96 research outputs found
Extracting the Proton ubar content from pp->Direct Photon plus Jet Cross Sections
An analysis procedure is proposed to measure the antiquark distributions in
the proton over the region 0.01 < x < 0.1. The procedure involves the
measurement of high p_t asymmetric direct photon and jet final states in pp
interactions. This measurement can be made at the RHIC collider running in pp
mode at an energy of sqrt(s)=500 GeV/c. This analysis identifies a region of
phase space where the contribution from quark-antiquark annihilation
uncharacteristically approaches the magnitude of the contribution from the
leading process, quark-gluon Compton scattering. The forward-backward angular
asymmetry in the parton center of mass is sensitive to the antiquark content of
the proton and the ubar parton density function can be extracted.Comment: 21 pages, 7 figure
Scale Dependence of Polarized DIS Asymmetries
We compare the dependence of the polarized deep inelastic scattering
proton asymmetry, driven by the leading order Altarelli Parisi evolution
equations, to those arising from fixed order and
approximations. It is shown that the evolution effects associated with gluons,
which are not properly taken into account by the leading order approximation,
cannot be neglected in the analysis of the most recent experimental data.Comment: Latex file, (9 figures in postcript available from
[email protected]
Production of -pairs at HERA-
The production of -pairs as a possible measure of the polarized gluon
distribution is studied for proton--nucleon collisions at
\sqrt{s} =40\;\mbox{GeV}^2 (HERA-). Possibilities of
reconstructing the helicity state of at least one of the 's are
critically reviewed. The observation of production asymmetries in the single
polarized mode of HERA- is found to be not feasible.Comment: 8 pages, LATeX, 3 figures availabe as .uu-fil
Effects Of The Quantity On The Spin Structure Functions Of Nucleons In The Resonance Region
In this paper, we investigate the effects of the quantity on
the spin-structure functions of nucleons in the resonance region. The Schwinger
sum rule for the spin structure function at the real photon limit
is derived for the nucleon treated as a composite system, and it provides a
crucial constraint on the longitudinal transition operator which has not been
treated consistently in the literature. The longitudinal amplitude is evaluated in the quark model with the transition operator that
generates the Schwinger sum rule. The numerical results of the quantity
are presented for both spin structure functions and
in the resonance region. Our results show that this quantity
plays an important role in the low region, which can be tested in the
future experiments at CEBAF.Comment: 20 pages, latex, 4 postscript figures can be obtained from the autho
Nuclear effects in Deep Inelastic Scattering of polarized electrons off polarized 3He and the neutron spin structure functions
It is shown that the nuclear effects playing a relevant role in Deep
Inelastic Scattering of polarized electrons by polarized He are mainly
those arising from the effective proton and neutron polarizations generated by
the and waves in He. A simple and reliable equation relating the
neutron, , and He, , spin structure functions is proposed. It
is shown that the measurement of the first moment of the He structure
function can provide a significant check of the Bjorken Sum Rule.Comment: 11 pages (revTeX), DFUPG 75/93; 5 (postscript) figures available upon
request from the author
Experimental and Theoretical Results for Weak Charge Current Backward Proton Production
In this paper, we do three things in the study of deuteron break-up by high
energy neutrino beams. (1) We present previously unpublished data on neutrino
induced backward protons from deuteron targets; (2) we calculate the
contributions from both the two-nucleon (2N) and six-quark (6q) deuteron
components, which depend upon the overall normalization of the part that is 6q;
and (3) we suggest other signatures for distinguishing the 2N and 6q clusters.
We conclude that the 6q cluster easily explains the shape of the high momentum
backward proton spectrum, and its size is nicely explained if the amount of 6q
is one or a few percent by normalization of the deuteron. There is a crossover,
above which the 6q contribution is important or dominant, at 300--400 MeV/c
backward proton momentum.Comment: 8 pages, 5 figure
Leading and higher twists in the proton polarized structure function at large Bjorken x
A phenomenological parameterization of the proton polarized structure
function has been developed for x > 0.02 using deep inelastic data up to ~ 50
(GeV/c)**2 as well as available experimental results on both photo- and
electro-production of proton resonances. According to the new parameterization
the generalized Drell-Hearn-Gerasimov sum rule is predicted to have a
zero-crossing point at Q**2 = 0.16 +/- 0.04 (GeV/c)**2. Then, low-order
polarized Nachtmann moments have been estimated and their Q**2-behavior has
been investigated in terms of leading and higher twists for Q**2 > 1
(GeV/c)**2. The leading twist has been treated at NLO in the strong coupling
constant and the effects of higher orders of the perturbative series have been
estimated using soft-gluon resummation techniques. In case of the first moment
higher-twist effects are found to be quite small for Q**2 > 1 (GeV/c)**2, and
the singlet axial charge has been determined to be a0[10 (GeV/c)**2] = 0.16 +/-
0.09. In case of higher order moments, which are sensitive to the large-x
region, higher-twist effects are significantly reduced by the introduction of
soft gluon contributions, but they are still relevant at Q**2 ~ few (GeV/c)**2
at variance with the case of the unpolarized transverse structure function of
the proton. Our finding suggests that spin-dependent correlations among partons
may have more impact than spin-independent ones. As a byproduct, it is also
shown that the Bloom-Gilman local duality is strongly violated in the region of
polarized electroproduction of the Delta(1232) resonance.Comment: revised version to appear in Phys. Rev. D; extended discussion on the
generalized DHG sum rul
A QCD Analysis of Polarised Parton Densities
We present the results of a QCD fit to global data on deep-inelastic
polarised lepton-hadron scattering. We find that it is possible to fit the data
with strongly broken SU(2) flavour for the polarised sea densities. This can
easily be tested in production at polarised RHIC. The data fails to pin
down polarised singlet sea quark and gluon densities. We explore the
uncertainties in detail and show that improvement in statistics, achievable at
polarised HERA for measurement of A_1 at moderately low values of x, have large
payoffs in terms of the improvement in measurement of gluon and sea quark
densities.Comment: Revtex 17 pages, 19 postscript figures. Analysis extended to SU(2)
flavour symmetric and nonsymmetric se
Models for the Polarized Parton Distributions of the Nucleon
Polarized deep inelastic scattering (DIS) data are analyzed in leading and
next-to-leading order of QCD within the common `standard' scenario of polarized
parton distributions with a flavor-symmetric light sea (antiquark) distribution
, and a completely SU(3) broken `valence' scenario with
totally flavor-asymmetric light sea densities
. The latter flavor-broken
light sea distributions are modelled with the help of a Pauli-blocking ansatz
at the low radiative/dynamical input scales of
(0.40) GeV which complies with predictions of the chiral quark-soliton
model and expectations based on the statistical parton model as well as with
the corresponding, well established, flavor-broken unpolarized sea
(). Present semi-inclusive DIS data cannot yet uniquely
discriminate between those two flavor-symmetric and flavor-broken polarized
light sea scenarios.Comment: 39 pages, LaTe
A model for the dependence of polarized structure functions
We present an update of a phenomenological model for the spin dependent
structure functions of the proton and neutron. This model is based
on a broken SU(6) wavefunction parametrized by the unpolarized structure
functions. The two free parameters of the model are choosen to fulfill the
Bjorken and Ellis--Jaffe sum rules. The model respects isospin symmetry and has
zero strange sea polarization. Using new values for from hyperon beta
decay the resulting dependent asymmetries are in perfect agreement
with the existing data. Therefore we do not see any evidence for a ``spin
crisis''. With two choices for the dependence of and
is predicted and shown to be small for both cases.Comment: 18 pages and 11 figures as uudecoded ps file
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