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Jian-Wei Qiu

Publications and source records attributed to Jian-Wei Qiu.

107 records · Page 6Linked to original sources
arXiv2007

Transverse momentum broadening of vector bosons in heavy ion collisions at the LHC

We calculate in perturbative QCD the transverse momentum broadening of vector bosons in heavy ion collisions at the Large Hadron Collider (LHC). We predict transverse momentum broadening of $W/Z$ bosons constructed from their leptonic decay channels, which should be a clean probe of initial-state medium effect. We also predict the upper limit of transverse momentum broadening of J/$ψ$ and $Υ$ production as a function of N$_{\rm part}$ at the LHC energy.

hep-ph↗
arXiv2007

k_T factorization is violated in production of high-transverse-momentum particles in hadron-hadron collisions

We show that hard-scattering factorization is violated in the production of high-p_T hadrons in hadron-hadron collisions, in the case that the hadrons are back-to-back, so that k_T factorization is to be used. The explicit counterexample that we construct is for the single-spin asymmetry with one beam transversely polarized. The Sivers function needed here has particular sensitivity to the Wilson lines in the parton densities. We use a greatly simplified model theory to make the breakdown of factorization easy to check explicitly. But the counterexample implies that standard arguments for factorization fail not just for the single-spin asymmetry but for the unpolarized cross section for back-to-back hadron production in QCD in hadron-hadron collisions. This is unlike corresponding cases in e^+e^- annihilation, Drell-Yan, and deeply inelastic scattering. Moreover, the result endangers factorization for more general hadroproduction processes.

hep-ph↗
arXiv2007

Single Transverse-Spin Asymmetry in Hadronic Dijet Production

We study the single transverse-spin asymmetry for dijet production in hadronic collisions in both the collinear QCD factorization approach and the Brodsky-Hwang-Schmidt model. We show that a nonvanishing asymmetry is generated by both initial-state and final-state interactions, and that the final-state interactions dominate. We find that in the leading kinematic region where the transverse momentum imbalance of the two jets, q_\perp = P_{1\perp}+P_{2\perp}, is much less than the momentum of either jet, the contribution from the lowest non-trivial perturbative order to both the spin-averaged and the spin-dependent dijet cross sections can be factorized into a hard part that is a function only of the averaged jet momentum P_\perp = (P_{1\perp}-P_{2\perp})/2, and perturbatively generated transverse momentum dependent (TMD) parton distributions. We show that the spin asymmetry at this non-trivial perturbative order can be described by the TMD parton distributions defined in either semi-inclusive DIS or the Drell-Yan process. We derive the same hard parts from both the collinear factorization approach and in the context of the Brodsky-Hwang-Schmidt model, verifying that they are not sensitive to details of the factorized long distance physics.

hep-ph↗
arXiv2007

Asymmetric Di-jet Production in Polarized Hadronic Collisions

Using the collinear QCD factorization approach, we study the single-transverse-spin dependent cross section Delta sigma(S_perp) for the hadronic production of two jets of momenta P_1=P+q/2 and P_2=-P+q/2. We consider the kinematic region where the transverse components of the momentum vectors satisfy P_perp >> q_perp >> Lambda_QCD. For the case of initial-state gluon radiation, we show that at the leading power in q_perp/P_perp and at the lowest non-trivial perturbative order, the dependence of Delta sigma(S_perp) on q_perp decouples from that on P_perp, so that the cross section can be factorized into a hard part that is a function only of the single scale P_perp, and into perturbatively generated transverse-momentum dependent (TMD) parton distributions with transverse momenta k_perp = O(q_perp).

hep-ph↗
arXiv2007

Nuclear Modification to Parton Distribution Functions and Parton Saturation

We introduce a generalized definition of parton distribution functions (PDFs) for a more consistent all-order treatment of power corrections. We present a new set of modified DGLAP evolution equations for nuclear PDFs, and show that the resummed $α_s A^{1/3}/Q^2$-type of leading nuclear size enhanced power corrections significantly slow down the growth of gluon density at small-$x$. We discuss the relation between the calculated power corrections and the saturation phenomena.

hep-ph↗
arXiv2007

Multi-nucleon correlations in Deep Inelastic Scattering at large Bjorken xB

Using realistic nuclear many-body wave functions in the collinear factorization framework, we evaluate nuclear Deep Inelastic Scattering at large Bjorken xB, where correlations are needed to exceed the kinematic limits of a single free nucleon. We find that recent experimental data on cross-section ratios from the CLAS collaboration exhibit features that are not reproduced by modern 2- and 3-nucleon correlations in the nuclear wave function. New physical mechanisms are needed to explain data in the 2<xB<3 range.

nucl-th↗
arXiv2006

Single transverse-spin asymmetry in high transverse momentum pion production in pp collisions

We study the single-spin (left-right) asymmetry in single-inclusive pion production in hadronic scattering. This asymmetry is power-suppressed in the transverse momentum of the produced pion and can be analyzed in terms of twist-three parton correlation functions in the proton. We present new calculations of the corresponding partonic hard-scattering functions that include the so-called "non-derivative" contributions not previously considered in the literature. We find a remarkably simple structure of the results. We also present a brief phenomenological study of the spin asymmetry, taking into account data from fixed-target scattering and also the latest information available from RHIC. We make additional predictions that may be tested experimentally at RHIC.

hep-ph↗
arXiv2006

Nuclear effects on open charm production in p+A reactions

We calculate and resum the nuclear enhanced power corrections from the final state partonic scattering in nuclear matter to open charm production and correlations. In p+A reactions, we find that single and double inclusive D mesons can be suppressed as much as the neutral pions from the dynamical high twist shadowing. Effects of initial state energy loss in p+A collisions are also investigated and may lead to significantly weaker transverse momentum dependence of the nuclear suppression.

hep-ph↗
arXiv2006

NRQCD Factorization and Velocity-dependence of NNLO Poles in Heavy Quarkonium Production

We study the transition of a heavy quark pair from octet to singlet color configurations at next-to-next-to-leading order (NNLO) in heavy quarkonium production. We show that the infrared singularities in this process are consistent with NRQCD factorization to all orders in the heavy quark relative velocity v. This factorization requires the gauge-completed matrix elements that we introduced previously to prove NNLO factorization to order v ^2.

hep-ph↗
arXiv2006

Single-Transverse Spin Asymmetry in Semi-Inclusive Deep Inelastic Scattering

We study the single-transverse spin asymmetry in semi-inclusive hadron production in deep inelastic scattering. We derive the leading contribution to the asymmetry at moderate transverse momentum $P_{h\perp}$ of the produced hadron in terms of twist-three quark-gluon correlation functions, and compare with the approach based on the factorization at fixed transverse momentum involving the asymmetric transverse-momentum and spin-dependent quark distribution. We verify that the two approaches yield identical results in this regime. By a comparison with our earlier calculations for the single-spin asymmetry in the Drell-Yan process we recover the well-established process-dependence of the time-reversal-odd transverse-momentum-dependent quark distributions that generate single-spin phenomena.

hep-ph↗
arXiv2006

A Unified Picture for Single Transverse-Spin Asymmetries in Hard Processes

Using Drell-Yan pair production as an example, we explore the relation between two well-known mechanisms for single transverse-spin asymmetries in hard processes: twist-three quark-gluon correlations when the pair's transverse momentum is large, $q_\perp \gg Λ_{\rm QCD}$, and time-reversal-odd and transverse-momentum-dependent parton distributions when $q_\perp$ is much less than the pair's mass. We find that although the two mechanisms have their own domain of validity, they describe the same physics in the kinematic region where they overlap. This unifies the two mechanisms and imposes an important constraint on phenomenological studies of single spin asymmetries.

hep-ph↗
arXiv2005

Fragmentation, NRQCD and Factorization in Heavy Quarkonium Production

We discuss factorization in heavy quarkonium production in high energy collisions using NRQCD. Infrared divergences at NNLO are not matched by conventional NRQCD matrix elements. However, we show that gauge invariance and factorization require that conventional NRQCD production matrix elements be modified to include Wilson lines or non-abelian gauge links. With this modification NRQCD factorization for heavy quarkonium production is restored at NNLO.

hep-ph↗
arXiv2005

Fragmentation, NRQCD and NNLO Factorization Analysis in Heavy Quarkonium Production

We discuss heavy quarkonium production through parton fragmentation, including a review of arguments for the factorization of high-p_T particles into fragmentation functions for hadronic initial states. We investigate the further factorization of fragmentation functions in the NRQCD formalism, and argue that this requires a modification of NRQCD octet production matrix elements to include nonabelian phases, which makes them gauge invariant. We describe the calculation of uncanceled infrared divergences in fragmentation functions that must be factorized at NNLO, and verify that they are absorbed into the new, gauge invariant matrix elements.

hep-ph↗
arXiv2005

Rescattering effects in hadron-nucleus and heavy-ion collisions

We review the extension of the factorization formalism of perturbative QCD to {\it coherent} soft rescattering associated with hard scattering in high energy nuclear collisions. We emphasize the ability to quantify high order corrections and the predictive power of factorization approach in terms of universal nonperturbative matrix elements. Although coherent rescattering effects are power suppressed by hard scales of the scattering, they are enhanced by the nuclear size and could play an important role in understanding the novel nuclear dependence observed in high energy nuclear collisions.

hep-ph↗
arXiv2005

Fragmentation, Factorization and Infrared Poles in Heavy Quarkonium Production

We explore the role of soft gluon exchange in heavy quarkonium production at large transverse momentum. We find uncanceled infrared poles at NNLO that are not matched by conventional NRQCD matrix elements. We show, however, that gauge invariance and factorization require that conventional NRQCD production operators be modified to include nonabelian phases or Wilson lines. With appropriately modified operators, factorization is restored at NNLO. We also argue that, in the absence of special cancellations, infrared poles at yet higher orders may require the inclusion of additional nonlocal operators, not present in the NRQCD expansion in relative veloctiy.

hep-ph↗