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1.
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
2.
H. Buesching 《The European Physical Journal C - Particles and Fields》2005,43(1-4):303-310
Transverse momentum (
) spectra measured by the PHENIX experiment at RHIC in Au + Au, d + Au and pp collisions at
and in Au + Au collisions at
are presented. A suppression of the yield of high
hadrons in central Au + Au collisions by a factor 4-5 at
is found relative to the pp reference scaled by the nuclear overlap function
. In contrast, direct photons are not suppressed in central Au + Au collisions and no suppression of high
particles can be seen in d + Au collisions. This leads to the conclusion that the dense medium formed in central Au + Au
collisions is responsible for the suppression.
Arrival of the final proofs: 30 June 2005
PACS:
25.75.Dw 相似文献
3.
H. K. Wöhri 《The European Physical Journal C - Particles and Fields》2005,43(1-4):407-413
During the June 2002 run NA60 collected around 600 000 dimuon triggers in proton-nucleus collisions at 400 GeV. We show that
the collected dimuon mass spectra can be understood in terms of known sources. The specific target setup, consisting of Beryllium,
Indium and Lead targets, simultaneously exposed to the beam, allowed us to study the nuclear dependence of the production
cross-section of the
and
resonances. The elementary nucleon-nucleon production cross-sections at 400 GeV for the
,
and
mesons are also presented. By using the
-Dalitz decay, dominating the mass range below 450 MeV, we, furthermore, extracted the
production cross-section and its nuclear dependence. The results are discussed in the framework of previous measurements,
mostly obtained in different decay channels, performed by NA27, HELIOS-1 and CERES-TAPS.
Arrival of the final proofs: 1 July 2005
PACS:
25.75.Dw, 25.75.Nq 相似文献
4.
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
5.
C. A. Gagliardi 《The European Physical Journal C - Particles and Fields》2005,43(1-4):263-270
The STAR Collaboration has a broad range of recent results on intermediate and high-
phenomena in Au + Au collisions at
= 200 and 62 GeV and in d + Au at
= 200 GeV. These include new measurements of spectra, azimuthal anisotropies and di-hadron correlations. The comparison of
the 62 and 200 GeV Au + Au results indicates that jet quenching, elliptic flow and di-hadron correlation measurements are
very similar at the two energies. Meson-baryon differences that have been seen at intermediate
in 200 GeV Au + Au collisions are also present in 62 GeV Au + Au collisions and in 200 GeV d + Au collisions. Measurements
of backward-forward inclusive hadron yield asymmetries and forward-midrapidity di-hadron correlations in d + Au collisions
are consistent with the saturation picture. A brief review of these results is presented.
Arrival of the final proofs: 30 June 2005
PACS:
25.75.Dw, 25.75.Ld, 25.75.Gz 相似文献
6.
G. Roland 《The European Physical Journal C - Particles and Fields》2005,43(1-4):281-286
We present results from the PHOBOS experiment on charged hadron production over a large range in
, from Data from d + Au collisions at
GeV and Au + Au collisions at
and 200 GeV are shown. The data indicate that in Au + Au collisions a strongly interacting state of matter is formed, that
appears qualitatively different from the system formed in pp or d + Au collisions. The systematics of particle production
in d + Au and Au + Au collisions exhibit remarkably simple scaling rules, including an apparent factorization of the energy
and centrality dependence over a wide range of collision energies.
Arrival of the final proofs: 29 July 2005
PACS:
25.75.-q, 25.75.Dw, 25.75.Gz 相似文献
7.
Twist-3 distribution amplitudes of the pion and kaon are studied in this paper. We calculate the first several moments for the twist-3 distribution amplitudes (
and
) of the pion and kaon by applying the QCD sum rules. Our results show that (i) the first three moments of
and the first two moments of
and
of the pion and kaon can be obtained with 30
uncertainty; (ii) the fourth moment of the
and the second moment of the
can be obtained when the uncertainty are relaxed to 35
; (iii) the fourth moment of the
can be obtained only when the uncertainty are relaxed to 40
; (iv) we have
and
after including the
-corrections to the perturbative part. These moments will be helpful for constructing the twist-3 wave functions of the pion and kaon.Received: 6 January 2005, Revised: 29 March 2005, Published online: 22 June 2005PACS:
13.20.He, 11.55.Hx 相似文献
8.
A search for lepton-flavor-violating interactions
and
has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity
of
. The data were taken at center-of-mass energies,
, of 300 and
. No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such
interactions. For LQ masses below
, limits were set on
, where
is the coupling of the LQ to an electron and a first-generation quark q1, and
is the branching ratio of the LQ to the final-state lepton
(μ or
) and a quark q. For LQ masses much larger than
, limits were set on the four-fermion interaction term
for LQs that couple to an electron and a quark
and to a lepton
and a quark
, where
and
are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks
in R-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the
process
, the ZEUS limits are the most stringent to date.
Received: 1 April 2005, Revised: 13 July 2005, Published online: 18 October 2005 相似文献
9.
R. Shahoyan 《The European Physical Journal C - Particles and Fields》2005,43(1-4):209-213
NA60 is an experiment at the CERN-SPS devoted to the study of dimuon production in heavy-ion and proton-nucleus collisions.
The main topics under study are low mass vector meson production, J/
production and suppression, and the sources of the dimuon continuum in the mass range 1.2-2.7 GeV/c
2. In 2003, NA60 collected
million dimuon events from Indium-Indium collisions. We present preliminary results of the analysis of this data sample in
view of measuring the open charm contribution to the dimuon spectrum. Although we are still working on the final background
subtraction procedure, we can already demonstrate that the detector performance is good enough to allow the separation of
prompt dimuons from muon pairs originating in distant D
decays.
Arrival of the final proofs: 1 July 2005
PACS:
25.75.Dw, 25.75.Nq 相似文献
10.
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
11.
The Standard Model constraints on
which can be derived from the
decays are revisited in some depth. As experimental inputs, the
,
decays complemented by the
decays, the CP parameters
and
, and/or the value of
as determined by the global CKM fit are used. The constraints discussed here are model independent in the sense that they rely only on Isospin symmetry, following the Gronau-London proposal. A new bound on
and the function
are introduced. While another bound applied to BABAR results is shown to imply that
is negative. The Grossman-Quinn bound is rediscussed. A close form expression is given for
as a function of the measurements. Various scenarios for the future of the isospin analysis are explored. To probe the Standard Model the
plane is introduced.Received: 17 December 2004, Published online: 25 January 2005 相似文献
12.
J. Bielcikova 《The European Physical Journal C - Particles and Fields》2005,43(1-4):323-327
A study of elliptic flow and two-particle azimuthal correlations of charged particles (
GeV/c) and high-
pions (
GeV/c) in Pb + Au collisions at 158A GeV/c, close to midrapidity, is presented. Elliptic flow (v
2) rises linearly with
to a value of about 10
at 2 GeV/c. Beyond
1.5 GeV/c, the slope decreases and possibly indicates a v
2 saturation at high
. Two-pion azimuthal anisotropies for
1.2 GeV/c exceed the v
2 values by about 60
in semicentral collisions. This non-flow component is attributed to near-side and away-side jetlike correlations. While the
near-side peak remains constant with centrality 0.23
0.03 rad, as expected for fragmentation, the away-side peak experiences broadening and disappears in central collisions.
Arrival of the final proofs: 30 June 2005
PACS:
25.75.Ld, 25.75.Gz 相似文献
13.
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
14.
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
15.
The production of
, D0, D + , Ds + and
charm hadrons and their antiparticles in e p scattering at HERA was measured with the ZEUS detector using an integrated luminosity of
. The measurement has been performed in the photoproduction regime with the exchanged-photon virtuality
and for photon-proton centre-of-mass energies in the range
. The charm hadrons were reconstructed in the range of transverse momentum
and pseudorapidity
. The production cross sections were used to determine the ratio of neutral and charged D-meson production rates,
, the strangeness-suppression factor,
, and the fraction of charged D mesons produced in a vector state,
. The measured
and
values agree with those obtained in deep inelastic scattering and in e + e- annihilations. The measured
value is smaller than, but consistent with, the previous measurements. The fractions of c quarks hadronising as a particular charm hadron,
, were derived in the given kinematic range. The measured open-charm fragmentation fractions are consistent with previous
results, although the measured
is smaller and
is larger than those obtained in e + e- annihilations. These results generally support the hypothesis that fragmentation proceeds independently of the hard sub-process.
Received: 12 August 2005, Revised: 8 September 2005, Published online: 6 October 2005 相似文献
16.
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
17.
18.
A. Mischke 《The European Physical Journal C - Particles and Fields》2005,43(1-4):311-316
In this paper, preliminary results are presented on high
inclusive neutral pion measurements in d-Au collisions at
GeV in the pseudo-rapidity range
. Photons from the decay
are detected in the Barrel Electromagnetic Calorimeter of the STAR experiment at RHIC. The analysis of this first BEMC hadron
measurement is described in detail. The results are compared to earlier RHIC findings. Furthermore, the obtained
invariant differential cross sections show good agreement with next-to-leading order (NLO) perturbative QCD calculations.
Arrival of the final proofs: 4 July 2005
PACS:
25.75.-q 相似文献
19.
The COMPASS Collaboration 《The European Physical Journal C - Particles and Fields》2005,41(4):469-474
Narrow
and
resonances produced by quasi-real photons have been searched for by the COMPASS experiment at CERN. The study was stimulated by the recent observation of an exotic baryonic state decaying into
, at a mass of 1862 MeV, interpreted as a pentaquark. While the ordinary hyperon states
and
are clearly seen, no exotic baryon is observed in the data taken in 2002 and 2003.Received: 15 March 2005, Published online: 31 May 2005PACS:
13.60.Hb, 13.60.Rj, 14.20.Jn, 14.80.-j 相似文献
20.
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