469 research outputs found
Investigation of the high momentum component of nuclear wave function using hard quasielastic A(p,2p)X reactions
We present theoretical analysis of the first data on the high energy and
momentum transfer (hard) quasielastic reactions. The cross section
of hard reaction is calculated within the light-cone impulse
approximation based on two-nucleon correlation model for the high-momentum
component of the nuclear wave function. The nuclear effects due to modification
of the bound nucleon structure, soft nucleon-nucleon reinteraction in the
initial and final states of the reaction with and without color coherence have
been considered. The calculations including these nuclear effects show that the
distribution of the bound proton light-cone momentum fraction shifts
towards small values (), effect which was previously derived only
within plane wave impulse approximation. This shift is very sensitive to the
strength of the short range correlations in nuclei. Also calculated is an
excess of the total longitudinal momentum of outgoing protons. The calculations
are compared with data on the reaction obtained from the EVA/AGS
experiment at Brookhaven National Laboratory. These data show -shift in
agreement with the calculations. The comparison allows also to single out the
contribution from short-range nucleon correlations. The obtained strength of
the correlations is in agreement with the values previously obtained from
electroproduction reactions on nuclei.Comment: 30 pages LaTex file and 19 eps figure
Coherent QCD phenomena in the Coherent Pion-Nucleon and Pion-Nucleus Production of Two Jets at High Relative Momenta
We use QCD to compute the cross section for coherent production of a di-jet
(treated as a moving at high relative transverse momentum,). In the target rest frame,the space-time evolution of this reaction is
dominated by the process in which the high component of
the pion wave function is formed before reaching the target. It then interacts
through two gluon exchange. In the approximation of keeping the leading order
in powers of and all orders in
the amplitudes for other processes are
shown to be smaller at least by a power of . The resulting dominant
amplitude is proportional to ( is the fraction
light-cone(+)momentum carried by the quark in the final state) times the skewed
gluon distribution of the target. For the pion scattering by a nuclear target,
this means that at fixed (but ) the nuclear process in which there is only a single interaction is the
most important one to contribute to the reaction. Thus in this limit color
transparency phenomena should occur.These findings are in accord with E971
experiment at FNAL. We also re-examine a potentially important nuclear multiple
scattering correction which is positive and . The
meaning of the signal obtained from the experimental measurement of pion
diffraction into two jets is also critically examined and significant
corrections are identified.We show also that for values of achieved
at fixed target energies, di-jet production by the e.m. field of the nucleus
leads to an insignificant correction which gets more important as
increases.Comment: 23 pages, 9 figure
Neutron structure function and inclusive DIS from H-3 and He-3 at large Bjorken-x
A detailed study of inclusive deep inelastic scattering (DIS) from mirror A =
3 nuclei at large values of the Bjorken variable x is presented. The main
purpose is to estimate the theoretical uncertainties on the extraction of the
neutron DIS structure function from such nuclear measurements. On one hand,
within models in which no modification of the bound nucleon structure functions
is taken into account, we have investigated the possible uncertainties arising
from: i) charge symmetry breaking terms in the nucleon-nucleon interaction, ii)
finite Q**2 effects neglected in the Bjorken limit, iii) the role of different
prescriptions for the nucleon Spectral Function normalization providing baryon
number conservation, and iv) the differences between the virtual nucleon and
light cone formalisms. Although these effects have been not yet considered in
existing analyses, our conclusion is that all these effects cancel at the level
of ~ 1% for x < 0.75 in overall agreement with previous findings. On the other
hand we have considered several models in which the modification of the bound
nucleon structure functions is accounted for to describe the EMC effect in DIS
scattering from nuclei. It turns out that within these models the cancellation
of nuclear effects is expected to occur only at a level of ~ 3%, leading to an
accuracy of ~ 12 % in the extraction of the neutron to proton structure
function ratio at x ~ 0.7 -0.8$. Another consequence of considering a broad
range of models of the EMC effect is that the previously suggested iteration
procedure does not improve the accuracy of the extraction of the neutron to
proton structure function ratio.Comment: revised version to appear in Phys. Rev. C; main modifications in
Section 4; no change in the conclusion
Independence of , Poincare Invariance and the Non-Conservation of Helicity
A relativistic constituent quark model is found to reproduce the recent data
regarding the ratio of proton form factors, . We show that
imposing Poincare invariance leads to substantial violation of the helicity
conservation rule, as well as an analytic result that the ratio
for intermediate values of .Comment: 13 pages, 7 figures, to be submitted to Phys. Rev. C typos corrected,
references added, 1 new figure to show very high Q^2 behavio
Transportation Risk ANalysis tool for hazardous Substances (TRANS) – A user-friendly, semi-quantitative multi-mode hazmat transport route safety risk estimation methodology for Flanders
Corporate scramble for Africa?:Towards a postcolonial framework for transglocal development governance
Menus for Feeding Black Holes
Black holes are the ultimate prisons of the Universe, regions of spacetime
where the enormous gravity prohibits matter or even light to escape to
infinity. Yet, matter falling toward the black holes may shine spectacularly,
generating the strongest source of radiation. These sources provide us with
astrophysical laboratories of extreme physical conditions that cannot be
realized on Earth. This chapter offers a review of the basic menus for feeding
matter onto black holes and discusses their observational implications.Comment: 27 pages. Accepted for publication in Space Science Reviews. Also to
appear in hard cover in the Space Sciences Series of ISSI "The Physics of
Accretion onto Black Holes" (Springer Publisher
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Measurements of long-range near-side angular correlations in TeV proton-lead collisions in the forward region
Two-particle angular correlations are studied in proton-lead collisions at a
nucleon-nucleon centre-of-mass energy of TeV, collected
with the LHCb detector at the LHC. The analysis is based on data recorded in
two beam configurations, in which either the direction of the proton or that of
the lead ion is analysed. The correlations are measured in the laboratory
system as a function of relative pseudorapidity, , and relative
azimuthal angle, , for events in different classes of event
activity and for different bins of particle transverse momentum. In
high-activity events a long-range correlation on the near side, , is observed in the pseudorapidity range . This
measurement of long-range correlations on the near side in proton-lead
collisions extends previous observations into the forward region up to
. The correlation increases with growing event activity and is found
to be more pronounced in the direction of the lead beam. However, the
correlation in the direction of the lead and proton beams are found to be
compatible when comparing events with similar absolute activity in the
direction analysed.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-040.htm
Study of the production of and hadrons in collisions and first measurement of the branching fraction
The product of the () differential production
cross-section and the branching fraction of the decay () is
measured as a function of the beauty hadron transverse momentum, ,
and rapidity, . The kinematic region of the measurements is and . The measurements use a data sample
corresponding to an integrated luminosity of collected by the
LHCb detector in collisions at centre-of-mass energies in 2011 and in 2012. Based on previous LHCb
results of the fragmentation fraction ratio, , the
branching fraction of the decay is
measured to be \begin{equation*} \mathcal{B}(\Lambda_b^0\rightarrow J/\psi
pK^-)= (3.17\pm0.04\pm0.07\pm0.34^{+0.45}_{-0.28})\times10^{-4},
\end{equation*} where the first uncertainty is statistical, the second is
systematic, the third is due to the uncertainty on the branching fraction of
the decay , and the
fourth is due to the knowledge of . The sum of the
asymmetries in the production and decay between and
is also measured as a function of and .
The previously published branching fraction of , relative to that of , is updated.
The branching fractions of are determined.Comment: 29 pages, 19figures. All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-032.htm
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