Compilación de Proyectos de Investigación desde el año 2003 al 2012

Listado de Proyectos de investigación de UPIICSA desde 2003 a 201

Prompt and non-prompt J/ψ\hbox {J}/\psi production and nuclear modification at mid-rapidity in p–Pb collisions at sNN=5.02\mathbf{\sqrt{{ s}_{\text {NN}}}= 5.02} TeV

A measurement of beauty hadron production at mid-rapidity in proton-lead collisions at a nucleon–nucleon centre-of-mass energy $\sqrt{s_\text {NN}}=5.02$ TeV is presented. The semi-inclusive decay channel of beauty hadrons into $\hbox {J}/\psi$ is considered, where the $\hbox {J}/\psi$ mesons are reconstructed in the dielectron decay channel at mid-rapidity down to transverse momenta of 1.3 GeV/c. The $\hbox {b}\bar{\hbox {b}}$ production cross section at mid-rapidity, $\hbox {d}\sigma _{\hbox {b}\bar{\hbox {b}}}/\hbox {d}y$ , and the total cross section extrapolated over full phase space, $\sigma _{\text {b}\bar{\text {b}}}$ , are obtained. This measurement is combined with results on inclusive $\hbox {J}/\psi$ production to determine the prompt $\hbox {J}/\psi$ cross sections. The results in p–Pb collisions are then scaled to expectations from pp collisions at the same centre-of-mass energy to derive the nuclear modification factor $R_{\text {pPb}}$ , and compared to models to study possible nuclear modifications of the production induced by cold nuclear matter effects. $R_{\text {pPb}}$ is found to be smaller than unity at low $p_{\mathrm{T}}$ for both $\hbox {J}/\psi$ coming from beauty hadron decays and prompt $\hbox {J}/\psi$

Neutral pion and η meson production at mid-rapidity in Pb–Pb collisions at √sNN = 2.76 TeV

Neutral pion and η meson production in the transverse momentum range 1 < pT < 20 GeV/c have been measured at mid-rapidity by the ALICE experiment at the Large Hadron Collider (LHC) in central and semi-central Pb-Pb collisions at sNN−−−−√ = 2.76 TeV. These results were obtained using the photon conversion method as well as the PHOS and EMCal detectors. The results extend the upper pT reach of the previous ALICE π0 measurements from 12 GeV/c to 20 GeV/c and present the first measurement of η meson production in heavy-ion collisions at the LHC. The η/π0 ratio is similar for the two centralities and reaches at high pT a plateau value of 0.457 ± 0.013stat ± 0.018syst. A suppression of similar magnitude for π0 and η meson production is observed in Pb-Pb collisions with respect to their production in pp collisions scaled by the number of binary nucleon-nucleon collisions. We discuss the results in terms of NLO pQCD predictions and hydrodynamic models. The measurements show a stronger suppression with respect to what was observed at lower center-of-mass energies in the pT range 6 < pT < 10 GeV/c. At pT < 3 GeV/c, hadronization models describe the π0 results while for the η some tension is observed

φ meson production at forward rapidity in Pb–Pb collisions at √sNN = 2.76 TeV

ϕ meson measurements provide insight into strangeness production, which is one of the key observables for the hot medium formed in high-energy heavy-ion collisions. ALICE measured ϕ production through its decay in muon pairs in Pb-Pb collisions at sNN−−−√ = 2.76 TeV in the intermediate transverse momentum range 2<pT<5 GeV/c and in the rapidity interval 2.5<y<4. The ϕ yield was measured as a function of the transverse momentum and collision centrality. The nuclear modification factor was obtained as a function of the average number of participating nucleons. Results were compared with the ones obtained via the kaon decay channel in the same pT range at midrapidity. The values of the nuclear modification factor in the two rapidity regions are in agreement within uncertainties

Λ+c production in pp collisions at √s = 7 TeV and in p–Pb collisions at √sNN = 5.02 TeV

The pT-differential production cross section of prompt Λ+c charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at s√=7 TeV and in p-Pb collisions at sNN−−−√=5.02 TeV at midrapidity. The Λ+c and Λ¯¯¯¯−c were reconstructed in the hadronic decay modes Λ+c→pK−π+, Λ+c→pK0S and in the semileptonic channel Λ+c→e+νeΛ (and charge conjugates). The measured values of the Λ+c/D0 ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and pT intervals, where the Λ+c production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Λ+c nuclear modification factor, RpPb, is also presented. The RpPb is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium

Constraints on jet quenching in p-Pb collisions at sNN\mathbf{\sqrt{s_{NN}}} = 5.02 TeV measured by the event-activity dependence of semi-inclusive hadron-jet distributions

The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high-transverse momentum trigger hadron in p–Pb collisions at sNN=5.02 TeV. Jets are reconstructed from charged-particle tracks using the anti- kT algorithm with resolution parameter R=0.2 and 0.4. A data-driven statistical approach is used to correct the uncorrelated background jet yield. Recoil jet distributions are reported for jet transverse momentum 15<pT,jetch<50GeV/c and are compared in various intervals of p–Pb event activity, based on charged-particle multiplicity and zero-degree neutral energy in the forward (Pb-going) direction. The semi-inclusive observable is self-normalized and such comparisons do not require the interpretation of p–Pb event activity in terms of collision geometry, in contrast to inclusive jet observables. These measurements provide new constraints on the magnitude of jet quenching in small systems at the LHC. In p–Pb collisions with high event activity, the average medium-induced out-of-cone energy transport for jets with R=0.4 and 15<pT,jetch<50GeV/c is measured to be less than 0.4 GeV/c at 90% confidence, which is over an order of magnitude smaller than a similar measurement for central Pb–Pb collisions at sNN=2.76TeV . Comparison is made to theoretical calculations of jet quenching in small systems, and to inclusive jet measurements in p–Pb collisions selected by event activity at the LHC and in d–Au collisions at RHIC

ϕ\phi meson production at forward rapidity in Pb-Pb collisions at sNN=2.76\sqrt{s_\mathrm{NN}}=2.76 TeV

$\phi$ meson measurements provide insight into strangeness production, which is one of the key observables for the hot medium formed in high-energy heavy-ion collisions. ALICE measured $\phi$ production through its decay in muon pairs in Pb–Pb collisions at $\sqrt{s_\mathrm {NN}} = 2.76$ TeV in the intermediate transverse momentum range $2< p_\mathrm {T}< 5$  GeV/c and in the rapidity interval $2.5<y<4$ . The $\phi$ yield was measured as a function of the transverse momentum and collision centrality. The nuclear modification factor was obtained as a function of the average number of participating nucleons. Results were compared with the ones obtained via the kaon decay channel in the same $p_\mathrm {T}$ range at midrapidity. The values of the nuclear modification factor in the two rapidity regions are in agreement within uncertainties

Neutral pion and η\eta meson production in p-Pb collisions at sNN=5.02\sqrt{s_\mathrm{NN}} = 5.02 TeV

Neutral pion and $\eta$ meson invariant differential yields were measured in non-single diffractive p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}$  = 5.02 TeV with the ALICE experiment at the CERN LHC. The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of $\pi ^{0}$ and $\eta$ meson inclusive production are measured near mid-rapidity in a broad transverse momentum range of $0.3 4$\hbox {GeV}/c$at$0.483 \pm 0.015_{\mathrm{stat}} \pm 0.015_{\mathrm{sys}}$. A deviation from$m_{\mathrm{T}}$scaling is observed for$p_{\mathrm{T}}<$2$\hbox {GeV}/c$. The measured$\eta /\pi ^{0}$ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full$p_{\mathrm{T}}$range. The measured$\eta /\pi ^{0}$ratio at high$p_{\mathrm{T}}$also agrees within uncertainties with measurements from nucleus–nucleus collisions. The$\pi ^{0}$and$\eta $yields in p–Pb relative to the scaled pp interpolated reference,$R_{{\mathrm{pPb}}}$, are presented for$0.3 < p_{\mathrm{T}}<$20$\hbox {GeV}/c$and$0.7 < p_{\mathrm{T}}<$20$\hbox {GeV}/c$, respectively. The results are compared with theoretical model calculations. The values of$R_{{\mathrm{pPb}}}$are consistent with unity for transverse momenta above 2$\hbox {GeV}/c$ . These results support the interpretation that the suppressed yield of neutral mesons measured in Pb–Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium

Λc+\Lambda_{\rm c}^+ production in pp collisions at s=7\sqrt{s} = 7 TeV and in p-Pb collisions at sNN=5.02\sqrt{s_{\rm NN}} = 5.02 TeV

The p$_{T}$-differential production cross section of prompt Λ$_{c}^{+}$ charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at $\sqrt{s}=7$ TeV and in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV at midrapidity. The Λ$_{c}^{+}$ and ${\overline{\varLambda}}_{\overline{\mathrm{c}}}$ were reconstructed in the hadronic decay modes Λ$_{c}^{+}$ → pK$^{−}$π$^{+}$, Λ$_{c}^{+}$ → pK$_{S}^{0}$ and in the semileptonic channel Λ$_{c}^{+}$ → e$^{+}$ν$_{e}$Λ (and charge conjugates). The measured values of the Λ$_{c}^{+}$ /D$^{0}$ ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and p$_{T}$ intervals, where the Λ$_{c}^{+}$ production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Λ$_{c}^{+}$ nuclear modification factor, R$_{pPb}$, is also presented. The R$_{pPb}$ is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium

Neutral pion and η\eta meson production at mid-rapidity in Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

International audienceNeutral pion and η meson production in the transverse momentum range 1 <pT< 20 GeV/c have been measured at midrapidity by the ALICE experiment at the Large Hadron Collider (LHC) in central and semicentral Pb-Pb collisions at sNN  = 2.76 TeV. These results were obtained using the photon conversion method as well as the Photon Spectrometer (PHOS) and Electromagnetic Calorimeter detectors. The results extend the upper pT reach of the previous ALICE π0 measurements from 12 to 20 GeV/c and present the first measurement of η meson production in heavy-ion collisions at the LHC. The η/π0 ratio is similar for the two centralities and reaches at high pT a plateau value of 0.457 ± 0.013stat ± 0.018syst. A suppression of similar magnitude for π0 and η meson production is observed in Pb-Pb collisions with respect to their production in pp collisions scaled by the number of binary nucleon-nucleon collisions. We discuss the results in terms of Next to Leading Order (NLO) pQCD predictions and hydrodynamic models. The measurements show a stronger suppression than observed at lower center-of-mass energies in the pT range 6 <pT< 10 GeV/c. For pT< 3 GeV/c, hadronization models describe the π0 results while for the η some tension is observed