Deuteron yields from LHC: Continuum correlations and in-medium effects

To explain the production of light nuclei in heavy-ion collisions at extreme energies, we focus on the deuteron case. A Gibbs ensemble at chemical freeze-out is a prerequisite to investigate the non-equilibrium evolution of the expanding fireball. Quantum statistical approaches allow to describe correlations including bound state formation in the strongly interacting and hot system. We consider the virial approach to evaluate proton-neutron correlations. In generalization of the treatment of protons in pionic matter (pion-proton puzzle), the influence of the pion environment on deuteron-like correlations is evaluated using data for the pion-deuteron scattering phase shifts. Calculated yields for deuteron production are compared with the ones observed at the LHC.Comment: 15 pages, 3 figures; accepted for publication by Phys. Rev.

Diquarks and the production of charmed baryons

Utilizing a quark model characterized by parameters that effectively replicate the masses of ground state hadrons, we illustrate that $(us)$ or $(ds)$ diquarks exhibit greater compactness in comparison to $(ud)$ diquarks. Concretely, the binding energy of the $(us)$ diquark - defined as the diquark's mass minus the combined masses of its individual quarks - is found to be more attractive than that of the $(ud)$ diquark. This heightened attraction present in $(us)$ diquarks could lead to enhanced production of $\Xi_c/D$ particles in high-energy pp or ultrarelativistic heavy-ion collisions.Comment: 9 pages, 5 figure

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe

The ALICE experiment at the CERN LHC

ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries. Its overall dimensions are 161626 m3 with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008

Exotica production with ALICE

The high collision energies reached at the LHC lead to significant production yields of light (anti-)nuclei and (hyper-)nuclei in proton-proton, proton-lead and, in particular, lead-lead collisions. The excellent particle identification capabilities of the ALICE apparatus, based on the specific energy loss in the Time Projection Chamber and the velocity information in the Time-Of-Flight detector, allow for the detection of these rarely produced particles. Further, the Inner Tracking System gives the possibility to separate primary nuclei from those coming from weak decay of heavier systems. One example of such a weak decay is the measurement of the (anti-)hypertriton decay to ^3He + pi^- (^3H̅e̅ + pi^+). The aforementioned capabilities of the ALICE apparatus offer the unique opportunity to search for exotica, like the bound state of a Lambda and a neutron which would decay into a deuteron and a pion, or the bound state of two Lambda's. Results on the production of stable nuclei in Pb-Pb collisions at sqrts_NN = 2.76 TeV are presented, and compared with thermal model predictions. We further present the current status of the searches, by their upper limits on the production yields, and compare the results to thermal and coalescence model expectations

Recent results on strangeness from ALICE at LHC

Recent measurements performed in high-multiplicity proton-proton (pp) and proton-lead (p-Pb) collisions have shown features that are similar to those observed in lead-lead (Pb-Pb) collisions. These observations warrant a comprehensive measurement of the production of identified particles as a function of multiplicity in all systems. The production of different strange and multi-strange particle species at mid-rapidity measured as a function of multiplicity in pp collisions at TeV with the ALICE setup are conducted. Spectral shapes studied both for individual particles and via particle ratios such as as a function of p(T) exhibit an evolution with event multiplicity and the production rates of hyperons are observed to increase more strongly than those of non-strange hadrons. These phenomena are qualitatively similar to the ones observed in p-Pb and Pb-Pb collisions. The values in high-multiplicity pp and p–Pb collisions approach the ones in Pb–Pb

Highlights of the production of (anti-)(hyper-)nuclei and exotica with ALICE at the LHC

Measurements of the production of light (anti-)nuclei and (anti-)hypernuclei have been performed in different colliding systems at the LHC, namely pp, p–Pb and Pb–Pb. The results of the production in Pb–Pb collisions of light (anti-)(hyper-)nuclei follows the expectation of the thermal model, whereas the production of nuclei in pp and p–Pb collisions shows a closer agreement with the expectations from coalescence models. Both models can give predictions for the production yields of hypothetical states such as bound states of two Λ hyperons or of a Λ and a neutron, which are expected to decay weakly. These states are searched for with the ALICE apparatus. Since no signal is found, upper limits, which are significantly below the model expectations, are set. Furthermore, the most recent measurement of the lifetime of the hypertriton determined in Pb–Pb collisions at at the LHC gives a value exactly between the world average and the free lifetime. In addition, the new result is in agreement with other recent measurements in heavy-ion collisions