414 research outputs found
The AGL Equation from a Dipole Picture
The AGL equation includes all multiple pomeron exchanges in the double
logarithmic approximation (DLA) limit, leading to an unitarized gluon
distribution in the small regime. This equation was originally obtained
using the Glauber-Mueller approach. We demonstrate in this contribution that
the AGL equation can also be obtained from the dipole picture. Our conclusion
is that the AGL equation is a good candidate for an unitarized evolution
equation at small in the DLA limit.Comment: 3 pages. To be published in the proceedings of 7th International
Workshop on Deep Inelastic Scattering and QCD (DIS 99), Zeuthen, Germany, 19
- 23 Apr 199
Seeking the Shadowing in eA Processes
We consider the behavior of the slope of the nuclear structure function
in the kinematic region which will be explored in the eA HERA collider.
We demonstrate that, similarly to the nucleon case, a `turn over' is predicted
in this observable. Moreover, we predict that the presence of the shadowing
corrections implies that the maximum value of the slope is dependent of the
number of nucleons A, differently from the DGLAP predictions. Our conclusion is
that the measurement of this observable will allow to evidentiate the presence
of the shadowing corrections.Comment: 10 pages, 1 figur
Searching Saturation in eA Processes
The high density effects should be manifest at small x and/or large nuclei.
In this letter we consider the behavior of nuclear structure function
slope in the kinematic region which could be explored in the future eA
colliders as a search of these effects. We verify that the high density implies
that the maximum value of the slope occurs at large values of the photon
virtuality, i.e. in a perturbative regime, and is dependent of the number of
nucleons A and energy. Our conclusion is that the measurement of this
observable will allow to explicit the saturation.Comment: 13 pages, 2 figures, 1 tabl
Quarkonium+ production in coherent hadron - hadron interactions at LHC energies
In this paper we study the ( and )
production in coherent hadron - hadron interactions at LHC energies.
Considering the ultrarelativistic protons as a source of photons, we estimate
the cross section using the
non-relativistic QCD (NRQCD) factorization formalism and considering different
sets of values for the matrix elements. Our results for the total cross sections and rapidity distributions at
and 14 TeV demonstrate that the experimental analysis of the
production at LHC is feasible.Comment: 6 pages, 3 figures, 1 table. Improved version with a new figure.
Version to be published in European Physical Journal
The Description of at Very High Parton Densities
The behavior of the structure function at high energies (high densities) is
directly associated to the gluon distribution. In this paper we analyze the
asymptotic behavior of the structure function at very high densities
considering a leading and a higher twist relation between these two quantities.
We verify that (a) if the leading twist relation between the structure function
and the gluon distribution is used, we recover the black disc limit, and (b) a
softer behavior is predicted if a higher twist relation between and
is considered. While the first behavior is well-established by the current high
density approaches, the higher twist behavior is a new result. In both cases,
the structure function unitarizes and the Froissart boundary is not
violated in the asymptotic regime of high density QCD.Comment: 14 pages. Accepted for publication in Physics Letters
Constraining the free parameter of the high parton density effects
The high density parton effects are strongly dependent of the spatial gluon
distribution within the proton, with radius , which cannot be derived from
perturbative QCD. In this paper we assume that the unitarity corrections are
present in the HERA kinematical region and constrain the value of using the
data for the proton structure function and its slope. We obtain that the gluons
are not distributed uniformly in the whole proton disc, but behave as
concentrated in smaller regions.Comment: 16 pages, 5 figure
Charm production in diffractive deep inelastic scattering
The diffractive open charm production is computed in perturbative QCD
formalism and in the Regge approach. The results are compared with recent data
on charm diffractive structure function measured at DESY-HERA. Our results
demonstrate that this observable can be useful to discriminate the QCD
dynamics.Comment: LaTeX, 13 pages, 2 figures. Version to be published in Phys. Lett.
Unitarity Corrections to the Proton Structure Functions through the Dipole Picture
We study the dipole picture for the description of the deep inelastic
scattering, focusing on the structure functions which are driven directly by
the gluon distribution. One performs estimates using the effective dipole cross
section given by the Glauber-Mueller approach in QCD, which encodes the
corrections due to the unitarity effects associated with the saturation
phenomenon. We also address issues about frame invariance of the calculations
when analysing the observables.Comment: 16 pages, 8 figures. Version to be published in Phys. Rev.
Constraining the nuclear gluon distribution in processes at RHIC
A systematic determination of the gluon distribution is of fundamental
interest in understanding the parton structure of nuclei and the QCD dynamics.
Currently, the behavior of this distribution at small (high energy) is
completely undefined. In this paper we analyze the possibility of constraining
the nuclear effects present in using the inclusive observables which
would be measured in the future electron-nucleus collider at RHIC. We
demonstrate that the study of nuclear longitudinal and charm structure
functions allows to estimate the magnitude of shadowing and antishadowing
effects in the nuclear gluon distribution.Comment: 6 pages, 3 eps figure
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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