324 research outputs found
How Could the Proton Transversity be Measured
The perspectives of two new nonstandard methods of transversal quark
polarization measurement are considered: the jet handedness and the so-called
"Collins effect" due to spin dependent T-odd fragmentation function responsible
for the left-right asymmetry in fragmenting of transversally polarized quarks.
Recent experimental indications in favor of these effects are observed: 1.The
correlation of the T-odd one-particle fragmentation functions found by DELPHI
in -jet decay. Integrated over the fraction of longitudinal and
transversal momenta, this correlation is of 1.6% order, which means order of
13% for the analyzing power. 2.A rather large () handedness
transversal to the production plane observed in the diffractive production of
() triples from nuclei by the --beam.
It shows a clear dynamic origin and resembles the single spin asymmetry
behavior.
All this makes us hope to use these effects in polarized DIS experiments for
transversity measurement. The first estimation of transversity was done by
using the azimuthal asymmetry in semi-inclusive DIS recently measured by HERMES
and SMC.Comment: 8 pages, Latex, czjphys2.sty. Talk at Int. Workshop "PRAHA-SPIN99",
Prague 6-11 Sept 1999. To appear in Czech.J.Phys Supp
Erratum to "Azimuthal asymmetry in electro-production of neutral pions in semi-inclusive DIS" published in Phys. Lett. B522 (2001) 37
We correct our analysis of the HERMES experiment for the azimuthal
sin(phi)-spin asymmetry in semi-inclusive hadroproduction in DIS on
longitudinally (with respect to the lepton momentum) polarized target because
of discovered misprint in sign in the paper P.J.Mulders and R.D.Tangerman,
Nucl. Phys. B 461 (1996) 197.Comment: 3 pages, 4 figures. Sign of sin(2phi)-asymmetry correcte
Sivers and Collins Single Spin Asymmetries
The Sivers and Collins asymmetries are the most prominent Single Spin
Asymmetries (SSA)in Semi-Inclusive Deeply Inelastic Scattering (SIDIS)with
transverse target polarization. In this talk we present our understanding of
these phenomena.Comment: 9 pages, 23 eps figures. Talk at XII Workshop on High Energy Spin
Physics (DSPIN-07), Dubna, Sept. 3-7, 2007 and at ASI - SYMMETRIES AND SPIN
(SPIN-Praha-2007), Prague, July 8 - 14, 200
Azimuthal asymmetries at CLAS: Extraction of e^a(x) and prediction of A_{UL}
First information on the chirally odd twist-3 proton distribution function
e(x) is extracted from the azimuthal asymmetry, A_{LU}, in the
electro-production of pions from deeply inelastic scattering of longitudinally
polarized electrons off unpolarized protons, which has been recently measured
by CLAS collaboration. Furthermore parameter-free predictions are made for
azimuthal asymmetries, A_{UL}, from scattering of an unpolarized beam on a
polarized proton target for CLAS kinematics.Comment: 9 pages, 5 figures, late
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
Scaling Limit of Deeply Virtual Compton Scattering
I outline a perturbative QCD approach to the analysis of the deeply virtual
Compton scattering process in the limit of vanishing
momentum transfer . The DVCS amplitude in this limit exhibits a
scaling behaviour described by a two-argument distributions which
specify the fractions of the initial momentum and the momentum transfer carried by the constituents of the nucleon.The kernel
governing the evolution of the non-forward distributions
has a remarkable property: it produces the GLAPD evolution kernel
when integrated over and reduces to the Brodsky-Lepage evolution
kernel after the -integration. This property is used to
construct the solution of the one-loop evolution equation for the flavour
non-singlet part of the non-forward quark distribution.Comment: gziped, tar file of LaTeX paper plus 2 postscript figures,10 pages;
some changes in new terminolog
Old and new parton distribution and fragmentation functions
A short review of problems with parton distribution functions in nucleons,
non-polarized and polarized, is given. The main part is devoted to the
transversity distribution its possible measurement and its first experimental
probe via spin asymmetry in semi-inclusive DIS. It is argued that the proton
transversity distribution could be successfully measured in future DIS
experiments with {\it longitudinally} polarized target.Comment: 9 pages, latex, czjphys2.sty, 4 eps figures. Submitted at 35-th
Rancontre de Moriond, March 2000 and at Praha-SPIN-2000, July 2000. To be
published in Czechoslovak J. Phys. (Suppl) 51 (2001
On the azimuthal asymmetries in DIS
Using the recent experimental data on the left right asymmetry in
fragmentation of transversely polarized quarks and the theoretical calculation
of the proton transversity distribution in the effective chiral quark soliton
model we explain the azimuthal asymmetries in semi-inclusive hadron production
on longitudinal (HERMES) and transversely (SMC) polarized targets with no free
parameters. On this basis we state that the proton transversity distribution
could be successfully measured in future DIS experiments with longitudinally
polarized target.Comment: 8 pages, latex, 5 eps figures, uses epsfig and wrapfi
Azimuthal asymmetry in electro-production of neutral pions in SIDIS
Recently HERMES has observed an azimuthal asymmetry in electro-production of
neutral pions in semi-inclusive deep-inelastic scattering of unpolarized
positrons off longitudinally polarized protons. This asymmetry (like those
observed in the production of charged pions) is well reproduced theoretically
by using the non-perturbative calculation of the proton transversity
distribution in the effective chiral quark-soliton model combined with
experimental DELPHI-data on the new T-odd Collins fragmentation function. There
are no free, adjustable parameters in the analysis. Using the -dependence of
the HERMES azimuthal asymmetry and the calculated transversity distributions
the z-dependence of the Collins fragmentation function is obtained. The value
obtained from HERMES data is consistent with the DELPHI result, even though
these results refer to different scales.Comment: 12 pages, 10 figures. Fig.3c, Fig.4a updated, conclusions adde
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
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