Particle Production in pp and Heavy Ion Collisions from sNN\sqrt{s_{NN}} = 200 GeV to 5.5 TeV

Exploring the creation of Quark Gluon Plasma (QGP), a new state of Nuclear matter is the main aim in Relativistic Heavy Ion collision experiments which √ are being performed in the STAR experiment at RHIC ( s = 200 GeV) and √ ALICE ( s = 5.5 TeV) experiment at LHC. Various observables derived from the properties of the produced particles of the interacting system. Specialized detectors are built for detection of specific types of particles. Dedicated efforts are made in data analysis studying the observables in the soft and hard sector in AA collisions which are then compared with the results form pp and dAu collisions for attaining at a consistent picture. In this thesis as a part of the detector developmental work, fabrication and testing of the Photon Multiplic- ity Detector (PMD) installed in the ALICE experiment at LHC have been discussed. A detailed√ simulation using PYTHIA with GEANT is performed with pp collision (at s = 14 TeV) events at LHC as a readiness exercise of data analysis in such collisions. In this work, we have also analyzed the STAR data for pp and dAu collisions √ at s = 200 GeV for extracting the jT , kT of jets using the method of di- hadron correlations. Transverse momentum imbalance (kT ) of the di-jets in pp collisions, by its own nature, has a special importance in characterizing the intrinsic transverse momentum of partons and its broadening in vacuum. Interaction of the hard partons in nuclear medium is expected to lead to the additional broadening in kT . Centrality dependence of jT , kT in dAu collisions have been studied with the STAR data for the first time in wide kinematic region. Comparisons have been made with the results form PYTHIA and HIJING models. Jet transverse momentum ( jt2 ) and jet acoplanarity ef- √ 2 fect ( kt ) for pp at s = 200 GeV using π 0 -ch correlation for π 0 selected in the pT range 6.5-18.5 GeV/c are found to be 598 ± 28 (stat) GeV/c and 2.80±0.04(stat)±0.27(sys) GeV/c respectively. The effect of the k T broad- ening form the dAu data is found to be 10-20%. These results will help in interpreting the results from heavy ion collisions like AuAu at RHIC illumi- nating the formation of the high-density matter. We have also performed a simulation study for γ-jet detection as a golden channel in the Photon Spec- trometer (PHOS) acceptance in ALICE. The work consists of a method of using the transverse momentum imbalance of the di-jets to enhance the purity of the direct photon detection in pp for ALICE in LHC energy

Probing hadronization and jet substructure with leading particles in jet at H1

A momentum charge correlation ratio observable rc, generalized from the balance function [1], is measured using data recorded with the H1 experiment at HERA during 2003 to 2007. This variable distinguishes between same-sign and opposite-sign charged particle pairs[2] in a jet. The average rc is studied for two configurations (prongs) of the leading particles in the jet, defined with the help of declustering in a recursive soft drop technique. When resolved as as a function of other kimenatic variables, such as the formation time, this probes the transition from non-perturbative to perturbative aspects of QCD. This sets the path for a novel way of studying jet substructure and the evoluation of partons in a jet. The data of rc at different prongs reveal differences between the first and subsequent splits. Data are confronted with predictions from various event generators

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 lepton-jet correlation in deep-inelastic scattering with the H1 detector using machine learning for unfolding

The first measurement of lepton-jet momentum imbalance and azimuthal correlation in lepton-proton scattering at high momentum transfer is presented. These data, taken with the H1 detector at HERA, are corrected for detector effects using an unbinned machine learning algorithm OmniFold, which considers eight observables simultaneously in this first application. The unfolded cross sections are compared to calculations performed within the context of collinear or transverse-momentum-dependent (TMD) factorization in Quantum Chromodynamics (QCD) as well as Monte Carlo event generators. The measurement probes a wide range of QCD phenomena, including TMD parton distribution functions and their evolution with energy in so far unexplored kinematic regions

Measurement of prompt D0^{0}, D+^{+}, D∗+^{*+}, and DS+ {\mathrm{D}}_{\mathrm{S}}^{+} production in p–Pb collisions at sNN \sqrt{{\mathrm{s}}_{\mathrm{NN}}} = 5.02 TeV

International audienceThe measurement of the production of prompt D$^{0}$, D$^{+}$, D$^{*+}$, and ${\mathrm{D}}_{\mathrm{S}}^{+}$ mesons in proton–lead (p–Pb) collisions at the centre-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV, with an integrated luminosity of 292 ± 11 μb$^{−1}$, are reported. Differential production cross sections are measured at mid-rapidity (−0.96 < y$_{cms}$< 0.04) as a function of transverse momentum (p$_{T}$) in the intervals 0 < p$_{T}$< 36 GeV/c for D$^{0}$, 1 < p$_{T}$< 36 GeV/c for D$^{+}$ and D$^{*+}$, and 2 < p$_{T}$< 24 GeV/c for D$^{+}$ mesons. For each species, the nuclear modification factor R$_{pPb}$ is calculated as a function of p$_{T}$ using a proton-proton (pp) ref- erence measured at the same collision energy. The results are compatible with unity in the whole p$_{T}$ range. The average of the non-strange D mesons R$_{pPb}$ is compared with theoretical model predictions that include initial-state effects and parton transport model predictions. The p$_{T}$ dependence of the D$^{0}$, D$^{+}$, and D$^{*+}$ nuclear modification factors is also reported in the interval 1 < p$_{T}$< 36 GeV/c as a function of the collision centrality, and the central-to-peripheral ratios are computed from the D-meson yields measured in different centrality classes. The results are further compared with charged-particle measurements and a similar trend is observed in all the centrality classes. The ratios of the p$_{T}$-differential cross sections of D$^{0}$, D$^{+}$, D$^{*+}$, and ${\mathrm{D}}_{\mathrm{S}}^{+}$ mesons are also reported. The ${\mathrm{D}}_{\mathrm{S}}^{+}$ and D$^{+}$ yields are compared as a function of the charged-particle multiplicity for several p$_{T}$ intervals. No modification in the relative abundances of the four species is observed with respect to pp collisions within the statistical and systematic uncertainties

Λ3H^3_\Lambda\mathrm{H} and Λˉ3H‾^3_{\bar{\Lambda}}\mathrm{\overline{H}} lifetime measurement in Pb-Pb collisions at sNN=\sqrt{s_{\mathrm{NN}}} = 5.02 TeV via two-body decay

International audienceAn 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 d N /d( ct ) spectrum. The measured value, τ=242−38+34 (stat.) ± 17 (syst.) ps, is compatible with representative theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime puzzle

Exploration of jet substructure using iterative declustering in pp and Pb–Pb collisions at LHC energies

The ALICE collaboration at the CERN LHC reports novel measurements of jet substructure in pp collisions at $\sqrt{s}$= 7 TeV and central Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV. Jet substructure of track-based jets is explored via iterative declustering and grooming techniques. We present the measurement of the momentum sharing of two-prong substructure exposed via grooming, the $z_{\rm{g}}$, and its dependence on the opening angle, in both pp and Pb-Pb collisions. We also present the first measurement of the distribution of the number of branches obtained in the iterative declustering of the jet, which is interpreted as the number of its hard splittings. In Pb-Pb collisions, we observe a suppression of symmetric splittings at large opening angles and an enhancement of splittings at small opening angles relative to pp collisions, with no significant modification of the number of splittings. The results are compared to predictions from various Monte Carlo event generators to test the role of important concepts in the evolution of the jet in the medium such as color coherence

Measurement of electrons from heavy-flavour hadron decays as a function of multiplicity in p–Pb collisions at √sNN = 5.02 TeV

The multiplicity dependence of electron production from heavy-flavour hadron decays as a function of transverse momentum was measured in p-Pb collisions at sNN−−−√ = 5.02 TeV using the ALICE detector at the LHC. The measurement was performed in the centre-of-mass rapidity interval −1.07<ycms<0.14 and transverse momentum interval 2 <pT< 16 GeV/c. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the pT spectra measured for different multiplicity classes with those measured in pp collisions (QpPb) and in peripheral p-Pb collisions (QCP). The QpPb results obtained are consistent with unity within uncertainties in the measured pT interval and event classes. This indicates that heavy-flavour decay electron production is consistent with binary scaling and independent of the geometry of the collision system. Additionally, the results suggest that cold nuclear matter effects are negligible within uncertainties, in the production of heavy-flavour decay electrons at midrapidity in p-Pb collisions