594 research outputs found
The total cross section and elastic diffraction
The empirical scaling law, wherein the total photoabsorption cross section
depends on the single variable , provides
empirical evidence for saturation in the sense of for at fixed . The
total photoabsorption cross section is related to elastic diffraction in terms
of a sum rule. The excess of diffractive production over the elastic component
is due to inelastic diffraction that contains the production of hadronic states
of higher spins. Motivated by the diffractive mass spectrum, the generalized
vector dominance/color dipole picture (GVD/CDP) is extended to successfully
describe the DIS data in the full region of , all , where
the diffractive two-gluon-exchange mechanism dominates.Comment: 4 pages, Latex using espcrc2.sty, 1 figure using 1 eps file.
Presented at QCD2002, Montpellier, France, July 200
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
Determination of the longitudinal structure function at HERA
Recent results from the HERA experiment H1 on the longitudinal stucture
function of the proton are presented. They include proton structure
function analyses with particular emphasis on those kinematic regions which are
sensitive to . All results can be consistently described within the
framework of perturbative QCD.Comment: 16 pages, 11 figures (requires iopart, iopams and epsfig); Talk
presented in the Intern. Workshop on New Trends in HERA Physics 2001, 17-22
June 2001, Ringberg Castle, Tegernsee, Germany; To appear in the Proceeding
Fractal Inspired Models of Quark and Gluon Distributions and Longitudinal Structure Function FL(x, Q2) at small x
In recent years, Fractal Inspired Models of quark and gluon densities at
small x have been proposed. In this paper, we investigate longitudinal
structure function F-L (x, Q2) within this approach. We make predictions using
the QCD based approximate relation between the longitudinal structure function
and the gluon density. As the Altarelli-Martinelli equation for the
longitudinal structure function cannot be applied to Model I due to the
presence of a singularity in the Bjorken x-space we consider Model II only. The
qualitative feature of the prediction of Model II is found to be compatible
with the QCD expectation.Comment: 11 pages, 4 figures, Accepted for publication on 10-07-2010 in Indian
Journal of Physic
Small x behavior of the slope dlnF_2/dln(1/x) in the framework of perturbative QCD
Using an analytical parameterization for the behavior of the x slope of the
structure function F_2 at small x in perturbative QCD, at the leading twist
approximation of the Wilson operator product expansion, and applying a flat
initial condition in the DGLAP evolution equations, we found very good
agreement with new precise deep inelastic scattering experimental data from
HERA.Comment: 13 pages, 3 figures, late
Forward pi^0 Production and Associated Transverse Energy Flow in Deep-Inelastic Scattering at HERA
Deep-inelastic positron-proton interactions at low values of Bjorken-x down
to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons
are studied with the H1 experiment at HERA. The inclusive cross section for
pi^0 mesons produced at small angles with respect to the proton remnant (the
forward region) is presented as a function of the transverse momentum and
energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x.
Measurements are also presented of the transverse energy flow in events
containing a forward pi^0 meson. Hadronic final state calculations based on QCD
models implementing different parton evolution schemes are confronted with the
data.Comment: 27 pages, 8 figures and 3 table
Search for Doubly-Charged Higgs Boson Production at HERA
A search for the single production of doubly-charged Higgs bosons H^{\pm \pm}
in ep collisions is presented. The signal is searched for via the Higgs decays
into a high mass pair of same charge leptons, one of them being an electron.
The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment
at HERA. No evidence for doubly-charged Higgs production is observed and mass
dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs
boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only
decays into an electron and a muon via a coupling of electromagnetic strength
h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the
H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged
Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3,
masses below 112 GeV are ruled out.Comment: 15 pages, 3 figures, 1 tabl
Deep-Inelastic Inclusive ep Scattering at Low x and a Determination of alpha_s
A precise measurement of the inclusive deep-inelastic e^+p scattering cross
section is reported in the kinematic range 1.5<= Q^2 <=150 GeV^2 and
3*10^(-5)<= x <=0.2. The data were recorded with the H1 detector at HERA in
1996 and 1997, and correspond to an integrated luminosity of 20 pb^(-1). The
double differential cross section, from which the proton structure function
F_2(x,Q^2) and the longitudinal structure function F_L(x,Q^2) are extracted, is
measured with typically 1% statistical and 3% systematic uncertainties. The
measured partial derivative (dF_2(x,Q^2)/dln Q^2)_x is observed to rise
continuously towards small x for fixed Q^2. The cross section data are combined
with published H1 measurements at high Q^2 for a next-to-leading order DGLAP
QCD analysis.The H1 data determine the gluon momentum distribution in the range
3*10^(-4)<= x <=0.1 to within an experimental accuracy of about 3% for Q^2 =20
GeV^2. A fit of the H1 measurements and the mu p data of the BCDMS
collaboration allows the strong coupling constant alpha_s and the gluon
distribution to be simultaneously determined. A value of alpha
_s(M_Z^2)=0.1150+-0.0017 (exp) +0.0009-0.0005 (model) is obtained in NLO, with
an additional theoretical uncertainty of about +-0.005, mainly due to the
uncertainty of the renormalisation scale.Comment: 68 pages, 24 figures and 18 table
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