11 research outputs found

    Mid-rapidity anti-baryon to baryon ratios in pp collisions at s\sqrt{s} = 0.9, 2.76 and 7 TeV measured by ALICE

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    The ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for anti-proton/proton, anti-Λ/Λ\Lambda/\Lambda, anti-Ξ+/Ξ−\Xi^{+}/\Xi^{-} and anti-Ω+/Ω−\Omega^{+}/\Omega^{-} in pp collisions at s\sqrt{s} = 0.9, 2.76 and 7 TeV, measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of anti-proton/proton, anti-Λ/Λ\Lambda/\Lambda, anti-Ξ+/Ξ−\Xi^{+}/\Xi^{-} and anti-Ω+/Ω−\Omega^{+}/\Omega^{-}, reaching values compatible with unity for s\sqrt{s} = 7 TeV, complement the earlier anti-proton/proton measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of αJ\alpha_J ≈ 0.5, which are suppressed with increasing rapidity interval Δy\Delta y, Any significant contribution of an exchange not suppressed at large Δy\Delta y (reached at LHC energies) is disfavoured.publishedVersio

    Charmonium and e+e−e^+e^- pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

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    The ALICE Collaboration at the LHC has measured the J/ψJ/\psi and ψ\psi' photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 μb−1{\mu}b^{-1}, The cross section for coherent and incoherent J/ψJ/\psi production in the rapidity interval -0.9 < y < 0.9, are dσJ/ψcoh/dy=2.38−0.24+0.34(sta+sys)d\sigma_{J/\psi}^{coh}/dy = 2.38^{+0.34}_{-0.24}(sta+sys) mb and dσJ/ψinc/dy=0.98−0.17+0.19(sta+sys)d\sigma_{J/\psi}^{inc}/dy = 0.98^{+0.19}_{-0.17}(sta+sys) mb, respectively. The results are compared to theoretical models for J/ψJ/\psi production and the coherent cross section is found to be in good agreement with those models which include nuclear gluon shadowing consistent with EPS09 parametrization. In addition the cross section for the process γγ→e+e−\gamma\gamma \to e^+e^- has been measured and found to be in agreement with the STARLIGHT Monte Carlo predictions.publishedVersio

    Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

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    We present the first wide-range measurement of the charged-particle pseudorapidity density distribution, for different centralities (the 0-5%, 5-10%, 10-20%, and 20-30% most central events) in Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV at the LHC. The measurement is performed using the full coverage of the ALICE detectors, -5.0 < η\eta < 5.5, and employing a special analysis technique based on collisions arising from LHC ' satellite' bunches. We present the pseudorapidity density as a function of the number of participating nucleons as well as an extrapolation to the total number of produced charged particles NchN_{ch} = 17165 +/- 772 for the 0-5% most central collisions). From the measured d\)._{ch}\).d\).eta\) distribution we derive the rapidity density distribution, d\)._{ch}\).dy, under simple assumptions. The rapidity density distribution is found to be significantly wider than the predictions of the Landau model, which reproduce data well at RHIC energies. We assess the validity of longitudinal scaling by comparing to lower energy results from RHIC. Finally the mechanisms of the underlying particle production are discussed based on a comparison with various theoretical models.publishedVersio

    Mid-rapidity anti-baryon to baryon ratios in pp collisions at s\sqrt{s} = 0.9, 2.76 and 7 TeV measured by ALICE

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    The ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for anti-proton/proton, anti-Λ/Λ\Lambda/\Lambda, anti-Ξ+/Ξ−\Xi^{+}/\Xi^{-} and anti-Ω+/Ω−\Omega^{+}/\Omega^{-} in pp collisions at s\sqrt{s} = 0.9, 2.76 and 7 TeV, measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of anti-proton/proton, anti-Λ/Λ\Lambda/\Lambda, anti-Ξ+/Ξ−\Xi^{+}/\Xi^{-} and anti-Ω+/Ω−\Omega^{+}/\Omega^{-}, reaching values compatible with unity for s\sqrt{s} = 7 TeV, complement the earlier anti-proton/proton measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of αJ\alpha_J ≈ 0.5, which are suppressed with increasing rapidity interval Δy\Delta y, Any significant contribution of an exchange not suppressed at large Δy\Delta y (reached at LHC energies) is disfavoured

    J/psi Elliptic Flow in Pb-Pb Collisions at root s(NN)=2.76 TeV

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    We report on the first measurement of inclusive J/ψ elliptic flow v2 in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at √ s N N = 2.76     TeV in the rapidity range 2.5 < y < 4.0 . The dependence of the J/ψ v2 on the collision centrality and on the J/ψ transverse momentum is studied in the range 0≤ p T < 10     GeV / c . For semicentral Pb-Pb collisions at √ s N N = 2.76     TeV , an indication of nonzero v2 is observed with a largest measured value of v2=0.116 ± 0.046 ( stat ) ± 0.029 ( syst ) for J/ψ in the transverse momentum range 2≤ p T < 4     GeV / c . The elliptic flow measurement complements the previously reported ALICE results on the inclusive J/ψ nuclear modification factor and favors the scenario of a significant fraction of J/ψ production from charm quarks in a deconfined partonic phase

    Mid-rapidity anti-baryon to baryon ratios in pp collisions at root s=0.9, 2.76 and 7 TeV measured by ALICE

    No full text
    The ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for p − /p , Λ − − /Λ , Ξ − − + /Ξ − and Ω − − + /Ω − in pp collisions at s √ =0.9, 2.76 and 7 TeV , measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of p − /p , Λ − − /Λ , Ξ − − + /Ξ − and Ω − − + /Ω − , reaching values compatible with unity for s √ =7 TeV , complement the earlier p − /p measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of α J ≈0.5 , which are suppressed with increasing rapidity interval Δy. Any significant contribution of an exchange not suppressed at large Δy (reached at LHC energies) is disfavoured

    J/psipsi Elliptic Flow in Pb-Pb Collisions at sNN\sqrt{s_{NN}}=2.76 TeV

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    We report on the first measurement of inclusive J/ψ\psi elliptic flow, v2v_2, in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV in the rapidity range 2.5 < y < 4.0. The dependence of the J/ψv2\psi v_2 on the collision centrality and on the J/ψ\psi transverse momentum is studied in the range 0 \le p_T \lt \(10 GeV/c. For semi-central Pb-Pb collisions at \(\sqrt{s_{NN}} = 2.76 TeV, an indication of non-zero v2 is observed with a maximum value of v2 = 0.116 ±\pm 0.046(stat.) ±\pm 0.029(syst.) for J/ψ\psi in the transverse momentum range 2 ≤pT<\le p_T \lt 4 GeV/c. The elliptic flow measurement complements the previously reported ALICE results on the inclusive J/ψ\psi nuclear modification factor and favors the scenario of a significant fraction of J/ψ\psi production from charm quarks in a deconfined partonic phase

    J/psipsi Elliptic Flow in Pb-Pb Collisions at sNN\sqrt{s_{NN}}=2.76 TeV

    No full text
    We report on the first measurement of inclusive J/ψ\psi elliptic flow, v2v_2, in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV in the rapidity range 2.5 < y < 4.0. The dependence of the J/ψv2\psi v_2 on the collision centrality and on the J/ψ\psi transverse momentum is studied in the range 0 \le p_T \lt \(10 GeV/c. For semi-central Pb-Pb collisions at \(\sqrt{s_{NN}} = 2.76 TeV, an indication of non-zero v2 is observed with a maximum value of v2 = 0.116 ±\pm 0.046(stat.) ±\pm 0.029(syst.) for J/ψ\psi in the transverse momentum range 2 ≤pT<\le p_T \lt 4 GeV/c. The elliptic flow measurement complements the previously reported ALICE results on the inclusive J/ψ\psi nuclear modification factor and favors the scenario of a significant fraction of J/ψ\psi production from charm quarks in a deconfined partonic phase.publishedVersio

    Charmonium and e+e−e^+e^- pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

    No full text
    The ALICE Collaboration at the LHC has measured the J/ψJ/\psi and ψ\psi' photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 μb−1{\mu}b^{-1}, The cross section for coherent and incoherent J/ψJ/\psi production in the rapidity interval -0.9 < y < 0.9, are dσJ/ψcoh/dy=2.38−0.24+0.34(sta+sys)d\sigma_{J/\psi}^{coh}/dy = 2.38^{+0.34}_{-0.24}(sta+sys) mb and dσJ/ψinc/dy=0.98−0.17+0.19(sta+sys)d\sigma_{J/\psi}^{inc}/dy = 0.98^{+0.19}_{-0.17}(sta+sys) mb, respectively. The results are compared to theoretical models for J/ψJ/\psi production and the coherent cross section is found to be in good agreement with those models which include nuclear gluon shadowing consistent with EPS09 parametrization. In addition the cross section for the process γγ→e+e−\gamma\gamma \to e^+e^- has been measured and found to be in agreement with the STARLIGHT Monte Carlo predictions

    Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at root s(NN)=2.76 TeV

    No full text
    We present the first wide-range measurement of the charged-particle pseudorapidity density distribution, for different centralities (the 0–5%, 5–10%, 10–20%, and 20–30% most central events) in Pb–Pb collisions at View the MathML source at the LHC. The measurement is performed using the full coverage of the ALICE detectors, −5.0<η<5.5, and employing a special analysis technique based on collisions arising from LHC ‘satellite’ bunches. We present the pseudorapidity density as a function of the number of participating nucleons as well as an extrapolation to the total number of produced charged particles (View the MathML source for the 0–5% most central collisions). From the measured dNch/dη distribution we derive the rapidity density distribution, dNch/dy, under simple assumptions. The rapidity density distribution is found to be significantly wider than the predictions of the Landau model. We assess the validity of longitudinal scaling by comparing to lower energy results from RHIC. Finally the mechanisms of the underlying particle production are discussed based on a comparison with various theoretical models
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