arXiv subjects

J. P. Ma

Publications and source records attributed to J. P. Ma.

At least 73 records · Page 4Linked to original sources

arXiv2005

Heavy Quarkonium Physics

This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.

hep-ph↗

arXiv2005

Transverse Momentum Dependent Light-Cone Wave Function of B-Meson and Relation to the Momentum Integrated One

A direct generalization of the transverse momentum integrated(TMI) light-cone wave function to define a transverse momentum dependent(TMD) light-cone wave function will cause light-cone singularities and they spoil TMD factorization. We motivate a definition in which the light-cone singularities are regularized with non-light like Wilson lines. The defined TMD light-cone wave function has some interesting relations to the corresponding TMI one. When the transverse momentum is very large, the TMD light-cone wave function is determined perturbatively in term of the TMI one. In the impact $b$-space with a small $b$, the TMD light-cone wave function can be factorized in terms of the TMI one. In this letter we study these relations. By-products of our study are the renormalization evolution of the TMI light-cone wave function and the Collins-Soper equation of the TMD light-cone wave function, the later will be useful for resumming Sudakov logarithms.

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arXiv2004

Parity, Charge Conjugation and SU(3) Constraints on Threshold Enhancement in $J/ψ$ decays into $γp\bar p$ and $K p \barΛ$

We study the threshold enhancement effects of baryon-anti-baryon systems in $J/ψ$ decays at BES using parity $P$, charge conjugation $C$, and flavor SU(3) symmetries. The $P$ and $C$ symmetries restrict the $p\bar p$ in $J/ψ\to γp\bar p$ to be in a state with $C=+1$, while the $p\bar p$ in $J/ψ\to π^0 p\bar p$ to be with $C=-1$. Combining the $C$ and $P$ symmetries with flavor SU(3) symmetry, i.e. the CPS symmetry, we find that the $Λ\bar p$ system cannot be in $0^+$ and $0^-$ states in $J/ψ\to K^+ Λ\bar p$. We provide a consistent explanation of observation and non-observation of near threshold enhancements in $J/ψ\to K^+ Λ\bar p$ and $J/ψ\to π^0 p \bar p$, respectively. We also find that near baryon pair threshold enhancement can happen in several channels for $J/ψ$ decays and can be several times larger than that observed in $J/ψ\to K^+ Λ\bar p$ in some channels.

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arXiv2004

Predictions for $e^+e^-\to J/ψη_c$ with Light-Cone Wave-Functions

Predictions for $e^+e^-\to J/ψη_c$ from previous studies are made by taking charmonia as a nonrelativistic bound state and by using nonrelativistic QCD(NRQCD) approach. The predicted cross-section is smaller by an order of magnitude than the experimentally observed. We study the process by taking charm quark as a light quark and use light-cone wave-functions to parameterize nonperturbative effects related to charmonia. The total cross section of $e^+e^-\to J/ψη_c$ can be predicted, if these wave-functions are known. Motivated by studies of light-cone wave-functions of light hadrons, we make a reasonable assumption of the forms of light-cone wave-functions. With these light-cone wave-functions we can obtain the cross section which is more closer to the experimentally observed than that from NRQCD approach. We also discuss in detail the difference between two approaches.

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arXiv2004

On Unique Predictions for Single Spin Azimuthal Asymmetry

Theoretically there are two approaches to predict single spin azimuthal asymmetries. One is to take transverse momenta of partons into account by using transverse momentum dependent parton distributions, while another is to take asymmetries as a twist-3 effect. The nonperturbative effects in these approaches are parameterized with different matrix elements and predictions can be different. Recently, gauge invariant definitions of transverse momentum dependent parton distributions were derived. With these definitions it can be shown that there are relations between nonperturbative matrix elements in two approaches. These relations may enable us to unify two approaches and to have unique predictions for single spin azimuthal asymmetries.In this letter we derive these relations by using time-reversal symmetry and show that even with these relations the single spin azimuthal asymmetry in Drell-Yan process is predicted differently in different approaches.

hep-ph↗

arXiv2003

CP Test in J/Psi -> gamma phi phi Decay

We propose to test CP symmetry in the decay $\jp\to γϕϕ$, for which large data sample exists at BESII, and a data sample of $10^{10}$ $J/ψ$'s will be collected with BESIII and CLEO-C program. We suggest some CP asymmetries in this decay mode for CP test. Assuming that CP violation is introduced by the electric- and chromo-dipole moment of charm quark, these CP asymmetries can be predicted by using valence quark models. Our work shows a possible way to get information about the electric- and chromo-dipole moment of charm quark, which is little known. Our results show that with the current data sample of $J/ψ$, electric- and chromo-dipole moment can be probed at order of $10^{-14}e cm$. In the near future with a $10^{10}$ data sample, these moments can be probed at order of $10^{-16}e cm$.

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arXiv2003

Nonperturbative Corrections with Nonlocal Operators to Lifetime Ratios of Beauty Hadrons

The motion of spectator quarks in decay of a beauty hadron is a nonperturbative effect which can usually be neglected. We find that the motion in some decay channels, which contribute total decay widths of beauty hadrons, can not be neglected.The contributions from these decay channels to decay widths are proportional to certain averages of the squared inverse of the momentum carried by a spectator quark. This fact results in that these contributions, suppressed by $1/m_b^3$ formally, are effectively suppressed by $1/m_b$. We find these contributions can be factorized into products of perturbative coefficients and nonperturbative parameters. We calculate these coefficients and define these nonperturbative parameters in terms of HQET matrix elements.Since these parameters are unknown, we are unable to give numerical predictions in detail. But with a simple model it can be shown that these contributions can be large.

hep-ph↗

arXiv2003

Diffractive Photoproduction of Eta_c

Diffractive photoproduction of $η_c$ is an important process to study the effect of Odderon, whose existence is still not confirmed in experiment. A detailed interpretation of Odderon in QCD, i.e., in terms of gluons is also unclear.Taking charm quarks as heavy quarks, we can use NRQCD and take $η_c$ as a $c\bar c$ bound state. Hence, in the production of $η_c$a free $c\bar c$ pair is first produced and this pair is transformed into $η_c$ subsequently.In the forward region of the kinematics, the $c\bar c$ pair interacts with initial hadron through exchanges of soft gluons. This interaction can be studied with HQET, which provides a systematic expansion in the inverse of the $c$-quark mass $m_c$. We find that the calculation of the $S$-matrix element in the forward region can be formulated as the problem of solving a wave function of a $c$-quark propagating in a background field of soft gluons. At leading order we find that the differential cross-section can be expressed with four functions, which are defined with a twist-3 operator of gluons. The effect of exchanging a Odderon can be identified with this operator in our case. We discuss our results in detail and compare them with those obtained in previous studies. Our results and those from other studies show that the differential cross-section is very small in the forward region. We also show that the production through photon exchange is dominant in the extremely forward region, hence the effect of Odderon exchange can not be identified in this region.For completeness we also give results for diffractive photoproduction of $J/Ψ$.

hep-ph↗

arXiv2003

Factorization Approach for Inclusive Production of Doubly Heavy Baryon

We study inclusive production of doubly heavy baryon at a $e^+e^-$ collider and at hadron colliders through fragmentation. We study the production by factorizing nonpertubative- and perturbative effects. In our approach the production can be thought as a two-step process: A pair of heavy quarks can be produced perturbatively and then the pair is transformed into the baryon. The transformation is nonperturbative. Since a heavy quark moves with a small velocity in the baryon in its rest frame, we can use NRQCD to describe the transformation and perform a systematic expansion in the small velocity. At the leading order we find that the baryon can be formed from two states of the heavy-quark pair, one state is with the pair in $^3S_1$ state and in color ${\bf \bar 3}$, another is with the pair in $^1S_0$ state and in color ${\bf 6}$. Two matrix elements are defined for the transformation from the two states, their perturbative coefficients in the contribution to the cross-section at a $e^+e^-$ collider and to the function of heavy quark fragmentation are calculated. Our approach is different than previous approaches where only the pair in $^3S_1$ state and in color ${\bf \bar 3}$ is taken into account. Numerical results for $e^+e^-$ colliders at the two $B$-factories and for hadronic colliders LHC and Tevatron are given.

hep-ph↗

arXiv2002

Ratio of Photoproduction Rates of $\jpsi$ and $ψ(2S)$

There are different approaches for diffractive photoproduction of charmonia. Recently, a new approach is proposed, in which charm quarks are taken as heavy quarks and the nonperturbative effect related to charmonia can be handled with nonrelativistic QCD. The interaction between the $c\bar c$ pair and the initial hadron is through exchange of soft gluons. The exchange of soft gluons can be studied with heavy quark effective theory and an expansion in the inverse of charm quark mass $m_c$ can be employed. In this approach a simple formula for the S-matrix can be derived by neglecting higher orders in $m_c^{-1}$ and relativistic correction related to charmonia. The S-matrix is related to the usual gluon distribution $g(x)$ at small $x$. This result is different than those from other approaches. Confronting experiment the result is not in agreement with experimental measurement because large errors from higher order in $m_c^{-1}$ and from relativistic corrections. Nevertheless the ratio of cross sections of $\jpsi$ and $ψ(2S)$ can be predicted more precisely than cross-sections. In this letter we show that the ratio predicted in this approach with an estimation of relativistic corrections is in good agreement with the recent measurement at HERA.

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arXiv2002

Corrections For Two Photon Decays of chi_{c0} and chi_{c2} and Color Octet Contributions

Using the fact that the c-quark inside a charmonium moves with a small velocity v in the charmonium rest-frame, one can employ an expansion in v to study decays of charmonia and results at the leading order for chi_{c0,2} --> gamma gamma exist in the literature. We study corrections at the next-to-leading order in the framework of nonrelativistic QCD(NRQCD) factorization. The study presented here is different than previous approaches where chi_{c0,2} is taken as a bound-state of a c cbar pair and a nonrelativistic wave-function is used for the pair. We find that the corrections are consist not only of relativistic corrections, but also of corrections from Fock state components of chi_{c0,2} in which the c cbar pair is in a color-octet state. For chi_{c2} there is also a contribution from a Fock state component in which the pair is in a F-wave state. We determine the factorization formula for decay widths in the form of NRQCD matrix elements representing nonperturbative effects related to chi_{c0,2}, and calculate the perturbative coefficients at tree-level. Because the NRQCD matrix elements are unknown, a detailed prediction for the decay chi_{c0,2} --> gamma gamma can not be made, but the effect of these corrections can be determined at certain level. Estimations show that the effect is significant and can not be neglected.

hep-ph↗

arXiv2002

Radiative Decay of $Υ$ into a Scalar Glueball

We study the radiative decay of $Υ$ into a scalar glueball $Υ\to γG_s$ using QCD factorization. We find that for this process the non-perturbative effects can be factorized into a matrix element well defined in non-relativistic QCD (NRQCD) and the gluon distribution amplitude. The same NRQCD matrix element appears also in leptonic decay of $Υ$ and therefore can be determined from data. In the asymptotic limit the gluon distribution amplitude is known up to a normalization constant. Using a QCD sum-rule calculation for the normalization constant, we obtain $Br(Υ\to γG_s)$ to be in the range $(1\sim 2)\times 10^{-3}$. We also discuss some of the implications for $Υ\to γf_i$ decays. Near future data from CLEO-III can provide crucial information about scalar glueball properties.

hep-ph↗

arXiv2002

Soft Gluon Approach for Diffractive Photoproduction of J/psi

We study diffractive photoproduction of $J/ψ$ by taking the charm quark as a heavy quark. A description of nonperturbative effect related to $J/ψ$ can be made by using NRQCD. In the forward region of the kinematics, the interaction between the $c\bar c$-pair and the initial hadron is due to exchange of soft gluons. The effect of the exchange can be studied by using the expansion in the inverse of the quark mass $m_c$. At the leading order we find that the nonperturbative effect related to the initial hadron is represented by a matrix element of field strength operators, which are separated in the moving direction of $J/ψ$ in the space-time. The S-matrix element is then obtained without using perturbative QCD and the results are not based on any model. Corrections to the results can be systematically added. Keeping the dominant contribution of the S-matrix element in the large energy limit we find that the imaginary part of the S-matrix element is related to the gluon distribution for $x\to 0$ with a reasonable assumption, the real part can be obtained with another approximation or with dispersion relation. Our approach is different than previous approaches and also our results are different than those in these approaches. The differences are discussed in detail. A comparison with experiment is also made and a qualitative agreement is found.

hep-ph↗

arXiv2002

$\bar B^0 \to π^+ X$ in the Standard Model

In this paper we investigate the possibility of studying $B\to π$ form factor using the semi-inclusive decays $\bar B^0 \to π^+ + X_q$. In general $B\to PX$ semi-inclusive decays involve several hadronic parameters. But for $\bar B^0 \to π^+ X_q$ decays we find that in the factorization approximation, the only unknown hadronic parameters are the form factors $F^{B\to π}_{0,1}$. Therefore these form factors can be studied in $\bar B^0 \to π^+ X_q$ decays. Using theoretical model calculations for the form factors the branching ratios for $\bar B^0 \to π^+ X_d(ΔS = 0) $ and $\bar B^0 \to π^+ X_s (ΔS = -1)$, with the cut $E_π > 2.1$ GeV, are estimated to be in the ranges of $(3.1\sim 4.9) \times 10^{-5}(F^{B\to π}_1(0)/0.33)^2$ and $(2.5\sim 4.2)\times 10^{-5}(F_1^{B\to π}(0)/0.33)^2$, respectively, depending on the value of $γ$. The combined branching ratio for $\bar B^0 \to π^+ (X_d+ X_s)$ is about $7.4\times 10^{-5} (F^{B\to π}_1(0)/0.33)^2$ and is insensitive to $γ$. We also discuss CP asymmetries in these decay modes.

hep-ph↗

arXiv2002

Exclusive Decay of $1^{--}$ Quarkonia and $B_c$ Meson into a Lepton Pair Combined with Two Pions

We study the exclusive decay of $J/Ψ$, $Υ$ and $B_c$ into a lepton pair combined with two pions in the two kinematic regions. One is specified by the two pions having large momenta, but a small invariant mass. The other is specified by the two pions having small momenta. In both cases we find that in the heavy quark limit the decay amplitude takes a factorized form, in which the nonperturbative effect related to heavy meson is represented by a NRQCD matrix element. The nonperturbative effects related to the two pions are represented by some universal functions characterizing the conversion of gluons into the pions. Using models for these universal functions and chiral perturbative theory we are able to obtain numerical predictions for the decay widths. Our numerical results show that the decay of $\jpsi$ is at order of $10^{-5}$ with reasonable cuts and can be observed at BES II and the proposed BES III and CLEO-C. For other decays the branching ratio may be too small to be measured.

hep-ph↗

arXiv2002

Reexamining radiative decays of $1^{--}$ quarkonium into $η'$ and $η$

Recently CLEO has studied the radiative decay of $Υ$ into $η'$ and an upper limit for the decay has been determined. Confronting with this upper limit,most of theoretical predictions for the decay fails. After briefly reviewing these predictions we re-examine the decay by separating nonperturbative effect related to the quarkonium and that related to $η'$ or $η$, in which the later is parameterized by distribution amplitudes of gluons in $η'$. With this factorization approach we obtain theoretical predictions which are in agreement with experiment. Uncertainties in our predictions are discussed. The possibly largest uncertainties are from relativistic corrections for $J/Ψ$ and the value of the charm quark mass. We argue that the effect of these uncertainties can be reduced by using quarkonium masses instead of using quark masses. An example of the reduction is shown with an attempt to explain the violation of the famous 14% rule in radiative decays of charmonia.

hep-ph↗

arXiv2001

Calculating the I=2 Pion Scattering Length Using Tadpole Improved Clover Wilson Action on Coarse Anisotropic Lattices

In an exploratory study, using the tadpole improved clover Wilson quark action on small, coarse and anisotropic lattices, the $ππ$ scattering length in the I=2 channel is calculated within quenched approximation. A new method is proposed which enables us to make chiral extrapolation of our lattice results without calculating the decay constant on the lattice. Finite volume and finite lattice spacing errors are analyzed and the results are extrapolated towards the infinite volume and continuum limit. Comparisons of our lattice results with the new experiment and the results from Chiral Perturbation Theory are made. Good agreements are found.

hep-lat↗

arXiv2001

Spin Alignment of Heavy Meson Revisited

Using heavy quark effective theory a factorized form for inclusive production rate of a heavy meson can be obtained, in which the nonperturbative effect related to the heavy meson can be characterized by matrix elements defined in the heavy quark effective theory. Using this factorization, predictions for the full spin density matrix of a spin-1 and spin-2 meson can be obtained and they are characterized only by one coefficient representing the nonperturbative effect. Predictions for spin-1 heavy meson are compared with experiment performed at $e^+e^-$ colliders in the energy range from $\sqrt{s}=10.5$GeV to $\sqrt{s}=91$GeV, a complete agreement is found for $D^*$- and $B^*$-meson. There are distinct differences from the existing approach and they are discussed.

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