169 research outputs found
Probing small parton densities in ultraperipheral and collisions at the LHC
We calculate production rates for several hard processes in ultraperipheral
proton-nucleus and nucleus-nucleus collisions at the LHC. The resulting high
rates demonstrate that some key directions in small research proposed for
HERA will be accessible at the LHC through these ultraperipheral processes.
Indeed, these measurements can extend the HERA range by roughly a factor of
10 for similar virtualities. Nonlinear effects on the parton densities will
thus be significantly more important in these collisions than at HERA.Comment: Submitted to Phys. Rev. Lett., 4 pages, 5 figure
Tracking fast small color dipoles through strong gluon fields at the LHC
We argue that the process gamma +A \to J/psi + gap + X at large momentum
transfer provides a quick and effective way to test onset of a novel
perturbative QCD regime of strong absorption for the interaction of small
dipoles at the collider energies. We find that already the first heavy ion run
at the LHC will allow to study this reaction with sufficient statistics via
ultraperipheral collisions hence probing the interaction of q\bar q dipoles of
sizes ~ 0.2 fm with nuclear media down to x ~ 10^{-5}.Comment: 4 pages, final version published in PR
Novel hard semiexclusive processes and color singlet clusters in hadrons
Hard scattering to a three cluster final state is suggested as a method to
probe configurations in hadrons containing small size color singlet cluster and
a residual quark-gluon system of a finite mass. Examples of such processes
include
where could be a pion(kaon) or other state of finite mass which
does not increase with momentum transfer (). We argue that different
models of the nucleon may lead to very different qualitative predictions for
the spectrum of states . We find that in the pion model of nonperturbative
sea in a nucleon the cross section of these reactions is comparable
to the cross section of the corresponding two-body reaction. Studies of these
reactions are feasible using both fixed target detectors (EVA at BNL, HERMES at
DESY) and collider detectors with a good acceptance in the forward direction.Comment: 9 pages, 2 figures, to be published in the proceedings of the
Workshop: Exclusive Processes at High Momentum Transfer, Newport News,
Virginia, 15-18 May 200
Polarized light ions and spectator nucleon tagging at EIC
An Electron-Ion Collider (EIC) with suitable forward detection capabilities
would enable a unique experimental program of deep-inelastic scattering (DIS)
from polarized light nuclei (deuterium 2H, helium 3He) with spectator nucleon
tagging. Such measurements promise significant advances in several key areas of
nuclear physics and QCD: (a) neutron spin structure, by using polarized
deuterium and eliminating nuclear effects through on-shell extrapolation in the
spectator proton momentum; (b) quark/gluon structure of the bound nucleon at x
> 0.1 and the dynamical mechanisms acting on it, by measuring the spectator
momentum dependence of nuclear structure functions; (c) coherent effects in
QCD, by exploring shadowing in tagged DIS on deuterium at x << 0.1. The JLab
MEIC design (CM energy sqrt{s} = 15-50 GeV/nucleon, luminosity ~ 10^{34}
cm^{-2} s^{-1}) provides polarized deuterium beams and excellent coverage and
resolution for forward spectator tagging. We summarize the physics topics, the
detector and beam requirements for spectator tagging, and on-going R&D efforts.Comment: 6 pages, 2 figures. Prepared for proceedings of DIS 2014, XXII.
International Workshop on Deep-Inelastic Scattering and Related Subjects,
University of Warsaw, Poland, April 28 - May 2, 201
Ion induced quark-gluon implosion
We investigate nuclear fragmentation in the central proton-nucleus and
nucleus - nucleus collisions at the energies of LHC. We argue that within the
semi-classical approximation because of fast increase with energy of cross
sections of soft and hard interactions each nucleon is stripped in the average
process off ``soft'' partons and fragments into a collection of leading quarks
and gluons with large . Valence quarks and gluons are streaming in the
opposite directions when viewed in the c.m. of the produced system. The
resulting pattern of the fragmentation of the colliding nuclei leads to an
implosion of the quark and gluon constituents of the nuclei. The matter density
produced at the initial stage in the nucleus fragmentation region is estimated
to be 50 GeV/fm at the LHC energies and probably 10
GeV/fm at RHIC.Comment: 5 pages, final version, discussion of the signals of the new phase is
expande
Short-Distance Structure of Nuclei
One of Jefferson Lab's original missions was to further our understanding of
the short-distance structure of nuclei. In particular, to understand what
happens when two or more nucleons within a nucleus have strongly overlapping
wave-functions; a phenomena commonly referred to as short-range correlations.
Herein, we review the results of the (e,e'), (e,e'p) and (e,e'pN) reactions
that have been used at Jefferson Lab to probe this short-distance structure as
well as provide an outlook for future experiments.Comment: 16 pages, 8 figures, for publication in Journal of Physics
Measuring Double Parton Distributions in Nucleons at Proton-Nucleus Colliders
We predict a strong enhancement of multijet production in proton-nucleus
collisions at collider energies, as compared to a naive expectation of a cross
section . The study of the process would allow to measure, for the
first time, the double parton distribution functions in a nucleon in a model
independent way and hence to study both the longitudinal and the transverse
correlations of partons.Comment: 12 pages, 2 figure
Transverse nucleon structure and diagnostics of hard parton-parton processes at LHC
We propose a new method to determine at what transverse momenta particle
production in high-energy pp collisions is governed by hard parton-parton
processes. Using information on the transverse spatial distribution of partons
obtained from hard exclusive processes in ep/gamma p scattering, we evaluate
the impact parameter distribution of pp collisions with a hard parton-parton
process as a function of p_T of the produced parton (jet). We find that the
average pp impact parameters in such events depend very weakly on p_T in the
range 2 < p_T < few 100 GeV, while they are much smaller than those in
minimum-bias inelastic collisions. The impact parameters in turn govern the
observable transverse multiplicity in such events (in the direction
perpendicular to the trigger particle or jet). Measuring the transverse
multiplicity as a function of p_T thus provides an effective tool for
determining the minimum p_T for which a given trigger particle originates from
a hard parton-parton process. Additional tests of the proposed geometric
correlations are possible by measuring the dependence on the trigger rapidity.
Various strategies for implementing this method are outlined.Comment: 9 pages, 6 figure
Neutron spin structure with polarized deuterons and spectator proton tagging at EIC
The neutron's deep-inelastic structure functions provide essential
information for the flavor separation of the nucleon parton densities, the
nucleon spin decomposition, and precision studies of QCD phenomena in the
flavor-singlet and nonsinglet sectors. Traditional inclusive measurements on
nuclear targets are limited by dilution from scattering on protons, Fermi
motion and binding effects, final-state interactions, and nuclear shadowing at
x << 0.1. An Electron-Ion Collider (EIC) would enable next-generation
measurements of neutron structure with polarized deuteron beams and detection
of forward-moving spectator protons over a wide range of recoil momenta (0 <
p_R < several 100 MeV in the nucleus rest frame). The free neutron structure
functions could be obtained by extrapolating the measured recoil momentum
distributions to the on-shell point. The method eliminates nuclear
modifications and can be applied to polarized scattering, as well as to
semi-inclusive and exclusive final states. We review the prospects for neutron
structure measurements with spectator tagging at EIC, the status of R&D
efforts, and the accelerator and detector requirements.Comment: 11 pages, 3 figures. To appear in proceedings of Tensor Polarized
Solid Target Workshop, Jefferson Lab, March 10-12, 201
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