Measurement of K*(892) ± in proton+proton collisions with ALICE at the LHC and study of particle production using color string percolation model

Abstract

The basic questions are always been asked by the mankind that, “What are the constituents of matter and what are its properties?”. Many experiments are done to explain it and demonstrate the atom, its subatomic particles called nucleons (such as protons and neutrons) and further constituents of nucleons are called quarks. As the search turned to go into smaller scales, experiments needed to become even larger in the form of particle accelerators. On the pursuit of these fundamental questions numerous scientific fields are created. These fields include Quantum Mechanics, Quantum Chromodynamics (QCD), Quantum Electrodynamics (QED), Electro-Weak Theory (EWT), High-Energy Physics, and Particle Physics. Quarks exhibit the property of color confinement, which means a quark cannot be found in isolation. Confinement is the reason for bound state of quarks which are called as hadrons. The hadrons particularly, protons and neutrons together with electrons make up the visible matter of the Universe. With color confinement property, asymptotic freedom is also retained for quarks. In contrast to confinement, the asymptotic freedom suggests, at high temperatures or high baryon densities the quarks and gluons confined inside hadrons can be de-confined. This de-confined state of quarks and gluons is called as Quark-Gluon Plasma (QGP). In laboratory, QGP can be experimentally created by ultra-relativistic heavy-ion collisions. The experimental search for de-confined state of quarks and gluons started with the first heavy-ion collisions in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) and thereafter in the Large Hadron Collider (LHC) at CERN. At RHIC, various signatures like jet quenching, azimuthal anisotropy, J/ suppression, strangeness enhancement indicated the creation of QGP. At the LHC, thecolliding particles energy is in TeV scale, which is ⇠ 10 times higher than RHIC. A Large Ion Collider Experiment (ALICE) at LHC is a dedicated experiment for the creation of QGP and study its properties. To study the properties of strongly interacting matter produced in theultra-relativistic collisions, various probes are required. The lifetime of the fireball created in Pb–Pb collisions at LHC is O ⇠ 10 fm/c. The resonances by definition are very short-lived particle with lifetime ⌧ ⇠ 1 fm/c (10−23 s) can be used as an excellent probe for the study of system evolution in di↵erent time scale and to understand various in-medium phenomena. In this thesis, primarily K⇤± resonance is studied in detail. It is a vector meson (spin 1) containing a strange quark and having lifetime, ⌧K⇤± ⇠ 4 fm/c, which is comparable to the fireball created in Pb–Pb collisions. The formation of QGP and its properties can be explored by the study of such short living particle (which is one of the probes) when it transported through the medium. The transition of QCD matter from hadronic confined phase to QGP de-confined phase is fascinating. Theoretically, there are several signatures of first order phase transition and the critical point has been proposed. The color string percolation model (CSPM) is an approach to investigate the particle production through the percolation of color strings and the phase structure of the hadronic matter.A detailed formalism and methodology of CSPM is discussed in this thesis. In addition, thermodynamical and transport quantities like, energy density, shear viscosity, trace anomaly, speed of sound, entropy density and bulk viscosity of the matter produced in heavy-ion collisions at RHIC by using the CSPM are discussed. The energy and centrality dependence study of percolation parameters and various thermodynamical observables at RHIC energies are done. The electrical conductivity which is a well known observable for strongly interacting matter produced in heavy-ion collisions has drawn considerable interest. So, we estimate the normalised electrical conductivity to temperature ratio using the color string percolation approach. Limiting fragmentation (LF) is another interesting phenomena in high energy multiparticle production process. In this thesis we have revisited the phenomenon of limiting fragmentation for nucleus-nucleus (A+A) collisions in the pseudorapidity distributions of di↵erential cross-section of charged particles (d#AA/d⌘) by considering energy dependent inelastic cross-section (#in). The organization of the thesis is as follows: Chapter 1: This chapter gives an introduction to Standard Model, QCD, QGP and its various signatures. The motivations for relativistic pp and heavy-ion collisions are described. Subsequently, the motivation for resonance study in particular K⇤(892)± meson measurements are discussed. An introduction to color string percolation model for the particle production is also discussed here along with the hypothesis of limiting fragmentation for particle production in high-energy nuclear collisions. Chapter 2: In this chapter the experimental facilities at LHC which is based at CERN, Geneva are explained. The ALICE experiment and its di↵erent detectors are discussed in details. A detailed description of ITS and TPC detectors which are used significantly for the data analysis is given.Chapter 3: The transverse momentum spectra have been measured at mid-rapidity and compared with QCD-inspired models (PYTHIA6, PYTHIA8) and hybrid model (EPOS-LHC). Comparison of K⇤± results with the ones obtained for K⇤0 at the same collision energies are also discussed. The collision energy dependence of the transverse momentum pT spectra, integrated yields, hpT i and K⇤/K ratio are explored. Chapter 4: In this chapter the transport properties in heavy-ion collisions at RHIC energies using color string percolation model (CSPM) are discussed. The transport properties for example, the initial energy density ("), shear viscosity to entropy density ratio (⌘/s), trace anomaly ("), the squared speed of sound (C2 s ), entropy density, and bulk viscosity to entropy density ratio (⇣/s) are obtained and compared with the lattice QCD calculations for (2+1) flavor. Another observable, the normalised electrical conductivity (#el/T) of hot QCD matter as a function of temperature (T) using the CSPM and comparison with various existing results is also discussed. The centrality dependent behaviour of initial temperature of the percolation cluster, energy density, average transverse momentum, shear viscosity to entropy density ratio (⌘/s) and trace anomaly for di↵erent RHIC energies in the framework of CSPM is studied. Chapter 5: In this chapter, the phenomenon of limiting fragmentation for nucleus-nucleus (A+A) collisions in the pseudorapidity distribution of charged particles at various energies is studied. Energy dependent #in is used to get the pseudorapidity distributions of di↵erential cross-section of charged particles and study the phenomenon of LF. Chapter 6: In this chapter we summarise the results with important findings.