sheds some light on the long-standing "$ρπ$ puzzle". By determining the glueball components inside the pseudoscalar $η$ and $η^\prime$ in three different glueball-$q\bar{q}$ mixing schemes, we deduce that the lowest pseudoscalar glueball, if exists, has rather small $q\bar{q}$ component, and it makes the $η(1405)$ a preferable candidate for $0^{-+}$ glueball.

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arXiv2007

Production of $B_c$ or $\bar{B}_c$ meson and its excited states via $\bar{t}$-quark or $t$-quark decays

The production of $(b\bar{c})$-quarkonium ($\bar{B}_c$ meson and its excited states) or $(c\bar{b})$-quarkonium ($B_c$ meson and its excited states) via top quark $t$ or top anti-quark $\bar{t}$ decays, $t\to (b\bar{c})+c+W^+$ or $\bar{t}\to (c\bar{b})+\bar{c}+W^-$, respectively is studied within the framework of NRQCD. In addition to the production of the two color-singlet $S$-wave states $|(b\bar{c})(^1S_0)_{\bf 1}>$ or $|(c\bar{b})(^1S_0)_{\bf 1}>$ and $|(b\bar{c})(^3S_1)_{\bf 1}>$ or $|(c\bar{b})(^3S_1)_{\bf 1}>$, the production of the $P$-wave excited $(b\bar{c})$ or $(c\bar{b})$ states, i.e. the four color-singlet $P$-wave states $|(b\bar{c})(^1P_1)_{\bf 1}>$ or $|(c\bar{b})(^1P_1)_{\bf 1}>$, and $(b\bar{c})(^3P_J)_{\bf 1}>$ or $(c\bar{b})(^3P_J)_{\bf 1}>$ (with $J=(1,2,3)$), is also studied. According to the velocity scaling rule of NRQCD, for the production of $P$-wave excited states the contributions from the two color-octet components $|(b\bar{c})(^1S_0)_{\bf 8}>$ or $|(c\bar{b})(^1S_0)_{\bf 8}>$ and $|(b\bar{c})(^3S_1)_{\bf 8}>$ or $|(c\bar{b})(^3S_1)_{\bf 8}>$ are also taken into account. We quantitatively discuss the possibility and the advantages in experimental studies of $B_c$ or $\bar{B}_c$ meson and its excited states via the indirect production at LHC in high luminosity runs and at LHC possible upgraded versions such as SLHC, DLHC, TLHC etc. in future.

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arXiv2007

Fragmentation Function and Hadronic Production of the Heavy Supersymmetric Hadrons

The light top-squark $\sto$ may be the lightest squark and its lifetime may be `long enough' in a kind of SUSY models which have not been ruled out yet experimentally, so colorless `supersymmetric hadrons (superhadrons)' $(\sto \bar{q})$ ($q$ is a quark except $t$-quark) may be formed as long as the light top-squark $\sto$ can be produced. Fragmentation function of $\sto$ to heavy `supersymmetric hadrons (superhadrons)' $(\sto \bar{Q})$ ($\bar{Q}=\bar{c}$ or $\bar{b}$) and the hadronic production of the superhadrons are investigated quantitatively. The fragmentation function is calculated precisely. Due to the difference in spin of the SUSY component, the asymptotic behavior of the fragmentation function is different from those of the existent ones. The fragmentation function is also applied to compute the production of heavy superhadrons at hadronic colliders Tevatron and LHC under the so-called fragmentation approach. The resultant cross-section for the heavy superhadrons is too small to observe at Tevatron, but great enough at LHC, even when all the relevant parameters in the SUSY models are taken within the favored region for the heavy superhadrons. The production of `light superhadrons' $(\sto \bar{q})$ ($q=u, d, s$) is also roughly estimated. It is pointed out that the production cross-sections of the light superhadrons $(\sto \bar{q})$ may be much greater than those of the heavy superhadrons, so that even at Tevatron the light superhadrons may be produced in great quantities.

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arXiv2007

GENXICC: A Generator for Hadronic Production of the Double Heavy Baryons $Ξ_{cc}$, $Ξ_{bc}$ and $Ξ_{bb}$

We write down a generator program for the hadronic production of the double-heavy baryons $Ξ_{cc}$, $Ξ_{bc}$ and $Ξ_{bb}$ according to relevant publications. We name it as GENXICC and we test it by comparing its numerical results with those in references. It is written in a PYTHIA-compatible format and it can be easily implemented into PYTHIA. GENXICC is also written in modularization manner, with {\bf make}, a GNU C compiler, one may apply the generator to various situations or experimental environments very conveniently.

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arXiv2007

Lifetime of doubly charmed baryons

In this work, we evaluate the lifetimes of the doubly charmed baryons $Ξ_{cc}^{+}$, $Ξ_{cc}^{++}$ and $Ω_{cc}^{+}$. We carefully calculate the non-spectator contributions at the quark level where the Cabibbo-suppressed diagrams are also included. The hadronic matrix elements are evaluated in the simple non-relativistic harmonic oscillator model. Our numerical results are generally consistent with that obtained by other authors who used the diquark model. However, all the theoretical predictions on the lifetimes are one order larger than the upper limit set by the recent SELEX measurement. This discrepancy would be clarified by the future experiment, if more accurate experiment still confirms the value of the SELEX collaboration, there must be some unknown mechanism to be explored.

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arXiv2007

Hadronic Production of the Doubly Charmed Baryon $Ξ_{cc}$ with Intrinsic Charm

The effects of the intrinsic charm on the hadronic production of $Ξ_{cc}$ are studied. By taking reasonable intrinsic charm component into account, the change of the theoretical prediction on the production of $Ξ_{cc}$ for LHC and Tevatron is small, but in contrast it may enhance significantly for SELEX. The reason is that the collision energy at LHC and Tevatron is so large that the gluon-gluon fusion sub-process, which is irrelevant to intrinsic charm, becomes dominant. But the situation for SELEX is quite different. Our numerical results for SELEX show that by considering all the contributions from various sub-processes, the predicted cross-section may be enhanced by a factor so big as $10^2$ due to a modulating intrinsic charm being taken into account. Therefore, the hadronic production of $Ξ_{cc}$ at SELEX may be sensitive enough in observing the intrinsic charm inside the incident hadrons.

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