Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

First experimental test of HAL QCD lattice calculations for the multi strange hyperon - nucleon interaction with ALICE

The use of non-traditional femtoscopy in small collision systems is a promising technique to improve our knowledge on nucleon-hyperon and hyperon-hyperon interactions. This article gives an overview on the experimental status and prospects for the measurement of the p–Ξ − and p–Ω − correlation functions, using the ALICE data collected in pp collisions at 13 TeV, triggered for high-multiplicity. Such studies are relevant for the understanding of the nuclear Equation of State and its relation to dense objects like neutron stars. Recently the HAL-QCD collaboration conducted calculations without relying on constraints by data and with quarks and gluons as degrees of freedom. Their results converge for the interactions between heavier Ξ − and Ω − hyperons and nucleons and in the p–Ω − system they predict a bound state. This work highlights the feasibility of exploiting the ALICE data to study the existence of a di-baryon bound state and provides the most precise test of the lattice results for the p–Ξ − interaction

Analysis techniques for femtoscopy and correlation studies in small collision systems and their applications to the investigation of p–Λ and Λ–Λ interactions with ALICE

Femtoscopy is a technique relating the correlations between pairs of particles to their emission source and interaction potential. Traditionally femtoscopy is used to study the properties of the emission source, mostly by using charged pion correlations, for which the correlation function is determined only by the Bose-Einstein statistics and Coulomb interaction. The topic of this work is the non-traditional baryon–baryon femtoscopy, the goal of which is to study the interaction potential between different baryon pairs, assuming the emission source is fixed. Such an approach is quite challenging as it requires an exact treatment of the strong potential in order to compute the correlation function, as well as knowledge on the profile and size of the emission source. In the work presented here, a new “Correlation Analysis Tool using the Schrödinger equation” (CATS) has been developed to tackle the issue related to the modeling of the correla- tion function. In previous works it was proposed that in small collision systems the source is approximately the same for all baryon–baryon pairs and this feature leads to the opportunity of using the p–p correlations to fix the source, allowing to study the interaction of other pairs. However, the limits of validity of this method were never quantitatively studied. In particular, the decays of short-lived resonances are expected to influence the emission source differently based on the particle species involved. In this work a new model was developed to handle this effect, making possible to perform non-traditional femtoscopy with much higher precision. This new analysis techniques and method developed were used by the ALICE col- laboration to study a multitude of different baryon–baryon systems, including p–Λ, p–Σ^0 , p–Ξ − , Λ–Λ, p–Ω^− and has even been applied to the meson sector to study the p–K^− interaction. Aside the development of CATS and the new source model, the author was the main analyzer of the p–Λ and Λ–Λ systems, therefore these results will be discussed in detail. In particular, the study of p–Λ has an important link to the equation of state of nuclear matter and the existence of massive neutron stars. In this work the chiral effective field theory computations are verified against the p–Λ data collected by the ALICE collaboration. The Λ–Λ system is of great theo- retical interest, as some models predict the existence of a bound state, the so called H-dibaryon, which could be composed of two Λs. The current work provides fur- ther experimental constraints on the Λ–Λ scattering parameters and binding energy of the hypothetical bound state

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at sNN=5.02 TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-of- flight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number

Measuring KS0^0_{\rm S}K±^{\rm \pm} interactions using Pb-Pb collisions at sNN=2.76{\sqrt{s_{\rm NN}}=2.76} TeV

We present the first ever measurements of femtoscopic correlations between the KS0 and K ± particles. The analysis was performed on the data from Pb–Pb collisions at sNN=2.76 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the a0(980) resonance. The extracted kaon source radius and correlation strength parameters for KS0K− are found to be equal within the experimental uncertainties to those for KS0K+ . Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the a0 resonance are tested. Our results are also compatible with the interpretation of the a0 having a tetraquark structure instead of that of a diquark

Measurement of deuteron spectra and elliptic flow in Pb–Pb collisions at sNN\sqrt{s_{\mathrm {NN}}} = 2.76 TeV at the LHC

The transverse momentum ( $p_\mathrm{T}$ ) spectra and elliptic flow coefficient ( $v_{2}$ ) of deuterons and anti-deuterons at mid-rapidity ( $|y| 1.8 GeV$/c$within the experimental uncertainties. The measurement of the coalescence parameter$B_2$is performed, showing a$p_\mathrm{T} $dependence in contrast with the simplest coalescence model, which fails to reproduce also the measured$v_{2}$coefficient. In addition, the coalescence parameter$B_2$and the elliptic flow coefficient in the 20–40$v_{2}$($p_\mathrm{T} $) and the$B_2$($p_\mathrm{T} $ ) trend

Searches for transverse momentum dependent flow vector fluctuations in Pb-Pb and p-Pb collisions at the LHC

International audienceThe measurement of azimuthal correlations of charged particles is presented for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the CERN Large Hadron Collider. These correlations are measured for the second, third and fourth order flow vector in the pseudorapidity region |η| < 0.8 as a function of centrality and transverse momentum p$_{T}$ using two observables, to search for evidence of p$_{T}$-dependent flow vector fluctuations. For Pb-Pb collisions at 2.76 TeV, the measurements indicate that p$_{T}$-dependent fluctuations are only present for the second order flow vector. Similar results have been found for p-Pb collisions at 5.02 TeV. These measurements are compared to hydrodynamic model calculations with event-by-event geometry fluctuations in the initial state to constrain the initial conditions and transport properties of the matter created in Pb–Pb and p–Pb collisions

Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity in pp and Pb–Pb collisions at √sNN = 5.02 TeV

The differential invariant yield as a function of transverse momentum (pT) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0–10%), semi-central (30–50%) and peripheral (60–80%) lead–lead (Pb–Pb) collisions at √sNN = 5.02 TeV in the pT intervals 0.5–26 GeV/c (0–10% and 30–50%) and 0.5–10 GeV/c (60–80%). The production cross section in proton–proton (pp) collisions at √s = 5.02 TeV was measured as well in 0.5 < pT < 10 GeV/c and it lies close to the upper band of perturbative QCD calculation uncertainties up to pT = 5 GeV/c and close to the mean value for larger pT. The modification of the electron yield with respect to what is expected for an incoherent superposition of nucleon–nucleon collisions is evaluated by measuring the nuclear modification factor RAA. The measurement of the RAA in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The RAA shows a suppression with respect to unity at intermediate pT, which increases while moving towards more central collisions. Moreover, the measured RAA is sensitive to the modification of the parton distribution functions (PDF) in nuclei, like nuclear shadowing, which causes a suppression of the heavy-quark production at low pT in heavy-ion collisions at LHC