910 research outputs found
Restoration of factorization for low hadron hadroproduction
We discuss the applicability of the factorization theorem to low-
hadron production in hadron-hadron collision in a simple toy model, which
involves only scalar particles and gluons. It has been shown that the
factorization for high- hadron hadroproduction is broken by soft gluons in
the Glauber region, which are exchanged among a transverse-momentum-dependent
(TMD) parton density and other subprocesses of the collision. We explain that
the contour of a loop momentum can be deformed away from the Glauber region at
low , so the above residual infrared divergence is factorized by means of
the standard eikonal approximation. The factorization is then restored in
the sense that a TMD parton density maintains its universality. Because the
resultant Glauber factor is independent of hadron flavors, experimental
constraints on its behavior are possible. The factorization can also be
restored for the transverse single-spin asymmetry in hadron-hadron collision at
low in a similar way, with the residual infrared divergence being
factorized into the same Glauber factor.Comment: 12 pages, 2 figures, version to appear in EPJ
Dijet Production at Large Rapidity Intervals
We examine dijet production at large rapidity intervals at Tevatron energies,
by using the theory of Lipatov and collaborators which resums the leading
powers of the rapidity interval. We analyze the growth of the Mueller-Navelet
-factor in this context and find it to be negligible. However, we do find a
considerable enhancement of jet production at large transverse momenta. In
addition, we show that the correlation in transverse momentum and azimuthal
angle of the tagging jets fades away as the rapidity interval is increased.Comment: 12 pages, preprint DESY 93-139, SCIPP 93/3
QCD factorization for forward hadron scattering at high energies
We consider the QCD factorization of DIS structure functions at small x and
amplitudes of 2->2 -hadronic forward scattering at high energy. We show that
both collinear and k_T-factorization for these processes can be obtained
approximately as reductions of a more general (totally unintegrated) form of
the factorization. The requirement of ultraviolet and infrared stability of the
factorization convolutions allows us to obtain restrictions on the fits for the
parton distributions in k_T- and collinear factorization.Comment: 18 pages, 10 figures In the present version misprints found in the
prevcious version are corrected and some more details are explaine
Measuring Parton Densities in the Pomeron
We present a program to measure the parton densities in the pomeron using
diffractive deep inelastic scattering and diffractive photoproduction, and to
test the resulting parton densities by applying them to other processes such as
the diffractive production of jets in hadron-hadron collisions. Since QCD
factorization has been predicted NOT to apply to hard diffractive scattering,
this program of fitting and using parton densities might be expected to fail.
Its success or failure will provide useful information on the space-time
structure of the pomeron.Comment: Contains revisions based on Phys. Rev. D referee comments. RevTeX
version 3, epsf, 31 pages. Uuencoded compressed postscript figures appended.
Uncompressed postscript files available at
ftp://ftp.phys.psu.edu/pub/preprint/psuth136
QCD analysis of the diffractive structure function F_2^{D(3)}
The proton diffractive structure function measured in the H1 and
ZEUS experiments at HERA is analyzed in terms of both Regge phenomenology and
perturbative QCD evolution. A new method determines the values of the Regge
intercepts in ``hard'' diffraction, confirming a higher value of the Pomeron
intercept than for soft physics. The data are well described by a QCD analysis
in which point-like parton distributions, evolving according to the DGLAP
equations, are assigned to the leading and sub-leading Regge exchanges. The
gluon distributions are found to be quite different for H1 and ZEUS. A {\it
global fit} analysis, where a higher twist component is taken from models,
allows us to use data in the whole available range in diffractive mass and
gives a stable answer for the leading twist contribution. We give sets of quark
and gluon parton distributions for the Pomeron, and predictions for the charm
and the longitudinal proton diffractive structure function from the QCD fit. An
extrapolation to the Tevatron range is compared with CDF data on single
diffraction. Conclusions on factorization breaking depend critically whether H1
(strong violation) or ZEUS (compatibility at low ) fits are taken into
account.Comment: 24 page
Generalized parton distributions and Deeply Virtual Compton Scattering in Color Glass Condensate model
Within the framework of the Color Glass Condensate model, we evaluate quark
and gluon Generalized Parton Distributions (GPDs) and the cross section of
Deeply Virtual Compton Scattering (DVCS) in the small- region. We
demonstrate that the DVCS cross section becomes independent of energy in the
limit of very small , which clearly indicates saturation of the DVCS
cross section. Our predictions for the GPDs and the DVCS cross section at
high-energies can be tested at the future Electron-Ion Collider and in
ultra-peripheral nucleus-nucleus collisions at the LHC.Comment: 20 pages, 8 Figure
Factorization and infrared properties of non-perturbative contributions to DIS structure functions
In this paper we present a new derivation of the QCD factorization. We deduce
the k_T- and collinear factorizations for the DIS structure functions by
consecutive reductions of a more general theoretical construction. We begin by
studying the amplitude of the forward Compton scattering off a hadron target,
representing this amplitude as a set of convolutions of two blobs connected by
the simplest, two-parton intermediate states. Each blob in the convolutions can
contain both the perturbative and non-perturbative contributions. We formulate
conditions for separating the perturbative and non-perturbative contributions
and attributing them to the different blobs. After that the convolutions
correspond to the QCD factorization. Then we reduce this totally unintegrated
(basic) factorization first to the k_T- factorization and finally to the
collinear factorization. In order to yield a finite expression for the Compton
amplitude, the integration over the loop momentum in the basic factorization
must be free of both ultraviolet and infrared singularities. This obvious
mathematical requirement leads to theoretical restrictions on the
non-perturbative contributions (parton distributions) to the Compton amplitude
and the DIS structure functions related to the Compton amplitude through the
Optical theorem. In particular, our analysis excludes the use of the singular
factors x^{-a} (with a > 0) in the fits for the quark and gluon distributions
because such factors contradict to the integrability of the basic convolutions
for the Compton amplitude. This restriction is valid for all DIS structure
functions in the framework of both the k_T- factorization and the collinear
factorization if we attribute the perturbative contributions only to the upper
blob.Comment: 19 pages, 6 figure
Study of the Linked Dipole Chain Model in heavy quark production at the Tevatron
We present calculations of charm and beauty production at Tevatron within the
framework of kT-factorization, using the unintegrated gluon distributions as
obtained from the Linked Dipole Chain model. The analysis covers transverse
momentum and rapidity distributions and the azimuthal correlations between b
and bbar quarks (or rather muons from their decay) which are powerful tests for
the different unintegrated gluon distributions. We compare the theoretical
results with recent experimental data taken by D0 and CDF collaborations at the
Tevatron Run I and II.Comment: 16 page
Double-logarithmic behavior of inelastic fermion form factors in QED and QCD
The effective kinematic diagram technique is applied to study inelastic form
factors of electron and quark in QED and QCD. The explicit expressions for
these form factors in the double-logarithmic approximation are presented. The
self-consistency of the results is shown by demonstrating the fulfillment of
the Kinoshita-Lee-Nauenberg theorem.Comment: 8 pages, REVTeX. Misprints corrected, references adde
A matrix formulation for small-x singlet evolution
We propose a matrix evolution equation in (x,kt)-space for flavour singlet,
unintegrated quark and gluon densities, which generalizes DGLAP and BFKL
equations in the relevant limits. The matrix evolution kernel is constructed so
as to satisfy renormalization group constraints in both the ordered and
antiordered regions of exchanged momenta kt, and incorporates the known NLO
anomalous dimensions in the MSbar scheme as well as the NLx BFKL kernel. We
provide a hard Pomeron exponent and effective eigenvalue functions that include
the n_f-dependence, and give also the matrix of resummed DGLAP splitting
functions. The results connect smoothly with those of the single-channel
approach. The novel P_{qa} splitting functions show resummation effects delayed
down to x=0.0001, while both P_{ga} entries show a shallow dip around x=0.001,
similarly to the gluon-gluon single-channel results. We remark that the matrix
formulation poses further constraints on the consistency of a BFKL framework
with the MSbar scheme, which are satisfied at NLO, but marginally violated by
small n_f/N_c^2-suppressed terms at NNLO.Comment: 36 pages, 5 figure
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