Simulation studies of R2(Δη,Δφ)\rm{R_{2}}(\Delta\eta, \Delta\varphi) and P2(Δη,Δφ)\rm{P_{2}}(\Delta\eta, \Delta\varphi) correlation functions in pp collisions with the PYTHIA and HERWIG models

We report studies of charge-independent (CI) and charge-dependent (CD) two-particle differential-number correlation functions, $\rm{R_{2}}(\Delta\eta, \Delta\varphi)$, and transverse momentum ($p_{\rm T}$) correlation functions, $\rm{P_{2}}(\Delta\eta, \Delta\varphi)$, of charged particles in $\sqrt{\textit{s}}$ = 2.76 TeV pp collisions with the PYTHIA and HERWIG models. Model predictions are presented for inclusive charged hadrons ($h^\pm$), as well as pions ($\pi^\pm$), kaons (K$^\pm$), and (anti-)protons ($\rm \bar{p}$/p) in the ranges $0.2 < \textit{p}_{\rm T} \le 2.0~\rm{GeV}/\textit{c}$, $2.0 < \textit{p}_{\rm T} \le 5.0~\rm{GeV}/\textit{c}$, and $5.0 < \textit{p}_{\rm T} \le 30.0~\rm{GeV}/\textit{c}$, with full azimuthal coverage in the range $|\eta|< 1.0$. We compare the model predictions for the strength and shape of the $\rm{R_{2}}$ and $\rm{P_{2}}$ correlators as these pertain to recent measurements by the ALICE collaboration. The $\rm{R_{2}}$ and $\rm{P_{2}}$ correlation functions estimated with PYTHIA and HERWIG exhibit qualitatively similar near-side and away-side correlation structures but feature important differences. Our analysis indicates that comparative studies of $\rm{R_{2}}$ and $\rm{P_{2}}$ correlation functions would provide valuable insight towards the understanding of particle production in pp collisions, and by extension, should also be useful in studies of heavy-ion collisions. Comparison of the $\Delta \eta$ dependence of $\rm{R_{2}}$ and $\rm{P_{2}}$ could contribute, in particular, to a better understanding and modeling of the angular ordering of particles produced by hadronization in jets, as well as a better description of jet fragmentation functions of identified species at low momentum fraction $(z)$.Comment: 22 pages, 24 captioned figure

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

Measurement of R2(Δη,Δφ)R_{2}(\Delta\eta,\Delta\varphi) and P2(Δη,Δφ)P_{2}(\Delta\eta,\Delta\varphi) correlation functions in pp collisions at s\sqrt{\textit{s}} = 13 TeV with ALICE at the LHC

ALICE (A Large Ion Collider Experiment) is a multi-purpose detector at LHC (Large Hadron Collider) designed to explore a hot and dense QCD matter known as quark-gluon plasma (QGP), which was believed to be formed after a few microseconds of the Big Bang. Correlation functions are used to study this new state of matter by analyzing the particles produced in ultra-relativistic high-energy collisions. In this thesis, the two-particle differential-number correlation function ($R_{2}(\Delta\eta,\Delta\varphi)$) and transverse momentum ($\textit{p}_{\rm T}$) correlation function ($P_{2}(\Delta\eta,\Delta\varphi)$) are used instead of other correlation functions because they do not rely on the detection efficiencies and mixed event background subtraction technique used in previous studies. The particle production mechanism, flow, diffusivity, jets, charge and momentum conservation, resonance decays, Bose-Einstein correlations, and other aspects of high-energy collisions were better understood using charge-independent and charge-dependent combinations of $R_{2}(\Delta\eta,\Delta\varphi)$ and $P_{2}(\Delta\eta,\Delta\varphi)$. Simulation studies of charge-independent and charge-dependent combinations of $R_{2}(\Delta\eta,\Delta\varphi)$ and $P_{2}(\Delta\eta,\Delta\varphi)$ correlation functions were performed using PYTHIA and HERWIG models in pp collisions at $\sqrt{\textit{s}}$ = 2.76 TeV. Unidentified ($h^{\pm}$) and identified ($\pi$$^{\pm}$, K$^{\pm}$ and p($\bar{p}))$ charged hadrons were selected in three different $\textit{p}_{\rm T}$ ranges ( 0.2 - 2.0 $\rm{GeV}/\textit{c}$, 2.0 - 5.0 $\rm{GeV}/\textit{c}$ and 5.0 - 30.0 $\rm{GeV}/\textit{c}$ ) to understand the soft and hard QCD processes. The shapes and strengths of $R_{2}$ and $P_{2}$ were compared to get a better understanding and modeling of the angular ordering of particles created by hadronization in jets, as well as a better description of the jet fragmentation functions of identified species at low momentum fraction ($z$). $R_{2}$ and $P_{2}$ were measured in pp collisions at $\sqrt{\textit{s}}$ = 13 TeV for unidentified charged hadrons ($h^{\pm}$) in the $\textit{p}_{\rm T}$ interval of 0.2 - 2.0 $\rm{GeV}/\textit{c}$. This work complements the recent ALICE measurements to gain a better understanding of the jet contribution and nature of collectivity in small systems. Both $R_{2}$ and $P_{2}$ have near-side and away-side correlation structures that are qualitatively similar but quantitatively different. In addition, for both charge-independent and charge-dependent combinations, like in the simulation work and the published ALICE results for p-Pb and Pb-Pb collisions, $P_{2}$ has a substantially narrower near-side peak than $R_{2}$. This work served as a baseline for p-Pb and Pb-Pb results, as they are sensitive to the interplay between the underlying event and mini-jets in pp collisions

Measurement of R2(Δη,Δφ)R_{2}(\Delta\eta, \Delta\varphi) and P2(Δη,Δφ)P_{2}(\Delta\eta, \Delta\varphi) correlation functions in pp collisions at s\sqrt{\textit{s}} = 13 TeV using ALICE data

Two-particle normalized cumulants of particle number correlations ($R_{2}$)and transverse momentum correlations ($P_{2}$), measured as a function ofrelative pseudorapidity and azimuthal angle difference $(\Delta\eta, \Delta\varphi)$,provide key information about particle production mechanisms,diffusivity, and conservation of charge and momentum in high-energycollisions. To complement the recent ALICE measurements in Pb--Pbcollisions, as well as for better understanding of the jetcontribution and nature of collectivity in small systems, theseobservables are measured in pp collisions at $\sqrt{\textit{s}}$ = 13 TeVwith similar transverse momentum range, 0.2 $\leq$ $\textit{p}_{\rm T}$ $\leq$ 2.0$\rm{GeV}/\textit{c}$. The $R_{2}$ and $P_{2}$ results on the near-and away-side are qualitatively similar, but differ quantitatively. Amuch narrower near-side peak is observed for $P_{2}$ compared to$R_{2}$ for both charge-independent and charge-dependent combinations,as in the recently published ALICE results for p--Pb and Pb--Pbcollisions. Since these results are sensitive to the interplay between the underlying event and mini-jets in pp collisions, they not only establish a baseline for heavy-ion collisions, but also allow a better understanding of signals that are compatible with the presence of collective effects in small systems

Simulation Studies of R2(Δ η, Δ ϕ) and P2(Δ η, Δ ϕ) Correlation Functions in pp Collisions with the PYTHIA and HERWIG Models

We presented a study of charge-independent (CI) and charge-dependent (CD) two-particle differential number correlation functions R2 and transverse momentum correlation functions P2 in pp collisions at s=2.76 TeV with the PYTHIA and HERWIG models.Calculations were presented for unidentified hadrons in three pT ranges 0.2 &lt; pT≤ 2.0 GeV/c, 2.0 &lt; pT≤ 5.0 GeV/c, and 5.0 &lt; pT≤ 30.0 GeV/c.PYTHIA and HERWIG both qualitatively reproduce the near-side peak and away-side ridge correlation features reported by experiments.At low pT, both models produce narrower near-side peaks in P2 correlations than in R2 as reported by the ALICE collaboration in p–Pb and Pb–Pb collisions.This suggests that the narrower shape of the P2 near-side peak is largely determined by the pT dependent angular ordering of hadrons produced in jets.Both PYTHIA and HERWIG predict widths that decrease with increasing pT.Widths extracted for P2 correlators are typically significantly narrower than those of the R2 counterparts [1]

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

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

HΛ3 and H‾Λ‾3 lifetime measurement in Pb–Pb collisions at √sNN=5.02 TeV via two-body decay

An improved value for the lifetime of the (anti-)hypertriton has been obtained using the data sample of Pb–Pb collisions at √sNN = 5.02 TeV collected by the ALICE experiment at the LHC. The (anti-)hypertriton has been reconstructed via its charged two-body mesonic decay channel and the lifetime has been determined from an exponential fit to the dN/d(ct) spectrum. The measured value, τ = 242+34 −38 (stat.) ± 17 (syst.) ps, is compatible with representative theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime puzzle

Study of the Λ–Λ interaction with femtoscopy correlations in pp and p–Pb collisions at the LHC

This work presents new constraints on the existence and the binding energy of a possible – bound state, the H-dibaryon, derived from – femtoscopic measurements by the ALICE collaboration. The results are obtained from a new measurement using the femtoscopy technique in pp collisions at √s = 13 TeV and p–Pb collisions at √sNN = 5.02 TeV, combined with previously published results from pp collisions at √s = 7 TeV. The – scattering parameter space, spanned by the inverse scattering length f −1 0 and the effective range d0, is constrained by comparing the measured – correlation function with calculations obtained within the Lednický model. The data are compatible with hypernuclei results and lattice computations, both predicting a shallow attractive interaction, and permit to test different theoretical approaches describing the – interaction. The region in the (f −1 0 ,d0) plane which would accommodate a – bound state is substantially restricted compared to previous studies. The binding energy of the possible – bound state is estimated within an effective-range expansion approach and is found to be B = 3.2+1.6 −2.4(stat)+1.8 −1.0(syst) MeV