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On the Mechanisms of Heavy-Quarkonium Hadroproduction

Description: We discuss the various mechanisms potentially at work in hadroproduction of heavy quarkonia in the light of computations of higher-order QCD corrections both in the Colour-Singlet (CS) and Colour-Octet (CO) channels and the inclusion of the contribution arising from the s-channel cut in the CS channel. We also discuss new observables meant to better discriminate between these different mechanisms.
Date: December 1, 2008
Creator: Lansberg, J.P.
Partner: UNT Libraries Government Documents Department

Real Next-to-Next-to-Leading Order QCD Corrections to J/psi and Upsilon Hadroproductiom in Association with a Photon

Description: We update the study of the QCD corrections to direct J/{psi} and {Upsilon} hadroproduction in association with a photon in the QCD-based approach of the Colour-Singlet (CS) Model. After comparison with the recent full next-to-leading-order (NLO) computation for this process, we provide an independent confirmation to the inclusive case that NLO QCD corrections to quarkonium-production processes whose LO exhibits a non-leading P{sub T} behavior can be reliably computed at mid and large P{sub T} by considering only the real emission contributions accompanied with a kinematical cut. In turn, we evaluate the leading part of the {alpha}{sub S}{sup 4}{alpha} contributions, namely those coming from (J/{psi}, {Upsilon}) + {gamma} associated with two light partons. We find that they are dominant at mid and large P{sub T}. This confirms our expectations from the leading P{sub T} scaling of the new topologies appearing at NNLO. We obtain that the yield from the CS becomes one order of magnitude larger than the upper value of the potential Colour-Octet yield. The polarization of the {sup 3}S{sub 1} quarkonia produced in association with a photon is confirmed to be longitudinal at mid and large P{sub T}.
Date: June 19, 2009
Creator: Lansberg, J.P.
Partner: UNT Libraries Government Documents Department

Effective Lagrangian for Two-photon and Two-gluon Decays of P-wave Heavy Quarkonium chi_c(0,2) and chi_(b0,2) states

Description: In the traditional non-relativistic bound state calculation, the two-photon decay amplitudes of the P-wave {chi}{sub c0,2} and {chi}{sub b0,2} states depend on the derivative of the wave function at the origin which can only be obtained from potential models. However by neglecting the relative quark momenta, the decay amplitude can be written as the matrix element of a local heavy quark field operator which could be obtained from other processes or computed with QCD sum rules technique or lattice simulation. Following the same line as in recent work for the two-photon decays of the S-wave {eta}{sub c} and {eta}{sub b} quarkonia, we show that the effective Lagrangian for the two-photon decays of the P-wave {chi}{sub c0,2} and {chi}{sub b0,2} is given by the heavy quark energy-momentum tensor local operator or its trace, the {anti Q}Q scalar density and that the expression for {chi}{sub c0} two-photon and two-gluon decay rate is given by the f{sub {chi}{sub c0}} decay constant and is similar to that of {eta}{sub c} which is given by f{sub {eta}{sub c}}. From the existing QCD sum rules value for f{sub {chi}{sub c0}}, we get 5 keV for the {chi}{sub c0} two-photon width, somewhat larger than measurement, but possibly with large uncertainties.
Date: June 3, 2009
Creator: Lansberg, J. P. & Pham, T. N.
Partner: UNT Libraries Government Documents Department

Centrality, Rapidity And Transverse-Momentum Dependence of Cold Nuclear Matter Effects on J/Psi Production in D Au, Cu Cu And Au Au Collisions at S(NN)**(1/2)

Description: We have carried out a wide study of Cold Nuclear Matter (CNM) effects on J/{Psi} = production in dAu, CuCu and AuAu collisions at {radical}s{sub NN} = 200 GeV. We have studied the effects of three different gluon-shadowing parameterizations, using the usual simplified kinematics for which the momentum of the gluon recoiling against the J/{Psi} is neglected as well as an exact kinematics for a 2 {yields} 2 process, namely g + g {yields} J/{psi} + g as expected from LO pQCD. We have shown that the rapidity distribution of the nuclear modification factor R{sub dAu}, and particularly its anti-shadowing peak, is systematically shifted toward larger rapidities in the 2 {yields} 2 kinematics, irrespective of which shadowing parameterization is used. In turn, we have noted differences in the effective final-state nuclear absorption needed to fit the PHENIX dAu data. Taking advantage of our implementation of a 2 {yields} 2 kinematics, we have also computed the transverse momentum dependence of the nuclear modification factor, which cannot be predicted with the usual simplified kinematics. All the corresponding observables have been computed for CuCu and AuAu collisions and compared to the PHENIX and STAR data. Finally, we have extracted the effective nuclear absorption from the recent measurements of RCP in dAu collisions by the PHENIX collaboration.
Date: November 11, 2011
Creator: Ferreiro, E. G.; Fleuret, F.; Lansberg, J. P. & Rakotozafindrabe, A.
Partner: UNT Libraries Government Documents Department

Physics Opportunities of a Fixed-Target Experiment using the LHC Beams

Description: We outline the many physics opportunities offered by a multi-purpose fixed-target experiment using the proton and lead-ion beams of the LHC extracted by a bent crystal. In a proton run with the LHC 7-TeV beam, one can analyze pp, pd and pA collisions at center-of-mass energy {radical}s{sub NN} {approx_equal} 115 GeV and even higher using the Fermi motion of the nucleons in a nuclear target. In a lead run with a 2.76 TeV-per-nucleon beam, {radical}s{sub NN} is as high as 72 GeV. Bent crystals can be used to extract about 5 x 10{sup 8} protons/sec; the integrated luminosity over a year reaches 0.5 fb{sup -1} on a typical 1 cm-long target without nuclear species limitation. We emphasize that such an extraction mode does not alter the performance of the collider experiments at the LHC. By instrumenting the target-rapidity region, gluon and heavy-quark distributions of the proton and the neutron can be accessed at large x and even at x larger than unity in the nuclear case. Single diffractive physics and, for the first time, the large negative-xF domain can be accessed. The nuclear target-species versatility provides a unique opportunity to study nuclear matter versus the features of the hot and dense matter formed in heavy-ion collisions, including the formation of the quark-gluon plasma, which can be studied in PbA collisions over the full range of target-rapidity domain with a large variety of nuclei. The polarization of hydrogen and nuclear targets allows an ambitious spin program, including measurements of the QCD lensing effects which underlie the Sivers single-spin asymmetry, the study of transversity distributions and possibly of polarized parton distributions. We also emphasize the potential offered by pA ultra-peripheral collisions where the nucleus target A is used as a coherent photon source, mimicking photoproduction processes in ep collisions. Finally, we note ...
Date: March 16, 2012
Creator: Brodsky, S.J.; /SLAC; Fleuret, F.; Polytechnique, /Ecole; Hadjidakis, C.; Lansberg, J.P. et al.
Partner: UNT Libraries Government Documents Department

On the Physical Relevance of the Study of gamma* gamma -> pi pi at small t and large Q2

Description: We discuss the relevance of a dedicated measurement of exclusive production of a pair of neutral pions in a hard {gamma}*{gamma} scattering at small momentum transfer. In this case, the virtuality of one photon provides us with a hard scale in the process, enabling us to perform a QCD calculation of this reaction rate using the concept of Transition Distribution Amplitudes (TDA). Those are related by sum rules to the pion axial form factor F{sub A}{sup {pi}} and, as a direct consequence, a cross-section measurement of this process at intense beam electron-positron colliders such as CLEO, KEK-B and PEP-II, or Super-B would provide us with a unique measurement of the neutral pion axial form factor F{sub A}{sup {pi}0} at small scale. We believe that our models for the photon to meson transition distribution amplitudes are sufficiently constrained to give reasonable orders of magnitude for the estimated cross sections. Cross sections are large enough for quantitative studies to be performed at high luminosity e{sup +}e{sup -} colliders. After verifying the scaling and the {phi} independence of the cross section, one should be able to measure these new hadronic matrix elements, and thus open a new gate to the understanding of the hadronic structure. In particular, we argued here that the study of {gamma}*{gamma} {yields} {pi}{sup 0}{pi}{sup 0} in the TDA regime could provide with a unique experimental measurement of the {pi}{sup 0} axial form factor.
Date: August 26, 2010
Creator: Lansberg, J.P.; /SLAC; Pire, B.; /Ecole Polytechnique, CPHT; Szymanowski, L. & /Warsaw, Inst. Nucl. Studies
Partner: UNT Libraries Government Documents Department

Cold Nuclear Matter effects on J/psi production at RHIC: comparing shadowing models

Description: We present a wide study on the comparison of different shadowing models and their influence on J/{psi} production. We have taken into account the possibility of different partonic processes for the c{bar c}-pair production. We notice that the effect of shadowing corrections on J/{psi} production clearly depends on the partonic process considered. Our results are compared to the available data on dAu collisions at RHIC energies. We try different break up cross section for each of the studied shadowing models.
Date: June 19, 2009
Creator: Ferreiro, E.G.; U., /Santiago de Compostela; Fleuret, F.; Polytechnique, /Ecole; Lansberg, J.P.; /SLAC et al.
Partner: UNT Libraries Government Documents Department

Cold Nuclear Matter Effects on J/psi Production: Intrinsic and Extrinsic Transverse Momentum Effects

Description: Cold nuclear matter effects on J/{psi} production in proton-nucleus and nucleus-nucleus collisions are evaluated taking into account the specific J/{psi}-production kinematics at the partonic level, the shadowing of the initial parton distributions and the absorption in the nuclear matter. We consider two different parton processes for the c{bar c}-pair production: one with collinear gluons and a recoiling gluon in the final state and the other with initial gluons carrying intrinsic transverse momentum. Our results are compared to RHIC observables. The smaller values of the nuclear modification factor R{sub AA} in the forward rapidity region (with respect to the mid rapidity region) are partially explained, therefore potentially reducing the need for recombination effects.
Date: August 26, 2010
Creator: Ferreiro, E.G.; U., /Santiago de Compostela; Fleuret, F.; Polytechnique, /Ecole; Lansberg, J.P.; U., /Heidelberg et al.
Partner: UNT Libraries Government Documents Department

Quarkonium Physics at a Fixed-Target Experiment Using the LHC Beams

Description: We outline the many quarkonium-physics opportunities offered by a multi-purpose fixed-target experiment using the p and Pb LHC beams extracted by a bent crystal. This provides an integrated luminosity of 0.5 fb{sup -1} per year on a typical 1cm-long target. Such an extraction mode does not alter the performance of the collider experiments at the LHC. With such a high luminosity, one can analyse quarkonium production in great details in pp, pd and pA collisions at {radical}s{sub NN} {approx_equal} 115 GeV and at {radical}s{sub NN} {approx_equal} 72 GeV in PbA collisions. In a typical pp (pA) run, the obtained quarkonium yields per unit of rapidity are 2-3 orders of magnitude larger than those expected at RHIC and about respectively 10 (70) times larger than for ALICE. In PbA, they are comparable. By instrumenting the target-rapidity region, the large negative-x{sub F} domain can be accessed for the first time, greatly extending previous measurements by Hera-B and E866. Such analyses should help resolving the quarkonium-production controversies and clear the way for gluon PDF extraction via quarkonium studies. The nuclear target-species versatility provides a unique opportunity to study nuclear matter and the features of the hot and dense matter formed in PbA collisions. A polarised proton target allows the study of transverse-spin asymmetries in J/{Psi} and {Upsilon} production, providing access to the gluon and charm Sivers functions.
Date: April 9, 2012
Creator: Lansberg, J.P.; /Orsay, IPN; Brodsky, S.J.; /SLAC; Fleuret, F.; Polytechnique, /Ecole et al.
Partner: UNT Libraries Government Documents Department

Quarkonium production in high energyproton-proton and proton-nucleus collisions

Description: We present a brief overview of the most relevant current issues related to quarkonium production in high energy proton-proton and proton-nucleus collisions along with some perspectives. After reviewing recent experimental and theoretical results on quarkonium production in pp and pA collisions, we discuss the emerging field of polarization studies. Afterwards, we report on issues related to heavy-quark production, both in pp and pA collisions, complemented by AA collisions. To put the work in broader perpectives, we emphasize the need for new observables to investigate the quarkonium production mechanisms and reiterate the qualities that make quarkonia a unique tool for many investigations in particle and nuclear physics.
Date: March 14, 2011
Creator: del Valle, Z C; Corcella, G; Fleuret, F; Ferreiro, E G; Kartvelishvili, V; Kopeliovich, B et al.
Partner: UNT Libraries Government Documents Department