118914273
Direct photon production in a nuclear environment
15462403
Nuclear dependence in direct photon production.
We calculate the nuclear dependence of direct photon production in hadron-nucleus collisions. In terms of a multiple scattering picture, we factorize the cross section for direct photon production into calculable short-distance partonic parts times multiparton correlation functions in nuclei. We present the hadron-nucleus cross section as {ital A}{sup {alpha}} times the hadron-nucleon cross section. Using information on the multiparton correlation functions extracted from photon-nucleus experiments, we compute the value of {alpha} as a function of transverse momentum of the direct photon. We also compare our results with recent data from Fermilab experiment E706. {copyright} {ital 1996 The American Physical Society.}
118936305
Multiple scattering and energy loss in semi-inclusive deeply inelastic eA scattering
We calculate the multiple scattering effect on single hadron production in semi-inclusive lepton-nucleus deeply inelastic scattering. We show that the quantum interference of multiple scattering amplitudes leads to suppression in hadron productions. At the leading power in medium length, the suppression can be approximately expressed in terms of a shift in $z$ of the fragmentation function $D(z)$, and could be therefore interpreted as the collisional energy loss. We compare our calculation with existing experimental data. We also discuss the effect of quark mass on the suppression. Our approach can be extended to other observables in hadronic collisions.
42222465
Universality in the nuclear dependence coefficient alpha(q(T))
We derive the nuclear dependence coefficient alpha(q(T)) for Drell-Yan and J/psi production. We show that at small q(T), alpha(q(T)) is given by a universal functional form: alpha(q(T)) = a+bq(2)(T), and the parameters a and b are completely determined by either perturbatively calculable or independently measurable quantities. This universal functional form alpha(q(T)) is insensitive to A, and is consistent with existing data.
30405678
Multiple scattering, parton energy loss, and modified fragmentation functions in deeply inelastic eA scattering
Modified quark fragmentation functions in deeply inelastic eA collisions and their QCD evolution equations are derived for the first time in the framework of multiple parton scattering. Induced radiation gives rise to additional terms in the evolution equations and thus softens the modified quark fragmentation functions. The results in the next-leading-twist depend on both diagonal and off-diagonal twist-four parton distributions and the combination of which clearly manifests the LPM interference pattern. The predicted modification depends quadratically on the nuclear size ( A2/3). Generalization to the case of hot QCD medium is also discussed.
13900650
Nuclear dependence in the Drell-Yan transverse momentum distribution
We calculate the nuclear enhancement in the Drell-Yan transverse momentum distribution in hadron-nucleus collisions. In terms of the multiple scattering picture, we compute the contributions from double scattering. Applying the generalized factorization theorem, we express the nuclear enhancement in terms of twist-4 nuclear parton correlation functions. Using the known information on these twist-4 parton correlation functions, we estimate the nuclear enhancement for Drell-Yan pairs in the large q{sub T} region. We also discuss the source of nuclear suppression in the small q{sub T} region. {copyright} {ital 1998} {ital The American Physical Society}
119515469
Bethe-Salpeter equation for heavy baryons $\Omega_{Q}^{(*)}$ in the diquark picture
In the heavy quark limit, the heavy baryons omega(Q)((*)) (omega stands for Sigma, Xi or Omega and Q = b or c) are regarded as composed of a heavy quark and an axial vector, light diquark with good spin and isospin quantum numbers. Based on this diquark picture we establish the Bethe-Salpeter (BS) equation for omega(Q)((*)) in the limit where the heavy quark has infinite mass, m(Q)-->(infinity). It is found that in this limit there are three components in the BS wave function for omega(Q)((*)). Assuming the kernel to consist of a scalar confinement term and a one-gluon-exchange term we derive three coupled integral equations for the three BS scalar functions in the covariant instantaneous approximation. Numerical solutions for the three BS scalar functions are presented, including a discussion of their dependence on the various input parameters. These solutions are applied to calculate the Isgur-Wise functions xi(omega) and zeta(omega) for the weak transitions Omega(b)((*)) --> Omega(c)((*)). Using these we give predictions for the Cabibbo-allowed nonleptonic decay widths and up-down asymmetries for Omega(b)-->Omega(c)((*)) plus a pseudoscalar or vector meson. [S0556-2821(99)07909-6].
16156190
Dissipative potential induced by QCD at finite temperature and density
In the framework of QCD at finite temperature, we have obtained dissipative factors for the effective potential between q and {bar q} which would partly explain the J/{psi} suppression in the quark gluon plasma (QGP). The derivation of the dissipative potential in the QGP is presented and the case in the hadron matter (HM) is briefly discussed. The suppression effects are numerically estimated based on simple approximations and a comparison with that caused by the Debye screening mechanism is also presented. {copyright} {ital 1997} {ital The American Physical Society}
119271994
$CP$ violation for $B^{0}\rightarrow \rho^{0}(\omega)\rho^{0}(\omega) \rightarrow \pi^+\pi^-\pi^+\pi^-$ in QCD factorization
In the QCD factorization (QCDF) approach we study the direct $CP$ violation in $\bar{B}^{0}\rightarrow\rho^0(\omega)\rho^0(\omega)\rightarrow\pi^+\pi^-\pi^+\pi^-$ via the $\rho-\omega$ mixing mechanism. We find that the $CP$ violation can be enhanced by double $\rho-\omega$ mixing when the masses of the $\pi^+\pi^-$ pairs are in the vicinity of the $\omega$ resonance, and the maximum $CP$ violation can reach 28{\%}. We also compare the results from the naive factorization and the QCD factorization.
1763711
Electromagnetic radiation of baryons containing two heavy quarks
The two heavy quarks in a baryon which contains two heavy quarks and a light one can constitute a scalar or axial vector diquark. We study the electromagnetic radiation of such baryons: (i) ${\ensuremath{\Xi}}_{{(\mathrm{bc})}_{1}}\ensuremath{\rightarrow}{\ensuremath{\Xi}}_{{(\mathrm{bc})}_{0}}+\ensuremath{\gamma},$ (ii) ${\ensuremath{\Xi}}_{{(\mathrm{bc})}_{1}}^{*}\ensuremath{\rightarrow}{\ensuremath{\Xi}}_{{(\mathrm{bc})}_{0}}+\ensuremath{\gamma},$ (iii) ${\ensuremath{\Xi}}_{{(\mathrm{bc})}_{0}}^{**}(1/2,l=1)\ensuremath{\rightarrow}{\ensuremath{\Xi}}_{{(\mathrm{bc})}_{0}}+\ensuremath{\gamma},$ (iv) ${\ensuremath{\Xi}}_{{(\mathrm{bc})}_{0}}^{**}(3/2,l=1)\ensuremath{\rightarrow}{\ensuremath{\Xi}}_{{(\mathrm{bc})}_{0}}+\ensuremath{\gamma},$ and (v) ${\ensuremath{\Xi}}_{{(\mathrm{bc})}_{0}}^{**}(3/2,l=2)\ensuremath{\rightarrow}{\ensuremath{\Xi}}_{{(\mathrm{bc})}_{0}}+\ensuremath{\gamma},$ where ${\ensuremath{\Xi}}_{{(\mathrm{bc})}_{0(1)}},{\ensuremath{\Xi}}_{{(\mathrm{bc})}_{1}}^{*}$ are S-wave bound states of a heavy scalar or axial vector diquark and a light quark, and ${\ensuremath{\Xi}}_{{(\mathrm{bc})}_{0}}^{**}(lg~1)$ are P- or D-wave bound states of a heavy scalar diquark and a light quark. The analysis indicates that these processes can be attributed to two categories and the physical mechanisms which are responsible for them are completely distinct. Measurements can provide good judgment for the diquark structure and a better understanding of the physical picture.
118071058
Enhanced direct CP violation in B+- ---> rho0 pi+-
We study direct CP violation in the hadronic decay $B^{\pm} \to \rho^{0}\pi^{\pm}$, including the effect of $\rho - \omega$ mixing. We find that the CP violating asymmetry is strongly dependent on the CKM matrix elements, especially the Wolfenstein parameter $\eta$. For fixed $N_{c}$ (the effective parameter associated with factorization), the CP violating asymmetry, $a$, has a maximum of order $30%-50%$ when the invariant mass of the $\pi^{+}\pi^{-}$ pair is in the vicinity of the $\omega$ resonance. The sensitivity of the asymmetry, $a$, to $N_{c}$ is small. Moreover, if $N_{c}$ is constrained using the latest experimental branching ratios from the CLEO collaboration, we find that the sign of $\sin \delta$ is always positive. Thus, a measurement of direct CP violation in $B^{\pm} \to \rho^{0}\pi^{\pm}$ would remove the mod$(\pi)$ ambiguity in ${\rm arg}[ - \frac{V_{td}V_{tb}^{\star}}{V_{ud}V_{ub}^{\star}}]$.