224 research outputs found
Neutrino induced threshold production of two pions and N^*(1440) electroweak form factors
We study the threshold production of two pions induced by neutrinos in
nucleon targets. The contribution of nucleon, pion and contact terms are
calculated using a chiral Lagrangian. The contribution of the Roper resonance,
neglected in earlier studies, has also been taken into account. The numerical
results for the cross sections are presented and compared with the available
experimental data. It has been found that in the two pion channels with
and in the final state, the contribution of the
is quite important and could be used to determine the
electroweak transition form factors if experimental data with better statistics
become available in the future.Comment: This version corrects a mistake on the helicity amplitudes sign.
Additional comments on resonance-background relative sign are added. Other
minor corrections. Matches published version. 17 pages, 7 figure
Disappearance of Elliptic Flow: A New Probe for the Nuclear Equation of State
Using a relativistic hadron transport model, we investigate the utility of
the elliptic flow excitation function as a probe for the stiffness of nuclear
matter and for the onset of a possible quark-gluon-plasma (QGP)
phase-transition at AGS energies 1 < E_Beam < 11 AGeV. The excitation function
shows a strong dependence on the nuclear equation of state, and exhibits
characteristic signatures which could signal the onset of a phase transition to
the QGP.Comment: 11 pages, 4 Postscript figures, uses epsf.sty, submitted to Physical
Review Letter
The total yields of K^+(892), Sigma^+(1385) and Sigma^0 in neutrino-induced reactions at <E_nu> = 10 GeV
Using the data obtained with SKAT bubble chamber, the total yields of
, and are estimated for the first time in
neutrino-induced reactions at moderate energies ( = 10.4 GeV). It is
shown, that the recently observed \cite{ref1,ref2} enhancement of the and
yields in interactions (as compared to interactions)
is contributed only slightly by the and production,
respectively. The decay contribution to the and yields is found
to be in qualitative agreement with higher energy ( 40 GeV) data.
It is shown, that the energy dependence of the mean multiplicity in
interactions is approximately linear in the range of 10-60 GeV, while that for in interactions (for
= 20-21) is approximately logarithmic in the range of
10-150 GeV.Comment: 6 pages, 3 figure
Charged-Particle Multiplicities in Charged-Current Neutrino-- and Anti-Neutrino--Nucleus Interactions
The CHORUS experiment, designed to search for
oscillations, consists of a nuclear emulsion target and electronic detectors.
In this paper, results on the production of charged particles in a small sample
of charged-current neutrino-- and anti-neutrino--nucleus interactions at high
energy are presented. For each event, the emission angle and the ionization
features of the charged particles produced in the interaction are recorded,
while the standard kinematic variables are reconstructed using the electronic
detectors. The average multiplicities for charged tracks, the pseudo-rapidity
distributions, the dispersion in the multiplicity of charged particles and the
KNO scaling are studied in different kinematical regions. A study of
quasi-elastic topologies performed for the first time in nuclear emulsions is
also reported. The results are presented in a form suitable for use in the
validation of Monte Carlo generators of neutrino--nucleus interactions.Comment: 17 pages, 5 figure
A Search for Selectrons and Squarks at HERA
Data from electron-proton collisions at a center-of-mass energy of 300 GeV
are used for a search for selectrons and squarks within the framework of the
minimal supersymmetric model. The decays of selectrons and squarks into the
lightest supersymmetric particle lead to final states with an electron and
hadrons accompanied by large missing energy and transverse momentum. No signal
is found and new bounds on the existence of these particles are derived. At 95%
confidence level the excluded region extends to 65 GeV for selectron and squark
masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure
Low Q^2 Jet Production at HERA and Virtual Photon Structure
The transition between photoproduction and deep-inelastic scattering is
investigated in jet production at the HERA ep collider, using data collected by
the H1 experiment. Measurements of the differential inclusive jet
cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the
transverse energy and the pseudorapidity of the jets in the virtual
photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3
< y < 0.6. The interpretation of the results in terms of the structure of the
virtual photon is discussed. The data are best described by QCD calculations
which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure
Hadron Production in Diffractive Deep-Inelastic Scattering
Characteristics of hadron production in diffractive deep-inelastic
positron-proton scattering are studied using data collected in 1994 by the H1
experiment at HERA. The following distributions are measured in the
centre-of-mass frame of the photon dissociation system: the hadronic energy
flow, the Feynman-x (x_F) variable for charged particles, the squared
transverse momentum of charged particles (p_T^{*2}), and the mean p_T^{*2} as a
function of x_F. These distributions are compared with results in the gamma^* p
centre-of-mass frame from inclusive deep-inelastic scattering in the
fixed-target experiment EMC, and also with the predictions of several Monte
Carlo calculations. The data are consistent with a picture in which the
partonic structure of the diffractive exchange is dominated at low Q^2 by hard
gluons.Comment: 16 pages, 6 figures, submitted to Phys. Lett.
Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD
With the H1 detector at the ep collider HERA, D* meson production cross
sections have been measured in deep inelastic scattering with four-momentum
transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88
GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe
the differential cross sections within theoretical and experimental
uncertainties. Using these calculations, the NLO gluon momentum distribution in
the proton, x_g g(x_g), has been extracted in the momentum fraction range
7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon
momentum fraction x_g has been obtained from the measured kinematics of the
scattered electron and the D* meson in the final state. The results compare
well with the gluon distribution obtained from the analysis of scaling
violations of the proton structure function F_2.Comment: 27 pages, 9 figures, 2 tables, submitted to Nucl. Phys.
The A - dependence of and neutrinoproduction on nuclei
For the first time, the A- dependence of the production of ,
and, for comparison, mesons is investigated in neutrinonuclear
reactions, using the data obtained with SKAT bubble chamber. An exponential
parametrization () of the particle yields results in
for particles (combined and
), while for mesons the A- dependence is much weaker,
. A nuclear enhancement of the ratio
is found; this ratio increases from for -
interactions up to at and at
. It is observed, that the multiplicity rise of 's occures
predominantely in the backward hemisphere of the hadronic c.m.s. It is shown,
that the A- dependence of the nuclear enhancement of the and
yields can be reproduced in the framework of a model, incorporating the
secondary intranuclear interactions of pions originating from the primary - interactions, while only (299)% of that for at
can be attributed to intranuclear interactions.Comment: 18 pages, 8 figure
The yields of light meson resonances in neutrinonuclear interactions at <E_nu> = 10 GeV
The total yields of the all well-established light mesonic resonances (up to
the (1020) meson) are estimated in neutrinonuclear interactions at < E_nu
> = 10 GeV, using the data obtained with SKAT bubble chamber. For some
resonances, the yields in the forward and backward hemispheres in the hadronic
c.m.s. are also extracted. From the comparison of the obtained and available
higher-energy data, an indication is obtained that the resonance yields rise
almost linearly as a function of the mean mass of the neutrinoproduced
hadronic system. The fractions of pions originating from the light resonance
decays are inferred.Comment: 15 pages, 7 figure
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