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Universality of Unintegrated Gluon Distributions at small x

Description: We systematically study dijet production in various processes in the small-x limit and establish an effective kt-factorization for hard processes in a system with dilute probes scattering on a dense target. In the large-Nc limit, the unintegrated gluon distributions involved in different processes are shown to be related to two widely proposed ones: the Weizsacker-Williams gluon distribution and the dipole gluon distribution.
Date: January 4, 2011
Creator: Dominguez, Fabio; Marquet, Cyrille; Xiao, Bowen & Yuan, Feng
Partner: UNT Libraries Government Documents Department

Longitudinal double-spin asymmetry for inclusive jet production in vec p + vec p collisions at sqrt s = 200 GeV

Description: We report a new STAR measurement of the longitudinal double-spin asymmetry A{sub LL} for inclusive jet production at mid-rapidity in polarized p + p collisions at a center-of-mass energy of {radical}s = 200 GeV. The data, which cover jet transverse momenta 5 < p{sub T} < 30 GeV/c, are substantially more precise than previous measurements. They provide significant new constraints on the gluon spin contribution to the nucleon spin through the comparison to predictions derived from one global fit of polarized deep-inelastic scattering measurements.
Date: October 7, 2007
Creator: Coll, STAR
Partner: UNT Libraries Government Documents Department

Naturalness and Higgs Decays in the MSSM with a Singlet

Description: The simplest extension of the supersymmetric standard model--the addition of one singlet superfield--can have a profound impact on the Higgs and its decays. We perform a general operator analysis of this scenario, focusing on the phenomenologically distinct scenarios that can arise, and not restricting the scope to the narrow framework of the NMSSM. We reexamine decays to four b quarks and four {tau}'s, finding that they are still generally viable, but at the edge of LEP limits. We find a broad set of Higgs decay modes, some new, including those with four gluon final states, as well as more general six and eight parton final states. We find the phenomenology of these scenarios is dramatically impacted by operators typically ignored, specifically those arising from D-terms in the hidden sector, and those arising from weak-scale colored fields. In addition to sensitivity of m{sub z}, there are potential tunings of other aspects of the spectrum. In spite of this, these models can be very natural, with light stops and a Higgs as light as 82 GeV. These scenarios motivate further analyses of LEP data as well as studies of the detection capabilities of future colliders to the new decay channels presented.
Date: November 21, 2005
Creator: Chang, Spencer; Fox, Patrick J. & Weiner, Neal
Partner: UNT Libraries Government Documents Department

EXPLORING THE POLARIZATION OF GLUONS IN THE NUCLEON.

Description: We give an overview of the current status of investigations of the polarization of gluons in the nucleon. We describe some of the physics of the spin-dependent gluon parton distribution and its phenomenology in high-energy polarized hadronic scattering. We also review the recent experimental results.
Date: October 22, 2007
Creator: STRATMANN,M. & VOGELSANG,W.
Partner: UNT Libraries Government Documents Department

Gluon density in nuclei

Description: In this talk we present our detailed study (theory and numbers) on the shadowing corrections to the gluon structure functions for nuclei. Starting from rather controversial information on the nucleon structure function which is originated by the recent HERA data, we develop the Glauber approach for the gluon density in a nucleus based on Mueller formula and estimate the value of the shadowing corrections in this case. Then we calculate the first corrections to the Glauber approach and show that these corrections are big. Based on this practical observation we suggest the new evolution equation which takes into account the shadowing corrections and solve it. We hope to convince you that the new evolution equation gives a good theoretical tool to treat the shadowing corrections for the gluons density in a nucleus and, therefore, it is able to provide the theoretically reliable initial conditions for the time evolution of the nucleus-nucleus cascade. The initial conditions should be fixed both theoretically and phenomenologically before to attack such complicated problems as the mixture of hard and soft processes in nucleus-nucleus interactions at high energy or the theoretically reliable approach to hadron or/and parton cascades for high energy nucleus-nucleus interaction. 35 refs., 24 figs., 1 tab.
Date: October 1996
Creator: Ayala, A. L.; Ducati, M. B. G. & Levin, E. M.
Partner: UNT Libraries Government Documents Department

Power corrections, renormalons and resummation

Description: I briefly review three topics of recent interest concerning power corrections, renormalons and Sudakov resummation: (a) 1/Q corrections to event shape observables in e(+)e(-) annihilation, (b) power corrections in Drell-Yan production and (c) factorial divergences that arise in resummation of large infrared (Sudakov) logarithms in moment or `real` space.
Date: August 1, 1996
Creator: Beneke, M.
Partner: UNT Libraries Government Documents Department

Strings and supersymmetry as tools for perturbative QCD

Description: We review techniques simplifying the analytic calculation of one-loop QCD amplitudes with many external legs, for use in next-to-leading-order corrections to multi-jet processes. We explain how a supersymmetry-inspired organization works well in conjunction with other tools, namely the color and helicity decompositions of amplitudes, and the constraints imposed by perturbative unitarity and collinear singularities. String theory seems most useful as a heuristic guide. Using these techniques, the complete set of one-loop five-parton QCD amplitudes, as well as certain sequences of special helicity amplitudes with an arbitrary number of external gluons, have been obtained.
Date: July 1, 1995
Creator: Dixon, L.
Partner: UNT Libraries Government Documents Department

Study of the uncertainty of the gluon distribution

Description: The uncertainty in the calculation of many important new processes at the Tevatron and LHC is dominated by that concerning the gluon distribution function. We investigate the uncertainty in the gluon distribution of the proton by systematically varying the gluon parameters in the global QCD analysis of parton distributions. The results depend critically on the parton momentum fraction x and the QCD scale Q{sup 2}. The uncertainties are presented for integrated gluon-gluon and gluon-quark luminosities for both the Tevatron and LHC as a function of {radical}{tau}={radical}x{sub 1}x{sub 2}={radical}{cflx s}/s, the most relevant quantity for new particle production. The uncertainties are reasonably small, except for large x.
Date: July 1, 1998
Creator: Huston, J., FERMI
Partner: UNT Libraries Government Documents Department

Hadron mass scaling in Regge phenomenology

Description: The authors show that Regge phenomenology is consistent with the only scaling law for the hadron masses, M{sup *}/M = ({alpha}{prime}/{alpha}{prime}{sup *}){sup 1/2}, where asterisk indicates a finite-temperature quantity. Phenomenological models further suggest the following expression of the above scaling in terms of the temperature-dependent gluon condensate: M{sup *}/M = ({alpha}{prime}/{alpha}{prime}{sup *}){sup 1/2} = (<G{sub {mu}{nu}}{sup {alpha}}>{sup *}/<G{sup {alpha}{mu}{nu}}>){sup 1/4}.
Date: December 1998
Creator: Burakovsky, L.
Partner: UNT Libraries Government Documents Department

THE FIRST FERMI IN A HIGH ENERGY NUCLEAR COLLISION.

Description: At very high energies, weak coupling, non-perturbative methods can be used to study classical gluon production in nuclear collisions. One observes in numerical simulations that after an initial formation time, the produced partons are on shell, and their subsequent evolution can be studied using transport theory. At the initial formation time, a simple non-perturbative relation exists between the energy and number densities of the produced partons, and a scale determined by the saturated parton density in the nucleus.
Date: August 9, 1999
Creator: KRASNITZ,A.
Partner: UNT Libraries Government Documents Department

Next to leading order three jet production at hadron colliders

Description: I present results from a next-to-leading order event generator of purely gluonic jet production. This calculation is the first step in the construction of a full next-to-leading order calculation of three jet production at hadron colliders. Several jet algorithms commonly used in experiments are implemented and their numerical stability is investigated. A numerical instability is found in the iterative cone algorithm which makes it inappropriate for use in fixed order calculations beyond leading order.
Date: May 1, 1997
Creator: Kilgore, W.B.
Partner: UNT Libraries Government Documents Department

A systematic study of J/psi suppression in cold nuclear matter

Description: Understanding the effects of cold nuclear matter on J/psi production is a key requirement in order to interpret the J/psi suppression reported in heavy-ion collisions. Based on a Glauber model, the J/psi-nucleon inelastic cross section is determined from a statistical analysis of J/psi world data on nuclear targets. The global fit of all data gives sigmaJ/psiN = 3.4 +/- 0.2 mb, significantly smaller than previous estimates, yet the chi2 of the fit is pretty large, chi2/ndf = 1.5. A similar value, sigmaJ/psiN = 3.5 +/- 0.2 +/- 1.7 mb, is obtained when the De Florian-Sassot modifications of the nuclear parton densities are included in the analysis, although we emphasize that the present uncertainties on gluon (anti)shadowing do not allow for a precise determination of sigmaJ/psiN. Finally, the possible energy dependence of the J/psi-nucleon inelastic cross section is investigated within this framework. No significant energy dependence of the J/psi-N interaction is observed.
Date: April 5, 2008
Creator: Arleo, Francois & Tram, Vi-Nham
Partner: UNT Libraries Government Documents Department

Unraveling duality violations in hadronic tau decays

Description: There are some indications from recent determinations of the strong coupling constant alpha_s and the gluon condensate that the Operator Product Expansion may not be accurate enough to describe non-perturbative effects in hadronic tau decays. This breakdown of the Operator Product Expansion is usually referred to as being due to"Duality Violations." With the help of a physically motivated model, we investigate these duality violations. Based on this model, we argue how they may introduce a non-negligible systematic error in the current analysis, which employs finite-energy sum rules with pinched weights. In particular, this systematic effect might affect the precision determination of alpha_s from tau decays. With a view to a possible future application to real data, we present an alternative method for determining the OPE coefficients that might help estimating, and possibly even reducing, this systematic error.
Date: March 3, 2008
Creator: Cata, Oscar; Cata, Oscar; Golterman, Maarten & Peris, Santiago
Partner: UNT Libraries Government Documents Department

Longitudinal Double Spin Asymmetry in Inclusive Jet Production atSTAR

Description: This contribution reports on the first measurement of the longitudinal double-spin asymmetry A{sub LL} for the inclusive production of jets in polarized proton-proton collisions at {radical}s = 200 GeV. The data were collected with STAR at RHIC in the years 2003 and 2004, and correspond to a sampled integrated luminosity of 0.3 pb{sup -1} with beam polarizations up to 45%. The results on A{sub LL} cover jet transverse momenta 5 < p{sub T} < 17 GeV/c and agree with perturbative QCD evaluations based on deep-inelastic scattering parametrizations for the gluon polarization in the proton. The results disfavor large positive gluon polarization in the polarized proton.
Date: August 15, 2006
Creator: Kowalik, Katarzyna & Collaboration, STAR
Partner: UNT Libraries Government Documents Department

Longitudinal double-spin asymmetry and cross section for inclusivejet production in polarized proton collisions at sqrt(s) = 200 GeV

Description: We report a measurement of the longitudinal double-spinasymmetry A_LL and the differential cross section for inclusivemidrapidity jet production in polarized proton collisions at sqrt(s)=200GeV. The cross section data cover transverse momenta 5<pT<50GeV/c and agree with next-to-leading order perturbative QCD evaluations.The A_LL data cover 5<pT<17 GeV/c and disfavor at 98 percentC.L. maximal positive gluon polarization in the polarizednucleon.
Date: August 10, 2006
Creator: Abelev, B.I.; Adams, J.; Aggarwal, M.M.; Ahammed, Z.; Amonett,J.; Anderson, B.D. et al.
Partner: UNT Libraries Government Documents Department

Dilepton Production from Collisions of Polarized Spin 1/2 Hadrons. 2. Parton-model predictions

Description: Parton-model predictions for lepton-pair production from polarized spin-1/2 particles are considered within the context of a formalism explained in a companion paper. The polarization effects in the quantum-chromodynamic 2 {yields} 2 subprocesses which contribute to lepton-pair production are found to be quite simple. Following the work of Ralston and Soper, polarized distribution functions are defined for gluons as well as quarks. Finally, a detailed discussion of polarization and the hard-scattering formalism is presented for the two cases of intrinsic parton transverse momentum allowed or forbidden.
Date: June 1, 1980
Creator: Donohue, J.T.; U., /Argonne /Bordeaux; Gottlieb, Steven A. & /Argonne
Partner: UNT Libraries Government Documents Department

The glasma initial state and JIMWLK factorization

Description: We review recent work on understanding the next to leading order corrections to the classical fields that dominate the initial stages of a heavy ion collision. We have recently shown that the leading ln 1/x divergences of these corrections to gluon multiplicities can be factorized into the JIMWLK evolution of the color charge density distributions.
Date: August 26, 2008
Creator: Gelis,F.; Lappi, T. & Venugopalan, R.
Partner: UNT Libraries Government Documents Department

kt-factorization for Hard Processes in Nuclei

Description: Two widely proposed kt-dependent gluon distributions in the small-x saturation regime are investigated using two particle back-to-back correlations in high energy scattering processes. The Weizsacker-Williams gluon distribution, interpreted as the number density of gluon inside the nucleus, is studied in the quark-antiquark jet correlation in deep inelastic scattering. On the other hand, the unintegrated gluon distribution, defined as the Fourier transform of the color-dipole cross section, is probed in the direct photon-jet correlation in pA collisions. Dijet-correlation in pA collisions depends on both gluon distributions through combination and convolution in the large Nc limit. We calculate these processes in two approaches: the transverse momentum dependent factorization approach and the color-dipole/color glass condensate formalism, and they agree with each other completely.
Date: September 13, 2010
Creator: Dominguez, Fabio; Xiao, Bo-Wen & Yuan, Feng
Partner: UNT Libraries Government Documents Department

Perturbative Gluon Exchange in a Covariant Quark Model of the Pion

Description: A covariant pion wave function, which reproduces the low energy data, is used to calculate the perturbative gluon exchange contributions to the pion charge form factor. It is found that the perturbative process dominates at q > 3.5 GeV/c. The dependence on the quark mass and the asymptotic behavior of the form factor are explicitly displayed.
Date: September 1, 1990
Creator: Gross, Franz & Ito, Hiroshi
Partner: UNT Libraries Government Documents Department

Collins Asymmetry at Hadron Colliders

Description: We study the Collins effect in the azimuthal asymmetricdistribution of hadrons inside a high energy jet in the single transversepolarized proton proton scattering. From the detailed analysis ofone-gluon and two-gluon exchange diagrams contributions, the Collinsfunction is found the same as that in the semi-inclusive deep inelasticscattering and e+e- annihilations. The eikonal propagators in thesediagrams do not contribute to the phase needed for the Collins-typesingle spin asymmetry, and the universality is derived as a result of theWard identity. We argue that this conclusion depends on the momentum flowof the exchanged gluon and the kinematic constraints in the fragmentationprocess, and is generic and model-independent.
Date: January 17, 2008
Creator: Yuan, Feng
Partner: UNT Libraries Government Documents Department

Exploration of deeply virtual Compton scattering on the neutron in the Hall A of Jefferson Laboratory

Description: Generalized Parton Distributions (GPDs) are universal functions which provide a comprehensive description of hadron properties in terms of quarks and gluons. Deeply Virtual Compton Scattering (DVCS) is the simplest hard exclusive process involving GPDs. In particular, the DVCS on the neutron is mostly sensitive to E, the less constrained GPD, wich allows to access to the quark angular momentum. The first dedicated DVCS experiment on the neutron ran in the Hall A of Jefferson Lab in fall 2004. The high luminosity of the experiment and the resulting background rate recquired specific devices which are decribed in this document. The analysis methods and the experiment results, leading to preliminary constraints on the GPD E, are presented.
Date: December 8, 2006
Creator: Mazouz, Malek
Partner: UNT Libraries Government Documents Department

NLO evolution of color dipoles

Description: The small-x deep inelastic scattering in the saturation region is governed by the non-linear evolution of Wilson-lines operators. In the leading logarithmic approximation it is given by the BK equation for the evolution of color dipoles. In the next-to-leaing order the BK equation gets contributions from quark and gluon loops as well as from the tree gluon diagrams with quadratic and cubic nonlinearities. We calculate the gluon contribution to small-x evolution of Wilson lines (the quark part was obtained earlier).
Date: January 1, 2008
Creator: Balitsky, Ian & Chirilli, Giovanni
Partner: UNT Libraries Government Documents Department

Measurement of D* Mesons in Jets from p + p Collisions at sqrt s = 200 GeV

Description: We report the measurement of charged D* mesons in inclusive jets produced in proton-proton collisions at a center of mass energy {radical}s = 200 GeV with the STAR experiment at RHIC. For D* mesons with fractional momenta 0.2 &lt; z &lt; 0.5 in inclusive jets with 11.5 GeV mean transverse energy, the production rate is found to be N(D*{sup +} + D*{sup -})/N(jet) = 0.015 {+-} 0.008(stat) {+-} 0.007(sys). This rate is consistent with perturbative QCD evaluation of gluon splitting into a pair of charm quarks and subsequent hadronization.
Date: May 16, 2009
Creator: Coll, STAR
Partner: UNT Libraries Government Documents Department