393 research outputs found
A Quantitative Investigation of the Pomeron
A comparative investigation of various Pomeron models is carried out through
the study of their predicted values of , B, and
in high energy pp and p scattering.
Our results strongly support a picture of the Pomeron in which we have both
moderate blackening and expansion of the p() - p amplitude in impact
parameter space as a function of energy in the ISR-SSC domain. In particular,
we obtain an excellent reproduction of the data with a hybrid eikonal model
which combines the hard Lipatov-like QCD Pomeron with the old fashioned soft
Pomeron and Regge terms. Our analysis shows that the additive quark model, at
least in the naive form, is not compatible with the data.Comment: pages 15, Late
Towards a new global QCD analysis: low x DIS data from non-linear evolution
A new approach to global QCD analysis is developed. The main ingredients are
two QCD-based evolution equations. The first one is the Balitsky-Kovchegov
nonlinear equation, which sums higher twists while preserving unitarity. The
second equation is linear and it is responsible for the correct short distance
behavior of the theory, namely it includes the DGLAP kernel. Our approach
allows extrapolation of the parton distributions to very high energies
available at the LHC as well as very low photon virtualities, .
All existing low data on the structure function is reproduced using
one fitting parameter. The resulting .
Analyzing the parameter at
very low and well below we find . A result which agrees with the "soft pomeron" intercept without
involving soft physics.Comment: 27 pages, 11 figure
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Dips at nonsense wrong-signature points
A model for residues of odd- and even-signature trajectories is presented which successfully accounts for the presence of dips in the differential cross sections of two-body reactions near the forward directions. © 1970 The American Physical Society
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.
Specifying and Verifying Concurrent Algorithms with Histories and Subjectivity
We present a lightweight approach to Hoare-style specifications for
fine-grained concurrency, based on a notion of time-stamped histories that
abstractly capture atomic changes in the program state. Our key observation is
that histories form a partial commutative monoid, a structure fundamental for
representation of concurrent resources. This insight provides us with a
unifying mechanism that allows us to treat histories just like heaps in
separation logic. For example, both are subject to the same assertion logic and
inference rules (e.g., the frame rule). Moreover, the notion of ownership
transfer, which usually applies to heaps, has an equivalent in histories. It
can be used to formally represent helping---an important design pattern for
concurrent algorithms whereby one thread can execute code on behalf of another.
Specifications in terms of histories naturally abstract granularity, in the
sense that sophisticated fine-grained algorithms can be given the same
specifications as their simplified coarse-grained counterparts, making them
equally convenient for client-side reasoning. We illustrate our approach on a
number of examples and validate all of them in Coq.Comment: 17 page
Diffraction dissociation in proton-proton collisions at = 0.9 TeV, 2.76 TeV and 7 TeV with ALICE at the LHC
The relative rates of single- and double- diffractive processes were measured
with the ALICE detector by studying properties of gaps in the pseudorapidity
distribution of particles produced in proton-proton collisions at =
0.9 TeV, 2.76 TeV and 7 TeV. ALICE triggering efficiencies are determined for
various classes of events, using a detector simulation validated with data on
inclusive particle production. Cross-sections are determined using van der Meer
scans to measure beam properties and obtain a measurement of the luminosity
A unitarity bound and the components of photon - proton interactions
We show how and why the small distance ("hard") interaction, calculable in
perturbative QCD, provides a mass cutoff in Gribov's formula for photon-proton
collisions. This enables us to find a new and more restrictive bound for this
process, .A simple model the published
experimental data over a wide range of photon virtualities () and energies
(), is developed. This model provides a quantitative way of evaluating the
relative rate of the small and large distance contributions, in the different
kinematic regions. The main results of the analysis are (i) that even at and high energies the short distance contribution is not small, and it
provides a possible explanation for the experimental rise of the
photoproduction cross section; and (ii) at large values of , the long
distance processes still contribute to the total cross section.Comment: latex file with 8 figs. in eps files, small changes in text and in
Fig.
Nuclear exclusive vector meson photoproduction
We calculate the nuclear cross section for vector meson exclusive
photoproduction within the QCD color dipole picture and in the Regge approach.
For the former approach, we have considered the phenomenological saturation
model, whereas for the latter we use a model based on the dipole Pomeron
framework. Theoretical estimates for scattering on both light and heavy nuclei
are given for a large range on energy.Comment: 18 pages, 3 figures. Includes additional discussions, references and
a comparison with the GLLMN model. Extended version to be published in Eur.
Phys. J.
Higher Order Effects in Non Linear Evolution from a Veto in Rapidities
Higher order corrections to the Balitsky-Kovchegov equation have been
estimated by introducing a rapidity veto which forbids subsequent emissions to
be very close in rapidity and is known to mimic higher order corrections to the
linear BFKL equation. The rapidity veto constraint has been first introduced
using analytical arguments obtaining a power growth with energy, Q_s (Y) ~
exp(lambda Y), of the saturation scale of lambda ~ 0.45. Then a numerical
analysis for the non-linear Balitsky-Kovchegov equation has been carried out
for phenomenological rapidities: when a veto of about two units of rapidity is
introduced for a fixed value of the coupling constant of alpha_s = 0.2 the
saturation scale lambda decreases from ~ 0.6 to ~ 0.3, and when running
coupling effects are taken into account it decreases from ~ 0.4 to ~ 0.3.Comment: 17 pages, 10 figure
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