119423682
How big is the source that produces quark gluon plasma in heavy ion collisions
We study, for the first time, the spatial extension of the 
"source" that produces quark gluon plasma (QGP) in ultra relativistic heavy ion collisions. The longitudinal dimension is studied as a function of time as the system evolves. The source size is found to exhibit a novel non-classical feature.
121727752
Phase space description of the production of quark gluon plasma in heavy-ion collisions
A new source term is proposed to describe the production of quark gloun plasma in heavy-ion collisions.
10923413
Infrared renormalization-group flow for heavy-quark masses.
A short-distance heavy-quark mass depends on two parameters: the renormalization scale mu and a scale R controlling the absorption of infrared fluctuations. The radius for perturbative corrections that build up the mass beyond its pointlike definition in the pole scheme is approximately 1/R. Treating R as a variable gives a renormalization-group equation. R evolution improves the stability of conversion between short-distance mass schemes, allowing us to avoid large logs and the renormalon. R evolution can also be used to study IR renormalons without using bubble chains, yielding a convergent sum rule for the coefficient of the O(Lambda(QCD)) renormalon ambiguity of the pole mass.
62817139
R evolution: Improving perturbative QCD
Perturbative QCD results in the MS scheme can be dramatically improved by switching to a scheme that accounts for the dominant power law dependence on the factorization scale in the operator product expansion. We introduce the ''MSR scheme'' which achieves this in a Lorentz and gauge invariant way and has a very simple relation to MS. Results in MSR depend on a cutoff parameter R, in addition to the {mu} of MS. R variations can be used to independently estimate (i.) the size of power corrections, and (ii.) higher-order perturbative corrections (much like {mu} in MS). We give two examples at three-loop order, the ratio of mass splittings in the B*-B and D*-D systems, and the Ellis-Jaffe sum rule as a function of momentum transfer Q in deep inelastic scattering. Comparing to data, the perturbative MSR results work well even for Q{approx}1 GeV, and power corrections are reduced compared to MS.
119181326
Two-loop jet function and jet mass for top quarks
We compute the two-loop heavy-quark jet function in the heavy-quark limit. This is one of the key ingredients in next-to-next-to-leading order and next-to-next-to-leading-log order computations of the invariant mass distribution of top-jets at a future e{sup +}e{sup -} collider. The shape of the top-invariant mass distribution is affected by large logs which we compute at next-to-next-to-leading-log order. Exploiting the non-Abelian exponentiation theorem, a definition of the top jet mass is given which is transitive and whose renormalization group evolution is determined by the cusp-anomalous dimension to all orders in perturbation theory. Relations of the jet mass to the pole, MS, and 1S masses are presented at two-loop order.
119262820
Parton fragmentation within an identified jet at NNLL
The fragmentation of a light parton i to a jet containing a light energetic hadron h, where the momentum fraction of this hadron as well as the invariant mass of the jet is measured, is described by “fragmenting jet functions”. We calculate the oneloop matching coefficients $ {\mathcal{J}_{ij}} $ that relate the fragmenting jet functions $ \mathcal{G}_i^h $ to the standard, unpolarized fragmentation functions Dhj for quark and gluon jets. We perform this calculation using various IR regulators and show explicitly how the IR divergences cancel in the matching. We derive the relationship between the coefficients $ {\mathcal{J}_{ij}} $ and the quark and gluon jet functions. This provides a cross-check of our results. As an application we study the process e+e- → Xπ+ on the Υ(4S) resonance where we measure the momentum fraction of the π+ and restrict to the dijet limit by imposing a cut on thrust T. In our analysis we sum the logarithms of τ = 1-T in the cross section to next-to-next-to-leading-logarithmic accuracy (NNLL). We find that including contributions up to NNLL (or NLO) can have a large impact on extracting fragmentation functions from e+e- → dijet + h.
117335698
Effect of isospin dependent cross-section on nuclear stopping
Nuclear stopping in heavy ion collisions (HIC) has been studied by means of rapidity distribution and asymmetry of nucleon momentum distribution. It is an important quantity in determining the outcome of a reaction. Fen Fu {\it et al.,} \cite{2} calculate both the radial flow and the degree of nuclear stopping in Pb + Pb and Ni + Ni at 0.4, 0.8 and 1.2 GeV/neucleon. They found that the expansion velocity as well as the degree of nuclear stopping are higher in the heavier system at all energies.
119232111
Effect of isospin-dependent cross-section on fragment production in the collision of charge asymmetric nuclei
To understand the role of isospin effects on fragmentation due to the collisions of charge asymmetric nuclei, we have performed a complete systematical study using isospin-dependent quantum molecular dynamics model. Here simulations have been carried out for $^{124}{\rm X}_{n}+^{124}{\rm X}_{n}$, where n varies from 47 to 59 and for $^{40}{\rm Y}_{m}+^{40}{\rm Y}_{m}$, where m varies from 14 to 23. Our study shows that isospin-dependent cross-section shows its influence on fragmentation in the collision of neutron-rich nuclei.
117283830
Isospin effects on fragment production
To understand the isospin effects in nearly symmetric nuclear matter we performed a complete systematical theoretical study within an Isospin dependent Quantum Molecular Dynamical Model (IQMD) and using Minimum Spanning Tree (MST) algorithm. Simulations are carried out for the reactions $_{124}Sn^{50}+_{124}Sn^{50}$ and $_{107}Sn^{50}+_{124}Sn^{50}$. The collision geometry is varied from central to peripheral. We find that neutron rich colliding nuclei are better candidate to study the isospin effects
118299250
Intermediate Mass Fragment Production In Symmetric Collisions
We present a complete systematic theoretical study of multifragmentation and its associated phenomena in heavy ion collisions. This study is performed within an Isospin dependent Quantum Molecular Dynamical Model (IQMD) and using Minimum Spanning Tree (MST) algorithm. Simulations are carried out to study the different parameters like time evolution of multiplicity, mass distribution, impact parameter dependence and IMF's production dependence of projectile & target mass. The rise and fall in multiplicity of IMF's is observed. Results are compared with experimental data of ALADIN and are found to be in close agreement.