-
B Abelev,
J Adam,
D Adamová,
A M Adare,
M M Aggarwal,
G Aglieri Rinella,
M Agnello,
A G Agocs,
A Agostinelli,
Z Ahammed, [......],
D Zhou,
X Zhu,
J Zhu,
H Zhu,
A Zichichi,
A Zimmermann,
G Zinovjev,
Y Zoccarato,
M Zynovyev,
M Zyzak
[show abstract]
[hide abstract]
ABSTRACT: The transverse momentum (p_{T}) distribution of primary charged particles is measured in minimum bias (non-single-diffractive) p+Pb collisions at sqrt[s_{NN}]=5.02 TeV with the ALICE detector at the LHC. The p_{T} spectra measured near central rapidity in the range 0.5<p_{T}<20 GeV/c exhibit a weak pseudorapidity dependence. The nuclear modification factor R_{pPb} is consistent with unity for p_{T} above 2 GeV/c. This measurement indicates that the strong suppression of hadron production at high p_{T} observed in Pb+Pb collisions at the LHC is not due to an initial-state effect. The measurement is compared to theoretical calculations.
Physical Review Letters 02/2013; 110(8):082302. · 7.37 Impact Factor
-
B Abelev,
J Adam,
D Adamová,
A M Adare,
M M Aggarwal,
G Aglieri Rinella,
M Agnello,
A G Agocs,
A Agostinelli,
Z Ahammed, [......],
Y Zhou,
J Zhu,
H Zhu,
X Zhu,
A Zichichi,
A Zimmermann,
G Zinovjev,
Y Zoccarato,
M Zynovyev,
M Zyzak
[show abstract]
[hide abstract]
ABSTRACT: The charged-particle pseudorapidity density measured over four units of pseudorapidity in nonsingle-diffractive p+Pb collisions at a center-of-mass energy per nucleon pair sqrt[s_{NN}]=5.02 TeV is presented. The average value at midrapidity is measured to be 16.81±0.71 (syst), which corresponds to 2.14±0.17 (syst) per participating nucleon, calculated with the Glauber model. This is 16% lower than in nonsingle-diffractive pp collisions interpolated to the same collision energy and 84% higher than in d+Au collisions at sqrt[s_{NN}]=0.2 TeV. The measured pseudorapidity density in p+Pb collisions is compared to model predictions and provides new constraints on the description of particle production in high-energy nuclear collisions.
Physical Review Letters 01/2013; 110(3):032301. · 7.37 Impact Factor
-
B Abelev,
J Adam,
D Adamová,
A M Adare,
M M Aggarwal,
G Aglieri Rinella,
A G Agocs,
A Agostinelli,
S Aguilar Salazar,
Z Ahammed, [......],
D Zhou,
F Zhou,
J Zhu,
X Zhu,
A Zichichi,
A Zimmermann,
G Zinovjev,
Y Zoccarato,
M Zynovyev,
M Zyzak
[show abstract]
[hide abstract]
ABSTRACT: Measurements of charge-dependent azimuthal correlations with the ALICE detector at the LHC are reported for Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV. Two- and three-particle charge-dependent azimuthal correlations in the pseudorapidity range |η|<0.8 are presented as a function of the collision centrality, particle separation in pseudorapidity, and transverse momentum. A clear signal compatible with a charge-dependent separation relative to the reaction plane is observed, which shows little or no collision energy dependence when compared to measurements at RHIC energies. This provides a new insight for understanding the nature of the charge-dependent azimuthal correlations observed at RHIC and LHC energies.
Physical Review Letters 01/2013; 110(1):012301. · 7.37 Impact Factor
-
B Abelev,
J Adam,
D Adamová,
A M Adare,
M M Aggarwal,
G Aglieri Rinella,
A G Agocs,
A Agostinelli,
S Aguilar Salazar,
Z Ahammed, [......],
D Zhou,
F Zhou,
Y Zhou,
J Zhu,
X Zhu,
A Zichichi,
A Zimmermann,
G Zinovjev,
Y Zoccarato,
M Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The first measurement of neutron emission in electromagnetic dissociation of ^{208}Pb nuclei at the LHC is presented. The measurement is performed using the neutron zero degree calorimeters of the ALICE experiment, which detect neutral particles close to beam rapidity. The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at sqrt[s_{NN}]=2.76 TeV with neutron emission are σ_{singleEMD}=187.4±0.2(stat)_{-11.2}^{+13.2}(syst) b and σ_{mutualEMD}=5.7±0.1(stat)±0.4(syst) b, respectively. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model.
Physical Review Letters 12/2012; 109(25):252302. · 7.37 Impact Factor
-
B Abelev,
J Adam,
D Adamová,
A M Adare,
M M Aggarwal,
G Aglieri Rinella,
A G Agocs,
A Agostinelli,
S Aguilar Salazar,
Z Ahammed, [......],
Y Zhou,
F Zhou,
J Zhu,
X Zhu,
A Zichichi,
A Zimmermann,
G Zinovjev,
Y Zoccarato,
M Zynovyev,
M Zyzak
[show abstract]
[hide abstract]
ABSTRACT: In this Letter we report the first results on π^{±}, K^{±}, p, and p[over ¯] production at midrapidity (|y|<0.5) in central Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV, measured by the ALICE experiment at the LHC. The p_{T} distributions and yields are compared to previous results at sqrt[s_{NN}]=200 GeV and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with sqrt[s_{NN}], which in hydrodynamic models is expected as a consequence of the increasing particle density. While the K/π ratio is in line with predictions from the thermal model, the p/π ratio is found to be lower by a factor of about 1.5. This deviation from thermal model expectations is still to be understood.
Physical Review Letters 12/2012; 109(25):252301. · 7.37 Impact Factor
-
ALICE Collaboration,
B. Abelev,
J. Adam,
D. Adamová,
A. M. Adare,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs,
A. Agostinelli,
S. Aguilar Salazar, [......],
X. Zhang,
Y. Zhou,
D. Zhou,
F. Zhou,
X. Zhu,
A. Zichichi,
A. Zimmermann,
G. Zinovjev,
Y. Zoccarato,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The ALICE Collaboration reports the measurement of the relative J/ψ
yield as a function of charged particle pseudorapidity density
dNch/dη in pp collisions at s=7 TeV at the LHC.
J/ψ particles are detected for pt>0, in the rapidity
interval |y|<0.9 via decay into e+e-, and
in the interval 2.5<y<4.0 via decay into
μ+μ- pairs. An approximately linear
increase of the J/ψ yields normalized to their event average
(dN/dy)/<dN/dy> with
(dNch/dη)/<dNch/dη> is observed in
both rapidity ranges, where dNch/dη is measured within
|η|<1 and pt>0. In the highest multiplicity
interval with <dNch/dη(bin)>=24.1, corresponding to
four times the minimum bias multiplicity density, an enhancement
relative to the minimum bias J/ψ yield by a factor of about 5 at
2.5<y<4 (8 at |y|<0.9) is observed.
Physics Letters B 05/2012; 712:165-175. · 3.95 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The ALICE experiment at the Large Hadron Collider (LHC) at CERN consists of a
central barrel, a muon spectrometer and of additional detectors for trigger and
event classification purposes. The low transverse momentum threshold of the
central barrel gives ALICE a unique opportunity to study the low mass sector of
central production at the LHC. I will report on first analysis results of meson
production in double gap events in minimum-bias proton-proton collisions at
sqrt{s} = 7 TeV, and will describe a dedicated double gap trigger for future
data taking.
05/2012;
-
The ALICE Collaboration,
K. Aamodt,
N. Abel,
U. Abeysekara,
A. Abrahantes Quintana,
A. Acero,
D. Adamová,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs, [......],
X. Zhang,
D. Zhou,
S. Zhou,
J. Zhu,
A. Zichichi,
A. Zinchenko,
G. Zinovjev,
M. Zinovjev,
Y. Zoccarato,
V. Zycháček
[show abstract]
[hide abstract]
ABSTRACT: 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 450GeV 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|<0.5, we obtain dN
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
[`(p)]\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.
European Physical Journal C 04/2012; 65(1):111-125. · 3.63 Impact Factor
-
The ALICE Collaboration,
K. Aamodt,
N. Abel,
U. Abeysekara,
A. Abrahantes Quintana,
A. Abramyan,
D. Adamová,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs, [......],
X. Zhang,
D. Zhou,
S. Zhou,
J. Zhu,
A. Zichichi,
A. Zinchenko,
G. Zinovjev,
Y. Zoccarato,
V. Zycháček,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The production of π
+, π
−, K+, K−, p, and [`(p)]\overline{\mathrm{p}} at mid-rapidity has been measured in proton-proton collisions at Ös = 900GeV\sqrt{s} = 900~\mathrm{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 (p
t) spectra. Since these various particle identification tools give the best separation capabilities over different momentum
ranges, the results are combined to extract spectra from p
t=100MeV/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 p
t are compared with previous measurements, and the trends as a function of collision energy are discussed.
European Physical Journal C 04/2012; 71(6):1-22. · 3.63 Impact Factor
-
K. Aamodt,
A. Abrahantes Quintana,
D. Adamová,
A. M. Adare,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs,
S. Aguilar Salazar,
Z. Ahammed,
N. Ahmad, [......],
P. Zelnicek,
A. Zenin,
I. Zgura,
M. Zhalov,
X. Zhang,
D. Zhou,
A. Zichichi,
G. Zinovjev,
Y. Zoccarato,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The production of mesons containing strange quarks ($\mbox {$\mbox {, φ) and both singly and doubly strange baryons ($\mbox {$\mbox {, $\mbox {$\mbox {, and $\mbox {$\mbox {) are measured at mid-rapidity in pp collisions at
_boxclose_boxclose_boxclose\sqrt{s}=0.9TeV{\rm TeV} with the ALICE experiment at the LHC. The results are obtained from the analysis of about 250k minimum bias events recorded
in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at mid-rapidity for inelastic pp collisions are presented. For mesons, we report yields
(〈dN/dy〉) of 0.184±0.002(stat.)±0.006(syst.) for $\mbox {$\mbox { and 0.021±0.004(stat.)±0.003(syst.) forφ. For baryons, we find 〈dN/dy〉=0.048±0.001(stat.)±0.004(syst.) for $\mbox {$\mbox {, 0.047±0.002(stat.)±0.005(syst.) for $\mbox {$\mbox { and 0.0101±0.0020(stat.)±0.0009(syst.) for $\mbox {$\mbox {. The results are also compared with predictions for identified particle spectra from QCD-inspired models and provide a baseline
for comparisons with both future pp measurements at higher energies and heavy-ion collisions.
European Physical Journal C 04/2012; 71(3):1-24. · 3.63 Impact Factor
-
The ALICE Collaboration,
K. Aamodt,
N. Abel,
U. Abeysekara,
A. Abrahantes Quintana,
A. Abramyan,
D. Adamová,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs, [......],
X. Zhang,
D. Zhou,
S. Zhou,
J. Zhu,
A. Zichichi,
A. Zinchenko,
G. Zinovjev,
Y. Zoccarato,
V. Zycháček,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: Charged-particle production was studied in proton–proton collisions collected at the LHC with the ALICE detector at centre-of-mass
energies 0.9TeV and 2.36TeV in the pseudorapidity range |η|<1.4. In the central region (|η|<0.5), at 0.9TeV, we measure charged-particle pseudorapidity density dNch/dh = 3.02±0.01(stat.)+0.08-0.05(syst.)\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta=3.02\pm 0.01(\mathit{stat.})^{+0.08}_{-0.05}(\mathit{syst.}) for inelastic interactions, and dNch/dh = 3.58±0.01(stat.)+0.12-0.12(syst.)\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta=3.58\pm0.01(\mathit{stat.})^{+0.12}_{-0.12}(\mathit{syst.}) for non-single-diffractive interactions. At 2.36TeV, we find dNch/dh = 3.77±0.01(stat.)+0.25-0.12(syst.)\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta=3.77\pm0.01(\mathit{stat.})^{+0.25}_{-0.12}(\mathit{syst.}) for inelastic, and dNch/dh = 4.43±0.01(stat.)+0.17-0.12(syst.)\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta=4.43\pm0.01(\mathit{stat.})^{+0.17}_{-0.12}(\mathit{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.)24.7\%\pm0.5\%(\mathit{stat.})^{+5.7}_{-2.8}\%(\mathit{syst.}) for inelastic and 23.7%±0.5%(stat.)+4.6-1.1%(syst.)23.7\%\pm0.5\%(\mathit{stat.})^{+4.6}_{-1.1}\%(\mathit{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 proton–antiproton
data and to model predictions.
European Physical Journal C 04/2012; 68(1):89-108. · 3.63 Impact Factor
-
ALICE Collaboration,
B. Abelev,
J. Adam,
D. Adamova,
A. M. Adare,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs,
A. Agostinelli,
S. Aguilar Salazar, [......],
X. Zhang,
D. Zhou,
Y. Zhou,
F. Zhou,
X. Zhu,
A. Zichichi,
A. Zimmermann,
G. Zinovjev,
Y. Zoccarato,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The ALICE Collaboration has measured inclusive J/psi production in pp
collisions at a center of mass energy sqrt(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^mu_int=19.9 nb^-1, and the corresponding signal statistics are
N_J/psi^e+e-=59 +/- 14 and N_J/psi^mu+mu-=1364 +/- 53. We present
dsigma_J/psi/dy for the two rapidity regions under study and, for the forward-y
range, d^2sigma_J/psi/dydp_t in the transverse momentum domain 0<p_t<8 GeV/c.
The results are compared with previously published results at sqrt(s)=7 TeV and
with theoretical calculations.
03/2012;
-
ALICE Collaboration,
B. Abelev,
J. Adam,
D. Adamová,
A. M. Adare,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs,
A. Agostinelli,
S. Aguilar Salazar, [......],
D. Zhou,
F. Zhou,
Y. Zhou,
X. Zhu,
J. Zhu,
A. Zichichi,
A. Zimmermann,
G. Zinovjev,
Y. Zoccarato,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The production of the prompt charm mesons $D^0$, $D^+$, $D^{*+}$, and their
antiparticles, was measured with the ALICE detector in Pb-Pb collisions at the
LHC, at a centre-of-mass energy $\sqrt{s_{NN}}=2.76$ TeV per nucleon--nucleon
collision. The $\pt$-differential production yields in the range $2<p_t<16$
GeV/c at central rapidity, $|y|<0.5$, were used to calculate the nuclear
modification factor $R_{AA}$ with respect to a proton-proton reference obtained
from the cross section measured at $\sqrt{s}=7$ TeV and scaled to
$\sqrt{s}=2.76$ TeV. For the three meson species, $R_{AA}$ shows a suppression
by a factor 3-4, for transverse momenta larger than 5 GeV/c in the 20% most
central collisions. The suppression is reduced for peripheral collisions.
03/2012;
-
K Aamodt,
B Abelev,
A Abrahantes Quintana,
D Adamová,
A M Adare,
M M Aggarwal,
G Aglieri Rinella,
A G Agocs,
A Agostinelli,
S Aguilar Salazar, [......],
X Zhang,
D Zhou,
F Zhou,
Y Zhou,
X Zhu,
A Zichichi,
A Zimmermann,
G Zinovjev,
Y Zoccarato,
M Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The yield of charged particles associated with high-p(t) trigger particles (8<p(t)<15 GeV/c) is measured with the ALICE detector in Pb-Pb collisions at √s(NN)=2.76 TeV relative to proton-proton collisions at the same energy. The conditional per-trigger yields are extracted from the narrow jetlike correlation peaks in azimuthal dihadron correlations. In the 5% most central collisions, we observe that the yield of associated charged particles with transverse momenta p(t)>3 GeV/c on the away side drops to about 60% of that observed in pp collisions, while on the near side a moderate enhancement of 20%-30% is found.
Physical Review Letters 03/2012; 108(9):092301. · 7.37 Impact Factor
-
B Abelev,
A Abrahantes Quintana,
D Adamová,
A M Adare,
M M Aggarwal,
G Aglieri Rinella,
A G Agocs,
A Agostinelli,
S Aguilar Salazar,
Z Ahammed, [......],
X Zhang,
F Zhou,
D Zhou,
Y Zhou,
X Zhu,
A Zichichi,
A Zimmermann,
G Zinovjev,
Y Zoccarato,
M Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The ALICE Collaboration has studied J/ψ production in pp collisions at √s=7 TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, and results on the J/ψ polarization parameters λ(θ) and λ(φ) were obtained. The study was performed in the kinematic region 2.5<y<4, 2<p(t)<8 GeV/c, in the helicity and Collins-Soper reference frames. In both frames, the polarization parameters are compatible with zero, within uncertainties.
Physical Review Letters 02/2012; 108(8):082001. · 7.37 Impact Factor
-
B. Abelev,
A. Abrahantes Quintana,
D. Adamová,
A. M. Adare,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs,
A. Agostinelli,
S. Aguilar Salazar,
Z. Ahammed, [......],
X. Zhang,
F. Zhou,
D. Zhou,
Y. Zhou,
X. Zhu,
A. Zichichi,
A. Zimmermann,
G. Zinovjev,
Y. Zoccarato,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The ALICE Collaboration has studied J/ψ production in pp collisions
at s=7TeV at the LHC through its muon pair decay. The polar and
azimuthal angle distributions of the decay muons were measured, and
results on the J/ψ polarization parameters
λθ and λϕ were obtained.
The study was performed in the kinematic region 2.5<y<4,
2<pt<8GeV/c, in the helicity and Collins-Soper
reference frames. In both frames, the polarization parameters are
compatible with zero, within uncertainties.
Physical Review Letters 01/2012; 108(8):82001. · 7.37 Impact Factor
-
ALICE Collaboration,
B. Abelev,
J. Adam,
D. Adamová,
A. M. Adare,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs,
A. Agostinelli,
S. Aguilar Salazar, [......],
X. Zhang,
Y. Zhou,
D. Zhou,
F. Zhou,
X. Zhu,
A. Zichichi,
A. Zimmermann,
G. Zinovjev,
Y. Zoccarato,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: 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=16.5
nb. 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<12 GeV/c. The results are compared
to predictions based on perturbative QCD calculations.
Physics Letters B 01/2012; 708:265-275. · 3.95 Impact Factor
-
K Aamodt,
B Abelev,
A Abrahantes Quintana,
D Adamova,
A M Adare,
M M Aggarwal,
Aglieri G Rinella,
A G Agocs,
A Agostinelli,
S Aguilar Salazar, [......],
D Zhou,
F Zhou,
Y Zhou,
X Zhu,
A Zichichi,
A Zimmermann,
G Zinovjev,
Y Zoccarato,
M Zynovyev,
ALICE Collaboration
Physics Letters B 01/2012; 708(3-5):249-264. · 3.95 Impact Factor
-
B Abelev,
A Abrahantes Quintana,
D Adamova,
A M Adare,
M M Aggarwal,
Aglieri G Rinella,
A G Agocs,
A Agostinelli,
S Aguilar Salazar,
Z Ahammed, [......],
D Zhou,
Y Zhou,
F Zhou,
X Zhu,
A Zichichi,
A Zimmermann,
G Zinovjev,
Y Zoccarato,
M Zynovyev,
ALICE Collaboration
Physics Letters B 01/2012; 710(4-5):557-568. · 3.95 Impact Factor
-
B Abelev,
J Adam,
D Adamova,
A M Adare,
M M Aggarwal,
Aglieri G Rinella,
A G Agocs,
A Agostinelli,
S Aguilar Salazar,
Z Ahammed, [......],
Y Zhou,
J Zhu,
X Zhu,
A Zichichi,
A Zimmermann,
G Zinovjev,
Y Zoccarato,
M Zynovyev,
M Zyzak,
ALICE Collaboration
Physical Review D 01/2012; 86(11). · 4.56 Impact Factor
