715 research outputs found
Heavy Quark Mass Effects in Deep Inelastic Scattering and Global QCD Analysis
A new implementation of the general PQCD formalism of Collins, including
heavy quark mass effects, is described. Important features that contribute to
the accuracy and efficiency of the calculation of both neutral current (NC) and
charged current (CC) processess are explicitly discussed. This new
implementation is applied to the global analysis of the full HERA I data sets
on NC and CC cross sections, with correlated systematic errors, in conjunction
with the usual fixed-target and hadron collider data sets. By using a variety
of parametrizations to explore the parton parameter space, robust new parton
distribution function (PDF) sets (CTEQ6.5) are obtained. The new quark
distributions are consistently higher in the region x ~ 10^{-3} than previous
ones, with important implications on hadron collider phenomenology, especially
at the LHC. The uncertainties of the parton distributions are reassessed and
are compared to the previous ones. A new set of CTEQ6.5 eigenvector PDFs that
encapsulates these uncertainties is also presented.Comment: 32 pages, 12 figures; updated, Publication Versio
Associated production of Z boson and a pair of new quarks at the LHC
The associated production of boson and a pair of new quarks at the Large
Hadron Collider (LHC) is studied. The cross sections for both sequential
fermions and vector-like fermions are presented. It is found that for
sequential fermions the cross sections can reach fb for heavy
quark mass from 1000 GeV to 200 GeV.
For vector-like quarks, the cross sections are suppressed by mixing parameter
. Focusing on process , we investigate the
possibility of detecting the signal. For a with light mass and a
large branching ratio of , it is found that only several signal
events (parton level) can be produced with 1000 fb integrated
luminosity. Although the signal events are rare, all the final states are
produced centrally and multi lepton final states are clear at hadron collider,
which could be easily detected.Comment: 11 pages,5 figures, accepted by Communications in Theoretical Physic
Discovering the Higgs Bosons of Minimal Supersymmetry with Muons and a Bottom Quark
We investigate the prospects for the discovery at the CERN Large Hadron
Collider of a neutral Higgs boson produced with one bottom quark followed by
Higgs decay into a muon pair. We work within the framework of the minimal
supersymmetric model. The dominant physics background from the production of , , j=g,u,d,s,c, and is calculated
with realistic acceptance cuts. Promising results are found for the CP-odd
pseudoscalar () and the heavier CP-even scalar () Higgs bosons with
masses up to 600 GeV. This discovery channel with one energetic bottom quark
greatly improves the discovery potential of the LHC beyond the inclusive
channel .Comment: Version to appear in Phys. Rev. Let
Light Gluino Constituents of Hadrons and a Global Analysis of Hadron Scattering Data
Light strongly interacting supersymmetric particles may be treated as
partonic constituents of nucleons in high energy scattering processes. We
construct parton distribution functions for protons in which a light gluino is
included along with standard model quark, antiquark, and gluon constituents. A
global analysis is performed of a large set of data from deep-inelastic lepton
scattering, massive lepton pair and vector boson production, and hadron jet
production at large values of transverse momentum. Constraints are obtained on
the allowed range of gluino mass as a function of the value of the strong
coupling strength alpha_s(M_Z) determined at the scale of the Z boson mass. We
find that gluino masses as small as 10 GeV are admissible provided that
alpha_s(M_Z) \ge 0.12. Current hadron scattering data are insensitive to the
presence of gluinos heavier than ~ 100 - 150 GeV.Comment: 31 pages, 12 figures, RevTe
Probing Top Anomalous Couplings at the Tevatron and the Large Hadron Collider
Chromomagnetic and chromoelectric dipole interactions of the top quark are
studied in a model independent framework. Limits are set on the scale of new
physics that might lead to such contributions using available Tevatron data.
Prospects at the LHC are reviewed.Comment: Version published in Praman
Uncertainties on parton distribution functions from the ZEUS NLO QCD fit to data on deep inelastic scattering
An NLO QCD analysis of the ZEUS data on deep inelastic scattering
together with fixed-target data has been performed from which the gluon and
quark densities of the proton and the value of the strong coupling parameter,
, have been extracted. The study includes a full treatment of
the experimental systematic uncertainties, including point-to-point
correlations. Different ways of incorporating correlated systematic
uncertainties into the fit are discussed and compared.Comment: 8 pages, 1 figure. Invited talk at the Conference on Advanced
Statistical Techniques in Particle Physics, March 18-22 2002, Durham, U
Extracting MSSM Masses From Heavy Higgs Decays to Four Leptons at the LHC
It is well known that finding and measuring the masses of particles in the
Minimal Supersymmetric Standard Model (MSSM) at the Large Hadron Collider (LHC)
may be possible using invariant mass distributions in exclusive channels
containing n_j jets and n_l leptons. We perform this analysis for the (n_j,
n_l) = (0,4) decay of heavy Higgs bosons to neutralinos, pp \to H/A \to \chi_i
\chi_j (i,j =2,3,4), which then decay to four leptons and two lightest
neutralinos \chi_1 via on-shell sleptons. When i=j and the sleptons are
degenerate, our Monte Carlo study shows that the LHC will be able to measure
the Higgs and relevant neutralino and slepton masses to roughly
30%; however, if one of these is already known within 5%, the other three may
be found to equal or better accuracy. This would provide the first accurate
measurement of the H/A mass via invariant mass distribution techniques.Comment: version to be published in PR
A closer look at string resonances in dijet events at the LHC
The first string excited state can be observed as a resonance in dijet
invariant mass distributions at the LHC, if the scenario of low-scale string
with large extra dimensions is realized. A distinguished property of the dijet
resonance by string excited states from that the other "new physics" is that
many almost degenerate states with various spin compose a single resonance
structure. It is examined that how we can obtain evidences of low-scale string
models through the analysis of angular distributions of dijet events at the
LHC. Some string resonance states of color singlet can obtain large mass shifts
through the open string one-loop effect, or through the mixing with closed
string states, and the shape of resonance structure can be distorted. Although
the distortion is not very large (10% for the mass squared), it might be able
to observe the effect at the LHC, if gluon jets and quark jets could be
distinguished in a certain level of efficiency.Comment: 12 pages, 8 figure
Radiative decay Z_H-> \gamma A_H in the little Higgs model with T-parity
In the little Higgs model with T-parity (LHTM), the only tree-level
kinematically allowed two-body decay of the Z_H boson is Z_H-> A_H H and thus
one-loop induced two-body decays may have a significant rate. We study the
Z_H-> \gamma A_H decay, which is induced at the one-loop level by a fermion
triangle and is interesting as it depends on the mechanism of anomaly
cancellation of the model. All the relevant two- and three-body decays of the
Z_H gauge boson arising at the tree-level are also calculated. We consider a
small region of the parameter space where the scale of the symmetry breaking f
is still allowed to be as low as 500 GeV by electroweak precision data. We
first analyze the scenario of a Higgs boson with a mass of 120 GeV. We found
that the Z_H->\gamma A_H branching ratio can be of the order of a tree-level
three-body decay and may be at the reach of detection at the LHC for f close to
500 GeV, but it may be difficult to detect for f=1 TeV. There is also an
scenario where the Higgs boson has an intermediate mass such that the Z_H-> A_H
H decay is closed, the Z_H-> \gamma A_H gets considerably enhanced and the
chances of detection get a large boost.Comment: 19 pages, 9 figures, 2 table
Vector Boson Pair Production via Vector Boson Fusion at NLO QCD
NLO QCD corrections to Vector Boson Pair Production via Vector Boson Fusion
have recently been calculated and implemented in a parton-level Monte-Carlo
program with full experimental cuts. We briefly sketch the elements of the
calculation and show numerical results for the Large Hadron Collider.Comment: 6 pages, 3 figures, presented by G.Bozzi at IFAE 2007 (Napoli, April
2007) and HEP 2007 (Manchester, July 2007
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