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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Measurement of f0(980) Elliptic Flow in Proton-Lead Collisions at the Large Hadron Collider and Its Possible Quark Content

An Gu (17593179) 07 December 2023 (has links)
<h4>Exotic hadrons are hadrons with constituent quark content different from the normal meson and baryon. The f<sub>0</sub>(980) hadron is one of the exotic hadron candidates, which was first discovered in $\pi\pi$ scattering experiments in the 1970's. It could be a ordinary quarnk-antiquark meson, a tetraquark exotic state, a kaon-antikaon molecule, or a quark-antiquark-gluon hybrid state.</h4><p dir="ltr">Anisotropic flow (v<sub>n</sub>) is a powerful tool to probe the dynamics of relativistic heavy ion collisions. The observed approximate scaling of v<sub>n</sub> by the number of constituent quarks (NCQ) suggests the importance of partonic degree of freedom in these collisions. Large v<sub>n</sub> and NCQ-scaling have also been observed in high-multiplicity proton-lead (pPb) collisions at the LHC, suggesting similar dynamics in pPb collisions. The empirically established NCQ-scaling can be exploited to probe the constituent quark content of the f<sub>0</sub>(980) hadron.</p><p dir="ltr">We measure the elliptic flow (v<sub>2</sub>) of f<sub>0</sub>(980) in high-multiplicity pPb collisions at 8 TeV with the Compact Muon Solenoid (CMS) detector at the LHC, through its main pion-pion ($\pi^+\pi^-$) decay channel. The invariant mass spectrum is obtained from opposite sign pion pairs, and the combinatorial background is estimated by same-sign pion pairs and subtracted. The f<sub>0</sub>(980) signal and the remaining residual background are modeled by relativistic Breit-Wigner and polynomial functions, respectively. The yield of f<sub>0</sub>(980) is extracted as a function of azimuthal angle relative to the event plane, and the f<sub>0</sub>(980) v<sub>2</sub> is measured as function of $p_T$, corrected for the event-plane resolution. The non-flow component in f<sub>0</sub>(980) v<sub>2</sub> has been estimated by that of K<sub>s</sub><sup>0</sup>. By comparing the measured v<sub>2</sub> of the f<sub>0</sub>(980) to those of other hadrons, we infer the number of constituent quarks for the f<sub>0</sub>(980) assuming NCQ scaling. The f<sub>0</sub>(980) is found to be a 2-quark state in this work. We discuss the systematic uncertainties involved in our study, implications of our result, and possible future works in this endeavor.</p>
2

Applications of analyticity to scalar meson phenomenology

Cherry, Stuart Nicholas January 2001 (has links)
The scalar mesons have caused much debate amongst hadronic physicists for many years. Even today the number of scalars is hotly contested, and there is almost no agreement on the composition of any of the experimentally observed states, except perhaps for the K*(_0) (1430). This thesis attempts to shed light on both of these problems via the application of analyticity to two different quantities. Recently a number of authors have proposed the existence of a light, strange, scalar meson known as the k. We perform a direct search of the best available πK scattering data to determine whether or not this resonance exists. This is done by constructing contour integrals from these data and determining the number of poles present inside the contour. We do not need to model either the internal dynamics of the state nor the form of the background scattering. The number of poles found tells us the number of resonances present and their positions allow us to estimate the resonance parameters. We find that there is only one resonance in scalar πK scattering below 1800 MeV and this is identified with the established K*(_0)(1430). We find no evidence for the k. Secondly, applying Cauchy's Theorem to the vacuum polarisation function leads to a relation between experimental and theoretical integrals known as a Finite Energy Sum Rule (FESR). FESRs are used to explore the scalar, isoscalar non-strange current and allow us to determine which of the experimentally observed scalar, isoscalar mesons is most likely to be the uũ + dd state. We find that the lightest scalar, isoscalar uũ dd state is not the fo(980) as suggested by some authors, but is rather the light, broad object known as the fo(400 - 1200). We are also able to estimate the average light quark mass and find m(_q)(l GeV(^2)) = 4.7 ± 0.9 MeV which is consistent with the recent estimates of this quantity from unquenched lattice QCD.

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