We studied the 12C(p,2p+n) reaction at beam momenta of 5.9, 8.0, and 9.0 GeV/c. For quasielastic (p,2p) events p(f), the momentum of the knocked-out proton before the reaction, was compared (event by ...event) with p(n), the coincident neutron momentum. For |p(n)|>k(F)=0.220 GeV/c (the Fermi momentum) a strong back-to-back directional correlation between p(f) and p(n) was observed, indicative of short-range n-p correlations. From p(n) and p(f) we constructed the distributions of c.m. and relative motion in the longitudinal direction for correlated pairs. We also determined that 49+/-13% of events with |p(f)|>k(F) had directionally correlated neutrons with |p(n)|>k(F).
The transparency of carbon for (p,2p) quasielastic events was measured at beam momenta ranging from 5.9 to 14.5 GeV/c at 90 degrees c.m. The four-momentum transfer squared (Q2) ranged from 4.7 to ...12.7 (GeV/c)(2). We present the observed beam momentum dependence of the ratio of the carbon to hydrogen cross sections. We also apply a model for the nuclear momentum distribution of carbon to obtain the nuclear transparency. We find a sharp rise in transparency as the beam momentum is increased to 9 GeV/c and a reduction to approximately the Glauber level at higher energies.
Hard scattering to a three cluster final state is suggested as a method to
probe configurations in hadrons containing small size color singlet cluster and
a residual quark-gluon system of a finite ...mass. Examples of such processes
include $e + N \to e+ p +M_X (\Lambda+M_X'), p+p \to p+p+M_X(p+\Lambda+M_X')$
where $M_X(M_X')$ could be a pion(kaon) or other state of finite mass which
does not increase with momentum transfer ($Q^2$). We argue that different
models of the nucleon may lead to very different qualitative predictions for
the spectrum of states $M_X$. We find that in the pion model of nonperturbative
$q \bar q$ sea in a nucleon the cross section of these reactions is comparable
to the cross section of the corresponding two-body reaction. Studies of these
reactions are feasible using both fixed target detectors (EVA at BNL, HERMES at
DESY) and collider detectors with a good acceptance in the forward direction.
Hard scattering to a three cluster final state is suggested as a method to probe configurations in hadrons containing small size color singlet cluster and a residual quark-gluon system of a finite ...mass. Examples of such processes include \(e + N \to e+ p +M_X (\Lambda+M_X'), p+p \to p+p+M_X(p+\Lambda+M_X')\) where \(M_X(M_X')\) could be a pion(kaon) or other state of finite mass which does not increase with momentum transfer (\(Q^2\)). We argue that different models of the nucleon may lead to very different qualitative predictions for the spectrum of states \(M_X\). We find that in the pion model of nonperturbative \(q \bar q\) sea in a nucleon the cross section of these reactions is comparable to the cross section of the corresponding two-body reaction. Studies of these reactions are feasible using both fixed target detectors (EVA at BNL, HERMES at DESY) and collider detectors with a good acceptance in the forward direction.
Phys.Rev.C70:015208,2004 We summarize the results of two experimental programs at the Alternating
Gradient Synchrotron of BNL to measure the nuclear transparency of nuclei
measured in the A(p,2p) ...quasielastic scattering process near 90 Deg .in the pp
center of mass. The incident momenta varied from 5.9 to 14.4 GeV/c,
corresponding to 4.8 < Q^2 < 12.7 (GeV/c)^2. First, we describe the
measurements with the newer experiment, E850, which had more complete kinematic
definition of quasielastic events. In E850 the angular dependence of the
nuclear transparency near 90 Deg. c.m., and the nuclear transparency for
deuterons was studied. Second, we review the techniques used in an earlier
experiment, E834, and show that the two experiments are consistent for the
Carbon data. E834 also determines the nuclear transparencies for Li, Al, Cu,
and Pb nuclei as well as for C. We find for both E850 and E834 that the A(p,2p)
nuclear transparency, unlike that for A(e,e'p) nuclear transparency, is
incompatible with a constant value versus energy as predicted by Glauber
calculations. The A(p,2p) nuclear transparency for C and Al increases by a
factor of two between 5.9 and 9.5 GeV/c incident proton momentum. At its peak
the A(p,2p) nuclear transparency is about 80% of the constant A(e,e'p) nuclear
transparency. Then the nuclear transparency falls back to the Glauber level
again. This oscillating behavior is generally interpreted as an interplay
between two components of the pN scattering amplitude; one short ranged and
perturbative, and the other long ranged and strongly absorbed in the nuclear
medium. We suggest a number of experiments for further studies of nuclear
transparency effects.
Phys.Rev.Lett. 90 (2003) 042301 We studied the $^{12}$C(p,2p+n) reaction at beam momenta of 5.9, 8.0 and 9.0
GeV/c. For quasielastic (p,2p) events we reconstructed {\bf p_f} the momentum
of the ...knocked-out proton before the reaction; {\bf p_f} was then compared
(event-by-event) with {\bf p_n}, the measured, coincident neutron momentum. For
$|p_n|$ > k$_F$ = 0.220 GeV/c (the Fermi momentum) a strong back-to-back
directional correlation between {\bf p_f} and {\bf p_n} was observed,
indicative of short-range n-p correlations. From {\bf p_n} and {\bf p_f} we
constructed the distributions of c.m. and relative motion in the longitudinal
direction for correlated pairs. After correcting for detection efficiency, flux
attenuation and solid angle, we determined that 49 $\pm$ 13 % of events with
$|p_f|$ > k_F had directionally correlated neutrons with $|p_n|$ > k$_F$. Thus
short-range 2N correlations are a major source of high-momentum nucleons in
nuclei.
Phys.Rev.Lett. 87 (2001) 212301 The transparency of carbon for (p,2p) quasi-elastic events was measured at
beam energies ranging from 6 to 14.5 GeV at 90 degrees c.m. The four momentum
transfer ...squared q*q ranged from 4.8 to 16.9 (GeV/c)**2. We present the
observed energy dependence of the ratio of the carbon to hydrogen cross
sections. We also apply a model for the nuclear momentum distribution of carbon
to normalize this transparency ratio. We find a sharp rise in transparency as
the beam energy is increased to 9 GeV and a reduction to approximately the
Glauber level at higher energies.
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