共查询到20条相似文献,搜索用时 343 毫秒
1.
P. Huovinen 《The European Physical Journal A - Hadrons and Nuclei》2008,37(1):121-128
We study the effect of separate chemical and kinetic freeze-outs to the ideal hydrodynamical flow in Au + Au collisions at
RHIC ( energy). Unlike earlier studies we explore how these effects can be counteracted by changes in the initial state of the hydrodynamical
evolution. We conclude that the reproduction of pion, proton and antiproton yields necessitates a chemical freeze-out temperature
of T ≈ 150MeV instead of T = 160–170 MeV motivated by thermal models. Contrary to previous reports, this lower temperature makes it possible to reproduce
the p
T spectra of hadrons if one assumes very small initial time, τ
0 = 0.2 fm/c. However, the p
T differential elliptic flow, v
2(p
T) remains badly reproduced. This points to the need to include dissipative effects (viscosity) or some other refinement to
the model. 相似文献
2.
The lattice QCD studies indicate that the critical temperature T
c ≃ 260-280 MeV of the deconfinement phase transition in quenched QCD is considerably smaller than the lowest-lying glueball
mass m
G ≃ 1500-1700 MeV, i.e., T
c ≪ m
G. As a consequence of this large difference, the thermal excitation of the glueball in the confinement phase is strongly suppressed
by the statistical factor e
-mG/Tc ≃ 0.00207 even near T ≃ T
c. We consider its physical implication, and argue the abnormal feature of the deconfinement phase transition in quenched QCD
from the statistical viewpoint. To appreciate this, we demonstrate a statistical argument of the QCD phase transition using
the recent lattice QCD data. From the phenomenological relation between T
c and the glueball mass, the deconfinement transition is found to take place in quenched QCD before a reasonable amount of
glueballs is thermally excited. In this way, quenched QCD reveals a question “what is the trigger of the deconfinement phase
transition ?”
Received: 18 November 2002 / Accepted: 4 February 2003 / Published online: 29 April 2003 相似文献
3.
A. K. Chaudhuri 《The European Physical Journal C - Particles and Fields》2009,61(2):331-338
In a hydrodynamic model, we have studied J/ψ production in Au+Au/Cu+Cu collisions at RHIC energy,
GeV. At the initial time, J/ψ’s are randomly distributed in the fluid. As the fluid evolves in time, the free streaming J/ψ’s are dissolved if the local fluid temperature exceeds a threshold temperature T
J/ψ
. Sequential melting of charmonium states (χ
c
, ψ
′ and J/ψ), with melting temperatures
, T
J/ψ
≈2T
c
and feed-down fraction F≈0.3, explains the PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions. J/ψ
p
T
spectra and the nuclear modification factor in Au+Au collisions are also well explained in the model. The model however overpredicts
the centrality dependence of J/ψ suppression in Cu+Cu collisions by 20–30%. The J/ψ
p
T
spectra are underpredicted by 20–30%. The model predicts that in central Pb+Pb collisions at LHC energy,
GeV, J/ψ’s are suppressed by a factor of ∼10. The model predicted a J/ψ
p
T
distribution in Pb+Pb collisions at LHC is similar to that in Au+Au collisions at RHIC. 相似文献
4.
H. Fujii 《The European Physical Journal C - Particles and Fields》2009,62(1):69-73
Properties of the QCD critical point, an endpoint of the first order boundary line in the temperature T–baryochemical potential μ
B
plane, are discussed with the Nambu–Jona-Lasinio model. It is demonstrated that the softening of the sigma mesonic mode is
inherent to the crossover transition of the chiral symmetry while the spectral enhancement of the particle–hole mode near
zero frequency is associated with the QCD critical point. Phenomenological implications in heavy-ion experiments are mentioned
briefly. 相似文献
5.
Jiangyong Jia 《The European Physical Journal C - Particles and Fields》2009,62(1):255-264
We review the di-hadron correlation results from RHIC. A consistent physical picture was constructed based on the correlation
landscape in p
T
, Δφ, Δη and particle species. We show that the data are consistent with competition between fragmentation of survived jets and response
of the medium to quenched jets. At intermediate p
T
where the medium response are important, a large fraction of trigger hadrons do not come from jet fragmentation. We argue
that these hadrons can strongly influence the interpretation of the low p
T
correlation data. We demonstrate this point through a simple geometrical jet absorption model simulation. The model shows
that the correlation between medium response hadrons dominates the pair yield and mimics the double hump structure of the
away-side Δφ distribution at low p
T
. This correlation was also shown to lead to complications in interpreting the results on reaction plane dependence and three
particle correlations. Finally, we briefly discuss several related experimental issues which are important for proper interpretations
of the experimental data. 相似文献
6.
A. M. Hamed 《The European Physical Journal C - Particles and Fields》2009,61(4):597-601
The presented results are the first measurements at RHIC for direct γ-charged hadron azimuthal correlations in heavy ion collisions. We use these correlations to study the color charge density
of the medium through the medium-induced modification of high-p
T
parton fragmentation. Azimuthal correlations of direct photons at high transverse energy (8<p
T
<16 GeV) with away-side charged hadrons of transverse momentum (3<p
T
<6 GeV/c) have been measured over a broad range of centrality for Au+Au collisions and p+p collisions at
GeV in the STAR experiment. A transverse shower shape analysis in the STAR Barrel Electromagnetic Calorimeter Shower Maximum
Detector is used to discriminate between the direct photons and photons from the decays of high p
T
π
0. The per-trigger away-side yield of direct γ is smaller than from π
0 trigger at the same centrality class. Within the current uncertainty the I
CP
of direct γ and π
0 are similar. 相似文献
7.
L. Bravina A. Capella E. G. Ferreiro A. B. Kaidalov K. Tywoniuk E. Zabrodin 《The European Physical Journal C - Particles and Fields》2009,61(4):865-870
One observes strong suppression effects for hard probes, e.g. the production of J/ψ or high-p
T
particles, in nucleus–nucleus (AA) collisions at RHIC. Surprisingly, the magnitude of the suppression is quite similar to that at SPS. In order to establish
whether these features arise due to the presence of a thermalized system of quarks and gluons formed in the course of the
collision, one should investigate the impact of suppression mechanisms which do not explicitly involve such a state. We calculate
shadowing for gluons in the Glauber–Gribov theory and propose a model invoking a rapidity-dependent absorptive mechanism motivated
by energy-momentum conservation effects. Furthermore, final-state suppression due to interaction with comoving matter (hadronic
or pre-hadronic) has been shown to describe the data at SPS. We extend this model by including the backward reaction channel,
i.e. recombination of open charm, which is estimated directly from pp data at RHIC. Strong suppression of charmonium both in pA and AA collisions at LHC is predicted. This is in stark contrast with the predictions of models assuming QGP formation and thermalization
of heavy quarks. 相似文献
8.
S Kailas R Vandenbosch A Charlop A Garcia S Gil S J Luke B McLain D Prindle 《Pramana》1990,35(5):439-447
The fusion cross section for the system6Li+28Si has been measured atE∼36 MeV. Combining this with the data available at lower energies, the nucleus-nucleus real potentials have been determined
for a range of interaction distances. 相似文献
9.
R. Arnaldi K. Banicz K. Borer J. Castor B. Chaurand W. Chen C. Cicalò A. Colla P. Cortese S. Damjanovic A. David A. de Falco A. Devaux L. Ducroux H. En’yo J. Fargeix A. Ferretti M. Floris A. F?rster P. Force N. Guettet A. Guichard H. Gulkanian J. M. Heuser M. Keil L. Kluberg Z. Li C. Louren?o J. Lozano F. Manso P. Martins A. Masoni A. Neves H. Ohnishi C. Oppedisano P. Parracho P. Pillot T. Poghosyan G. Puddu E. Radermacher P. Ramalhete P. Rosinsky E. Scomparin J. Seixas S. Serci R. Shahoyan P. Sonderegger H. J. Specht R. Tieulent G. Usai R. Veenhof H. K. W?hri 《The European Physical Journal C - Particles and Fields》2009,61(4):711-720
The NA60 experiment at the CERN SPS has measured muon pairs with unprecedented precision in 158 A GeV In–In collisions. A strong excess of pairs above the known sources is observed in the whole mass region 0.2<M<2.6 GeV. The mass spectrum for M<1 GeV is consistent with a dominant contribution from π
+
π
−→ρ→μ
+
μ
− annihilation. The associated ρ spectral function shows a strong broadening, but essentially no shift in mass. For M>1 GeV, the excess is found to be prompt, not due to enhanced charm production, with pronounced differences to Drell–Yan pairs.
The slope parameter T
eff associated with the transverse momentum spectra rises with mass up to the ρ, followed by a sudden decline above. The rise for M<1 GeV is consistent with radial flow of a hadronic emission source. The seeming absence of significant flow for M>1 GeV and its relation to parton–hadron duality is discussed in detail, suggesting a dominantly partonic emission source
in this region. A comparison of the data to the present status of theoretical modeling is also contained. The accumulated
empirical evidence, including also a Planck-like shape of the mass spectra at low p
T
and the lack of polarization, is consistent with a global interpretation of the excess dimuons as thermal radiation. We conclude
with first results on ω in-medium effects. 相似文献
10.
The measurement of charmonium suppression in relativistic heavy ion collisions is posited to be an unambiguous probe of the
properties of the strongly interacting quark gluon plasma (sQGP). In hot and dense QCD matter Debye color screening prevents
charm and anti-charm quark pairs from forming J/ψ mesons if the screening radius is smaller than the binding radius. However, one must have a clear understanding of the expected
suppression in normal density QCD matter before interpreting any additional anomalous suppression. The PHENIX experiment has
measured J/ψ production from colliding proton + proton and deuteron + gold beams at 200 GeV from the relativistic heavy ion collider (RHIC).
The deuteron + gold data can be compared to the proton + proton baseline in order to establish the typical suppression in
cold nuclear matter (CNM). For PHENIX, a suppression of J/ψ in cold nuclear matter is observed as one goes forward in rapidity (in the deuteron-going direction), corresponding to a
region more sensitive to initial state low-x gluons in the gold nucleus. These results can be convoluted with the nuclear-environment-modified parton distribution functions,
extracted from deep inelastic scattering (DIS) and Drell-Yan (DY) data, in order to estimate the J/ψ break up cross section in cold nuclear matter. One can also use a data driven method that does not rely on the assumption
of the production mechanism, or PDF parameterization, to extrapolate to the heavy ion collision case. At this time both the
predictions for CNM effect suppression in heavy ion collisions are somewhat ambiguous. Future results using the data acquired
by the PHENIX experiment in run-6 (p + p) and run-8 (d + Au) will be vital for our understanding. These data, which are in
the process of being analyzed, will provide a needed improvement in the statistical and systematic precision of constraints
for CNM effects. These constraints must be improved in order to make firm conclusions concerning additional hot nuclear matter
charmonium suppression in the sQGP. 相似文献
11.
Ashok Kumar 《Pramana》1990,35(5):449-459
A relatively simple procedure using nuclear interaction calculated microscopically from two-nucleon potential employing equivalence
of resonating group method and generator coordinate method has been used to calculate the differential cross-sections (DCS)
forα +20Ne elastic scattering atE
lab=18.0, 20.2, 21.9, 23.0 and 27.2 MeV. The absorption effects due to the opening of the non-elastic channels are taken into
account approximately by the sharp cut-off of lower partial waves. The anomalous large oscillations of the DCS at backward
angles atE
lab=18.0 and 27.2 MeV are reproduced. The calculated results are in fair agreement with the experimental data. 相似文献
12.
K. Nünighoff Ch. Pohl S. Koulikov F. Cantargi H. Conrad D. Filges H. Glückler F. Goldenbaum R. Granada G. Hansen T. Matzerath N. Paul S. Petriw H. Schaal H. Soltner H. Stelzer W. Ninaus M. Wohlmuther 《The European Physical Journal A - Hadrons and Nuclei》2008,38(1):115-123
In this article we describe the experimental results of a methane hydrate moderator as well as as mesitylene moderator operated
at a temperature around 20K at the JESSICA (Jülich Experimental Spallation Target Set-up In COSY Area) experiment at the Jülich
cooler synchrotron COSY. For the first time the cold neutron spectrum of a methane hydrate moderator was experimentally investigated.
A comparison with a solid methane and an ice moderator atT = 20 K will be shown. MCNPX simulations with new developedS(α,β) scattering kernels will be compared with experimental data. The applicability of mesitylene and methane hydrate as cold
moderators at spallation neutron sources will be discussed. 相似文献
13.
Hiroshi Masui 《The European Physical Journal C - Particles and Fields》2009,62(1):169-173
One of the most striking results is the large elliptic flow (v
2) at RHIC. Detailed mass and transverse momentum dependence of elliptic flow are well described by ideal hydrodynamic calculations
for p
T<1 GeV/c, and by parton coalescence/recombination picture for p
T=2–6 GeV/c. The systematic error on v
2 is dominated by so-called “non-flow effects”, which are correlations other than flow, such as resonance decays and jets.
It is crucial to understand and reduce the systematic error from non-flow effects in order to understand the underlying collision
dynamics. In this paper, we present the centrality dependence of v
2 with respect to the first harmonic event plane at ZDC-SMD (v
2{ZDC-SMD}) in Au + Au collisions at
GeV. A large rapidity gap (|Δη|>6) between midrapidity and the ZDC-SMD could enable us to minimize possible non-flow contributions. We compare the results
of v
2{ZDC-SMD} with v
2{BBC}, which is measured by event plane determined at |η|=3.1–3.9. Possible non-flow contributions in those results will be discussed. 相似文献
14.
The total (p, n) reaction cross section for48Ca has been measured as a function of proton energy in the energy range 1.885 to 5.100 MeV with an overall resolution of ∼
2 keV and in ∼ 5 keV energy steps. The fluctutions in fine resolution data have been analysed to determine the average coherence
width 〈Γ〉. The excitation function averaged over large energy intervals has been analyzed in terms of the optical model. The
isobaric analogue resonances atE
p
∼ 1.95 and 4 MeV have been shape-analyzed to extract the proton partial width and the spectroscopic factorS
n
. A comparison of the gross structures observed in ∼ 55 keV averaged excitation function with the predictions of Izumo’s partial
equilibrium model has also been made. 相似文献
15.
16.
R. Arnaldi K. Banicz K. Borer J. Castor B. Chaurand W. Chen C. Cicalò A. Colla P. Cortese S. Damjanovic A. David A. de Falco A. Devaux L. Ducroux H. En’yo J. Fargeix A. Ferretti M. Floris A. F?rster P. Force N. Guettet A. Guichard H. Gulkanian J. M. Heuser M. Keil L. Kluberg Z. Li C. Louren?o J. Lozano F. Manso P. Martins A. Masoni A. Neves H. Ohnishi C. Oppedisano P. Parracho P. Pillot T. Poghosyan G. Puddu E. Radermacher P. Ramalhete P. Rosinsky E. Scomparin J. Seixas S. Serci R. Shahoyan P. Sonderegger H. J. Specht R. Tieulent G. Usai R. Veenhof H. K. W?hri 《The European Physical Journal C - Particles and Fields》2009,59(3):607-623
The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c
2 produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon
pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions.
In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson
production, but made of prompt muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of
this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to
the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons
are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass
and significantly lower than those found at masses below 1 GeV/c
2, rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c
2 to be of largely partonic origin, when radial flow has not yet built up. 相似文献
17.
Zhangbu Xu Thomas Ullrich 《The European Physical Journal C - Particles and Fields》2009,61(4):687-691
We report results on quarkonium production from the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). J/ψ spectra in p+p and Cu+Cu collisions at
GeV with transverse momenta in the range of 0.5–14 GeV/c and 5–8 GeV/c, respectively, are presented. We find that for p
T
>5 GeV/c yields in p+p collisions are consistent with those in minimum-bias Cu+Cu collisions scaled with the respective number of binary nucleon-nucleon
collisions. In this range the nuclear modification factor, R
AA
, is measured to be 0.9±0.2 (stat). For the first time at RHIC, high-p
T
J/ψ-hadron correlations were studied in p+p collisions. Implications from our measurements on J/ψ production mechanisms, constraints on open bottom yields, and J/ψ dissociation mechanisms at high-p
T
are discussed. In addition, we give a brief status of measurements of ϒ production in p+p and Au+Au collisions and present projections of future quarkonia measurements based on an upgrades to the STAR detector and
increased luminosity achieved through stochastic cooling of RHIC. 相似文献
18.
D. Blaschke M.K. Volkov V.L. Yudichev 《The European Physical Journal A - Hadrons and Nuclei》2003,17(1):103-110
The phase diagram for quark matter is investigated within a simple Nambu-Jona-Lasinio model without vector correlations. It
is found that the phase structure in the temperature-density plane depends sensitively on the parametrization of the model.
We present two schemes of parametrization of the model where, within the first one, a first-order phase transition from a
phase with broken chiral symmetry to a color superconducting phase for temperatures below the triple point at T
t = 55 MeV occurs, whereas for the second one a second-order phase transition for temperatures below T
t = 7 MeV is found. In the latter case, there is also a coexistence phase of broken chiral symmetry with color superconductivity,
which is a new finding within this class of models. Possible consequences for the phenomenology of the QCD phase transition
at high baryon densities are discussed.
Received: 3 January 2003 / Accepted: 21 February 2003 / Published online: 24 April 2003 相似文献
19.
P.?Stok?osa W.?P?aczek M.?Skrzypek 《The European Physical Journal C - Particles and Fields》2009,60(2):213-232
We present two Monte Carlo algorithms of the Markovian type which solve the modified QCD evolution equations at NLO level.
The modifications with respect to the standard DGLAP evolution concern the argument of the strong coupling constant, α
S. We first analyze the z-dependent argument and then the k
T
-dependent one. The evolution time variable is identified with the rapidity. The two algorithms are tested to 0.05% precision
level. We find that the NLO corrections in the evolution of the parton momentum distributions with k
T
-dependent coupling constant are of the order of 10 to 20%, and in the small-x region even up to 30%, with respect to the LO contributions.
The project is partly supported by the EU grant MTKD-CT-2004-510126, realized in a partnership with the CERN Physics Department
and by the Polish Ministry of Science and Information Society Technologies grant No. 620/E-77/6.PR UE/DIE 188/2005-2008. 相似文献
20.
Chengfu Mu Pengfei Zhuang 《The European Physical Journal C - Particles and Fields》2008,58(2):271-279
We investigate the effect of the restoration of chiral symmetry on the quark potential in a quark–meson plasma by considering
meson exchanges in the two flavor Nambu–Jona-Lasinio model at finite temperature and density. There are two possible oscillations
in the chiral restoration phase; one is the Friedel oscillation due to the sharp quark Fermi surface at high density, and
the other is the Yukawa oscillation driven by the complex meson poles at high temperature. The quark–meson plasma is strongly
coupled in the temperature region 1≤T/T
c≤3, with T
c being the critical temperature of the chiral phase transition. The maximum coupling in this region is located at the phase
transition point. 相似文献