119295507
Heavy lepton pair production in nucleus–nucleus collisions at LHC energy – a case study
Abstract We present a study of τ + τ − lepton pair production in Pb + Pb collisions at s NN = 5.5 TeV . The larger τ ± mass (∼1.77 GeV) compared to e ± and μ ± leads to considerably small hadronic contribution to the τ + τ − pair invariant mass ( M ) distribution relative to the production from thermal partonic sources. The quark–anti-quark annihilation processes via intermediary virtual photon, Z and Higgs bosons have been considered for the production of τ + τ − . We observe that the contribution from Drell–Yan process dominates over thermal yield for τ + τ − pair mass from 4 to 20 GeV at the LHC energy. We also present the ratio of τ lepton pair yields for nucleus–nucleus collisions relative to yields from p + p collisions scaled by number of binary collisions at LHC energies as a function τ pair mass. The ratio is found to be significantly above unity for the mass range 4 to 6 GeV. This indicates the possibility of detecting τ + τ − pair from quark–gluon plasma (QGP) in the mass window 4 ⩽ M (GeV) ⩽ 6 .
119158093
The consequences of SU (3) colorsingletness, Polyakov Loop and Z (3) symmetry on a quark–gluon gas
Based on quantum statistical mechanics we show that the SU(3) color singlet ensemble of a quark-gluon gas exhibits a Z(3) symmetry through the normaized character in fundamental representation and also becomes equivalent, within a stationary point approximation, to the ensemble given by Polyakov Loop. Also Polyakov Loop gauge potential is obtained by considering spatial gluons along with the invariant Haar measure at each space point. The probability of the normalized character in SU(3) vis-a-vis Polyakov Loop is found to be maximum at a particular value exhibiting a strong color correlation. This clearly indicates a transition from a color correlated to uncorrelated phase or vise-versa. When quarks are included to the gauge fields, a metastable state appears in the temperature range 145 T(MeV) 170 due to the explicit Z(3) symmetry breaking in the quark-gluon system. Beyond T 170 MeV the metastable state disappears and stable domains appear. At low temperature a dynamical recombination of ionized Z(3) color charges to a color singlet Z(3) confined phase is evident along with a confining background that originates due to circulation of two virtual spatial gluons but with conjugate Z(3) phases in a closed loop. We also discuss other possible consequences of the center domains in the color deconfined phase at high temperature.
55844228
Working group report: Heavy ion physics
The 8th workshop on high energy physics phenomenology (WHEPP-8) was held at the Indian Institute of Technology, Mumbai, India during January 5–16, 2004. One of the four working groups, group III was dedicated to QCD and heavy ion physics (HIC). The present manuscript gives a summary of the activities of group III during the workshop (see also [1] for completeness). The activities of group III were focused to understand the collective behaviours of the system formed after the collisions of two nuclei at ultra-relativistic energies from the interactions of the elementary degrees of freedom, i.e. quarks and gluons, governed by non-abelian gauge theory, i.e. QCD. This was initiated by two plenary talks on experimental overview of heavy ion collisions and lattice QCD and several working group talks and discussions.
119102585
Thermodynamic properties of strongly interacting matter in a finite volume using the Polyakov–Nambu–Jona-Lasinio model
We present the thermodynamic properties of strongly interacting matter in finite volume in the framework of Polyakov loop enhanced Nambu$-$Jona-lasinio model within mean field approximation. We considered both the 2 flavor and 2+1 flavor matter. Our primary observation was a qualitative change in the phase transition properties that resulted in the lowering of the temperature corresponding to the critical end point. This would make it favorable for detection in heavy-ion experiments that intend to create high density matter with considerably small temperatures. We further demonstrate the possibility of obtaining chiral symmetry restoration even within the confined phase in finite volumes.
122350530
Models for Strong Interaction Physics
Abstract We review the developments in various models describing strong interaction physics. The models provide an intuitive way of understanding the complex phenomenon associated with strong interactions. Models also help us to delve into regions of couplings and other thermodynamic conditions of interest that are still out of reach of the first principle method - quantum chromodynamics. At the same to ascertain the merits of the models they should be contrasted to the results obtained from quantum chromodynamics at least in its region of validity, and to the available experimental data. Here we shall discuss about our progress in that direction.
17726542
Formation and collapse of false vacuum bubbles in relativistic heavy-ion collisions
Abstract It is possible that under certain situations, in a relativistic heavy-ion collision, partons may expand out forming a shell like structure. We analyze the process of hadronization in such a picture for the case when the quark–hadron transition is of first order, and argue that the inside region of such a shell must correspond to a supercooled (to T=0 ) deconfined vacuum. Hadrons from that region escape out, leaving a bubble of pure deconfined vacuum with large vacuum energy. This bubble undergoes relativistic collapse, with highly Lorentz contracted bubble walls, and may concentrate the entire energy into extremely small regions. Eventually different portions of bubble wall collide, with the energy being released in the form of particle production. Thermalization of this system can lead to very high temperatures. With a reasonably conservative set of parameters, at LHC, the temperature of the hot spot can reach as high as 3 GeV, and well above it with more optimistic parameters. Such a hot spot can leave signals like large P T partons, dileptons, and enhanced production of heavy quarks. We also briefly discuss a speculative possibility where the electroweak symmetry may get restored in the highly dense region resulting from the decay of the bubble wall via the phenomenon of non-thermal symmetry restoration (which is usually employed in models of pre-heating after inflation). If that could happen then the possibility may arise of observing sphaleron induced baryon number violation in relativistic heavy-ion collisions.
116924174
Search for new strange resonances in inclusive charged kaon spectra from p̄p annihilation at rest
Charged spectra from pp annihilations at rest have been measured using the PS183 spectrometer at LEAR. From these data, charged kaon spectra are produced using time‐of‐flight separation. The spectra show structures corresponding to annihilation into the K±K−+ and K*±K−+ channels. A search for structures indicating other resonances is discussed.
118620496
Observation of narrow lines in the spectra of charged mesons produced in antiproton-proton annihilation at rest
116328057
The KTeV Pure CsI Calorimeter
KTeV is currently building a state-of-the-art pure CsI electromagnetic calorimeter with a sophisticated digital readout. The CsI array is expected to have better than 1% resolution over a dynamic range of 2--64 GeV. The design of the CsI array is driven by the difficult physics goal of attempting to measure the CP violation parameter Re({epsilon}{prime}/{epsilon}) to 1 part in 10000 in a high-rate neutral beam environment. The physics requirements and their impact on the final design will be discussed.
123205836
The E760 lead-glass central calorimeter: design and initial test results
The central calorimeter in Fermilab experiment E760++ has been designed to measure the topology and energies of electrons and photons in the decay of charmonium formed in pp annihilation. The calorimeter is composed of 1280 lead-glass Cherenkov counters read out with photomultiplier tubes. This paper discusses design criteria for the calorimeter and describes how these criteria were met. Data from tests in low energy (10–84 MeV) and medium energy (1–4 GeV) beams are presented showing a spatial resolution of 9 mm, an energy resolution of (3.0 ± 0.3)%√E[GeV] + (1.5 ± 0.5)%, and an effective energy threshold below 10 MeV.
125459484
Status of the KTeV experiment at Fermilab