The p T -differential inclusive production cross section of the prompt charm-strange meson D + s ... more The p T -differential inclusive production cross section of the prompt charm-strange meson D + s in the rapidity range |y| < 0.5 was measured in proton-proton collisions at √ s = 7 TeV at the LHC using the ALICE detector. The analysis was performed on a data sample of 2.98×10 8 events collected with a minimum-bias trigger. The corresponding integrated luminosity is L int = 4.8 nb −1 . Reconstructing the decay D + s → φ π + , with φ → K − K + , and its charge conjugate, about 480 D ± s mesons were counted, after selection cuts, in the transverse momentum range 2 < p T < 12 GeV/c. The results are compared with the prediction of a model based on perturbative QCD. The ratios of the cross sections of four D meson species (namely D 0 , D + , D * + and D + s ) were determined both as a function of p T and integrated over p T after extrapolating to full p T range, together with the strangeness suppression factor in charm fragmentation. The obtained values are found to be compatible within uncertainties with those measured by other experiments in e + e − , ep and pp interactions at various centre-of-mass energies.
The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at √ s N... more The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at √ s NN = 2.76 TeV at the Large Hadron Collider is presented. We observe a growing trend with energy now not only for the longitudinal and the outward but also for the sideward pion source radius. The pion homogeneity volume and the decoupling time are significantly larger than those measured at RHIC.
The production cross section of electrons from semileptonic decays of beauty hadrons was measured... more The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y| < 0.8) in the transverse momentum range 1 < p T < 8 GeV/c with the ALICE experiment at the CERN LHC in pp collisions at a center of mass energy √ s = 7 TeV using an integrated luminosity of 2.2 nb −1 . Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark-antiquark pairs. * See Appendix A for the list of collaboration members Electrons from beauty hadron decays in pp collisions at √ s = 7 TeV 1
The inclusive charged particle transverse momentum distribution is measured in proton-proton coll... more The inclusive charged particle transverse momentum distribution is measured in proton-proton collisions at √ s = 900 GeV at the LHC using the ALICE detector. The measurement is performed in the central pseudorapidity region (|η| < 0.8) over the transverse momentum range 0.15 < p T < 10 GeV/c. The correlation between transverse momentum and particle multiplicity is also studied. Results are presented for inelastic (INEL) and non-single-diffractive (NSD) events. The average transverse momentum for |η| < 0.8 is p T INEL = 0.483±0.001 (stat.) ±0.007 (syst.) GeV/c and p T NSD = 0.489 ± 0.001 (stat.) ±0.007 (syst.) GeV/c, respectively. The data exhibit a slightly larger p T than measurements in wider pseudorapidity intervals. The results are compared to simulations with the Monte Carlo event generators PYTHIA and PHOJET.
Measurements of the sphericity of primary charged particles in minimum bias proton-proton collisi... more Measurements of the sphericity of primary charged particles in minimum bias proton-proton collisions at √ s = 0.9, 2.76 and 7 TeV with the ALICE detector at the LHC are presented. The observable is linearized to be collinear safe and is measured in the plane perpendicular to the beam direction using primary charged tracks with p T ≥ 0.5 GeV/c in |η| ≤ 0.8. The mean sphericity as a function of the charged particle multiplicity at mid-rapidity (N ch ) is reported for events with different p T scales ("soft" and "hard") defined by the transverse momentum of the leading particle. In addition, the mean charged particle transverse momentum versus multiplicity is presented for the different event classes, and the sphericity distributions in bins of multiplicity are presented. The data are compared with calculations of standard Monte Carlo event generators. The transverse sphericity is found to grow with multiplicity at all collision energies, with a steeper rise at low N ch , whereas the event generators show the opposite tendency. The combined study of the sphericity and the mean p T with multiplicity indicates that most of the tested event generators produce events with higher multiplicity by generating more back-to-back jets resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with tune PERUGIA-2011 exhibits a noticeable improvement in describing the data, compared to the other tested generators.
The production of mesons containing strange quarks (K 0 S , φ ) and both singly and doubly strang... more The production of mesons containing strange quarks (K 0 S , φ ) and both singly and doubly strange baryons (Λ, Λ, and Ξ − + Ξ + ) are measured at central rapidity in pp collisions at √ s = 0.9 TeV with the ALICE experiment at the LHC. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at central rapidities for inelastic pp collisions are presented. For mesons, we report yields ( dN/dy ) of 0.184 ± 0.002 (stat.) ± 0.006 (syst.) for K 0 S and 0.021 ± 0.004 (stat.) ± 0.003 (syst.) for φ . For baryons, we find dN/dy = 0.048 ± 0.001 (stat.) ± 0.004 (syst.) for Λ, 0.047 ± 0.002 (stat.) ± 0.005 (syst.) for Λ and 0.0101 ± 0.0020 (stat.) ± 0.0009 (syst.) for Ξ − + Ξ + . The results are also compared with predictions for identified particle spectra from QCDinspired models and provide a baseline for comparisons with both future pp measurements at higher energies and heavy-ion collisions. * See Appendix A for the list of collaboration members Strange particle production in pp at √ s = 0.9 TeV 3
On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), tw... more On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |η|N ch/dη=3.10±0.13(stat.)±0.22(syst.) for all inelastic interactions, and dN ch/dη=3.51±0.15(stat.)±0.25(syst.) for non-single diffractive interactions. These results are consistent with previous measurements in proton–antiproton interactions at the same centre-of-mass energy at the CERN Sp \(\overline{\mathrm{p}}\) S collider. They also illustrate the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase.
The production of π + , π − , K + , K − , p, and p at mid-rapidity has been measured in proton-pr... more The production of π + , π − , K + , K − , p, and p at mid-rapidity has been measured in proton-proton collisions at √ s = 900 GeV with the ALICE detector. Particle identification is performed using the specific energy loss in the inner tracking silicon detector and the time projection chamber. In addition, time-of-flight information is used to identify hadrons at higher momenta. Finally, the distinctive kink topology of the weak decay of charged kaons is used for an alternative measurement of the kaon transverse momentum (pt) spectra. Since these various particle identification tools give the best separation capabilities over different momentum ranges, the results are combined to extract spectra from pt = 100 MeV/c to 2.5 GeV/c. The measured spectra are further compared with QCD-inspired models which yield a poor description. The total yields and the mean pt are compared with previous measurements, and the trends as a function of collision energy are discussed. 6
Charged-particle production was studied in proton-proton collisions collected at the LHC with the... more Charged-particle production was studied in proton-proton collisions collected at the LHC with the ALICE detector at centre-of-mass energies 0.9 TeV and 2.36 TeV in the pseudorapidity range |η| < 1.4. In the central region (|η| < 0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density dN ch /dη = 3.02 ± 0.01(stat.) +0.08 −0.05 (syst.) for inelastic interactions, and dN ch /dη = 3.58 ± 0.01(stat.) +0.12 −0.12 (syst.) for nonsingle-diffractive interactions. At 2.36 TeV, we find dN ch /dη = 3.77 ± 0.01(stat.) +0.25 −0.12 (syst.) for inelastic, and dN ch /dη = 4.43 ± 0.01(stat.) +0.17 −0.12 (syst.) for non-single-diffractive collisions. The relative increase in charged-particle multiplicity from the lower to higher energy is 24.7%±0.5%(stat.) +5.7 −2.8 %(syst.) for inelastic and 23.7% ± 0.5%(stat.) +4.6 −1.1 %(syst.) for non-single-diffractive interactions. This increase is consistent with that reported by the CMS collaboration for non-single-diffractive events and larger than that found by a number of commonly used models. The multiplicity distribution was measured in different pseudorapidity intervals and studied in terms of KNO variables at both energies. The results are compared to protonantiproton data and to model predictions. 6
B. Abelev, A. Abrahantes Quintana, D. Adamova, AM Adare, MM Aggarwal, G. Aglieri Rinella, AG Agoc... more B. Abelev, A. Abrahantes Quintana, D. Adamova, AM Adare, MM Aggarwal, G. Aglieri Rinella, AG Agocs, A. Agostinelli, S. Aguilar Salazar, Z. Ahammed, N. Ahmad, A. Ahmad Masoodi, SU Ahn, A. Akindinov, D. Aleksandrov, B. Alessandro, R. Alfaro Molina, A. Alici, ...
The inclusive transverse momentum (p T ) distributions of primary charged particles are measured ... more The inclusive transverse momentum (p T ) distributions of primary charged particles are measured in the pseudo-rapidity range |η| < 0.8 as a function of event centrality in Pb-Pb collisions at √ s NN = 2.76 TeV with ALICE at the LHC. The data are presented in the p T range 0.15 < p T < 50 GeV/c for nine centrality intervals from 70-80% to 0-5%. The results in Pb-Pb are presented in terms of the nuclear modification factor R AA using a pp reference spectrum measured at the same collision energy. We observe that the suppression of high-p T particles strongly depends on event centrality. The yield is most suppressed in central collisions (0-5%) with R AA ≈ 0.13 at p T = 6-7 GeV/c. Above p T = 7 GeV/c, there is a significant rise in the nuclear modification factor, which reaches R AA ≈ 0.4 for p T > 30 GeV/c. In peripheral collisions (70-80%), only moderate suppression (R AA = 0.6-0.7) and a weak p T dependence is observed. The measured nuclear modification factors are compared to other measurements and model calculations.
The ALICE Collaboration has measured inclusive J/ψ production in pp collisions at a center of mas... more The ALICE Collaboration has measured inclusive J/ψ production in pp collisions at a center of mass energy √ s = 2.76 TeV at the LHC. The results presented in this Letter refer to the rapidity ranges |y| < 0.9 and 2.5 < y < 4 and have been obtained by measuring the electron and muon pair decay channels, respectively. The integrated luminosities for the two channels are L e int = 1.1 nb −1 and L µ int = 19.9 nb −1 , and the corresponding signal statistics are N e + e − J/ψ = 59 ± 14 and N µ + µ − J/ψ = 1364 ± 53. We present dσ J/ψ /dy for the two rapidity regions under study and, for the forward-y range, d 2 σ J/ψ /dydp t in the transverse momentum domain 0 < p t < 8 GeV/c. The results are compared with previously published results at √ s = 7 TeV and with theoretical calculations.
PbCl 2 -quantum dots formed within NaCl-matrice have been monitored in details using optical spec... more PbCl 2 -quantum dots formed within NaCl-matrice have been monitored in details using optical spectroscopy. Within context of nucleation theory and utilizing the evolution of absorption curves at various temperatures, surface energy between newly-formed QD and matrice (r ffi 0.06 Jm À2 ), resp. activation energy of diffusion of divalent lead ions in NaCl-matrice (E A ffi 0.4 eV) have been determinated. These quantities are in very good agreement with those obtained for other alkali chlorides and may serve to optimize preparation of QD within bulk solid.
The p T -differential inclusive production cross section of the prompt charm-strange meson D + s ... more The p T -differential inclusive production cross section of the prompt charm-strange meson D + s in the rapidity range |y| < 0.5 was measured in proton-proton collisions at √ s = 7 TeV at the LHC using the ALICE detector. The analysis was performed on a data sample of 2.98×10 8 events collected with a minimum-bias trigger. The corresponding integrated luminosity is L int = 4.8 nb −1 . Reconstructing the decay D + s → φ π + , with φ → K − K + , and its charge conjugate, about 480 D ± s mesons were counted, after selection cuts, in the transverse momentum range 2 < p T < 12 GeV/c. The results are compared with the prediction of a model based on perturbative QCD. The ratios of the cross sections of four D meson species (namely D 0 , D + , D * + and D + s ) were determined both as a function of p T and integrated over p T after extrapolating to full p T range, together with the strangeness suppression factor in charm fragmentation. The obtained values are found to be compatible within uncertainties with those measured by other experiments in e + e − , ep and pp interactions at various centre-of-mass energies.
The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at √ s N... more The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at √ s NN = 2.76 TeV at the Large Hadron Collider is presented. We observe a growing trend with energy now not only for the longitudinal and the outward but also for the sideward pion source radius. The pion homogeneity volume and the decoupling time are significantly larger than those measured at RHIC.
The production cross section of electrons from semileptonic decays of beauty hadrons was measured... more The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y| < 0.8) in the transverse momentum range 1 < p T < 8 GeV/c with the ALICE experiment at the CERN LHC in pp collisions at a center of mass energy √ s = 7 TeV using an integrated luminosity of 2.2 nb −1 . Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark-antiquark pairs. * See Appendix A for the list of collaboration members Electrons from beauty hadron decays in pp collisions at √ s = 7 TeV 1
The inclusive charged particle transverse momentum distribution is measured in proton-proton coll... more The inclusive charged particle transverse momentum distribution is measured in proton-proton collisions at √ s = 900 GeV at the LHC using the ALICE detector. The measurement is performed in the central pseudorapidity region (|η| < 0.8) over the transverse momentum range 0.15 < p T < 10 GeV/c. The correlation between transverse momentum and particle multiplicity is also studied. Results are presented for inelastic (INEL) and non-single-diffractive (NSD) events. The average transverse momentum for |η| < 0.8 is p T INEL = 0.483±0.001 (stat.) ±0.007 (syst.) GeV/c and p T NSD = 0.489 ± 0.001 (stat.) ±0.007 (syst.) GeV/c, respectively. The data exhibit a slightly larger p T than measurements in wider pseudorapidity intervals. The results are compared to simulations with the Monte Carlo event generators PYTHIA and PHOJET.
Measurements of the sphericity of primary charged particles in minimum bias proton-proton collisi... more Measurements of the sphericity of primary charged particles in minimum bias proton-proton collisions at √ s = 0.9, 2.76 and 7 TeV with the ALICE detector at the LHC are presented. The observable is linearized to be collinear safe and is measured in the plane perpendicular to the beam direction using primary charged tracks with p T ≥ 0.5 GeV/c in |η| ≤ 0.8. The mean sphericity as a function of the charged particle multiplicity at mid-rapidity (N ch ) is reported for events with different p T scales ("soft" and "hard") defined by the transverse momentum of the leading particle. In addition, the mean charged particle transverse momentum versus multiplicity is presented for the different event classes, and the sphericity distributions in bins of multiplicity are presented. The data are compared with calculations of standard Monte Carlo event generators. The transverse sphericity is found to grow with multiplicity at all collision energies, with a steeper rise at low N ch , whereas the event generators show the opposite tendency. The combined study of the sphericity and the mean p T with multiplicity indicates that most of the tested event generators produce events with higher multiplicity by generating more back-to-back jets resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with tune PERUGIA-2011 exhibits a noticeable improvement in describing the data, compared to the other tested generators.
The production of mesons containing strange quarks (K 0 S , φ ) and both singly and doubly strang... more The production of mesons containing strange quarks (K 0 S , φ ) and both singly and doubly strange baryons (Λ, Λ, and Ξ − + Ξ + ) are measured at central rapidity in pp collisions at √ s = 0.9 TeV with the ALICE experiment at the LHC. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at central rapidities for inelastic pp collisions are presented. For mesons, we report yields ( dN/dy ) of 0.184 ± 0.002 (stat.) ± 0.006 (syst.) for K 0 S and 0.021 ± 0.004 (stat.) ± 0.003 (syst.) for φ . For baryons, we find dN/dy = 0.048 ± 0.001 (stat.) ± 0.004 (syst.) for Λ, 0.047 ± 0.002 (stat.) ± 0.005 (syst.) for Λ and 0.0101 ± 0.0020 (stat.) ± 0.0009 (syst.) for Ξ − + Ξ + . The results are also compared with predictions for identified particle spectra from QCDinspired models and provide a baseline for comparisons with both future pp measurements at higher energies and heavy-ion collisions. * See Appendix A for the list of collaboration members Strange particle production in pp at √ s = 0.9 TeV 3
On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), tw... more On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |η|N ch/dη=3.10±0.13(stat.)±0.22(syst.) for all inelastic interactions, and dN ch/dη=3.51±0.15(stat.)±0.25(syst.) for non-single diffractive interactions. These results are consistent with previous measurements in proton–antiproton interactions at the same centre-of-mass energy at the CERN Sp \(\overline{\mathrm{p}}\) S collider. They also illustrate the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase.
The production of π + , π − , K + , K − , p, and p at mid-rapidity has been measured in proton-pr... more The production of π + , π − , K + , K − , p, and p at mid-rapidity has been measured in proton-proton collisions at √ s = 900 GeV with the ALICE detector. Particle identification is performed using the specific energy loss in the inner tracking silicon detector and the time projection chamber. In addition, time-of-flight information is used to identify hadrons at higher momenta. Finally, the distinctive kink topology of the weak decay of charged kaons is used for an alternative measurement of the kaon transverse momentum (pt) spectra. Since these various particle identification tools give the best separation capabilities over different momentum ranges, the results are combined to extract spectra from pt = 100 MeV/c to 2.5 GeV/c. The measured spectra are further compared with QCD-inspired models which yield a poor description. The total yields and the mean pt are compared with previous measurements, and the trends as a function of collision energy are discussed. 6
Charged-particle production was studied in proton-proton collisions collected at the LHC with the... more Charged-particle production was studied in proton-proton collisions collected at the LHC with the ALICE detector at centre-of-mass energies 0.9 TeV and 2.36 TeV in the pseudorapidity range |η| < 1.4. In the central region (|η| < 0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density dN ch /dη = 3.02 ± 0.01(stat.) +0.08 −0.05 (syst.) for inelastic interactions, and dN ch /dη = 3.58 ± 0.01(stat.) +0.12 −0.12 (syst.) for nonsingle-diffractive interactions. At 2.36 TeV, we find dN ch /dη = 3.77 ± 0.01(stat.) +0.25 −0.12 (syst.) for inelastic, and dN ch /dη = 4.43 ± 0.01(stat.) +0.17 −0.12 (syst.) for non-single-diffractive collisions. The relative increase in charged-particle multiplicity from the lower to higher energy is 24.7%±0.5%(stat.) +5.7 −2.8 %(syst.) for inelastic and 23.7% ± 0.5%(stat.) +4.6 −1.1 %(syst.) for non-single-diffractive interactions. This increase is consistent with that reported by the CMS collaboration for non-single-diffractive events and larger than that found by a number of commonly used models. The multiplicity distribution was measured in different pseudorapidity intervals and studied in terms of KNO variables at both energies. The results are compared to protonantiproton data and to model predictions. 6
B. Abelev, A. Abrahantes Quintana, D. Adamova, AM Adare, MM Aggarwal, G. Aglieri Rinella, AG Agoc... more B. Abelev, A. Abrahantes Quintana, D. Adamova, AM Adare, MM Aggarwal, G. Aglieri Rinella, AG Agocs, A. Agostinelli, S. Aguilar Salazar, Z. Ahammed, N. Ahmad, A. Ahmad Masoodi, SU Ahn, A. Akindinov, D. Aleksandrov, B. Alessandro, R. Alfaro Molina, A. Alici, ...
The inclusive transverse momentum (p T ) distributions of primary charged particles are measured ... more The inclusive transverse momentum (p T ) distributions of primary charged particles are measured in the pseudo-rapidity range |η| < 0.8 as a function of event centrality in Pb-Pb collisions at √ s NN = 2.76 TeV with ALICE at the LHC. The data are presented in the p T range 0.15 < p T < 50 GeV/c for nine centrality intervals from 70-80% to 0-5%. The results in Pb-Pb are presented in terms of the nuclear modification factor R AA using a pp reference spectrum measured at the same collision energy. We observe that the suppression of high-p T particles strongly depends on event centrality. The yield is most suppressed in central collisions (0-5%) with R AA ≈ 0.13 at p T = 6-7 GeV/c. Above p T = 7 GeV/c, there is a significant rise in the nuclear modification factor, which reaches R AA ≈ 0.4 for p T > 30 GeV/c. In peripheral collisions (70-80%), only moderate suppression (R AA = 0.6-0.7) and a weak p T dependence is observed. The measured nuclear modification factors are compared to other measurements and model calculations.
The ALICE Collaboration has measured inclusive J/ψ production in pp collisions at a center of mas... more The ALICE Collaboration has measured inclusive J/ψ production in pp collisions at a center of mass energy √ s = 2.76 TeV at the LHC. The results presented in this Letter refer to the rapidity ranges |y| < 0.9 and 2.5 < y < 4 and have been obtained by measuring the electron and muon pair decay channels, respectively. The integrated luminosities for the two channels are L e int = 1.1 nb −1 and L µ int = 19.9 nb −1 , and the corresponding signal statistics are N e + e − J/ψ = 59 ± 14 and N µ + µ − J/ψ = 1364 ± 53. We present dσ J/ψ /dy for the two rapidity regions under study and, for the forward-y range, d 2 σ J/ψ /dydp t in the transverse momentum domain 0 < p t < 8 GeV/c. The results are compared with previously published results at √ s = 7 TeV and with theoretical calculations.
PbCl 2 -quantum dots formed within NaCl-matrice have been monitored in details using optical spec... more PbCl 2 -quantum dots formed within NaCl-matrice have been monitored in details using optical spectroscopy. Within context of nucleation theory and utilizing the evolution of absorption curves at various temperatures, surface energy between newly-formed QD and matrice (r ffi 0.06 Jm À2 ), resp. activation energy of diffusion of divalent lead ions in NaCl-matrice (E A ffi 0.4 eV) have been determinated. These quantities are in very good agreement with those obtained for other alkali chlorides and may serve to optimize preparation of QD within bulk solid.
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Papers by Karel Polák