1,799 research outputs found
J/ suppression at 200 GeV in the comovers interaction model
The yield of per binary nucleon-nucleon collision in and
collisions at GeV is computed in the framework of the
dual parton model, supplemented with final state interaction (comovers
interaction). For the latter we use the same value of the cross-section,
mb, which describes the anomalous suppression
observed at CERN-SPS energies. Several possibilities for the value of the
absorptive cross-section are considered. Shadowing is introduced in both the
comovers and the yields. A comparison with the results at CERN-SPS,
including a prediction for collisions, is also presented.Comment: 15 pages, 3 figure
Evidence for xi- and t-dependent damping of the Pomeron Flux in the proton
We show that a triple-Regge parametrization of inclusive single diffraction
agrees with the data in the following two domains: (a) xi > 0.03 at all t, (b)
|t| > 1 GeV^2 at all xi. Since the triple-Regge parametrization fails when
applied to the full xi-t range of the total single-diffractive cross section,
we conclude that damping occurs only at low-xi and low-|t|. We give a (``toy'')
parametrization of the damping factor, D(xi), valid at low-|t|, which describes
the diffractive differential cross-section (dsig/dt) data at the ISR and
roughly accounts for the observed s-dependence of diffractive total
cross-section up to Tevatron energies. However, an effective damping factor
calculated for the CDF fitted function for dsig/dxidt at sqrt(s} = 1800 GeV and
|t| = 0.05 GeV^2, suggests that, at fixed-xi, damping increases as s increases.
We conjecture that, in the regions where the triple-Regge formalism describes
the data and there is no evidence of damping, factorization is valid and the
Pomeron-flux-factor may be universal. With the assumption that the observed
damping is due to multi-Pomeron exchange, our results imply that the recent UA8
demonstration that the effective Pomeron trajectory flattens for |t| > 1 GeV$^2
is evidence for the onset of the perturbative 2-gluon pomeron. Our damping
results may also shed some light on the self-consistency of recent measurements
of hard-diffractive jet production cross sections in the UA8, CDF and ZEUS
experiments.Comment: 19 pages, 7 Encapsulated Postscript figures, LaTex, Phys. Lett. B (in
press - 1998
Baryon stopping and hyperon enhancement in the improved dual parton model
We present an improved version of the dual parton model which contains a new
realization of the diquark breaking mechanism of baryon stopping. We reproduce
in this way the net baryon yield in nuclear collisions. The model, which also
considers strings originating from diquark-antidiquark pairs in the nucleon
sea, reproduces the observed yields of p and Lambda and their antiparticles and
underestimates cascades by less than 50 %. However, Omega's are underestimated
by a factor five. Agreement with data is restored by final state interaction,
with an averaged cross-section as small as 0.14 mb. Hyperon yields increase
significantly faster than antihyperons, in agreement with experiment.Comment: 40 pages, 18 postscript figure
Elliptic Flow and Fixed p_T Suppression in a Final State Interaction Model
It has been shown that a final state interaction model, used to describe
J/psi suppression, can also describe the fixed p_T suppression of the pi^0 (and
charged pions) yield at all values of p_T, with a final state interaction
cross-section sigma close to one milibarn. We propose an extension of the model
to the pion motion in the transverse plane - which introduces a dependence of
the suppression on the azimuthal angle theta_R. Using the same value of sigma,
we obtain values of the elliptic flow v_2 close to the experimental ones, for
all values of p_T, including the soft p_T region.Comment: 21 pages, 6 figure
Anomalous suppression of production at large transverse momentum in Au + Au and d + Au collisions at 200 GeV
We propose a model of suppression of large -pions in heavy ion
collisions based on the interaction of the large pion with the dense
medium created in the collision. The model is practically the same as the one
previously introduced to describe suppression. Both the and the
centrality dependence of the data are reproduced. In deuteron-gold collisions,
the effect of the final state interaction with the dense medium turns out to be
negligibly small. Here the main features of the data are also reproduced both
at mid and at forward rapidities.Comment: 20 pages, latex, 3 postscript figures. Last version, to be published
in EJP
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