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Studying the underlying event at CDF
A study of ''underlying event'' in Run 2 at CDF is presented. Several PYTHIA 6.2 tunes (with multiple parton interactions) are examined and compared with HERWIG (without multiple parton interactions) and with the ATLAS PYTHIA tune (with multiple parton interactions) and they are extrapolated to the LHC
Drell-Yan Non-Singlet Spin Cross Sections and Spin Asymmetry to (II)
We present predictions for the non-singlet Drell-Yan longitudinal spin cross
sections and spin asymmetry, , in proton-proton collisions at large
at the RHIC energy of 200\gev at next-to-leading order QCD. The higher
order corrections to the non-singlet polarized cross section,
, are sizeable and similar to those found for the unpolarized
cross section. The non-singlet asymmetry parameter, , is very
stable against higher order corrections and is a direct measurement of the
non-singlet (i.e. valence) polarized quark distributions within the proton.Comment: 24 pages, 13 figure
Spin Dependent Drell-Yan beyond Leading Order: Non-Singlet Virtual corrections to
We present parton-level analytical results for the next-to-leading order
non-singlet virtual and real corrections to the Drell-Yan differential
cross-section. The dependence of the differential cross section on the helicity
of the initial state partons is shown explicitly (the spins of the final state
partons are summed). The calculation is implemented in dimensional
regularization within the scheme and with the t'Hooft Veltman
prescriptions for the n-dimensional . Both the polarized initial
state and the unpolarized cross sections can be obtained from our result. Our
unpolarized cross section agrees with the previous result of Ellis, Martinelli
and Petronzio in the non-singlet sector.Comment: 12 pages, 7 figures, one chapter added, change in figure
Area Decay Law Implementation for Quark String Fragmentation
We apply the Area Decay Law (ADL) straightforwardly to simulate a quark
string hadronization and compare the results with the explicit analytic
calculations. We show that the usual "inclusive" Monte--Carlo simulations do
not correspond to the ADL because of two mistakes: not proper simulation of
two--dimensional probability density and lack of an important combinatorial
factor in a binary tree simulation. We also show how to simulate area decay law
"inclusively" avoiding the above--mentioned mistakes.Comment: 5 pages (REVTEX) + 3 figures (available in ps format from
G.G.Leptoukh , IPGAS-HE/93-3, to be
published in Phys. Rev.
Large Transverse Momenta in Statistical Models of High Energy Interactions
The creation of particles with large transverse momenta in high energy
hadronic collisions is a long standing problem. The transition from small-
(soft) to hard- parton scattering `high-pt' events is rather smooth. In this
paper we apply the non-extensive statistical framework to calculate transverse
momentum distributions of long lived hadrons created at energies from low
(sqrt(s)~10 GeV) to the highest energies available in collider experiments
(sqrt(s)~2000 GeV). Satisfactory agreement with the experimental data is
achieved. The systematic increase of the non-extensivity parameter with energy
found can be understood as phenomenological evidence for the increased role of
long range correlations in the hadronization process.
Predictions concerning the rise of average transverse momenta up to the
highest cosmic ray energies are also given and discussed.Comment: 20 pages, 10 figure
On asimuthal anisotropy in fragmentation of classical relativistic string
A fragmenting relativistic string is widely used for modelling particle
production via quark-gluon strings formed in hadron inelastic interactions of
high energies. In this note we focus on motion and fragmentation of
relativistic string with non-zero transverse separation of its ends and study
this scenario as a possible mechanism bringing anisotropy into the asimuthal
angle disribution of produced particles in inelastic interactions of hadrons.Comment: 12 pages, 6 figure
Spin Dependent Drell Yan in QCD to (I). (The Non-Singlet Sector)
A study of the order corrections to the Drell Yan (non-singlet)
cross section for incoming states of arbitrary longitudinal helicities is
presented. The study is performed in the case of the transverse momentum
distributions, , of the lepton pair and extends the calculation of Ellis
Martinelli and Petronzio (EMP) to the polarized case. We use the
scheme and the t'Hooft-Veltman regularization for the helicity projectors. From
our results one can obtain the bulk of the totally inclusive NNLO cross section
for the production of a Drell Yan pair in the non-singlet sector by a simple
integration over the heavy photon momentum. We show that in the
helicity is not conserved, unless a finite renormalization is done to reenter
into a physical scheme (). This aspect of the calculation follows
the same trend as in polarized production of single and double photon to
. In the unpolarized limit we reproduce all the results of EMP.Comment: 39 pages, 7 figures (included
A Phenomenological Analysis of Gluon Mass Effects in Inclusive Radiative Decays of the and $\Upsilon
The shapes of the inclusive photon spectra in the processes \Jp \to \gamma
X and \Up \to \gamma X have been analysed using all available experimental
data.
Relativistic, higher order QCD and gluon mass corrections were taken into
account in the fitted functions. Only on including the gluon mass corrections,
were consistent and acceptable fits obtained. Values of
GeV and GeV were found for the
effective gluon masses (corresponding to Born level diagrams) for the \Jp and
\Up respectively. The width ratios \Gamma(V \to {\rm hadrons})/\Gamma(V \to
\gamma+ {\rm hadrons}) V=\Jp, \Up were used to determine and . Values consistent with the current world
average were obtained only when gluon mass correction factors,
calculated using the fitted values of the effective gluon mass, were applied. A
gluon mass GeV, as suggested with these results, is consistent with
previous analytical theoretical calculations and independent phenomenological
estimates, as well as with a recent, more accurate, lattice calculation of the
gluon propagator in the infra-red region.Comment: 50 pages, 11 figures, 15 table
t' at the LHC: the physics of discovery
A search for a fourth family at the LHC is presently a low priority, but we
argue that an effective search can be conducted early with only a few inverse
femtobarns of data. We discuss a method based on invariant masses of single
jets for identifying the 's originating from heavy quark decays. This can
significantly increase signal to background in the reconstruction of the
mass. We also study the various types of physics that can impact the background
estimate, most notably higher order effects, initial state radiation, and
models of the underlying event.Comment: 16 pages, 12 figures, small improvements, version to appear in JHE
The dihadron fragmentation function and its evolution
Dihadron fragmentation functions and their evolution are studied in the
process of annihilation. Under the collinear factorization
approximation and facilitated by the cut-vertex technique, the two hadron
inclusive cross section at leading order (LO) is shown to factorize into a
short distance parton cross section and a long distance dihadron fragmentation
function. We provide the definition of such a dihadron fragmentation function
in terms of parton matrix elements and derive its DGLAP evolution equation at
leading log. The evolution equation for the non-singlet quark fragmentation
function is solved numerically with a simple ansatz for the initial condition
and results are presented for cases of physical interest.Comment: 27 pages, 2 column, Revtex4, 21 figure
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