809 research outputs found
Physics with the ALICE experiment
ALICE experiment at LHC collects data in pp collisions at =0.9,
2.76 and 7 TeV and in PbPb collisions at 2.76 TeV. Highlights of the detector
performance and an overview of experimental results measured with ALICE in pp
and AA collisions are presented in this paper. Physics with proton-proton
collisions is focused on hadron spectroscopy at low and moderate .
Measurements with lead-lead collisions are shown in comparison with those in pp
collisions, and the properties of hot quark matter are discussed.Comment: Presented at the Conference of the Nuclear Physics Division of the
Russian Academy of Science, 11-25.11.2011, ITEP, Moscow. 16 pages, 14 figure
Femtoscopy of Pb-Pb and pp collisions at the LHC with the ALICE experiment
We report on the results of femtoscopic analysis of Pb-Pb collisions at
sqrt(s_NN)=2.76 TeV and pp collisions at sqrt(s)=0.9, 2.76 and 7 TeV with
identical pions and kaons. Detailed femtoscopy studies in heavy-ion collisions
at SPS and RHIC have shown that emission region sizes ("HBT radii") decrease
with increasing pair transverse momentum k_T, which is understood as a
manifestation of the collective behavior of matter. The trend was predicted to
persist at the LHC. The data from Pb-Pb collisions confirm the existence of a
flowing medium and provide strict constraints on the dynamical models. Similar
analysis is carried out for pp collisions for pions and kaons and qualitative
similarities to heavy-ion data are seen, especially in collisions producing
large number of particles. The observed trends give insight into the soft
particle production mechanism in pp collisions. 3D radii were also found to
universally scale with event multiplicity in heavy-ion collisions. We extend
the range of multiplicities both upwards with the Pb-Pb data and downwards with
the pp data to test the scaling in new areas. In particular the high
multiplicity pp collisions reach particle densities comparable to the ones
measured in peripheral Cu-Cu and Au-Au collisions at RHIC. This allows for the
first time to directly compare freeze-out sizes for systems with very different
initial states.Comment: 8 pages, 5 figures, Proceedings of the Quark Matter 2011 plenary tal
Production of Neutral Pions and Eta-mesons in pp Collisions Measured with ALICE
Invariant cross sections for neutral pions and eta mesons in pp collisions at
sqrt(s) = 0.9, 2.76, and 7 TeV were measured by the ALICE detector at the Large
Hadron Collider. Next-to-leading order (NLO) perturbative QCD calculations
describe the pi0 and eta spectra at 0.9 TeV, but overestimate the measured
cross sections at 2.76 TeV and 7 TeV. The measured eta/pi0 ratio is consistent
with mT scaling at 2.76 TeV. At 7 TeV indications for a violation of mT scaling
were found.Comment: 4 pages, 2 figures, to appear in the proceedings of the XXII
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions,
Quark Matter 2011, Annec
Cross section normalization in proton-proton collisions at = 2.76 TeV and 7 TeV, with ALICE at LHC
Measurements of the cross sections of the reference processes seen by the
ALICE trigger system were obtained based on beam properties measured from van
der Meer scans. The measurements are essential for absolute cross section
determinations of physics processes.
The paper focuses on instrumental and technical aspects of detectors and
accelerators, including a description of the extraction of beam properties from
the van der Meer scan. As a result, cross sections of reference processes seen
by the ALICE trigger system are given for proton-proton collisions at two
energies; =2.76 TeV and 7 TeV, together with systematic uncertainties
originating from beam intensity measurements and other detector effects.
Consistency checks were performed by comparing to data from other experiments
in LHC.Comment: Quark Matter 2011 Conference Proceedings, 4 pages, 2 figure
Tilting towards Russia, but anchored in NATO. Turkey’s foreign policy activism and its implications
Turkey strengthened ties with Russia after the military coup attempt on July 15, 2016, triggering widespread concerns that Ankara is ‘drifting away’ from NATO. In this article, we argue that although a rapprochement has taken place, there is no Turkish realignment with Russia. Furthermore, an exit from NATO is regarded as unlikely. However, with its pursuit of greater strategic autonomy, Ankara risks marginalisation within NATO and could become a second-tier member of the allianc
Diffraction dissociation in proton-proton collisions at = 0.9 TeV, 2.76 TeV and 7 TeV with ALICE at the LHC
The relative rates of single- and double- diffractive processes were measured
with the ALICE detector by studying properties of gaps in the pseudorapidity
distribution of particles produced in proton-proton collisions at =
0.9 TeV, 2.76 TeV and 7 TeV. ALICE triggering efficiencies are determined for
various classes of events, using a detector simulation validated with data on
inclusive particle production. Cross-sections are determined using van der Meer
scans to measure beam properties and obtain a measurement of the luminosity
Jet reconstruction and jet background classification with the ALICE experiment in PbPb collisions at the LHC
For a quantitative interpretation of reconstructed jet properties in
heavy-ion collisions it is paramount to characterize the contribution from the
underlying event and the influence of background fluctuations on the jet
signal. In addition to the pure number fluctuations, region-to-region
correlated background within one event can enhance or deplete locally the level
of background and modify the jet energy. We show a first detailed assessment of
background effects using different probes embedded into heavy-ion data and
quantify their influence on the reconstructed jet spectrum.Comment: 4 pages, 2 figures, Proceedings for the XXII International Conference
on Ultra-Relativistic Nucleus-Nucleus Collisions, Quark Matter 2011, Annec
Variation of jet quenching from RHIC to LHC and thermal suppression of QCD coupling constant
We perform a joint jet tomographic analysis of the data on the nuclear
modification factor from PHENIX at RHIC and ALICE at LHC. The
computations are performed accounting for radiative and collisional parton
energy loss with running coupling constant. Our results show that the observed
slow variation of from RHIC to LHC indicates that the QCD coupling
constant is suppressed in the quark-gluon plasma produced at LHC.Comment: 9 pages, 2 figure
Forward-Backward Correlations and Event Shapes as probes of Minimum-Bias Event Properties
Measurements of inclusive observables, such as particle multiplicities and
momentum spectra, have already delivered important information on
soft-inclusive ("minimum-bias") physics at the Large Hadron Collider. In order
to gain a more complete understanding, however, it is necessary to include also
observables that probe the structure of the studied events. We argue that
forward-backward (FB) correlations and event-shape observables may be
particulary useful first steps in this respect. We study the sensitivity of
several different types of FB correlations and two event shape variables -
transverse thrust and transverse thrust minor - to various sources of
theoretical uncertainty: multiple parton interactions, parton showers, colour
(re)connections, and hadronization. The power of each observable to furnish
constraints on Monte Carlo models is illustrated by including comparisons
between several recent, and qualitatively different, PYTHIA 6 tunes, for pp
collisions at sqrt(s) = 900 GeV.Comment: 13 page
Analyses of multiplicity distributions with \eta_c and Bose-Einstein correlations at LHC by means of generalized Glauber-Lachs formula
Using the negative binomial distribution (NBD) and the generalized
Glauber-Lachs (GGL) formula, we analyze the data on charged multiplicity
distributions with pseudo-rapidity cutoffs \eta_c at 0.9, 2.36, and 7 TeV by
ALICE Collaboration and at 0.2, 0.54, and 0.9 TeV by UA5 Collaboration. We
confirm that the KNO scaling holds among the multiplicity distributions with
\eta_c = 0.5 at \sqrt{s} = 0.2\sim2.36 TeV and estimate the energy dependence
of a parameter 1/k in NBD and parameters 1/k and \gamma (the ratio of the
average value of the coherent hadrons to that of the chaotic hadrons) in the
GGL formula. Using empirical formulae for the parameters 1/k and \gamma in the
GGL formula, we predict the multiplicity distributions with \eta_c = 0.5 at 7
and 14 TeV. Data on the 2nd order Bose-Einstein correlations (BEC) at 0.9 TeV
by ALICE Collaboration and 0.9 and 2.36 TeV by CMS Collaboration are also
analyzed based on the GGL formula. Prediction for the 3rd order BEC at 0.9 and
2.36 TeV are presented. Moreover, the information entropy is discussed
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