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ALICE Collaboration,Abelev, B.,Adam, J.,Adamova, D.,Adare, A.M.,Aggarwal, M.M.,Aglieri Rinella, G.,Agocs, A.G.,Agostinelli, A.,Aguilar Salazar, S.,Ahammed, Z.,Ahmad, N.,Ahmad Masoodi, A.,Ahn, S.A.,Ahn North-Holland Pub. Co 2012 Physics letters: B Vol.718 No.2
The p<SUB>T</SUB>-differential inclusive production cross section of the prompt charm-strange meson D<SUB>s</SUB><SUP>+</SUP> 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 2.98x10<SUP>8</SUP> events collected with a minimum-bias trigger. The corresponding integrated luminosity is L<SUB>int</SUB>=4.8 nb<SUP>-1</SUP>. Reconstructing the decay D<SUB>s</SUB><SUP>+</SUP>→φπ<SUP>+</SUP>, with φ→K<SUP>-</SUP>K<SUP>+</SUP>, and its charge conjugate, about 480 D<SUB>s</SUB><SUP>+/-</SUP> mesons were counted, after selection cuts, in the transverse momentum range 2<p<SUB>T</SUB><12 GeV/c. The results are compared with predictions from models based on perturbative QCD. The ratios of the cross sections of four D meson species (namely D<SUP>0</SUP>, D<SUP>+</SUP>, D<SUP>@?+</SUP> and D<SUB>s</SUB><SUP>+</SUP>) were determined both as a function of p<SUB>T</SUB> and integrated over p<SUB>T</SUB> after extrapolating to full p<SUB>T</SUB> 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<SUP>+</SUP>e<SUP>-</SUP>, ep and pp interactions at various centre-of-mass energies.
Multi-strange baryon production in pp collisions at s=7 TeV with ALICE
ALICE Collaboration,Abelev, B.,Adam, J.,Adamova, D.,Adare, A.M.,Aggarwal, M.M.,Aglieri Rinella, G.,Agocs, A.G.,Agostinelli, A.,Aguilar Salazar, S.,Ahammed, Z.,Ahmad, N.,Ahmad Masoodi, A.,Ahn, S.U.,Aki North-Holland Pub. Co 2012 Physics letters: B Vol.712 No.4
A measurement of the multi-strange Ξ<SUP>-</SUP> and Ω<SUP>-</SUP> baryons and their antiparticles by the ALICE experiment at the CERN Large Hadron Collider (LHC) is presented for inelastic proton-proton collisions at a centre-of-mass energy of 7 TeV. The transverse momentum (p<SUB>T</SUB>) distributions were studied at mid-rapidity (|y|<0.5) in the range of 0.6<p<SUB>T</SUB><8.5 GeV/c for Ξ<SUP>-</SUP> and Ξ@?<SUP>+</SUP> baryons, and in the range of 0.8<p<SUB>T</SUB><5 GeV/c for Ω<SUP>-</SUP> and Ω@?<SUP>+</SUP>. Baryons and antibaryons were measured as separate particles and we find that the baryon to antibaryon ratio of both particle species is consistent with unity over the entire range of the measurement. The statistical precision of the current data has allowed us to measure a difference between the mean p<SUB>T</SUB> of Ξ<SUP>-</SUP> (Ξ@?<SUP>+</SUP>) and Ω<SUP>-</SUP> (Ω@?<SUP>+</SUP>). Particle yields, mean p<SUB>T</SUB>, and the spectra in the intermediate p<SUB>T</SUB> range are not well described by the PYTHIA Perugia 2011 tune Monte Carlo event generator, which has been tuned to reproduce the early LHC data. The discrepancy is largest for Ω<SUP>-</SUP> (Ω@?<SUP>+</SUP>). This PYTHIA tune approaches the p<SUB>T</SUB> spectra of Ξ<SUP>-</SUP> and Ξ@?<SUP>+</SUP> baryons below p<SUB>T</SUB><0.85 GeV/c and describes the Ξ<SUP>-</SUP> and Ξ@?<SUP>+</SUP> spectra above p<SUB>T</SUB>>6.0 GeV/c. We also illustrate the difference between the experimental data and model by comparing the corresponding ratios of (Ω<SUP>-</SUP>+Ω@?<SUP>+</SUP>)/(Ξ<SUP>-</SUP>+Ξ@?<SUP>+</SUP>) as a function of transverse mass.
ALICE Collaboration,Abelev, B.,Adam, J.,Adamova, D.,Adare, A.M.,Aggarwal, M.M.,Aglieri Rinella, G.,Agocs, A.G.,Agostinelli, A.,Aguilar Salazar, S.,Ahammed, Z.,Ahmad, N.,Ahmad Masoodi, A.,Ahn, S.A.,Ahn North-Holland Pub. Co 2013 Physics letters: B Vol.720 No.1
<P>The inclusive transverse momentum (p(T)) distributions of primary charged particles are measured in the pseudo-rapidity range vertical bar eta vertical bar <0.8 as a function of event centrality in Pb-Pb collisions at root 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 approximate to 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 approximate to 0.4 for p(T) > 30 GeV/c. In peripheral collisions (70-80%), only moderate suppression (R-AA approximate to 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. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.</P>
Heavy flavour decay muon production at forward rapidity in proton-proton collisions at s=7 TeV
ALICE Collaboration,Abelev, B.,Adam, J.,Adamova, D.,Adare, A.M.,Aggarwal, M.M.,Aglieri Rinella, G.,Agocs, A.G.,Agostinelli, A.,Aguilar Salazar, S.,Ahammed, Z.,Ahmad, N.,Ahmad Masoodi, A.,Ahn, S.U.,Aki North-Holland Pub. Co 2012 Physics letters: B Vol.708 No.3
The production of muons from heavy flavour decays is measured at forward rapidity in proton-proton collisions at s=7 TeV collected with the ALICE experiment at the LHC. The analysis is carried out on a data sample corresponding to an integrated luminosity L<SUB>int</SUB>=16.5 nb<SUP>-1</SUP>. The transverse momentum and rapidity differential production cross sections of muons from heavy flavour decays are measured in the rapidity range 2.5<y<4, over the transverse momentum range 2<p<SUB>t</SUB><12 GeV/c. The results are compared to predictions based on perturbative QCD calculations.
Abelev, B.,Adam, J.,Adamová,, D.,Adare, A. M.,Aggarwal, M. M.,Aglieri Rinella, G.,Agocs, A. G.,Agostinelli, A.,Aguilar Salazar, S.,Ahammed, Z.,Ahmad Masoodi, A.,Ahmad, N.,Ahn, S. A.,Ahn, S. U.,A Springer Berlin Heidelberg 2013 The European physical journal. C, Particles and fi Vol.73 No.6
<P>Measurements of cross sections of inelastic and diffractive processes in proton–proton collisions at LHC energies were carried out with the ALICE detector. The fractions of diffractive processes in inelastic collisions were determined from a study of gaps in charged particle pseudorapidity distributions: for single diffraction (diffractive mass <I>M</I><SUB><I>X</I></SUB><200 GeV/<I>c</I><SUP>2</SUP>) [FORMULA OMISSION], and [FORMULA OMISSION], respectively at centre-of-mass energies [FORMULA OMISSION]; for double diffraction (for a pseudorapidity gap Δ<I>η</I>>3) <I>σ</I><SUB>DD</SUB>/<I>σ</I><SUB>INEL</SUB>=0.11±0.03,0.12±0.05, and [FORMULA OMISSION], respectively at [FORMULA OMISSION]. To measure the inelastic cross section, beam properties were determined with van der Meer scans, and, using a simulation of diffraction adjusted to data, the following values were obtained: [FORMULA OMISSION] mb at [FORMULA OMISSION] and [FORMULA OMISSION] at [FORMULA OMISSION]. The single- and double-diffractive cross sections were calculated combining relative rates of diffraction with inelastic cross sections. The results are compared to previous measurements at proton–antiproton and proton–proton colliders at lower energies, to measurements by other experiments at the LHC, and to theoretical models.</P>
ALICE Collaboration,Abelev, B.,Adam, J.,Adamova, D.,Adare, A.M.,Aggarwal, M.,Aglieri Rinella, G.,Agnello, M.,Agocs, A.G.,Agostinelli, A.,Ahammed, Z.,Ahmad, N.,Ahmad, A.,Ahn, S.A.,Ahn, S.U.,Ajaz, M.,Ak North-Holland Pub. Co 2013 Physics letters: B Vol.719 No.1
Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5<p<SUB>T,assoc</SUB><p<SUB>T,trig</SUB><4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and p<SUB>T</SUB> bins, and the widths show no significant evolution with event multiplicity or p<SUB>T</SUB>. These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge.
Measurement of electrons from beauty hadron decays in pp collisions at s=7 TeV
ALICE Collaboration,Abelev, B.,Adam, J.,Adamova, D.,Adare, A.M.,Aggarwal, M.M.,Aglieri Rinella, G.,Agocs, A.G.,Agostinelli, A.,Aguilar Salazar, S.,Ahammed, Z.,Ahmad, N.,Ahmad Masoodi, A.,Ahn, S.A.,Ahn North-Holland Pub. Co 2013 Physics letters: B Vol.721 No.1
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<SUB>T</SUB><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<SUP>-1</SUP>. 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.
Two-pion Bose-Einstein correlations in central Pb-Pb collisions at s<sub>NN</sub>=2.76 TeV
ALICE Collaboration,Aamodt, K.,Abrahantes Quintana, A.,Adamova, D.,Adare, A.M.,Aggarwal, M.M.,Aglieri Rinella, G.,Agocs, A.G.,Aguilar Salazar, S.,Ahammed, Z.,Ahmad, N.,Ahmad Masoodi, A.,Ahn, S.U.,Akin North-Holland Pub. Co 2011 Physics letters: B Vol.696 No.4
The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at s<SUB>NN</SUB>=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.
Light vector meson production in pp collisions at s=7 TeV
ALICE Collaboration,Abelev, B.,Abrahantes Quintana, A.,Adamova, D.,Adare, A.M.,Aggarwal, M.M.,Aglieri Rinella, G.,Agocs, A.G.,Agostinelli, A.,Aguilar Salazar, S.,Ahammed, Z.,Ahmad, N.,Ahmad Masoodi, A North-Holland Pub. Co 2012 Physics letters: B Vol.710 No.4
<P>The ALICE experiment has measured low-mass dimuon production in pp collisions at root s = 7 TeV in the dimuon rapidity region 2.5 < y < 4. The observed dimuon mass spectrum is described as a superposition of resonance decays (eta, rho, omega, eta', phi) into muons and semi-leptonic decays of charmed mesons. The measured production cross sections for omega and phi are sigma(omega)(1 < p(t) < 5 GeV/c. 2.5 < y < 4) = 5.28 +/- 0.54(stat) +/- 0.49(syst) mb and sigma(phi)(1 < p(t) < 5 GeV/c. 2.5 < y < 4) = 0.940 +/- 0.084(stat) +/- 0.076(syst) mb. The differential cross sections d(2)sigma/dy dp(t) are extracted as a function of p(t) for omega and phi. The ratio between the rho and omega cross section is obtained. Results for the phi are compared with other measurements at the same energy and with predictions by models. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.</P>
Neutral pion and η meson production in proton-proton collisions at s=0.9 TeV and s=7 TeV
ALICE Collaboration,Abelev, B.,Abrahantes Quintana, A.,Adamova, D.,Adare, A.M.,Aggarwal, M.M.,Aglieri Rinella, G.,Agocs, A.G.,Agostinelli, A.,Aguilar Salazar, S.,Ahammed, Z.,Ahmad, N.,Ahmad Masoodi, A North-Holland Pub. Co 2012 Physics letters. Section B Vol.717 No.1
The first measurements of the invariant differential cross sections of inclusive π<SUP>0</SUP> and η meson production at mid-rapidity in proton-proton collisions at s=0.9 TeV and s=7 TeV are reported. The π<SUP>0</SUP> measurement covers the ranges 0.4<p<SUB>T</SUB><7 GeV/c and 0.3<p<SUB>T</SUB><25 GeV/c for these two energies, respectively. The production of η mesons was measured at s=7 TeV in the range 0.4<p<SUB>T</SUB><15 GeV/c. Next-to-Leading Order perturbative QCD calculations, which are consistent with the π<SUP>0</SUP> spectrum at s=0.9 TeV, overestimate those of π<SUP>0</SUP> and η mesons at s=7 TeV, but agree with the measured η/π<SUP>0</SUP> ratio at s=7 TeV.