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Register a new userHBT radii : Comparative studies on collision systems and beam energies
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Debasish Das
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Two-particle Hanbury-Brown-Twiss (HBT) interferometry is an important probe for understanding the space-time structure of particle emission sources in high energy heavy ion collisions. We present the comparative studies of HBT radii in Pb+Pb collisions at $sqrt{s_{rm{NN}}}$ = 17.3 GeV with Au+Au collisions at $sqrt{s_{rm{NN}}}$ = 19.6 GeV. To further our understanding for this specific energy regime we also compare the HBT radii for Au+Au collisions at $sqrt{s_{rm{NN}}}$ = 19.6 GeV with Cu+Cu collisions at $sqrt{s_{rm{NN}}}$ = 22.4 GeV. We have found interesting similarity in the $R_{rm out}/R_{rm side}$ ratio with $m_{rm T}$ across the collision systems while comparing the data for this specific energy zone which is interesting as it acts as a bridge from SPS energy regime to the RHIC energy domain.
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The effect of initial state momentum-space anisotropy on invariant mass dependence of HBT radii extracted from the leptonpair interferometry is presented here. We have studied the Bose-Einstein Correlation Function (BECF) for two identical virtual photons decaying to leptonpairs at most central collision of LHC energy having fixed transverse momentum of one of the virtual photons ($k_{1T}$= 2 GeV). The {em free streaming interpolating} model with fixed initial condition has been used for the evolution in anisotropic Quark Gluon Plasma (aQGP) and the relativistic (1+2)d hydrodynamics model with cylindrical symmetry and longitudinal boost invariance has been used for both isotropic Quark Gluon Plasma (iQGP) and hadronic phases. We found a significant change in the spatial and temporal dimension of the evolving system in presence of initial state momentum-space anisotropy.
The first ($v_1^{text{even}}$), second ($v_2$) and third ($v_3$) harmonic coefficients of the azimuthal particle distribution at mid-rapidity, are extracted for charged hadrons and studied as a function of transverse momentum ($p_T$) and mean charged particle multiplicity density $langle mathrm{N_{ch}} rangle$ in U+U ($roots =193$~GeV), Au+Au, Cu+Au, Cu+Cu, $d$+Au and $p$+Au collisions at $roots = 200$~GeV with the STAR Detector. For the same $langle mathrm{N_{ch}} rangle$, the $v_1^{text{even}}$ and $v_3$ coefficients are observed to be independent of collision system, while $v_2$ exhibits such a scaling only when normalized by the initial-state eccentricity ($varepsilon_2$). The data also show that $ln(v_2/varepsilon_2)$ scales linearly with $langle mathrm{N_{ch}} rangle^{-1/3}$. These measurements provide insight into initial-geometry fluctuations and the role of viscous hydrodynamic attenuation on $v_n$ from small to large collision systems.
We describe RHIC pion data in central A+A collisions and make predictions for LHC based on hydro-kinetic model, describing continuous 4D particle emission, and initial conditions taken from Color Glass Condensate (CGC) model.
The COSY-11 collaboration measured the pp -> ppeta and pp -> ppeta reactions in order to perform comparative studies of the interactions within the proton-proton-meson system. This thesis presents in detail the analysis of the pp -> ppeta reaction which was measured at the proton beam momentum of 3.260 GeV/c. The elaboration results in differential distributions of squared invariant proton-proton (s_pp) and proton-eta (s_peta) masses, as well as in angular distributions and the total cross section at an excess energy of 16.4 MeV. The differential distributions s_pp and s_peta are compared to theoretical predictions and to the analogous spectra determined for the pp -> ppeta reaction. The comparison of the results for the eta and eta meson production rather excludes the hypothesis that the enhancement observed in the invariant mass distributions is due to the meson-proton interaction. Further, the shapes of the distributions do not favour any of the postulated theoretical models.
In non-central collisions between ultra-relativistic heavy ions, the freeze-out distribution is anisotropic, and its major longitudinal axis may be tilted away from the beam direction. The shape and orientation of this distribution are particularly interesting, as they provide a snapshot of the evolving source and reflect the space-time aspect of anisotropic flow. Experimentally, this information is extracted by measuring pion HBT radii as a function of angle with respect to the reaction plane. Existing formulae relating the oscillations of the radii and the freezeout anisotropy are in principle only valid for Gaussian sources with no collective flow. With a realistic transport model of the collision, which generates flow and non-Gaussian sources, we find that these formulae approximately reflect the anisotropy of the freezeout distribution.
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