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1.
We revisit the standard treatment due to Xu et al. of
suppression due to gluonic bombardment in an equilibrating quark-gluon plasma. Effects arising from gluon fugacity, relative g-
flux, and
meson formation time are explicitly incorporated in the formulation of the gluon number density, velocity-weighted cross section, and the survival probability. Our new formulae are applied to a numerical study of the pattern of
suppression in the central rapidity region at RHIC/LHC energies. The temperature and transverse momentum dependence of our graphs have noticeable differences from those of Xu et al.Received: 27 February 2004, Revised: 3 June 2004, Published online: 6 August 2004 相似文献
2.
The NA Collaboration 《The European Physical Journal C - Particles and Fields》2005,39(3):335-345
We present a new measurement of
production in Pb-Pb collisions at 158 GeV/nucleon, from the data sample collected in year 2000 by the NA50 Collaboration,
under improved experimental conditions with respect to previous years. With the target system placed in vacuum, the setup
was better adapted to study, in particular, the most peripheral nuclear collisions with unprecedented accuracy. The analysis
of this data sample shows that the
cross-sections ratio measured in the most peripheral Pb-Pb interactions is in good agreement with the nuclear absorption
pattern extrapolated from the studies of proton-nucleus collisions. Furthermore, this new measurement confirms our previous
observation that the
cross-sections ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb collisions and that this ratio
persistently decreases up to the most central collisions.
Received: 25 August 2004, Revised: 15 December 2004, Published online: 21 January 2005 相似文献
3.
M. A. Gomshi Nobary B. Javadi 《The European Physical Journal C - Particles and Fields》2005,42(1):37-42
We investigate the effect of Fermi motion on the direct fragmentation of the
and
states employing a light-cone wave function. Consistent with such a wave function we set up the kinematics of a heavy quark
fragmenting into quarkonia such that the Fermi motion of the constituents splits into a longitudinal as well as a transverse
direction and thus calculate the fragmentation functions for these states. In the framework of our investigation, we estimate
that the fragmentation probabilities of
and
may increase at least up to 14 percent when including this degree of freedom.
Received: 11 May 2004, Revised: 23 April 2005, Published online: 31 May 2005
PACS:
13.87.Fh, 13.85.Ni, 12.38.Bx, 12.39.Hg
An erratum to this article is available at . 相似文献
4.
M. B. Gay Ducati V. P. Gonçalves L. F. Mackedanz 《The European Physical Journal C - Particles and Fields》2004,34(2):229-236
At high energies the saturation effects associated to the high parton density should modify the behavior of the observables in proton-nucleus and nucleus-nucleus scattering. In this paper we investigate the saturation effects in the nuclear
production and estimate the modifications in the energy dependence of the cross section as well as in the length of the nuclear medium. In particular, we calculate the ratio of
to Drell-Yan cross sections and show that it is strongly modified if the high density effects are included. Moreover, our results are compared with the data from the NA50 Collaboration and predictions for the RHIC and LHC kinematic regions are presented. We predict an additional
suppression associated to the high density effects.Received: 10 October 2003, Revised: 23 December 2003, Published online: 25 February 2004 相似文献
5.
A. Capella C.A. Salgado D. Sousa 《The European Physical Journal C - Particles and Fields》2003,30(1):111-116
We compute the mid-rapidity densities of pions, kaons, baryons and antibaryons in Au-Au collisions at
GeV in the dual parton model supplemented with final state interaction (comovers interaction). The ratios
(
) increase between peripheral (
) and central (
collisions by a factor 2.4 (2.0) for the
, 4.8 (4.1) for the
and 16.5 (13.5) for the
. The ratio
increases by a factor 1.3 in the same centrality range. A comparison with the available data is presented.Received: 28 April 2003, Published online: 11 July 2003 相似文献
6.
The production of
and
charmonium states in proton-nucleus interactions has been investigated by the NA50 experiment, at the CERN SPS. High statistics data sets were collected with collisions induced by 450 GeV protons incident on Be, Al, Cu, Ag and W targets. The
and
production cross-sections have been determined for each p-A system and their dependences on the nucleus size have been studied, leading to the so-called normal nuclear absorption. Comparing the two patterns we see that the nuclear absorption is stronger for the
than for the
. Given the high statistics of the data samples, the
(or rapidity) differential cross-sections of the
and
states have also been studied, for each of the target nuclei.Received: 23 September 2003, Revised: 29 November 2003, Published online: 29 January 2004 相似文献
7.
Hubaut F. Monnier E. Pralavorio P. Smolek K. Simak V. 《The European Physical Journal C - Particles and Fields》2005,44(1):13-25
The inelastic production of
mesons in ep collisions has been studied with the ZEUS detector at HERA using an integrated luminosity of
. The
mesons were identified using the decay channel
. The measurements were performed in the kinematic range
,
, 0.2 < z < 0.9 and
, where Q2 is the virtuality of the exchanged photon, W is the photon-proton centre-of-mass energy, z is the fraction of the photon energy carried by the
meson in the proton rest frame and
is the rapidity of the
in the laboratory frame. The measured cross sections are compared to theoretical predictions within the non-relativistic QCD framework including colour-singlet and colour-octet contributions, as well as to predictions based on the kT-factorisation approach. Calculations of the colour-singlet process generally agree with the data, whereas inclusion of colour-octet terms spoils this agreement.Received: 18 May 2005, Revised: 24 June 2005, Published online: 27 July 2005 相似文献
8.
Parton percolation provides geometric deconfinement in the pre-equilibrium stage of nuclear collisions. The resulting parton condensate can lead to charmonium suppression. We formulate a local percolation condition viable for non-uniform collision environments and show that it correctly reproduces the suppression observed for S-U and Pb-Pb collisions at the SPS. Using this formulation, we then determine the behavior of
suppression for In-In collisions at the SPS and for Au-Au collisions at RHIC.Received: 3 November 2003, Published online: 15 January 2004 相似文献
9.
R. Arnaldi 《The European Physical Journal C - Particles and Fields》2005,43(1-4):167-172
The study of dilepton production in heavy-ion collisions at the CERN SPS provided some of the most interesting observations
done so far in the search for the quark gluon plasma. However, several aspects of the understanding of these measurements
need to be clarified. For example, the study of the J/
production in different colliding systems should help to disentangle which is the variable driving the J/
suppression. The NA60 experiment, with a new radiation tolerant Silicon pixel detector, studied Indium-Indium interactions
in the year 2003. In this paper, we present the J/
/ DY ratio, integrated over all the centralities of the collisions, together with a first study of the J/
transverse momentum and polarization.
Arrival of the final proofs: 1 July 2005
PACS:
25.75.Dw, 25.75.Nq, 13.20.Gd 相似文献
10.
R. Vogt 《The European Physical Journal C - Particles and Fields》2005,43(1-4):113-119
We discuss aspects of open and hidden charm production in deuterium-nucleus collisions at RHIC and LHC energies. We describe calculations of the total
cross section and the charm quark transverse momentum distributions. We next explain how shadowing and moderate nuclear absorption can explain the PHENIX
d Au/pp ratios and predict the combined effect of shadowing and absorption in 6.2 TeV d + Pb collisions.Arrival of the final proofs: 28 April 2005 相似文献
11.
M. Nardi 《The European Physical Journal C - Particles and Fields》2005,43(1-4):85-90
I discuss the charmonium suppression in deconfined medium by thermal dissociation and parton percolation. I point out the differences and show predictions for
suppression at different energy and/or for different interacting nuclei.Received: 14 February 2005, Published online: 31 May 2005PACS:
25.75.Nq,12.38.Mh,25.75.-q,24.85. + p 相似文献
12.
We explore CP violation in
decay processes in the presence of the anomalous right-handed
and
couplings. The complex anomalous top coupling can be a source of new CP violation and may lead to a deviation of the observed weak phase in
decays, which accounts for the present disagreement of the observed
between
and
decays. Direct CP violation is also predicted.
Received: 27 November 2002, Revised: 28 March 2003, Published online: 2 June 2003 相似文献
13.
Di-jet production is studied in collisions of quasi-real photons at e + e- centre-of-mass energies
from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive
-clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets resulting from either of the algorithms. The inclusive di-jet cross-section is measured as a function of the mean transverse energy
of the two leading jets, and as a function of the estimated fraction of the photon momentum carried by the parton entering the hard sub-process,
, for different regions of
. Angular distributions in di-jet events are measured and used to demonstrate the dominance of quark and gluon initiated processes in different regions of phase space. Furthermore the inclusive di-jet cross-section as a function of
and
is presented, where
is the jet pseudo-rapidity. Different regions of the
-
-space are explored to study and control the influence of an underlying event. The results are compared to next-to-leading order perturbative QCD calculations and to the predictions of the leading order Monte Carlo generator PYTHIA.Received: 20 December 2002, Published online: 17 October 2003 相似文献
14.
We investigate the physics potential of the annihilation decays
in the standard model and beyond. In a naive factorization approach, the branching ratios are estimated to be
and
. In the framework of QCD factorization, we compute the non-factorizable corrections and get
,
. Future measurements of these decays would be useful for testing the factorization frameworks. The smallness of these decays in the SM makes them sensitive probes of new physics. As an example, we will consider the possible admixture of the (V + A) charge current to the standard (V-A) current. This admixture will give a significant contribution to the decays.Received: 29 August 2003, Revised: 17 January 2004, Published online: 19 March 2004Corresponding author: Y.D. Yang 相似文献
15.
production in
interactions has been detected via its decays into
,K
+
K
-
K
+
K
- and
in the data taken with the DELPHI detector at LEP1 and LEP2 energies. The two-photon radiative width averaged over all observed decay channels is
= 13.9
2.0 (stat.)
1.4(syst.)
2.7 (BR) keV. No direct decay channel
has been observed. An upper limit
< 5.5 keV at 95% confidence level has been evaluated for this decay mode.Received: 3 July 2003, Published online: 7 November 2003 相似文献
16.
In the SUSY SO(10) GUT context, we study the exclusive processes
. Using the Wilson coefficients of the relevant operators including the new operators
which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like the invariant mass spectrum (IMS), lepton pair forward-backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients
, among new contributions, are dominant. Our results show that the NHB effects are sensitive to the FBA,
, and
of
decay, which are expected to be measured in B factories, the deviation of
in
can reach 0.1 from SM, which could be seen in B factories, and the average of the normal polarization
can reach several percent for
and it is 0.05 or so for
, which could be measured in the future super B factories and provide useful information to probe new physics and discriminate different models.Received: 30 October 2004, Published online: 9 March 2005 相似文献
17.
The fragmentation functions of the pion with distinction between
,
, and
are studied in the Field-Feynman recursive model, by taking into account the flavor structure in the excitation of quark-antiquark pairs by the initial quarks. The obtained analytical results are compatible with the available empirical results. The framework is also extended to predict the fragmentation functions of the kaon with distinction between
,
,
, and
. This work gives a significant modification of the original model, and the predictions can be tested by future experiments on the fragmentation functions of the kaon.Received: 30 January 2003, Revised: 12 June 2003, Published online: 15 August 2003Bo-Qiang Ma: Corresponding author 相似文献
18.
M. Rosati 《The European Physical Journal C - Particles and Fields》2005,43(1-4):173-178
The PHENIX experiment measured J/
production in pp, d + Au and Au + Au reactions at
= 200 GeV over a wide range of rapidity and transverse momentum. The nuclear modification factor obtained by comparing the
d + Au and pp cross sections as a function of rapidity, is consistent with shadowing of the gluon distribution functions.
J/
production in Au + Au collisions was compared to the production in pp collisions and it was found to be inconsistent with
models that predict strong enhancement relative to binary collision scaling.
Arrival of the final proofs: 29 June 2005
PACS:
25.75-q, 25.75-Dw,
* Deceased
Spokesperson 相似文献
19.
We explicitly take into account the effect of the hydrodynamic expansion profile on the gluonic break-up of the
's produced in an equilibrating parton plasma. Attention is paid to the space-time inhomogeneities as well as Lorentz frames
while deriving new expressions for the gluon number density ng, the average dissociation rate
, and the survival probability of
, S. A novel type of partial wave interference mechanism is found to operate in the formula of
. A non-relativistic longitudinal expansion from the small length of the initial cylinder is found to push the S(pT) graph above the no flow case considered by us earlier [9]. However, the relativistic flow corresponding to the large length
of the initial cylinder pushes the curve of S(pT) downwards at LHC but upwards at RHIC. This mutually different effect on S(pT) may be attributed to the different initial temperatures generated at LHC and RHIC.
Received: 16 March 2005, Published online: 27 September 2005
PACS:
12.38.Mh 相似文献
20.
We compute the one-loop
-functions describing the renormalisation of the coupling constant
and the frequency parameter
for the real four-dimensional duality-covariant non-commutative
-model, which is renormalisable to all orders. The contribution from the one-loop four-point function is reduced by the one-loop wavefunction renormalisation, but the
-function remains non-negative. Both
and
vanish at the one-loop level for the duality-invariant model characterised by
. Moreover,
also vanishes in the limit
, which defines the standard non-commutative
-quantum field theory. Thus, the limit
exists at least at the one-loop level.Received: 19 March 2004, Published online: 5 May 2004 相似文献