29148516
Multiple parton scattering in nuclei: Parton energy loss
Abstract Multiple parton scattering and induced parton energy loss are studied in deeply inelastic scattering (DIS) off nuclei. The effect of multiple scattering of a highly off-shell quark and the induced parton energy loss is expressed in terms of the modification to the quark fragmentation functions. We derive such modified quark fragmentation functions and their QCD evolution equations in DIS using the generalized factorization of higher twist parton distributions. We consider double-hard and hard-soft parton scattering as well as their interferences in the same framework. The final result, which depends on both the diagonal and off-diagonal twist-four parton distributions in nuclei, demonstrates clearly the Landau–Pomeranchuk–Migdal interference features and predicts a unique nuclear modification of the quark fragmentation functions.
7040957
Coherent multiple scattering effect in DIS
We present a QCD calculation of the coherent multiple scattering effect on single hadron production in semi-inclusive lepton-nucleus deep inelastic scattering (DIS). We show that the destructive interference of coherent multiple scattering leads to suppression in hadron productions. The suppression is similar to the expectations of energy loss calculations. We compare our calculation with experimental data.
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.
118914273
Direct photon production in a nuclear environment
16223404
Gluon minijet production in nuclear collisions at high energies
We show explicitly that the leading soft gluon p{sub T} distribution, predicted by Kovner, McLerran, and Weigert after solving classical Yang-Mills equations, can be understood in terms of conventional QCD perturbation theory. We also demonstrate that the key logarithm in their result represents the logarithm in DGLAP evolution equations. {copyright} {ital 1999} {ital The American Physical Society}
17365172
Heavy quark distribution functions in heavy baryons
Using the Bethe-Salpeter (B-S) equations for heavy baryons Lambda_Q, Sigma_Q, Xi_Q and Omega_Q (Q=b or c), which were established in previous work, we calculate the heavy quark distribution functions in these baryons. The numerical results indicate that these distribution functions have an obvious peak at some fraction, alpha_0, of the baryon's light-cone ``plus'' momentum component carried by the heavy quark, and that as m_Q becomes heavier this peak becomes sharper and closer to 1. The dependence of the distribution functions on various input parameters in the B-S model is also discussed. The results are seen to be qualitatively similar to an existing phenomenological model.
119535783
A dynamical mechanism for the hairpin diagram
SummaryBased on the nonvalence quark-antiquark and gluon constituent structure of mesons we give a reasonable dynamical mechanism which can induce the hairpin diagram without violating the well-observed OZI rule. We calculate the hairpin amplitudes of
$$D^0 \to \overline K ^0 \eta $$
 and
$$\overline K ^0 \eta '$$
 normalized by
$$D^0 \to \overline K ^0 \pi ^0 $$
 and have found that the hairpin diagram can give rise to substantial contributions to the decays where a meson with aSU(3) flavor singlet component is involved in the final state. In this scenario, we also obtain the branching ratio of
$$D^0 \to \overline K ^0 \phi $$
 as 0.55% in comparison with the experimental data of 0.83%.
119218519
Perturbative and nonperturbative contributions to the strange quark asymmetry in the nucleon
There are two mechanisms for the generation of an asymmetry between the strange and anti-strange quark distributions in the nucleon: nonperturbative contributions originating from nucleons fluctuating into virtual baryon–meson pairs such as ΛK and ΣK, and perturbative contributions arising from gluons splitting into strange and anti-strange quark pairs. While the nonperturbative contributions are dominant in the large-x region, the perturbative contributions are more significant in the small-x region. We calculate this asymmetry taking into account both nonperturbative and perturbative contributions, thus giving a more accurate evaluation of this asymmetry over the whole domain of x. We find that the perturbative contributions are generally a few times larger in magnitude than the nonperturbative contributions, which suggests that the best region to detect this asymmetry experimentally is in the region 0.02<x<0.03. We find that the asymmetry may have more than one node, which is an effect that should be taken into account, e.g. for parameterizations of the strange and anti-strange quark distributions used in global analysis of parton distributions.
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.
120276294
Studies of heavy hadron physics
In the diquark picture, we establish Bethe-Salpeter equations for ground states of heavy baryons containing one heavy quark and two heavy quarks in the heavy quark limit, respectively. The Bethe-Salpeter equations for both heavy and light diquarks are also established. Assuming kernels to consist of a scalar confinement term and a one-gluon-exchange term we solve Bethe-Salpeter wave functions numerically in the covariant instantaneous approximation and give some applications including semileptonic and nonleptonic decay widths of heavy baryons, the average kinetic energy of the heavy quark in {Lambda}{sub Q}, {Sigma}{sub Q}{sup (*)}{yields}{Lambda}{sub Q}+{pi} decay widths, and heavy quark distribution functions. We also study possible molecular heavy bound states in the Bethe-Salpeter approach. Proof of QCD factorization for {Lambda}{sub b}{yields}{Lambda}{sub c}{pi} is presented in the framework of QCD factorization.