126 research outputs found
Group independent color decomposition of next-to-leading order matrix elements for e^+ e^- \to four partons
We present the next-to-leading order partonic cross sections involving an
electroweak vector boson and four massless partons (quarks, gluons or long
living gluinos) in a general gauge theory with a simple Lie Group. The vector
boson couples to a massless lepton pair and a quark-antiquark pair. The cross
sections are given in terms of group independent kinematical functions
multiplying the eigenvalues of the Casimir operators of the Lie group. This
kind of color decomposition is required for the calculation of O()
corrections to the group independent kinematical functions in the four-jet
production cross sections in electron-positron annihilation. The knowledge of
these corrections facilitates the simultaneous precision meaurement of the
strong coupling and the color charge factors using the four-jet LEP or SLC data
as well as the test whether these data favour or exclude the existence of a
light gluino.Comment: 11 pages, elsart styl
Higher Twist Contributions To R-Hadron Phenomenology In The Light Gluino Scenario
The open light gluino window allows non-trivial higher twist gluino
contributions to the proton wave function. Using a two-component model
originally developed for charm hadroproduction, higher twist intrinsic gluino
contributions to final state R-hadron formation are shown to enhance leading
twist production in the forward region. We calculate R-hadron
production at GeV in pp, pBe, and pCu interactions with
light gluino masses of 1.2, 1.5, 3.5, and 5.0 GeV.Comment: 22 pages, 10 figures, revte
A General Approach To Photon Radiation Off Fermions
Soft or collinear photon emission potentially poses numerical problems in the
phase-space integration of radiative processes. In this paper, a general
subtraction formalism is presented that removes such singularities from the
integrand of the numerical integration and adds back the analytically
integrated contributions that have been subtracted. The method is a
generalization of the dipole formalism of Catani and Seymour, which was
formulated for NLO QCD processes with massless unpolarized particles. The
presented formalism allows for arbitrary mass and helicity configurations in
processes with charged fermions and any other neutral particles. Particular
attention is paid to the limit of small fermion masses, in which collinear
singularities cause potentially large corrections. The actual application and
the efficiency of the formalism are demonstrated by the discussion of photonic
corrections to the processes \gamma \gamma --> t \bar t (\gamma), e^- \gamma
--> e^- \gamma (\gamma), and \mu^+ \mu^- --> \nu_e \bar\nu_e (\gamma).Comment: 51 pages, latex; two sentences dropped (in Sections 3.2 and 4.2); to
appear in Nucl. Phys.
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Next-to-Leading Order Calculation of Four-Jet Shape Variables
We present the next-to-leading order calculation of two four-jet event shape
variables, the D parameter and acoplanarity differential distributions. We find
large, more than 100% radiative corrections. The theoretical prediction for the
D parameter is compared to L3 data obtained at the Z peak and corrected to
hadron level.Comment: 11 pages, latex with aps, epsf, rotate styles 3 tables, 3 figures
typo in eq. 10 corrected, note and reference added, introduction revise
Proton-Proton Near-Forward Hard Elastic Scattering
We calculate the leading twist contribution to near-forward proton-proton
(and proton-antiproton) elastic scattering with large momentum transfer, in the
multiple scattering (Landshoff) mechanism. The amplitude in the near-forward
region is dominated by singlet exchange for all three valence quark-quark
scatterings. We assume the existence of a hard singlet quark-quark amplitude,
which we estimate to be . For a three-quark state whose
transverse size is less than , Sudakov resummation
accounts for both approximate \d \sigma^{pp}/ \d t \sim t^{-8} at moderate
, and \d \sigma^{pp}/ \d t \sim t^{-10} at larger . The transition from
approximate to behavior is strongly correlated with the
transverse size of the valence three-quark state in the proton.Comment: 34 pages, LaTe
An analysis of a Heavy Gluino LSP at CDF : The Heavy Gluino Window
In this paper we consider a heavy gluino to be the lightest supersymmetric
particle [LSP]. We investigate the limits on the mass of a heavy gluino LSP,
using the searches for excess events in the jets plus missing momentum channel
in Run I. The neutral and charged R-hadrons, containing a heavy gluino LSP,
have distinct signatures at the Fermilab Tevatron. The range of excluded gluino
masses depends on whether the R-hadron is charged or neutral and the amount of
energy deposited in the hadronic calorimeter. The latter depends on the energy
loss per collision in the calorimeter and the number of collisions; where both
quantities require a model for R-hadron- Nucleon scattering. We show how the
excluded range of gluino mass depends on these parameters. We find that gluinos
with mass in the range between GeV and GeV are excluded by
CDF Run I data. Combined with previous results of Baer et al., which use LEP
data to exclude the range 3 - 2225 GeV, our result demonstrates that an
allowed window for a heavy gluino with mass between 25 and 35 GeV is quite
robust. Finally we discuss the relevant differences of our analysis of Tevatron
data to that of Baer et al.Comment: 36 pages, 11 figures, added an acknowledgemen
Single top production at the LHC as a probe of R parity violation
We investigate the potential of the LHC to probe the R parity violating
couplings involving the third generation by considering single top production.
This study is based on particle level event generation for both signal and
background, interfaced to a simplified simulation of the ATLAS detector.Comment: 11 pages, 5 figures, 5 tables (LaTeX, style revtex), few references
adde
Quantum Color Transparency and Nuclear Filtering
Color transparency is the proposal that under certain circumstances the
strong interactions can be reduced in magnitude. We give a comprehensive review
of the physics, which hinges on the interface of perturbative QCD with
non--perturbative strong interactions. Color transparency is complementary to
{\it nuclear filtering}, which is the conversion of quark wave functions in
hadrons to small transverse space dimensions by interaction with a nuclear
medium. We review current approaches, including pictures based on modeling the
time evolution of hadronic wave--packets as well as the use of light cone
matrix elements. Spin plays an intrinsic role in testing and understanding the
physics and is discussed at length. We emphasize the use of data analysis
procedures which have minimal model dependence. We also review existing
experimental data and the experimental program planned at various facilities.
The subject has strong scientific complementarity and potential to make
progress in exploring hadron physics at current and future facilities.Comment: 131 pages, review article in LaTeX to appear in Physics Reports, no
postscipt figures, approximately 30 figures available from Ralston on reques
Complete Order alpha_s^3 Results for e^+ e^- to (gamma,Z) to Four Jets
We present the next-to-leading order (O(alpha_s^3)) perturbative QCD
predictions for e^+e^- annihilation into four jets. A previous calculation
omitted the O(alpha_s^3) terms suppressed by one or more powers of 1/N_c^2,
where N_c is the number of colors, and the `light-by-glue scattering'
contributions. We find that all such terms are uniformly small, constituting
less than 10% of the correction. For the Durham clustering algorithm, the
leading and next-to-leading logarithms in the limit of small jet resolution
parameter y_{cut} can be resummed. We match the resummed results to our
fixed-order calculation in order to improve the small y_{cut} prediction.Comment: Latex2e, 17 pages with 5 encapsulated figures. Note added regarding
subsequent related work. To appear in Phys. Rev.
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