共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
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
3.
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
4.
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
5.
O. Drapier 《The European Physical Journal C - Particles and Fields》2005,43(1-4):201-208
The PHENIX experiment at RHIC measured single electron spectra in p + p, d + Au and Au + Au collisions at
GeV, and in Au + Au collisions at
GeV. In these spectra, electrons from semi-leptonic decays of charmed particles are the dominant contribution after subtraction
of all 'photonic' sources (photon conversions, Dalitz decays, decays of light vector mesons). The p + p open charm production
cross-section is found to be in good agreement with pQCD NLO calculations. The shape of the distributions obtained for p +
p interactions is compared with those observed for nucleus-nucleus collisions. From p + p to d + Au and Au + Au interactions,
open charm production is found to scale with the number of binary collisions
. Au + Au data at
GeV is compatible with the ISR p + p results scaled by
. The elliptic flow parameter v2 of heavy flavor electrons has also been measured, and is found to be non-zero in the intermediate pT range.
Arrival of the final proofs: 29 June 2005
PACS:
.
* Deceased
Spokesperson 相似文献
6.
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
7.
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
8.
Multijet production rates in neutral current deep inelastic scattering have been measured in the range of exchanged boson
virtualities
. The data were taken at the ep collider HERA with centre-of-mass energy
using the ZEUS detector and correspond to an integrated luminosity of
. Jets were identified in the Breit frame using the kT cluster algorithm in the longitudinally invariant inclusive mode. Measurements of differential dijet and trijet cross sections
are presented as functions of jet transverse energy (
), pseudorapidity (
) and Q2 with
and
. Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant
, determined from the ratio of the trijet to dijet cross sections, is
.
Received: 1 April 2005, Revised: 28 June 2005, Published online: 30 August 2005 相似文献
9.
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
10.
For the first time at LEP the production of prompt photons is studied in the collisions of quasi-real photons using the OPAL data taken at
centre-of-mass energies between 183 GeV and 209 GeV. The total inclusive production cross-section for isolated prompt photons in the kinematic range of transverse momentum
GeV and pseudorapidity
is determined to be
. Differential cross-sections are compared to the predictions of a next-to-leading-order (NLO) calculation.Received: 6 May 2003, Published online: 4 November 2003 相似文献
11.
The anomalous weak dipole moments of the
lepton are measured in a data sample collected by ALEPH from 1990 to 1995 corresponding to an integrated luminosity of 155 pb-1. Tau leptons produced in the reaction
at energies close to the
mass are studied using their semileptonic decays to
,
,
or
. The real and imaginary components of both the anomalous weak magnetic dipole moment and the CP-violating anomalous weak electric dipole moment,
,
,
and
, are measured simultaneously by means of a likelihood fit built from the full differential cross section. No evidence of new physics is found. The following bounds are obtained (95% CL):
,
,
, and
.Received: 25 September 2002, Published online: 29 August 2003 相似文献
12.
The production rates and substructure of jets have been studied in charged current deep inelastic e
+
p scattering for Q
2 > 200 GeV2 with the ZEUS detector at HERA using an integrated luminosity of 110.5 pb-1. Inclusive jet cross sections are presented for jets with transverse energies
GeV and pseudorapidities in the range
. Dijet cross sections are presented for events with a jet having
GeV and a second jet having
GeV. Measurements of the mean subjet multiplicity,
, of the inclusive jet sample are presented. Predictions based on parton-shower Monte Carlo models and next-to-leading-order QCD calculations are compared to the measurements. The value of
, determined from
at
for jets with
GeV, is
. The mean subjet multiplicity as a function of Q
2 is found to be consistent with that measured in NC DIS.Received: 5 June 2003, Published online: 10 October 2003 相似文献
13.
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
14.
A measurement is presented of elastic deeply virtual Compton scattering
made using e + p collision data corresponding to a luminosity of 46.5 pb-1, taken with the H1 detector at HERA. The cross section is measured as a function of the photon virtuality, Q 2, the invariant mass of the
p system, W, and for the first time, differentially in the squared momentum transfer at the proton vertex, t, in the kinematic range
,
and
. QCD based calculations at next-to-leading order using generalized parton distributions can describe the data, as can colour dipole model predictions.Received: 19 May 2005, Revised: 23 June 2005, Published online: 19 August 2005 相似文献
15.
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
16.
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
17.
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
18.
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
19.
This paper presents DELPHI measurements and interpretations of cross-sections, forward-backward asymmetries, and angular distributions,
for the
process for centre-of-mass energies above the Z resonance, from
-207 GeV at the LEP collider. The measurements are consistent with the predictions of the Standard Model and are used to study
a variety of models including the S-Matrix ansatz for
scattering and several models which include physics beyond the Standard Model: the exchange of Z′ bosons, contact interactions
between fermions, the exchange of gravitons in large extra dimensions and the exchange of
in R-parity violating supersymmetry.
This paper is dedicated to the memory of Alan Segar. 相似文献
20.
R. Tomaschitz 《The European Physical Journal C - Particles and Fields》2006,45(2):493-511
We study superluminal cyclotron emission by electrons and muons in semiclassical orbits. The tachyonic line spectra of hydrogenic
ions such as
,
, and
, as well as their muonic counterparts
,
and
are calculated, in particular the tachyonic power transversally and longitudinally radiated, the total intensity, and the
power radiated in the individual harmonics. We also investigate tachyonic continuum radiation from electrons and protons cycling
in the surface and light cylinder fields of
-ray and millisecond pulsars, such as the Crab pulsar, PSR B1509-58, and PSR J0218 + 4232. The superluminal spectral densities
generated by non-relativistic, mildly relativistic and ultra-relativistic source particles are derived. We study the parameters
determining the global shape of the transversal and longitudinal densities and the energy scales of the broadband spectrum.
The observed cutoff frequency in the
-ray band of the pulsars is used to infer the upper edge of the orbital energy, and we conclude that electrons and nuclei
cycling in the surface fields can reach energies beyond the "ankle" of the cosmic ray spectrum. This suggests
-ray pulsars as sources of ultra-high energy cosmic rays.
Arrival of the final proofs: 17 November 2005
PACS:
41.60.Ap, 11.10.Lm, 36.10.Dr, 98.70.Sa 相似文献