arXiv subjects

Ivan Vitev

Publications and source records attributed to Ivan Vitev.

At least 91 records · Page 5Linked to original sources

arXiv2014

Multiple scattering effects on heavy meson production in p+A collisions at backward rapidity

We study the incoherent multiple scattering effects on heavy meson production in the backward rapidity region of p+A collisions within the generalized high-twist factorization formalism. We calculate explicitly the double scattering contributions to the heavy meson differential cross sections by taking into account both initial-state and final-state interactions, and find that these corrections are positive. We further evaluate the nuclear modification factor for muons that come form the semi-leptonic decays of heavy flavor mesons. Phenomenological applications in d+Au collisions at a center-of-mass energy $\sqrt{s}=200$ GeV at RHIC and in p+Pb collisions at $\sqrt{s}=5.02$ TeV at the LHC are presented. We find that incoherent multiple scattering can describe rather well the observed nuclear enhancement in the intermediate $p_T$ region for such reactions.

hep-ph↗

arXiv2014

Sivers Asymmetry with QCD Evolution

We analyze the Sivers asymmetry in both Drell-Yan (DY) production and semi-inclusive deep inelastic scattering (SIDIS), while considering properly defined transverse momentum dependent parton distribution and fragmentation functions and their QCD evolution. After finding a universal non-perturbative spin-independent Sudakov factor that can describe reasonably well the world's data of SIDIS, DY lepton pair and $W/Z$ production in unpolarized scatterings, we perform a global fitting of all the experimental data on the Sivers asymmetry in SIDIS from HERMES, COMPASS and Jefferson Lab. Then we make predictions for the asymmetry in DY lepton pair and $W$ boson production, which could be compared to the future experimental data in order to test the sign change of the Sivers function.

hep-ph↗

arXiv2014

Hard probes in heavy ion collisions: current status and prospects for application of QCD evolution techniques

In the past decade the observation of cross section modification for leading hadrons, heavy flavor and two particle correlations in heavy ion collisions has provided important insights into the dynamics of parton propagation in dense strongly-interacting matter. The development of the theory of reconstructed jets and related experimental measurements have further shed light on the characteristics of in-medium parton showers. So far, experimental results from ultra-relativistic nuclear collisions at RHIC and LHC have been analyzed in the framework of parton energy loss, where the precision of the theoretical predictions cannot be systematically improved. Only recently have higher order calculations and applications of resummation and evolution to heavy ion collisions begun to emerge. Several examples of such advances are discussed in these proceedings.

hep-ph↗

arXiv2014

Initial-State Bremsstrahlung versus Final-State Hydrodynamic Sources of Azimuthal Harmonics in p+A at RHIC and LHC

Recent pT<2~GeV azimuthal correlation data from the Beam Energy Scan (BES) and D+Au runs at RHIC/BNL and, especially, the surprising similarity of azimuthal $v_n\{2m\}(p_T)$ ``transeverse flow'' harmonics in $p+Pb$ and $Pb+Pb$ at LHC have challenged the uniqueness of local equilibrium ``perfect fluid'' interpretations of those data. We report results at QM14 on azimuthal harmonics associated with initial-state non-abelian ``wave interference'' effects predicted by perturbative QCD gluon bremsstrahlung and sourced by Color Scintillation Arrays (CSA) of color antennas. CSA are naturally identified with multiple projectile and target beam jets produced in inelastic p+A reactions. We find a remarkable similarity between azimuthal harmonics sourced by initial state CSA and those predicted with final state perfect fluid models of high energy p+A reactions. The question of which mechanism dominates in $p+A$ and $A+A$ remains open at this time.

hep-ph↗

arXiv2014

Jet quenching phenomenology from soft-collinear effective theory with Glauber gluons

We present the first application of a recently-developed effective theory of jet propagation in matter SCETG to inclusive hadron suppression in nucleus-nucleus collisions at the LHC. SCETG-based splitting kernels allow us to go beyond the traditional energy loss approximation and unify the treatment of vacuum and medium-induced parton showers. In the soft gluon emission limit, we establish a simple analytic relation between the QCD evolution and energy loss approaches to jet quenching. We quantify the uncertainties associated with the implementation of the in-medim modification of hadron production cross sections and show that the coupling between the jet and the medium can be constrained with better than 10% accuracy.

hep-ph↗

arXiv2014

QCD Evolution of the Sivers Asymmetry

We study the QCD evolution of the Sivers effect in both semi-inclusive deep inelastic scattering (SIDIS) and Drell-Yan production (DY). We pay close attention to the non-perturbative spin-independent Sudakov factor in the evolution formalism and find a universal form which can describe reasonably well the experimental data on the transverse momentum distributions in SIDIS, DY lepton pair and $W/Z$ production. With this Sudakov factor at hand, we perform a global fitting of all the experimental data on the Sivers asymmetry in SIDIS from HERMES, COMPASS and Jefferson Lab. We then make predictions for the Sivers asymmetry in DY lepton pair and $W$ production that can be compared to the future experimental measurements to test the sign change of the Sivers functions between SIDIS and DY processes and constrain the sea quark Sivers functions.

hep-ph↗

arXiv2014

Next-to-leading order forward hadron production in the small-$x$ regime: rapidity factorization

Single inclusive hadron production at forward rapidity in high energy p+A collisions is an important probe of the high gluon density regime of QCD and the associated small-$x$ formalism. We revisit an earlier one-loop calculation to illustrate the significance of the "rapidity factorization" approach in this regime. Such factorization separates the very small-$x$ unintegrated gluon density evolution and leads to a new correction term to the physical cross section at one-loop level. Importantly, this rapidity factorization formalism remedies the previous unphysical negative next-to-leading order contribution to the cross section. It is much more stable with respect to "rapidity" variation when compared to the leading-order calculation and provides improved agreement between theory and experiment in the forward rapidity region.

hep-ph↗

arXiv2014

An operator definition and derivation of collisional energy and momentum loss in relativistic plasmas

We present an operator definition of the collisional energy and momentum loss suffered by an energetic charged particle in the presence of a medium. Our approach uses the energy-momentum tensor of the medium to evaluate the energy and momentum transfer rates. We apply this formalism to an energetic lepton or quark propagating in thermal electron-positron or quark-gluon plasmas, respectively. By using two different approaches to describe the energetic charged particle, an external current approach and a diagrammatic approach, we show explicitly that the operator method reproduces the known results for collisional energy loss from the scattering rate formalism. We further use our results to evaluate the collisional energy and momentum loss for the cases of heavy quark propagation through a quark-gluon plasma and energetic muon propagation in an electron-positron plasma produced in a high-intensity laser field.

hep-ph↗

arXiv2013

Inclusive b-jet production in heavy ion collisions at the LHC

Theoretical and experimental advances in understanding light jet production and modification in Pb+Pb reactions at a center-of-mass energy 2.76 TeV have been a highlight of the LHC heavy ion program. At the same time, the detailed mechanisms of heavy quark energy loss in dense QCD matter are not yet fully understood. With this motivation, we present theoretical predictions for the nuclear-induced attenuation of the differential cross sections for inclusive b-jet production in heavy ion collisions at the LHC for comparison to upcoming data. We find that for transverse momenta pT > 75 GeV both hadronization and mass effects are negligible and this attenuation is comparable to the one observed for light jets. We discuss how the detailed b-jet quenching patterns can be used to gain new insight into the in-medium heavy flavor dynamics.

hep-ph↗

arXiv2013

Multiple scattering effects on inclusive particle production in the large-x regime

We study the multiple scattering effects on inclusive particle production in p+A and $γ$+A collisions. Specifically, we concentrate on the region where the parton momentum fraction in the nucleus $x\sim {\cal O}(1)$ and incoherent multiple interactions are relevant. By taking into account both initial-state and final-state double scattering, we derive the nuclear size-enhanced power corrections to the differential cross section for single inclusive hadron production in p+A and $γ$+A reactions, and for prompt photon production in p+A reactions. We find that the final result can be written in a simple compact form in terms of four-parton correlation functions, in which the second-derivative, first-derivative and non-derivative terms of the correlation distributions share the same hard-scattering functions. We expect our result to be especially relevant for understanding the nuclear modification of particle production in the backward rapidity regions in p+A and e+A collisions.

hep-ph↗

arXiv2013

Angular distributions of higher order splitting functions in the vacuum and in dense QCD matter

We study the collinear splitting functions needed for next-to-next-to-leading order calculations of jet production in the vacuum and in dense QCD matter. These splitting functions describe the probability of a parton to evolve into three-parton final state and are generalizations of the traditional DGLAP splitting kernels to a higher perturbative order. Of particular interest are the angular distributions of such splitting functions, which can elucidate the significance of multiple parton branching for jet observables and guide the construction of parton shower Monte Carlo generators. We find that to ${\cal O}(α_s^2)$ both the vacuum and the in-medium collinear splitting functions are neither angular ordered nor anti-angular ordered. Specifically, in dense QCD matter they retain the characteristic broad angular distribution already found in the ${\cal O}(α_s)$ result.

hep-ph↗

arXiv2013

High transverse momentum quarkonium production and dissociation in heavy ion collisions

We calculate the yields of quarkonia in heavy ion collisions at RHIC and the LHC as a function of their transverse momentum. Based upon non-relativistic quantum chromodynamics, our results include both color-singlet and color-octet contributions and feed-down effects from excited states. In reactions with ultra-relativistic nuclei, we focus on the consistent implementation of dynamically calculated nuclear matter effects, such as coherent power corrections, cold nuclear matter energy loss, and the Cronin effect in the initial state. In the final state, we consider radiative energy loss for the color-octet state and collisional dissociation of quarkonia as they traverse through the QGP. Theoretical results are presented for J/psi and Upsilon and compared to experimental data where applicable. At RHIC, a good description of the high-pT J/psi modification observed in central Cu+Cu and Au+Au collisions can be achieved within the model uncertainties. We find that measurements of J/psi yields in proton-nucleus reactions are needed to constrain the magnitude of cold nuclear matter effects. At the LHC, a good description of the experimental data can be achieved only in mid-central and peripheral Pb+Pb collisions. The large five-fold suppression of prompt J/psi in the most central nuclear reactions may indicate for the first time possible thermal effects at the level of the quarkonium wavefunction at large transverse momenta.

hep-ph↗

arXiv2013

Momentum imbalance of isolated photon-tagged jet production at RHIC and LHC

In collisions of ultra-relativistic nuclei, photon-tagged jets provide a unique opportunity to compare jet production and modification due to parton shower formation and propagation in strongly-interacting matter at vastly different center-of-mass energies. We present first results for the cross sections of jets tagged by an isolated photon to ${\cal O}(α_{\rm em} α_s^2)$ in central Au+Au reactions with $\sqrt{s_{NN}}=200$ GeV at RHIC and central Pb+Pb reactions with $\sqrt{s_{NN}}=2.76$ TeV at LHC. We evaluate the increase in the transverse momentum imbalance of the observed $γ$+jet state, induced by the dissipation of the parton shower energy due to strong final-state interactions. Theoretical predictions to help interpret recent and upcoming experimental data are presented.

hep-ph↗

arXiv2012

Transverse momentum-weighted Sivers asymmetry in semi-inclusive deep inelastic scattering at next-to-leading order

We study the next-to-leading order perturbative QCD corrections to the transverse momentum-weighted Sivers asymmetry in semi-inclusive hadron production in lepton-proton deep inelastic scattering. The corresponding differential cross section is evaluated as a convolution of a twist-three quark-gluon correlation function, often referred to as Qiu-Sterman function, the usual unpolarized fragmentation function, and a hard coefficient function. By studying the collinear divergence structure, we identify the evolution kernel for the Qiu-Sterman function. The hard coefficient function, which is finite and free of any divergence, is evaluated at one-loop order.

hep-ph↗

arXiv2012

Transverse momentum imbalance of back-to-back particle production in p+A and e+A collisions

We study the nuclear enhancement of the transverse momentum imbalance for back-to-back particle production in both p+A and e+A collisions. Specifically, we present results for photon+jet and photon+hadron production in p+A collisions, di-jet and di-hadron production in e+A collisions, and heavy-quark and heavy-meson pair production in both p+A and e+A collisions. We evaluate the effect of both initial-state and final-state multiple scattering, which determine the strength of the nuclear-induced transverse momentum imbalance in these processes. We give theoretical predictions for the experimentally relevant kinematic regions in d+Au collisions at RHIC, p+Pb collisions at LHC and e+A collisions at the future EIC and LHeC.

hep-ph↗

arXiv2012

Electroweak boson-tagged jet event asymmetries at the Large Hadron Collider

Tagged jet measurements provide a promising experimental channel to quantify the similarities and differences in the mechanisms of jet production in proton-proton and nucleus-nucleus collisions. We present the first calculation of the transverse momentum asymmetry of $Z^0/γ^*$-tagged jet events and the momentum imbalance of $γ$-tagged jet events in $\sqrt{s}=2.76$ TeV reactions at the LHC. Our results combine the ${\cal O}(G_Fα_s^2)$, ${\cal O}(G_Fα_s^2)$ perturbative cross sections with the radiative and collisional processes that modify parton showers in the presence of dense QCD matter. We find that strong asymmetry momentum and imbalance, respectively, are generated in central Pb+Pb reactions that have little sensitivity to the fluctuations of the underlying soft hadronic background. We present theoretical model predictions for their shape and magnitude.

hep-ph↗

arXiv2012

Nuclear modification of high transverse momentum particle production in p+A collisions at RHIC and LHC

We present results and predictions for the nuclear modification of the differential cross sections for inclusive light hadron and prompt photon production in minimum bias d+Au collisions at $\sqrt{s} = 200$ GeV and minimum bias p+Pb collisions at $\sqrt{s} = 5$ TeV at RHIC and LHC, respectively. Our calculations combine the leading order perturbative QCD formalism with cold nuclear matter effects that arise from the elastic, inelastic and coherent multiple scattering of partons in large nuclei. We find that a theoretical approach that includes the isospin effect, Cronin effect, cold nuclear matter energy loss and dynamical shadowing can describe the RHIC d+Au data rather well. The LHC p+Pb predictions will soon be confronted by new experimental results to help clarify the magnitude and origin of cold nuclear matter effects and facilitate precision dense QCD matter tomography.

hep-ph↗

arXiv2012

Probing nuclear matter with jets

Jet physics in relativistic heavy ion collisions, which combines perturbative QCD jet production with quark and gluon energy loss and in-medium parton shower modification, has emerged as a powerful tool to probe the properties of strongly-interacting matter formed in high-energy nuclear reactions. We present selected results for the modification of jet cross sections and related observables in the ambiance of hot and/or dense nuclear medium. We focus on the inclusive jet spectrum and dijets [${\cal O}(α_s^3) $], and $Z^0/γ^*$ tagged jets [${\cal O}(G_Fα_s^2) $] in the framework of perturbative QCD.

nucl-th↗