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Z. Conesa del Valle

Publications and source records attributed to Z. Conesa del Valle.

54 records · Page 3Linked to original sources
arXiv2012

Cold-nuclear-matter effcts on heavy-quark production in d+Au collisions at sqrt(s_NN)=200 GeV

The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in d+Au and p+p collisions at sqrt(s_NN)=200 GeV at the Relativistic Heavy Ion Collider, in the transverse-momentum range 0.85 < pT < 8.5 GeV/c. In central d+Au collisions, the nuclear modification factor R_dA at 1.5 < pT < 5 GeV/c displays evidence of enhancement of these electrons, relative to those produced in p+p collisions, and shows that the mass-dependent Cronin enhancement observed at RHIC extends to the heavy-D-meson family. A comparison with the neutral-pion data suggests that the difference in cold-nuclear-matter effects on light- and heavy-flavor mesons could contribute to the observed differences between the pi0 and heavy-flavor-electron nuclear modification factor R_AA.

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arXiv2012

Phenomenological interpolation of the inclusive J/psi cross section to proton-proton collisions at 2.76 TeV and 5.5 TeV

We present a study of the inclusive J/psi cross section at 2.76 TeV and 5.5 TeV. The energy dependence of the cross section, rapidity and transverse momentum distributions are evaluated phenomenologically. Their knowledge is crucial as a reference for the interpretation of A-A and p-A J/psi results at the LHC. Our approach is the following: first, we estimate the energy evolution of the pt-integrated J/psi cross section at mid-rapidity; then, we evaluate the rapidity dependence; finally, we study the transverse momentum distribution trend. Whenever possible, both theory driven (based on pQCD predictions) and functional form (data driven fits) calculations are discussed. Our predictions are compared with the recently obtained results by the ALICE collaboration in pp collisions at 2.76 TeV.

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arXiv2011

Suppression of back-to-back hadron pairs at forward rapidity in d+Au Collisions at sqrt(s_NN)=200 GeV

Back-to-back hadron pair yields in d+Au and p+p collisions at sqrt(s_NN)=200 GeV were measured with the PHENIX detector at the Relativistic Heavy Ion Collider. Rapidity separated hadron pairs were detected with the trigger hadron at pseudorapidity |eta|<0.35 and the associated hadron at forward rapidity (deuteron direction, 3.0<eta<3.8). Pairs were also detected with both hadrons measured at forward rapidity; in this case the yield of back-to-back hadron pairs in d+Au collisions with small impact parameters is observed to be suppressed by a factor of 10 relative to p+p collisions. The kinematics of these pairs is expected to probe partons in the Au nucleus with low fraction x of the nucleon momenta, where the gluon densities rise sharply. The observed suppression as a function of nuclear thickness, p_T, and eta points to cold nuclear matter effects arising at high parton densities.

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arXiv2011

Open Heavy Flavor Production in p-p and Pb-Pb collisions as seen by ALICE at the LHC

Charm and beauty production are probed with the ALICE experiment at the LHC by studying the single lepton transverse momentum distribution (electrons at mid-rapidity, muons at large-rapidities) and D mesons reconstructed in their hadronic decays. The differential production cross sections in proton proton interactions show a good agreement with perturbative QCD calculations at both sqrt(s) = 2.76 and 7 TeV. The measurements in lead lead reactions at sqrt(s_{NN})= 2.76 TeV evidence a reduction (or suppression) of the production rate at intermediate and high pt in the most central collisions with respect to the rate in proton proton interactions.

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arXiv2011

Reference heavy flavour cross sections in pp collisions at sqrt(s) = 2.76 TeV, using a pQCD-driven sqrt(s)-scaling of ALICE measurements at sqrt(s) = 7 TeV

We provide a reference in proton-proton collisions at the energy of the Pb-Pb 2010 run at the LHC, sqrt(s) = 2.76 TeV, for the pt-differential production cross section of D0, D+, and D*+ mesons in |y| < 0.5, of electrons from heavy flavour decays in |y| < 0.9, and of muons from heavy flavour decays in 2.5 < y < 4. The reference is obtained by applying a pQCD-driven scaling (based on the FONLL calculation) to ALICE preliminary data at sqrt(s) = 7 TeV. In order to validate the procedure, we scale the D meson cross section to sqrt(s) = 1.96 TeV and compare to the corresponding measurements from the CDF experiment.

hep-ph↗
arXiv2011

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

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 polarisation studies. Thereafter, we report on issues related to heavy-quark production, both in pp and pA collisions, complemented by AA collisions. To put the work in a broader perspective, we emphasize the need for new observables to investigate quarkonium production mechanisms and reiterate the qualities that make quarkonia a unique tool for many investigations in particle and nuclear physics.

hep-ph↗
arXiv2011

Production of omega mesons in p+p, d+Au, Cu+Cu, and Au+Au collisions at sqrt(s_NN)=200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured omega meson production via leptonic and hadronic decay channels in p+p, d+Au, Cu+Cu, and Au+Au collisions at sqrt(s_NN) = 200 GeV. The invariant transverse momentum spectra measured in different decay modes give consistent results. Measurements in the hadronic decay channel in Cu+Cu and Au+Au collisions show that omega production has a suppression pattern at high transverse momentum, similar to that of pi^0 and eta in central collisions, but no suppression is observed in peripheral collisions. The nuclear modification factors, R_AA, are consistent in Cu+Cu and Au+Au collisions at similar numbers of participant nucleons.

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arXiv2011

Ground and excited charmonium state production in p+p collisions at sqrt(s)=200 GeV

We report on charmonium measurements [J/psi(1S), psi'(2S), and chi_c(1P)] in p+p collisions at sqrt(s)=200 GeV. We find that the fraction of J/psi coming from the feed-down decay of psi' and chi_c in the midrapidity region ($|η|<0.35$) is 9.6+/-2.4% and 32+/-9%, respectively. We also report new, higher statistics p_T and rapidity dependencies of the J/psi yield via dielectron decay in the same midrapidity range and at forward rapidity (1.2<|eta|<2.4) via dimuon decay. These results are compared with measurements from other experiments and discussed in the context of current charmonium production models.

hep-ex↗
arXiv2010

Cold Nuclear Matter Effects on J/psi Yields as a Function of Rapidity and Nuclear Geometry in Deuteron-Gold Collisions at sqrt(s_NN) = 200 GeV

We present measurements of J/psi yields in d+Au collisions at sqrt(s_NN) = 200 GeV recorded by the PHENIX experiment and compare with yields in p+p collisions at the same energy per nucleon-nucleon collision. The measurements cover a large kinematic range in J/psi rapidity (-2.2 < y < 2.4) with high statistical precision and are compared with two theoretical models: one with nuclear shadowing combined with final state breakup and one with coherent gluon saturation effects. To remove model dependent systematic uncertainties we also compare the data to a simple geometric model. We find that calculations where the nuclear modification is linear or exponential in the density weighted longitudinal thickness are difficult to reconcile with the forward rapidity data.

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arXiv2010

Measurement of Transverse Single-Spin Asymmetries for J/psi Production in Polarized p+p Collisions at sqrt(s) = 200 GeV

We report the first measurement of transverse single-spin asymmetries in $J/ψ$ production from transversely polarized $p+p$ collisions at $\sqrt{s} = 200$ GeV with data taken by the PHENIX experiment in 2006 and 2008. The measurement was performed over the rapidity ranges $1.2 < |y| < 2.2$ and $ |y| < 0.35$ for transverse momenta up to 6 GeV/$c$. $J/ψ$ production at RHIC is dominated by processes involving initial-state gluons, and transverse single-spin asymmetries of the $J/ψ$ can provide access to gluon dynamics within the nucleon. Such asymmetries may also shed light on the long-standing question in QCD of the $J/ψ$ production mechanism. Asymmetries were obtained as a function of $J/ψ$ transverse momentum and Feynman-$x$, with a value of $-0.086 \pm 0.026^{\rm stat} \pm 0.003^{\rm syst}$ in the forward region. This result suggests possible nonzero trigluon correlation functions in transversely polarized protons and, if well defined in this reaction, a nonzero gluon Sivers distribution function.

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arXiv2010

Cross Section and Parity Violating Spin Asymmetries of W^+/- Boson Production in Polarized p+p Collisions at sqrt(s)=500 GeV

Large parity violating longitudinal single spin asymmetries A^{e^-}_L= -0.86^{+0.14}_{-0.30} and A^{e^+}_L= 0.88^{+0.12}_{-0.71} are observed for inclusive high transverse momentum electrons and positrons in polarized pp collisions at a center of mass energy of \sqrt{s}=500\ GeV with the PHENIX detector at RHIC. These e^{+/-} come mainly from the decay of W^{+/-} and Z^0 bosons, and the asymmetries directly demonstrate parity violation in the couplings of the W^{\pm} to the light quarks. The observed electron and positron yields were used to estimate W^\pm boson production cross sections equal to σ(pp \to W^+ X) \times BR(W^ \to ν_e)= 144.1+/-21.2(stat)^{+3.4}_{-10.3}(syst) +/- 15%(norm) pb, and σ(pp \to W^{-}X) \times BR(W^\to e^-\bar{ν_e}) = 31.7+/-12.1(stat)^{+10.1}_{-8.2}(syst)+/-15%(norm) pb.

hep-ex↗
arXiv2010

Nuclear modification factors of phi mesons in d+Au, Cu+Cu and Au+Au collisions at sqrt(S_NN)=200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has performed systematic measurements of phi meson production in the K+K- decay channel at midrapidity in p+p, d+Au, Cu+Cu and Au+Au collisions at sqrt(S_NN)=200 GeV. Results are presented on the phi invariant yield and the nuclear modification factor R_AA for Au+Au and Cu+Cu, and R_dA for d+Au collisions, studied as a function of transverse momentum (1<p_T<7 GeV/c) and centrality. In central and mid-central Au+Au collisions, the R_AA of phi exhibits a suppression relative to expectations from binary scaled p+p results. The amount of suppression is smaller than that of the neutral pion and the eta meson in the intermediate p_T range (2--5 GeV/c); whereas at higher p_T the phi, pi^0, and eta show similar suppression. The baryon (protons and anti-protons) excess observed in central Au+Au collisions at intermediate p_T is not observed for the phi meson despite the similar mass of the proton and the phi. This suggests that the excess is linked to the number of constituent quarks rather than the hadron mass. The difference gradually disappears with decreasing centrality and for peripheral collisions the R_AA values for both particles are consistent with binary scaling. Cu+Cu collisions show the same yield and suppression as Au+Au collisions for the same number of N_part. The R_dA of phi shows no evidence for cold nuclear effects within uncertainties.

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arXiv2009

Vector bosons in heavy-ion collisions at the LHC

Vector bosons become accessible experimental probes in heavy-ion collisions at the LHC. The capabilities of the LHC experiments to perform their measurement are outlined. The focus is given to their utility to study the possible formation and properties of the Quark Gluon Plasma (QGP) in the most central heavy-ion collisions. Their own sensitivity (if any) to the QGP is discussed. Their interest as references to observe multiple QGP sensitive probes is justified.

hep-ex↗
arXiv2008

Effect of heavy-quark energy loss on the muon differential production cross section in Pb-Pb collisions at \sqrtsNN=5.5 TeV

We study the nuclear modification factors RAA and RCP of the high transverse momentum 5<pt<60 GeV/c distribution of muons in Pb--Pb collisions at LHC energies. We consider two pseudo-rapidity ranges covered by the LHC experiments: $|η|<2.5$ and $2.5<η<4$. Muons from semi-leptonic decays of heavy quarks (c and b) and from leptonic decays of weak gauge bosons (W and Z) are the main contributions to the muon pt distribution above a few GeV/c. We compute the heavy quark contributions using available pQCD-based programs. We include the nuclear shadowing modification of the parton distribution functions and the in-medium radiative energy loss for heavy quarks, using the mass-dependent BDMPS quenching weights. Muons from W and Z leptonic decays, that dominate the yield at high pt, can be used as a medium-blind reference to observe the medium-induced suppression of beauty quarks.

hep-ph↗
arXiv2007

Studying the energy loss of heavy quarks via single muon production in PbPb collisions at $\sqrt{s_\mathrm{NN}}$=5.5 TeV

The effects of heavy quarks energy loss on the transverse momentum spectra of single muons are studied. The energy loss of heavy quarks when traversing the medium formed in PbPb collisions at $\sqrt{s_\mathrm{NN}}$=5.5 TeV is calculated by implementing the collision geometry and the quenching weights. The medium density is assumed to decrease at forward pseudo-rapidity and to be proportional with pseudo-rapidity multiplicity $dN/dη$. Muons from W decays can be used as a medium-blind reference to quantify the effect of heavy quarks energy loss on the single muon production.

hep-ph↗
arXiv2006

Electroweak boson detection in the ALICE muon spectrometer

The ALICE capabilities for W and Z detection at LHC are discussed. The contributions to single muon transverse momentum distribution are evaluated. The expected performance of the muon spectrometer for detecting W and Z bosons via their muonic decay is presented. Possible application for the study of in-medium effects in ultrarelativistic heavy ion collisions is discussed.

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