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Snowmass 2001: Jet energy flow project

Description: Conventional cone jet algorithms arose from heuristic considerations of LO hard scattering coupled to independent showering. These algorithms implicitly assume that the final states of individual events can be mapped onto a unique set of jets that are in turn associated with a unique set of underlying hard scattering partons. Thus each final state hadron is assigned to a unique underlying parton. The Jet Energy Flow (JEF) analysis described here does not make such assumptions. The final states of individual events are instead described in terms of flow distributions of hadronic energy. Quantities of physical interest are constructed from the energy flow distribution summed over all events. The resulting analysis is less sensitive to higher order perturbative corrections and the impact of showering and hadronization than the standard cone algorithms.
Date: December 5, 2002
Creator: al., C. F. Berger et
Partner: UNT Libraries Government Documents Department

Off-forward parton distribution

Description: Recent developments in studying off-forward parton distributions are discussed. In this talk, the author discusses the recent developments in studying the off-forward parton distributions (OFPD`s). He has written a topical review article on the subject, which will soon be published in Journal of Physics G. The interested audience can consult that article for details. His talk consists of three parts: definition of the new distributions, their physical significance, and experimental measurements.
Date: December 1, 1998
Creator: Ji, X.
Partner: UNT Libraries Government Documents Department

Evolution and models for skewed parton distribution

Description: The authors discuss the structure of the ''forward visible'' (FW) parts of double and skewed distributions related to usual distributions through reduction relations. They use factorized models for double distributions (DDs) {tilde f}(x,{alpha}) in which one factor coincides with the usual (forward) parton distribution and another specifies the profile characterizing the spread of the longitudinal momentum transfer. The model DDs are used to construct skewed parton distributions (SPDs). For small skewedness, the FW parts of SPDs H ({tilde x},{xi}) can be obtained by averaging forward parton densities f({tilde x}-{xi}{alpha}) with the weight {rho}({alpha}) coinciding with the profile function of the double distribution {tilde f}(x, {alpha}) at small x. They show that if the x{sup n} moments {tilde f}{sub n}({alpha}) of DDs have the asymptotic (1-{alpha}{sup 2}){sup n+1} profile, then the {alpha}-profile of {tilde f}(x,{alpha}) for small x is completely determined by small-x behavior of the usual parton distribution. They demonstrate that, for small {xi}, the model with asymptotic profiles for {tilde f}{sub n}({alpha}) is equivalent to that proposed recently by Shuvaev et al., in which the Gegenbauer moments of SPDs do not depend on {xi}. They perform a numerical investigation of the evolution patterns of SPDs and give interpretation of the results of these studies within the formalism of double distributions.
Date: May 17, 1999
Creator: Musatov, I.C. & Radyushkin, A.V.
Partner: UNT Libraries Government Documents Department


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

Shadowing and absorption effects on J/psi production in dA collisions

Description: The authors study medium modifications of J/{psi} production in cold nuclear media in deuterium-nucleus collisions. They discuss several parameterizations of the modifications of the parton densities in the nucleus, known as shadowing, an initial-state effect. They also include absorption of the produced J/{psi} by nucleons, a final-state effect. Both spatially homogeneous and inhomogeneous shadowing and absorption are considered. They use the number of binary nucleon-nucleon collisions as a centrality measure. Results are presented for d+Au collisions at {radical}S{sub NN} = 200 GeV and for d+Pb collisions at {radical}S{sub NN} = 6.2 TeV. To contrast the centrality dependence in pA and dA collisions, they also present pPb results at {radical}S{sub NN} = 8.8 TeV.
Date: November 1, 2004
Creator: Vogt, R.
Partner: UNT Libraries Government Documents Department

Probing small x parton densities in ultraperipheral AA and pAcollisions at the LHC

Description: We calculate photoproduction rates for several hard processes in ultraperipheral proton-lead and lead-lead collisions at the LHC with {radical}s{sub NN} = 8.8 and 5.5 TeV respectively which could be triggered in the large LHC detectors. We use ATLAS as an example. The lead ion is treated as a source of (coherently produced) photons with energies and intensities greater than those of equivalent ep collisions at HERA.We find very large rates for both inclusive and diffractive production which will extend the HERA x range by nearly an order of magnitude for similar virtualities. We demonstrate that it is possible to reach the kinematic regime where nonlinear effects are larger than at HERA.
Date: September 15, 2005
Creator: Strikman, Mark; Vogt, Ramona & White, Sebastian
Partner: UNT Libraries Government Documents Department

Are partons confined tachyons?

Description: The author notes that if hadrons are gravitationally stabilized ``black holes``, as discrete physics suggests, it is possible that partons, and in particular quarks, could be modeled as tachyons, i.e. particles having v{sup 2} > c{sup 2}, without conflict with the observational fact that neither quarks nor tachyons have appeared as ``free particles``. Some consequences of this model are explored.
Date: March 1, 1996
Creator: Noyes, H.P.
Partner: UNT Libraries Government Documents Department

An improved limit on jet handedness in Z{sup 0} decays

Description: We present the results of an improved search for jet handedness in hadronic decays of Z{sup degree} bosons collected by the SLD experiment at SLAC. Quark and antiquark jets, expected to be oppositely polarized in Z{sup degree} decays, were separated using the large forward-backward quark asymmetry induced by the highly polarized SLC electron beam. The larger data sample and beam polarization of the 1994/5 SLC/SLD run yield a factor of two improvement in our sensitivity to jet handedness. Assuming Standard Model values of quark polarizations we set an improved upper limit on the analyzing power of the handedness method.
Date: July 1995
Creator: Collaboration, The SLD
Partner: UNT Libraries Government Documents Department

The inclusive jet cross section at {radical}s = 630 GeV at D0

Description: The authors present a preliminary measurement of the cross section for central inclusive jet production at {radical}s = 630 GeV using {approximately} 400 nb{sup {minus}1} of data collected during the December 1995 Fermilab collider run at D0. These results are compared to NLO QCD predictions.
Date: September 1, 1996
Creator: Krane, J.
Partner: UNT Libraries Government Documents Department

Some highlights of the recent Fermilab Fixed Target Program of interest to the nuclear physics community

Description: Many of the high energy physics questions addressed by the Fermilab Fixed Target Experiments are also of interest to the members of the nuclear community. Some recent highlights of the program, including studies of A-dependence of cross sections, evidence for parton rescattering in nuclear media, studies of heavy quark production, evidence for color transparency, and insights into QCD from meson systems, are discussed.
Date: February 1, 1995
Creator: Conrad, J.; Papavassiliou, V. & Zielinski, M.
Partner: UNT Libraries Government Documents Department

Parton distributions from SMC and SLAC data

Description: We have extracted spin-weighted parton distributions in a proton from recent data at CERN and SLAC. The valence, sea quark and Antiquark spin-weighted distributions are determined separately. The data are all consistent with a small to moderate polarized gluon distribution, so that the anomaly term is not significant in the determination of the constituent contributions to the spin of the proton. We have analyzed the consistency of the results obtained from various sets of data and the Biorken sum rule. Although all data are consistent with the sum rule, the polarized distributions from different experiments vary, even with higher order QCD corrections taken into account. Results split into two models, one set implying a large polarized strange sea which violates the positivity bound, and the other set yielding a smaller polarized strange sea. Only further experiments which extract information about the polarized sea will reconcile these differences. We suggest specific experiments which can be performed to determine the size of the polarized sea and gluons.
Date: January 4, 1996
Creator: Ramsey, G. P. & Goshtasbpour, M.
Partner: UNT Libraries Government Documents Department

Rapidity gaps in deep inelastic scattering

Description: A simple semiquantitative picture of diffractive electroproduction is described. Although the diffractive component of F{sub 2} is approximately independent of Q{sup 2} and W{sup 2}, this mechanism is ``soft,`` i.e. it depends upon large-distance physics and is not readily describable within perturbative QCD.
Date: December 31, 1995
Creator: Bjorken, J.D.
Partner: UNT Libraries Government Documents Department

Gluonic three jet production at next to leading order

Description: I report results from a next-to-leading order event generator of purely gluonic jet production. This calculation, performed in collaboration with Walter Giele, is the first step in the construction of a full next-to-leading order calculation of three jet production at hadron colliders.
Date: August 1, 1996
Creator: Kilgore, W.B.
Partner: UNT Libraries Government Documents Department

Discovery mass reach for excited quarks at hadron colliders

Description: If quarks are composite particles then excited states are expected. We estimate the discovery mass reach as a function of integrated luminosity for excited quarks decaying to dijets at the Tevatron the mass reach is 0.94 TeV for Run 11 (2 fb{sup -1}) and 1. 1 TeV for TeV33 (30 fb{sup -1}). At the LHC the mass reach is 6.3 TeV for 100 fb{sup -1}. At a VLHC with a center of mass energy {radical}s, of 50 TeV (200 TeV) the mass reach is 25 TeV (78 TeV) for an integrated luminosity of 10{sup 4} fb{sup -1}. However, an excited quark with a mass of 25 TeV would be discovered at a hadron collider with {radical}s = 100 TeV and an integrated luminosity of 13 fb{sup -1}, illustrating a physics example where a factor of 2 in machine energy is worth a factor of 1000 in luminosity.
Date: September 10, 1996
Creator: Harris, R.M.
Partner: UNT Libraries Government Documents Department

A global QCD study of direct photon production

Description: A global QCD analysis of the direct photon production process from both fixed target and collider experiments is presented. These data sets now completely cover the parton x range from 0.01 to 0.6, thereby providing a stringent test of perturbative QCD and parton distributions. Previous detailed studies of direct photons emphasized fixed target data. The authors find most data sets have a steeper p{sub t} distribution than the QCD prediction. Neither global fits with new parton distributions nor improved photon fragmentation functions can resolve this problem since the deviation occurs at different x values for experiments at different energies. A more likely explanation is the need for additional broadening of the k{sub t} of the initial state partons. The magnitude and the possible physical origin of this effect are investigated and discussed.
Date: January 1, 1995
Creator: Huston, J.; Lai, H.L.; Tung, W.K.; Kovacs, E.; Kuhlmann, S. & Owens, J.F.
Partner: UNT Libraries Government Documents Department

Measurement of double parton scattering at CDF

Description: A strong signal for Double Parton scattering (DP) is observed in {anti p}p {yields} {gamma} + 3 jets data from the CDF experiment. The process-independent DP parameter, {sigma}{sub eff}, is obtained using a new technique. The result, {sigma}{sub eff} =(14.5{+-}1.7{sup + 1.7}{sub -2.3}) mb, represents a significant improvement over previous measurements. For the first time, the Feynman x dependence of the {sigma}{sub eff} parameter is investigated, and no dependence is seen.
Date: June 1, 1997
Creator: Behrends, S. B. & Lamoureux, J.
Partner: UNT Libraries Government Documents Department

Extracting {ital alpha}{sub s}from Tevatron data

Description: In this contribution we explore one of the many possibilities of determining the strong coupling constant {alpha}{sub s} at hadron colliders. The method considered is quite unique compared to other methods in that the value of {alpha}{sub s} is determined by the ``evolution rate`` of the parton density functions rather than by the ``event rate``.
Date: July 1, 1997
Creator: Giele, W.T.
Partner: UNT Libraries Government Documents Department

Parton Distributions Working Group

Description: This report summarizes the activities of the Parton Distributions Working Group of the QCD and Weak Boson Physics workshop held in preparation for Run II at the Fermilab Tevatron. The main focus of this working group was to investigate the different issues associated with the development of quantitative tools to estimate parton distribution functions uncertainties. In the conclusion, the authors introduce a Manifesto that describes an optimal method for reporting data.
Date: July 20, 2000
Creator: de Barbaro, L.; Keller, S. A.; Kuhlmann, S.; Schellman, H. & Tung, W.-K.
Partner: UNT Libraries Government Documents Department


Description: We report results of our ongoing nonperturbative numerical study of a classical effective theory describing low-x partons in the central region of a heavy-ion collision. In particular, we give estimates of the initial transverse energies and multiplicities for a wide range of collision regimes, including those at RHIC and at LHC.
Date: October 9, 2000
Partner: UNT Libraries Government Documents Department