2,964 research outputs found
Measurement of an excess in the yield of J/ at very low- in Pb--Pb collisions with the ALICE detector
We report on the measurement of J/ production at very low transverse
momentum ( 300 MeV/) in Pb--Pb collisions performed with the
ALICE detector at the LHC. We find an excess in the yield of J/ with
respect to expectations from hadronic production. Coherent photo-production of
J/ is proposed as a plausible origin of this excess. We show the nuclear
modification factor of very low- J/ as a function of
centrality. Then we measure the J/ coherent photoproduction cross section
in peripheral events assuming that it is the mechanism at the origin of the
measured excess. It's worth noting that the observation of J/ coherent
photoproduction in Pb--Pb collisions at impact parameters smaller than twice
the nuclear radius has never been observed so far and would open new
theoretical challenges.Comment: Proceeding of EDS Blois Conference, 29th June - 4th July 2015, Borgo,
Corsic
Vector meson production in the dimuon channel in the ALICE experiment at the LHC
The purpose of the ALICE experiment at the LHC is the study of the Quark
Gluon Plasma (QGP) formed in ultra-relativistic heavy-ion collisions, a state
of matter in which quarks and gluons are deconfined. The properties of this
state of strongly-interacting matter can be accessed through the study of light
vector mesons (, and ). Indeed, the strange quark content
() of the meson makes its study interesting in connection with
the strangeness enhancement observed in heavy-ion collisions. Moreover,
and spectral function studies give information on chiral symmetry
restoration. Vector meson production in pp collisions is important as a
baseline for heavy-ion studies and for constraining hadronic models. We present
results on light vector meson production obtained with the muon spectrometer of
the ALICE experiment in pp collisions at =7 TeV. Production ratios,
integrated and differential cross sections for and are
presented. Those results are extracted for GeV/ and
Analysis of the phenomenon of speculative trading in one of its basic manifestations: postage stamp bubbles
We document and analyze the empirical facts concerning one of the clearest
evidence of speculation in financial trading as observed in the postage
collection stamp market. We unravel some of the mechanisms of speculative
behavior which emphasize the role of fancy and collective behavior. In our
conclusion, we propose a classification of speculative markets based on two
parameters, namely the amplitude of the price peak and a second parameter that
measures its ``sharpness''. This study is offered to anchor modeling efforts to
realistic market constraints and observations.Comment: 9 pages, 5 figures and 2 tables, in press in Int. J. Mod. Phys.
B70/B7-2 is identical to CD86 and is the major functional ligand for CD28 expressed on human dendritic cells.
Dendritic cells comprise a system of highly efficient antigen-presenting cells involved in the initiation of T cell responses. Herein, we investigated the role of the CD28 pathway during alloreactive T cell proliferation induced by dendritic-Langerhans cells (D-Lc) generated by culturing human cord blood CD34+ progenitor cells with granulocyte/macrophage colony-stimulating factor and tumor necrosis factor alpha. In addition to expressing CD80 (B7/BB1), a subset of D-Lc expressed B70/B7-2. Binding of the CTLA4-Ig fusion protein was completely inhibited by a combination of monoclonal antibodies (mAbs) against CD80 and B70/B7-2, indicating the absence of expression of a third ligand for CD28/CTLA-4. It is interesting to note that mAbs against CD86 completely prevented the binding of CTLA4-Ig in the presence of mAbs against CD80 and bound to a B70/B7-2-transfected fibroblast cell line, demonstrating that the B70/B7-2 antigen is identical to CD86. CD28 triggering was essential during D-Lc-induced alloreaction as it was inhibited by mAbs against CD28 (9 out of 11 tested). However, none of six anti-CD80 mAbs demonstrated any activity on the D-Lc-induced alloreaction, though some were previously described as inhibitory in assays using CD80-transfected cell lines. In contrast, a mAb against CD86 (IT-2) was found to suppress the D-Lc-dependent alloreaction by 70%. This inhibitory effect was enhanced to > or = 90% when a combination of anti-CD80 and anti-CD86 mAbs was used. The present results demonstrate that D-Lc express, in addition to CD80, the other ligand for CTLA-4, CD86 (B70/B7-2), which plays a primordial role during D-Lc-induced alloreaction
Feasibility studies for quarkonium production at a fixed-target experiment using the LHC proton and lead beams (AFTER@LHC)
Used in the fixed-target mode, the multi-TeV LHC proton and lead beams allow
for studies of heavy-flavour hadroproduction with unprecedented precision at
backward rapidities - far negative Feyman-x - using conventional detection
techniques. At the nominal LHC energies, quarkonia can be studies in detail in
p+p, p+d and p+A collisions at sqrt(s_NN) ~ 115 GeV as well as in Pb+p and Pb+A
collisions at sqrt(s_NN) ~ 72 GeV with luminosities roughly equivalent to that
of the collider mode, i.e. up to 20 fb-1 yr-1 in p+p and p+d collisions, up to
0.6 fb-1 yr-1 in p+A collisions and up to 10 nb-1 yr-1 in Pb+A collisions. In
this paper, we assess the feasibility of such studies by performing fast
simulations using the performance of a LHCb-like detector.Comment: 12 pages, 14 figure
Feasibility Study for a Muon Forward Tracker in the ALICE Experiment
ALICE is the experiment dedicated to the study of the quark gluon plasma in
heavy-ion collisions at the CERN LHC. Improvements of ALICE sub-detectors are
envisaged for the upgrade plans of year 2017. The Muon Forward Tracker (MFT) is
a proposal in view of this upgrade, motivated both by the possibility to
overcome the intrinsic limitations of the Muon Spectrometer, and by the
possibility to perform new measurements of general interest for the whole ALICE
physics. The measurement of the offset of single muons and dimuons will permit
to disentangle open charm (m) and beauty (m) production. The MFT, thanks to its tracking capabilities, will allow to
improve the mass resolution of the resonances for a better separation between
and , and , and to a lesser extent
family resonances. In addition, it will help to reject a large
fraction of muons coming from pion and kaon decays, improving the signal over
background ratio. In order to evaluate the feasibility of this upgrade, a setup
composed by five silicon planes was simulated within the AliRoot framework. In
this report, we present preliminary results on the MFT performances in a
low-multiplicity environment
Heavy-ion Physics at a Fixed-Target Experiment Using the LHC Proton and Lead Beams (AFTER@LHC): Feasibility Studies for Quarkonium and Drell-Yan Production
We outline the case for heavy-ion-physics studies using the multi-TeV lead
LHC beams in the fixed-target mode. After a brief contextual reminder, we
detail the possible contributions of AFTER@LHC to heavy-ion physics with a
specific emphasis on quarkonia. We then present performance simulations for a
selection of observables. These show that , and
production in heavy-ion collisions can be studied in new energy and
rapidity domains with the LHCb and ALICE detectors. We also discuss the
relevance to analyse the Drell-Yan pair production in asymmetric
nucleus-nucleus collisions to study the factorisation of the nuclear
modification of partonic densities and of further quarkonia to restore their
status of golden probes of the quark-gluon plasma formation.Comment: 18 pages, 7 figure
Physics perspectives with AFTER@LHC (A Fixed Target ExpeRiment at LHC)
AFTER@LHC is an ambitious fixed-target project in order to address open questions in the domain of proton and neutron spins, Quark Gluon Plasma and high- physics, at the highest energy ever reached in the fixed-target mode. Indeed, thanks to the highly energetic 7 TeV proton and 2.76 A.TeV lead LHC beams, center-of-mass energies as large as = 115 GeV in pp/pA and = 72 GeV in AA can be reached, corresponding to an uncharted energy domain between SPS and RHIC. We report two main ways of performing fixed-target collisions at the LHC, both allowing for the usage of one of the existing LHC experiments. In these proceedings, after discussing the projected luminosities considered for one year of data taking at the LHC, we will present a selection of projections for light and heavy-flavour production.Peer Reviewe
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