arXiv subjects

A. Rakotozafindrabe

Publications and source records attributed to A. Rakotozafindrabe.

33 records · Page 2Linked to original sources

arXiv2012

Prospectives for A Fixed-Target ExpeRiment at the LHC: AFTER@LHC

We argue that the concept of a multi-purpose fixed-target experiment with the proton or lead-ion LHC beams extracted by a bent crystal would offer a number of ground-breaking precision-physics opportunities. The multi-TeV LHC beams will allow for the most energetic fixed-target experiments ever performed. The fixed-target mode has the advantage of allowing for high luminosities, spin measurements with a polarised target, and access over the full backward rapidity domain --uncharted until now-- up to x_F ~ -1.

hep-ex↗

arXiv2012

Spin and diffractive physics with A Fixed-Target ExpeRiment at the LHC (AFTER@LHC)

We report on the spin and diffractive physics at a future multi-purpose fixed-target experiment with proton and lead LHC beams extracted by a bent crystal. The LHC multi-TeV beams allow for the most energetic fixed-target experiments ever performed, opening new domains of particle and nuclear physics and complementing that of collider physics, in particular that of RHIC and the EIC projects. The luminosity achievable with AFTER using typical targets would surpass that of RHIC by more than 3 orders of magnitude. The fixed-target mode has the advantage to allow for measurements of single-spin asymmetries with polarized target as well as of single-diffractive processes in the target region.

hep-ex↗

arXiv2012

J/ψ and ψ' production in proton(deuteron)-nucleus collisions: lessons from RHIC for the proton-lead LHC run

We study the impact of different cold nuclear matter effects both on J/ψ and ψ' production, among them the modification of the gluon distribution in bound nucleons, commonly known as gluon shadowing, and the survival probability for a bound state to escape the nucleus --the nuclear absorption. Less conventional effects such as saturation and fractional energy loss are also discussed. We pay a particular attention to the recent PHENIX preliminary data on ψ' production in dAu collisions at sqrt{s}=200 GeV, which show a strong suppression for central collisions, 5 times larger than the one obtained for J/ψ production at the same energy. We conclude that none of the abovementioned mechanisms can explain this experimental result.

hep-ph↗

arXiv2012

Ultra-relativistic heavy-ion physics with AFTER@LHC

We outline the opportunities for ultra-relativistic heavy-ion physics which are offered by a next generation and multi-purpose fixed-target experiment exploiting the proton and ion LHC beams extracted by a bent crystal.

nucl-ex↗

arXiv2012

A Fixed-Target ExpeRiment at the LHC (AFTER@LHC) : luminosities, target polarisation and a selection of physics studies

We report on a future multi-purpose fixed-target experiment with the proton or lead ion LHC beams extracted by a bent crystal. The multi-TeV LHC beams allow for the most energetic fixed-target experiments ever performed. Such an experiment, tentatively named AFTER for "A Fixed-Target ExperRiment", gives access to new domains of particle and nuclear physics complementing that of collider experiments, in particular at RHIC and at the EIC projects. The instantaneous luminosity at AFTER using typical targets surpasses that of RHIC by more than 3 orders of magnitude. Beam extraction by a bent crystal offers an ideal way to obtain a clean and very collimated high-energy beam, without decreasing the performance of the LHC. The fixed-target mode also has the advantage of allowing for spin measurements with a polarised target and for an access over the full backward rapidity domain up to xF ~ - 1. Here, we elaborate on the reachable luminosities, the target polarisation and a selection of measurements with hydrogen and deuterium targets.

hep-ex↗

arXiv2012

Centrality, rapidity, and transverse-momentum dependence of gluon shadowing and antishadowing on $J/ψ$ production in $d$Au collisions at $\sqrt{s}$=200 GeV

We have carried out a wide study of shadowing and antishadowing effects on \jpsi\ production in \dAu\ collisions at $\sqrt{s_{NN}}=200$ GeV. We have studied the effects of three different gluon nPDF sets, using the exact kinematics for a $2\to 2$ process, namely $g+g\to J/ψ+g$ as expected from LO pQCD. We have computed the rapidity dependence of \RCP\ and $R_{d\rm Au}$ for the different centrality classes of the PHENIX data. For mid rapidities, we have also computed the transverse-momentum dependence of the nuclear modification factor, which cannot be predicted with the usual $2\to 1$ simplified kinematics. All these observables have been compared to the PHENIX data in \dAu\ collisions.

hep-ph↗

arXiv2011

Quarkonium as a tool: cold nuclear matter effects

We discuss the quarkonium production as a tool for the study of the Quark Gluon Plasma. In particular, we concentrate on the Cold Nuclear Matter effetcs. We show that quarkonium production is also useful for the study of Quantum Chromodynamics first principles and the nuclear Parton Distribution Functions.

hep-ph↗

arXiv2011

Cold Nuclear Matter Effects on extrinsic J/psi production at sqrt{s_{NN}}=2.76 TeV at the LHC

We evaluate the Cold Nuclear Matter effects on J/psi production in pPb and PbPb collisions at the current LHC energy, taking into account the gluon shadowing and the nuclear absorption. We use the complete kinematics in the underlying 2 to 2 partonic process, namely $g+g \to \jpsi + g$ as expected from LO pQCD. The resulting shadowing is responsible for a large J/psi suppression in pPb and PbPb, and shows a strong rapidity dependence.

hep-ph↗

arXiv2011

Cold Nuclear Matter Effects on jpsi Production with Extrinsic pT at $\sqrt{s_{NN}}=5.5\mathrm{~TeV}$ at the LHC

Taking into account the gluon shadowing and the $J/ψ$ nuclear absorption, we evaluate the Cold Nuclear Matter (CNM) effects on $J/ψ$ production in $p$Pb and PbPb collisions at the design LHC energy for PbPb collisions, $\sqrt{s_{NN}}=5.5$ TeV. In view of the good agreement between the yield prediction using the LO CSM and the ALICE data at 7 TeV, we employ the latter model to use a complete description of the kinematics of the underlying $2 \rightarrow 2$ partonic process, namely $g + g \rightarrow J/ψ+ g$. We observe a large $J/ψ$ suppression in $p$Pb and PbPb collisions due to the strong shadowing of the gluon distribution in the lead ion at the corresponding gluon momentum fractions. This suppression from CNM effects has a strong rapidity dependence which may compensate, partially or completely, that of of the predicted charm recombination in PbPb collisions.

hep-ph↗

arXiv2010

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 sqrt(s_NN)=200 GeV

We have carried out a wide study of Cold Nuclear Matter (CNM) effects on J/Psi production in d+Au, Cu+Cu and Au+Au collisions at sqrt(s_NN)=200 GeV. We have studied the effects of three different gluon-shadowing parametrisations, 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 -> 2 process, namely g+g -> J/psi+g as expected from LO pQCD. We have shown that the rapidity distribution of the nuclear modification factor R_dAu, and particularly its anti-shadowing peak, is systematically shifted toward larger rapidities in the 2 -> 2 kinematics, irrespective of which shadowing parametrisation is used. In turn, we have noted differences in the effective final-state nuclear absorption necessary to fit the PHENIX d+Au data. Taking advantage of our implementation of a 2 -> 2 kinematics, we have also computed the transverse momentum dependence of the latter nuclear modification factor, which cannot be predicted with the usual simplified kinematics. All the corresponding observables have been computed for Cu+Cu and Au+Au collisions and compared to the PHENIX and STAR data. Finally, we have extracted the effective nuclear absorption from the recent measurements of R_CP in d+Au by the PHENIX collaboration.

hep-ph↗

arXiv2010

On the theoretical and experimental uncertainties in the extraction of the J/psi absorption cross section in cold nuclear matter

We investigate the cold nuclear matter effects on $J/ψ$ production, whose understanding is fundamental to study the quark-gluon plasma. Two of these effects are of particular relevance: the shadowing of the parton distributions and the nuclear absorption of the $c\bar{c}$ pair. If $J/ψ$'s are not produced {\it via} a $2 \to 1$ process as suggested by recent theoretical works, one has to modify accordingly the way to compute the nuclear shadowing. This naturally induces differences in the absorption cross-section fit to the data. A careful analysis of these differences however requires taking into account the experimental uncertainties and their correlations, as done in this work for $d$Au collisions at $\sqrtsNN=200\mathrm{GeV}$, using several shadowing parametrisations.

hep-ph↗

arXiv2009

Cold nuclear matter effects on J/psi production: intrinsic and extrinsic transverse momentum effects

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-cbar 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_AA in the forward rapidity region (with respect to the mid rapidity region) are partially explained, therefore potentially reducing the need for recombination effects.

hep-ph↗

arXiv2009

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

We present a wide study on the comparison of different shadowing models and their influence on \jpsi 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 \jpsi 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.

hep-ph↗

arXiv2008

Perspectives on heavy-quarkonium production at the LHC

We summarise the perspectives on heavy-quarkonium production at the LHC, both for proton-proton and heavy-ion runs, as emanating from the round table held at the HLPW 2008 Conference. The main topics are: present experimental and theoretical knowledge, experimental capabilities, open questions, recent theoretical advances and potentialities linked to some new observables.

hep-ph↗

arXiv2008

Transverse momentum dependence of J/psi shadowing effects

We present a new approach to estimate the effect of the gluon shadowing in nucleus+nucleus collisions and its consequences on the J/psi production yield. Using kinematical information available from the measured J/psi production in proton+proton collisions at \sqrt s = 200 GeV, we build a Glauber Monte Carlo code which takes into account shadowing in two alternative ways: multiple scattering corrections or Q2 evolution of parton densities. We exploit the dependence of these different parameterizations to the J/psi transverse momentum and we give the first predictions on the resulting pT dependence of the nuclear modification factor in deuteron+gold collisions at the same energy.

hep-ph↗