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.
14754036
The R-evolution of QCD matrix elements
Perturbation series in QCD are generally asymptotic and suffer from so-called infrared renormalon ambiguities. In the context of the standard operator product expansion in MS-bar these ambiguities are compensated by matrix elements of higher dimension operators, but the procedure can be difficult to control due to large numerical cancellations. Explicit subtractions for matrix elements and coefficients, depending on a subtraction scale R, can avoid this problem. The appropriate choice for R in the Wilson coefficients can widely vary for different processes. In this talk we discuss renormalization group evolution with the scale R, and show that it sums large logarithms in the difference of processes with widely different R's. We also show that the solution of the R-evolution equations can be used to recover the all order asymptotic form of the singularities in the Borel transform of the perturbative series. For the normalization of these singularities we obtain a quickly converging sum rule that only needs the known perturbative coefficients as an input. This sum rule can be used as a novel test for renormalon ambiguities without replying on the large-beta_0 approximation.
118154866
Penguin Loops for Nonleptonic B-Decays in the Standard Model: Is there a Penguin Puzzle?
We compute standard model penguin amplitudes in nonleptonic B-decays to light charmless mesons using tree amplitude data to fix hadronic parameters. The leading calculation is carried out for the alphas(mb) penguin contributions from charm quark, up quark, and magnetic penguin loops in the NDR and HV renormalization schemes. Power suppressed penguins that are proportional to the chiral condensate are also computed using a new factorization formula for these terms, which is derived working to all orders in alphas(sqrt{mb\Lambda}). We demonstrate using SCET1 that this formula exhibits only small perturbative phases and does not have endpoint singularities. Due to our use of data to fix hadronic parameters we obtain significantly more accurate predictions for the short-distance standard model penguin amplitudes than have been found in the past. Analyzing data in B-> pi pi, B->K pi, and B->rho rho for the penguin amplitudes we find that standard model short-distance imaginary parts are an order of magnitude smaller than current measurements, while real parts are up to a factor of two smaller with the correct sign. This difference is most likely a consequence of long-distance charm contributions or new physics. Constraints on the type of new physics that could help explain the data are derived, and used to show that current data favors sizeable long-distance strong phases.
12390720
A formalism for the systematic treatment of rapidity logarithms in Quantum Field Theory
A bstractMany observables in QCD rely upon the resummation of perturbation theory to retain predictive power. Resummation follows after one factorizes the cross section into the relevant modes. The class of observables which are sensitive to soft recoil effects are particularly challenging to factorize and resum since they involve rapidity logarithms. Such observables include: transverse momentum distributions at pT much less then the high energy scattering scale, jet broadening, exclusive hadroproduction and decay, as well as the Sudakov form factor. In this paper we will present a formalism which allows one to factorize and resum the perturbative series for such observables in a systematic fashion through the notion of a “rapidity renormalization group”. That is, a Collin-Soper like equation is realized as a renormalization group equation, but has a more universal applicability to observables beyond the traditional transverse momentum dependent parton distribution functions (TMDPDFs) and the Sudakov form factor. This formalism has the feature that it allows one to track the (non-standard) scheme dependence which is inherent in any sce- nario where one performs a resummation of rapidity divergences. We present a pedagogical introduction to the formalism by applying it to the well-known massive Sudakov form fac- tor. The formalism is then used to study observables of current interest. A factorization theorem for the transverse momentum distribution of Higgs production is presented along with the result for the resummed cross section at NLL. Our formalism allows one to define gauge invariant TMDPDFs which are independent of both the hard scattering amplitude and the soft function, i.e. they are universal. We present details of the factorization and re- summation of the jet broadening cross section including a renormalization in p⊥ space. We furthermore show how to regulate and renormalize exclusive processes which are plagued by endpoint singularities in such a way as to allow for a consistent resummation.
116231150
R-evolving QCD matrix elements
118375178
Fragmentation with a Cut on Thrust: Predictions for B-factories
When high-energy single-hadron production takes place inside an identified jet, there are important correlations between the fragmentation and phase-space cuts. For example, when one-hadron yields are measured in on-resonance B-factory data, a cut on the thrust event shape T is required to remove the large b-quark contribution. This leads to a dijet final-state restriction for the light-quark fragmentation process. Here, we complete our analysis of unpolarized fragmentation of (light) quarks and gluons to a light hadron h with energy fraction z in e+e−→dijet+h at the center-of-mass energy Q=10.58  GeV. In addition to the next-to-next-to-leading order resummation of the logarithms of 1−T, we include the next-to-leading order nonsingular
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