Mahnaz Q. Haseeb

Analysis of Δ0(1232) production in collisions of protons with carbon nuclei at 4.2 GeV/c

The production of Δ0(1232)-resonances in p+12C collisions at 4.2 GeV/c was analyzed with 4π acceptance. The mass distribution of Δ0(1232) was reconstructed using an angular criterion. The fraction of charged π−-mesons coming from Δ0(1232) decay was estimated and compared to those obtained in earlier works. The momentum, transverse momentum, kinetic energy, and rapidity distributions as well as invariant cross sections of Δ0(1232)-resonances were reconstructed in the laboratory frame. The mean kinematical characteristics of the reconstructed Δ0(1232) were compared to those of participant protons in experiment and within some of the models. The freeze-out temperature of Δ0(1232) estimated in the present analysis was compared with those obtained using different methods for Δ(1232) produced with other sets of colliding nuclei at various incident energies. The relative number of nucleons excited to Δ0 (1232) at freeze-out conditions in p+12C collisions was estimated.

Comparison of characteristics of Δ0(1232) produced in p12C and d12C collisions at 4.2 A GeV/c

Reconstructed momentum, transverse momentum, kinetic energy, rapidity, and emission angle distributions along with their mean values were compared for Δ0(1232) resonances produced in p12C and d12C collisions at 4.2 A GeV/c. Mean momentum, transverse momentum, and rapidity of protons and negative pions coming from Δ0(1232) decay were extracted and compared with the corresponding mean values for protons and π− mesons in experiment and the relevant model calculations.

Second order thermal corrections to electron wavefunction

Abstract Second order perturbative corrections to electron wavefunction are calculated here, for the first time, at generalized temperature. Calculations of electron self energy are important for the renormalizability of electron mass and wavefunction in QED through order by order cancellation of singularities up to order α 2 . Cancellation of temperature dependent singularities is demonstrated by incorporating the results of both orders of integration between cold and hot loops. For finite terms, we have rewritten second order thermal corrections as well, in a concise form, to calculate wavefunction renormalization constant. Our results are in a form that includes intermediate temperatures T ∼ m (where m is electron mass) while limits of high temperature T ≫ m and low temperature T ≪ m are also retrievable from them. A comparison with the existing results is included as well. The renormalized mass and wavefunction are used to calculate particle processes in extremely hot systems such as stellar cores and primordial nucleosynthesis during very early universe. An application to the latter case is also discussed.

Gluon polarization at finite temperature and density

Abstract We calculate the gluon self-mass and the QCD coupling constant at finite temperature in the real-time formalism up to the first loop level. The expressions are derived in a form that is valid for all temperature ranges in QCD. Using these results the dynamically generated mass of gluons and the plasma screening length can be determined from their effective potential.

On spectral temperatures of negative pions produced in d 12 C, 4 He 12 C, and 12 C 12 C collisions at 4.2 A GeV/ c

The experimental transverse momentum distributions of negative pions produced in d12C, 4He12C, and 12C12C collisions at 4.2 A GeV/c were analyzed in the framework of Hagedorn Thermodynamic Model. The spectral temperatures of π− mesons as well as their relative contributions to the total multiplicity of π− mesons were extracted from fitting the pt spectra by two-temperature Hagedorn function. The results were compared systematically with the earlier results obtained from analysis of non-invariant center-of-mass energy spectra of negative pions produced in the analyzed collisions.

SECOND-ORDER CORRECTIONS TO THE MAGNETIC MOMENT OF ELECTRON AT FINITE TEMPERATURE

Magnetic moment of electron at finite temperature is directly related to the modified electron mass in the background heat bath. Magnetic moment of electron gets modified at finite temperature also, when it couples with the magnetic field, through its temperature-dependent physical mass. We show that the second-order corrections to the magnetic moment of electron is a complicated function of temperature. We calculate the self-mass induced thermal contributions to the magnetic moment of electron, up to the two-loop level, for temperatures valid around the era of primordial nucleosynthesis. A comparison of thermal behavior of the magnetic moment is also quantitatively studied in detail, around the temperatures below and above the nucleosynthesis temperature.

RAPIDITY AND ANGULAR DEPENDENCES OF SPECTRAL TEMPERATURES OF NEGATIVE PIONS PRODUCED IN 12C12C COLLISIONS AT 4.2A GeV/c

The average spectral temperatures of negative pions in 12C12C collisions at 4.2A GeV/c were extracted from transverse momentum as well as scaled center-of-mass kinetic energy distributions for different intervals of rapidity and emission angle of π- in the center-of-mass system (cms) of 12C12C collisions. The temperatures extracted from experimental spectra of negative pions were compared systematically with the corresponding temperatures deduced from spectra of π- calculated using Modified FRITIOF model. The dependence of the average spectral temperatures of negative pions on the rapidity and emission angle of π- in the cms of 12C12C collisions at 4.2A GeV/c was analyzed.

Second Order Corrections to QED Coupling at Low Temperature

We calculate the second-order corrections to vacuum polarization tensor of photons at low temperatures, i.e. T ≪ 1010K(T ≪ me). The thermal contributions to the QED coupling constant are evaluated at temperatures below the electron mass that is T < me. Renormalization of QED at these temperatures has explicitly been checked. The electromagnetic properties of such a thermal medium are modified. Parameters like electric permittivity and magnetic permeability of such a medium are no more constant and become functions of temperature.

Two loop low temperature corrections to electron self energy

We recalculate the two loop corrections in the background heat bath using real time formalism. The procedure of the integrations of loop momenta with dependence on finite temperature before the momenta without it has been followed. We determine the mass and wavefunction renormalization constants in the low temperature limit of QED, for the first time with this preferred order of integrations. The correction to electron mass and spinors in this limit is important in the early universe at the time of primordial nucleosynthesis as well as in astrophysics.

On centrality and rapidity dependences of transverse momentum spectra of negative pions in 12C + 12C collisions at 4.2 GeV/c per nucleon

The dependences of the experimental transverse momentum spectra of the negative pions, produced in minimum bias 12C + 12C collisions at a momentum of 4.2A GeV/c, on the collision centrality and the pion rapidity range were studied. To analyze quantitatively the change in the pt spectra of π- mesons with the changes of collision centrality and pion rapidity range, the extracted pt spectra were fitted by Hagedorn, Boltzmann, Simple Exponential and Gaussian functions. The values of the extracted spectral temperatures T1 and T2 were consistently larger for the pt spectra of π- mesons coming from midrapidity range as compared to those of the negative pions generated in the target and projectile fragmentation regions. The spectral temperatures T1 and T2 extracted from fitting the pt spectra of π- mesons in range pt = 0.1–1.2 GeV/c practically coincided with each other in peripheral, semicentral and central 12C + 12C collision events, and thus did not show any collision centrality dependence. However, the values...