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STUDY OF VECTOR MESON fragmentation USING A BROKEN SU(3) MODEL

INTERNATIONAL JOURNAL OF MODERN PHYSICS A 2012年第19期27卷

作者： Indumathi, D. Saveetha, H. Inst Math Sci Madras 600113 Tamil Nadu India Univ Madras Dept Theoret Phys Madras 600025 Tamil Nadu India

Inclusive hadro-production in e(+) e(-) annihilation processes is examined to study the fragmentation process. A broken SU(3) model is used to determine the quark and gluon fragmentation functions of octet vector mesons, rho and K*, in a simple way with an SU(3) breaking parameter lambda. These are expressed in terms of just two light quark fragmentation functions, V (x, Q(2)) and gamma(x, Q(2)) and the gluon fragmentation function D-g(x, Q(2)). These functions are parametrized at the low input scale of Q(0)(2) = 1.5 GeV2, evolved through LO DGLAP evolution including charm and bottom flavor at appropriate thresholds, and fitted by comparison with data at the Z-pole. The model is extended with the introduction of a few additional parameters to include a study of singlet-octet mixing and hence omega and phi fragmentation. The model gives good fits to the available data for x greater than or similar to 0.01, where x is the scaled energy of the hadron. The model is then applied successfully to omega, phi production in pp collisions at the relativistic heavy ion collider, RHIC, these data form an important baseline for the study of Quark Gluon Plasma in heavy nucleus collisions at RHIC, and also in future at the LHC.

关键词： fragmentation functions vector mesons QCD evolution

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QCDNUM: Fast QCD evolution and convolution

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COMPUTER PHYSICS COMMUNICATIONS 2011年第2期182卷 490-532页

作者： Botje, M. Nikhef NL-1098 XG Amsterdam Netherlands

The QCDNUM program numerically solves the evolution equations for parton densities and fragmentation functions in perturbative QCD. Un-polarised parton densities can be evolved up to next-to-next-to-leading order in powers of the strong coupling constant, while polarised densities or fragmentation functions can be evolved up to next-to-leading order. Other types of evolution can be accessed by feeding alternative sets of evolution kernels into the program. A versatile convolution engine provides tools to compute parton luminosities, cross-sections in hadron-hadron scattering, and deep inelastic structure functions in the zero-mass scheme or in generalised mass schemes. Input to these calculations are either the QCDNUM evolved densities, or those read in from an external parton density repository. Included in the software distribution are packages to calculate zero-mass structure functions in un-polarised deep inelastic scattering, and heavy flavour contributions to these structure functions in the fixed flavour number scheme. Program summary Program title: QCDNUM version: 17.00 Catalogue identifier: AEHV_v1_0 Program summary URL: http://***/summaries/AEHV_v1_*** Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU Public Licence No. of lines in distributed program, including test data, etc.: 45 736 No. of bytes in distributed program, including test data, etc.: 911 569 Distribution format: *** Programming language: Fortran-77 Computer: All Operating system: All RAM: Typically 3 Mbytes Classification: 11.5 Nature of problem: Evolution of the strong coupling constant and parton densities, up to next-to-next-to-leading order in perturbative QCD. Computation of observable quantities by Mellin convolution of the evolved densities with partonic cross-sections. Solution method: Parametrisation of the parton densities as linear or quadratic splines on a discrete grid, and evolution of the spline c

关键词： 11.5 quantum chromodynamics Lattice gauge theory QCD evolution DGLAP evolution equations Parton densities fragmentation functions Structure functions

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Double hadron lepto-production in the current and target fragmentation regions

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PHYSICS LETTERS B 2011年第1期706卷 46-52页

作者： Anselmino, M. Barone, V. Kotzinian, A. Univ Turin Ist Nazl Fis Nucl Dipartimento Fis Teor Sez Torino I-10125 Turin Italy Univ Piemonte Orientale Ist Nazl Fis Nucl Di STA Grp Collegato Alessandria I-15121 Alessandria Italy Yerevan Phys Inst Yerevan 375036 Armenia

We study the inclusive production of two hadrons in deep inelastic processes, lN -> lh(1)h(2)X, with h(1) in the current fragmentation region (CFR) and h(2) in the target fragmentation region (TFR). Assuming a factorized scheme, the recently introduced polarized and transverse momentum dependent fracture functions couple to the transverse momentum dependent fragmentation functions. This allows the full exploration of the fracture functions for transversely polarized quarks. Some particular cases are considered. (C) 2011 Elsevier B.V. All rights reserved.

关键词： Semi-inclusive DIS Current fragmentation Target fragmentation Fracture functions fragmentation functions Polarization Transverse momentum

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SOME FUNDAMENTAL ISSUES IN EXCLUSIVE AND SEMI-INCLUSIVE REACTIONS

SOME FUNDAMENTAL ISSUES IN EXCLUSIVE AND SEMI-INCLUSIVE REAC...

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4th Workshop on Exclusive Reactions at High Momentum Transfer

作者： Thomas, A. W. Univ Adelaide Sch Chem & Phys CSSM Adelaide SA 5005 Australia

ISBN: (纸本)9789814329552

We describe some of the recent developments in testing the Standard Model, beginning with the tremendous progress that has been made concerning our theoretical understanding of strangeness in the proton (the analogue of the Lamb shift in QED). We also summarise the contribution of parity violation, from electron-proton to neutrino-nucleus scattering, in testing the evolution of the weak charge of the proton predicted by the Standard Model. Finally, we describe recent progress in the calculation of fragmentation functions, which may prove important in the exploration of new observables such as transversity.

关键词： Weak charge of the proton Standard Model tests parity violation electron scattering neutrino-nucleus interaction charge symmetry violation fragmentation functions

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Particle Production in ep Collisions at HERA

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Nuclear Physics B - Proceedings Supplements 2011年 219-220卷 74-77页

作者： Valkárová, Alice Institute of Particle and Nuclear Physics Faculty of Mathematics and Physics of Charles University 180 00 Praha 8 V Holešovičkách 2 Czech Republic

Charged particle spectra were measured in deep inelastic interactions at HERA in different kinematic regions of x and Q 2 with the emphasis to study parton dynamics beyond DGLAP evolution. The data collected at HERA w... 详细信息

Charged particle spectra were measured in deep inelastic interactions at HERA in different kinematic regions of x and Q ² with the emphasis to study parton dynamics beyond DGLAP evolution. The data collected at HERA were compared with measurements obtained in e ⁺e ^- annihilation and with Monte Carlo models. Scaled momentum distributions of strange hadrons were studied and compared with models and NLO QCD calculations. © 2011 Elsevier B.V.

关键词： Charged hadrons Ep interactions fragmentation functions Strange particles

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The role of spin in fragmentation production J/ψ(1S) and γ(1S)

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NUCLEAR PHYSICS A 2010年第1-2期848卷 218-229页

作者： Sepahvand, Reza Dadfar, Sareh Lorestan Univ Fac Sci Dept Phys Khorramabad *** Iran

In this work we calculate the process independent fragmentation functions for a heavy quark Q to fragment into vector Q (Q) over bar(S-3(1)) and pseudoscalar Q (Q) over bar(S-1(0)) heavy quarkonium to leading order perturbative QCD We investigate the role of the spin orientation of the initial and final heavy quarks on the fragmentation functions In the special case we calculate fragmentation functions by using average over spin of initial state heavy quark and sum over spin of final states The universal fragmentation probabilities for the c -> J/psi(1S) and b -> r(1s) are about 10(-4) and 10(-5) respectively Moreover the spin dependent observables such as V/(V + P) and V I P ratios are estimated (C) 2010 Elsevier B V All rights reserved

关键词： fragmentation functions Spin Heavy quarkonium

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QCD evolution of jets in the quark-gluon plasma

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NUCLEAR PHYSICS A 2008年第1期808卷 178-191页

作者： Domdey, S. Ingelman, G. Pirner, H. J. Rathsman, J. Stachel, J. Zapp, K. Uppsala Univ S-75121 Uppsala Sweden Heidelberg Univ Inst Theoret Phys D-6900 Heidelberg Germany Heidelberg Univ Inst Phys DE-69120 Heidelberg Germany

The quark-gluon plasma (QGP) can be explored in relativistic heavy ion collisions by the jet quenching signature, i.e., by the energy loss of a high energy quark or gluon traversing the plasma. We introduce a novel QCD evolution formalism in the leading logarithm approximation, where normal parton radiation is interleaved with scattering on the plasma gluons occuring at a similar time scale. The idea is elaborated in two approaches. One extends the DGLAP evolution equations for fragmentation functions to include scatterings in the medium, which facilitates numerical solutions for comparison with data and provides a basis for a Monte Carlo implementation. The other approach is more general by including also the transverse momentum dependence of the jet evolution, which allows a separation of the scales also for the scattering term and provides a basis for analytical investigations. The two approaches are shown to be related and give the same characteristic softening of the jet depending on the temperature of the plasma. A substantial effect is found at the RHIC energy and is further enhanced at LHC. Systematic studies of data on the energy loss could, therefore, demonstrate the existence of the QGP and probe its properties. (C) 2008 Elsevier B.V. All rights reserved.

关键词： jet quenching fragmentation functions collisional energy loss

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Parton shower evolution in a 3D hydrodynamical medium

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Physical Review C 2008年第3期78卷 034908-034908页

作者： Thorsten Renk []Department of Physics University of Jyv?skyl? P. O. Box 35 FI-40014 Finland and Helsinki Institute of Physics University of Helsinki P. O. Box 64 FI-00014 Finland

We present a Monte Carlo simulation of the perturbative quantum chromodynamics shower developing after a hard process embedded in a heavy-ion collision. The main assumption is that the cascade of branching partons traverses a medium that (consistent with standard radiative energy loss pictures) is characterized by a local transport coefficient q^ that measures the virtuality per unit length transferred to a parton that propagates in this medium. This increase in parton virtuality alters the development of the shower and in essence leads to extra induced radiation and hence a softening of the momentum distribution in the shower. After hadronization, this leads to the concept of a medium-modified fragmentation function. On the level of observables, this is manifest as the suppression of high-transverse-momentum (PT) hadron spectra. We simulate the soft medium created in heavy-ion collisions by a 3D hydrodynamical evolution and average the medium-modified fragmentation function over this evolution to compare with data on single inclusive hadron suppression and extract the q^ that characterizes the medium. Finally, we discuss possible uncertainties of the model formulation and argue that the data in a soft momentum show evidence of qualitatively different physics that presumably cannot be described by a medium-modified parton shower.

关键词： INELASTIC EP 03SCATTERING RADIATIVE ENERGY-LOSS HEAVY-ION COLLISIONS PLUS AU COLLISIONS fragmentation functions PERTURBATION-THEORY MACH CONES QCD DISTRIBUTIONS STAR quantum chromodynamics ION COLLISIONS Three Dimensions energy losses perturbation theory Momentum distribution HADRONS PARTONS Monte Carlo technique

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Higher twist jet broadening and classical propagation

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Physical Review C 2008年第5期77卷 054903-054903页

作者： A. Majumder B. Müller Department of Physics Duke University Durham North Carolina 27708 USA

The transverse broadening of jets produced in deep-inelastic scattering (DIS) off a large nucleus is studied in the collinear limit. A class of medium enhanced higher twist corrections are resummed to calculate the transverse momentum distribution of the produced collinear jet. In contrast to previous approaches, resummation of the leading length enhanced higher twist corrections is shown to lead to a two-dimensional diffusion equation for the transverse momentum of the propagating jet. Results for the average transverse momentum obtained from this approach are then compared to the broadening expected from a classical Langevin analysis for the propagation of the jet under the action of the fluctuating color Lorentz force inside the nucleons. The set of approximations that lead to identical results from the two approaches are outlined. The relationship between the momentum diffusion constant D and the transport coefficient q^ is explicitly derived.

关键词： RADIATIVE ENERGY-LOSS QUARK-GLUON PLASMA MULTIPLE PARTON SCATTERING HADRON-HADRON CORRELATIONS HOT GAUGE-THEORIES NUCLEAR ENVIRONMENT fragmentation functions TRANSVERSE-MOMENTUM POWER CORRECTIONS MATTER

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Difficulty of extracting energy loss probability distributions from RAA

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Physical Review C 2008年第1期77卷 017901-017901页

作者： Thorsten Renk Univ Jyvaskyla Dept Phys FI-40014 Jyvaskyla Finland

The nuclear suppression of high transverse momentum PT hadrons is one of the most striking findings in heavy-ion collision experiments. It has long been recognized that the suppression can be theoretically described by folding the primary parton spectrum with an energy loss probability distribution which is suitably averaged over the collision geometry. However, an interesting problem is to what degree the procedure can be inverted, i.e., given a measurement of the suppression factor RAA with arbitrary precision, can the probability distribution of energy loss be extracted in a model-independent way? In this Brief Report, we present a conceptual study of the inversion problem for LHC energies and demonstrate that a measurement of RAA alone is insufficient to determine the distribution, other observables such as γ-hadron correlations must be taken into account.

关键词： fragmentation functions NUCLEI QUARKS QCD

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