158 research outputs found
A method to localize gamma-ray bursts using POLAR
The hard X-ray polarimeter POLAR aims to measure the linear polarization of
the 50-500 keV photons arriving from the prompt emission of gamma-ray bursts
(GRBs). The position in the sky of the detected GRBs is needed to determine
their level of polarization. We present here a method by which, despite of the
polarimeter incapability of taking images, GRBs can be roughly localized using
POLAR alone. For this purpose scalers are attached to the output of the 25
multi-anode photomultipliers (MAPMs) that collect the light from the POLAR
scintillator target. Each scaler measures how many GRB photons produce at least
one energy deposition above 50 keV in the corresponding MAPM. Simulations show
that the relative outputs of the 25 scalers depend on the GRB position. A
database of very strong GRBs simulated at 10201 positions has been produced.
When a GRB is detected, its location is calculated searching the minimum of the
chi2 obtained in the comparison between the measured scaler pattern and the
database. This GRB localization technique brings enough accuracy so that the
error transmitted to the 100% modulation factor is kept below 10% for GRBs with
fluence Ftot \geq 10^(-5) erg cm^(-2) . The POLAR localization capability will
be useful for those cases where no other instruments are simultaneously
observing the same field of view.Comment: 13 pages, 10 figure
Glauber theory of initial- and final-state interactions in (p,2p) scattering
We develop the Glauber theory description of initial- and final-state
interactions (IFSI) in quasielastic A(p,2p) scattering. We study the
IFSI-distortion effects both for the inclusive and exclusive conditions. In
inclusive reaction the important new effect is an interaction between the two
sets of the trajectories which enter the calculation of IFSI-distorted one-body
density matrix for inclusive (p,2p) scattering and are connected with
incoherent elastic rescatterings of the initial and final protons on spectator
nucleons. We demonstrate that IFSI-distortions of the missing momentum
distribution are large over the whole range of missing momentum both for
inclusive and exclusive reactions and affect in a crucial way the
interpretation of the BNL data on (p,2p) scattering. Our numerical results show
that in the region of missing momentum p_{m}\lsim 100-150 MeV/c the
incoherent IFSI increase nuclear transparency by 5-10\%. The incoherent IFSI
become dominant at p_{m}\gsim 200 MeV/c.Comment: Accepted in Z. Phys.A, Latex, 26 pages, uuencoded 9 figure
The apparent Coulomb reacceleration of neutrons in electrodissociation of the deuteron
We demonstrate that the final state - interaction in the reaction of
electrodissociation of the deuteron at large in a static external field
leads to the apparent reacceleration of neutrons. The shift of the neutron
velocity from the velocity of the deuteron beam is related to the
quantum-mechanical forward-backward asymmetry of the missing momentum
distribution in the scattering.Comment: LATEX, 9 pages, 1 figure available from the authors on request,
Juelich preprint KFA-IKP(TH)-1994-3
Spin-orbit final state interaction in the framework of Glauber theory for (e,e'p) reactions
We investigate the reactions D(e,e'p)n and D(\vec e,e'p)n at GeV energies and
discuss the opportunities to distinguish between different models for the
nuclear ground state by measuring the response functions. In calculating the
final-state interaction (FSI) we employ Glauber theory, and we also include
relativistic effects in the electromagnetic current. We include not only the
central FSI, but also the spin-orbit FSI which is usually neglected in (e,e'p)
calculations within the Glauber framework and we show that this contribution
plays a crucial role for the fifth response function. All of the methods
developed here can be applied to any target nucleus.Comment: 20 pages, 12 figures, minor change in figures 3 and 4 (changed beam
energy), correction of error in figure 4 in the previous replacemen
The Separable Kernel of Nucleon-Nucleon Interaction in the Bethe-Salpeter Approach
The dispersion relations for nucleon-nucleon (NN) T-matrix in the framework
of Bethe-Salpeter equation for two spin one-half particle system and with
separable kernel of interaction are considered in the paper. The developed
expressions are applied for construction of the separable kernel of interaction
for S partial-waves in singlet and triplet channels. We calculate the low
energy scattering parameters and the phase shifts and also the deuteron binding
energy with the separable interaction. The approach can be easily extended to
higher partial-waves for NN-scattering and other reactions (anti N N-, pi
N-scattering).Comment: RevTex 4 style, 9 pages, 1 figur
Reggeon and pion contributions in semi-exclusive diffractive processes at HERA
A detailed analysis of semi-exclusive diffractive processes in e-p DIS at
HERA, with the diffractive final states in the forward direction is presented.
The contributions of the subleading f_2, \omega, a_2, \rho reggeons and the
pion exchanges to the diffractive structure function with the forward proton or
neutron are estimated. It is found that the (a_2,\rho) reggeons are entirely
responsible for the forward neutron production at x_P < 10^{-3}. The \pi N
production in the forward region is estimated using the Deck mechanism. The
significance of this reaction for the processes measured at HERA, especially
with the leading neutron, is discussed.Comment: Strongly revised version accepted for publication in Phys.Rev.D.
Latex, 14 pages with 5 eps figures include
Quadrupole deformation of deuterons and final state interaction in scattering on tensor polarized deuterons at CEBAF energies
The strength of final state interaction (FSI) between struck proton and
spectator neutron in scattering depends on the alignment of
the deuteron. We study the resulting FSI effects in the tensor analyzing power
in detail and find substantial FSI effects starting at still low missing
momentum p_m \gsim 0.9 fm^{-1}. At larger p_m \gsim 1.5 fm^{-1}, FSI
completely dominates both missing momentum distribution and tensor analyzing
power. We find that to a large extent FSI masks the sensitivity of the tensor
analyzing power to models of the deuteron wave function. For the transversely
polarized deuterons the FSI induced forward-backward asymmetry of the missing
momentum distribution is shown to have a node at precisely the same value of
as the PWIA missing momentum distribution. The position of this node is
not affected by FSI and can be a tool to distinguish experimentally between
different models for the deuteron wave function.Comment: 24 pages, figures available from the authors on reques
POLAR: a space borne GRB polarimeter
International audienceThe direction and the level of polarization of high energy photons emitted by astrophysics sources are valuable observables for the understanding of the corresponding emission mechanisms, source geometry and strength of magnetic fields at work. POLAR is a novel compact space-borne detector conceived for a precise measurement of hard X-ray polarization and optimized for the detection of Gamma-Ray Burst (GRB) photons in the energy range 50-500 keV. In POLAR, the GRB photons undergo Compton scattering in a target made out of 1600 plastic scintillator bars. The azimuthal distribution of the scattered photons inside the target provides the information on the GRB polarization. The target is divided into 5x5 units, each one consisting of 8x8 scintillator bars optically coupled with a multi-anode photomultiplier. POLAR, thanks to its large modulation factor (mu_100=40%), its large effective area (Aeff = 250 cm2), and its large field of view ( 1/3 of the sky) will be able to determine the degree and angle of polarization of a strong GRB with a minimum detectable polarization of less than 10% (3sigma). In this communication the present design and status of the POLAR project is presented. Expected results through deep Monte Carlo simulation studies as well as the recent results of laboratory measurements are detailed
Spin observables of the reactions NN -> DeltaN and pd -> Delta (pp)(1S0) in collinear kinematics
A general formalism for double and triple spin-correlations of the reaction
NN -> DeltaN is developed for the case of collinear kinematics. A complete
polarization experiment allowing to reconstruct all of the four amplitudes
describing this process is suggested. Furthermore, the spin observables of the
inelastic charge-exchange reaction pd -> Delta^0(pp)(1S0) are analyzed in
collinear kinematics within the single pN scattering mechanism involving the
subprocess pn -> Delta^0p. The full set of spin observables related to the
polarization of one or two initial particles and one final particle is obtained
in terms of three invariant amplitudes of the reaction pd -> Delta (pp)(1S0)
and the transition form factor d->(pp)(1S0). A complete polarization experiment
for the reaction pd -> Delta^0(pp)(1S0) is suggested which allows one to
determine three independent combinations of the four amplitudes of the
elementary subprocess NN -> DeltaN.Comment: 12 pages, 1 figur
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