共查询到20条相似文献,搜索用时 46 毫秒
1.
J. Hüfner Y.B. He B.Z. Kopeliovich 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):239-244
Prompt gluons are an additional source for charmonium suppression in nuclear collisions, in particular for nucleus-nucleus
collisions. These gluons are radiated as bremsstrahlung in N-N collisions and interact inelastically with the charmonium states
while the nuclei still overlap. The spectra and mean number <n
g> of the prompt gluons are calculated perturbatively and the inelastic cross section σabs
Ψg is estimated. The integrated cross sections σ(A B →J/ψX) for p-A and A-B collisions and the dependence on transverse energy for S-U and Pb-Pb can be described quantitatively with
some adjustment of one parameter <n
g>σabs
Ψg.
Received: 20 August 1999 相似文献
2.
The QCD factorization theorem for diffractive processes in DIS is used to derive formulae for the leading twist contribution
to the nuclear shadowing of parton distributions in the low thickness limit (due to the coherent projectile (photon) interactions
with two nucleons). Based on the current analyzes of diffraction at HERA we find that the average strength of the interactions
which govern diffraction in the gluon sector at x≤ 10−3, Q
0= 2 GeV is ∼50mb. This is three times larger than in the quark sector and suggests that applicability of DGLAP approximation
requires significantly larger Q
0 in the gluon sector. We use this information on diffraction to estimate the higher order shadowing terms due to the photon
interactions with N≥ 3 nucleons which are important for the scattering of heavy nuclei and to calculate nuclear shadowing and Q
2 dependence of gluon densities. For the heavy nuclei the amount of the gluon shadowing: G
A(x,Q
0
2) /AG
N(x,Q
0
2)|x ≤ 10−3∼ 0.25–0.4 is sensitive to the probability of the small size configurations within wave function of the gluon “partonometer”
at the Q
0 scale. At this scale for A∼ 200 the nonperturbative contribution to the gluon density is reduced by a factor of 4–5 at x≤ 10−3 unmasking PQCD physics in the gluon distribution of heavy nuclei. We point out that the shadowing of this magnitude would
strongly modify the first stage of the heavy ion collisions at the LHC energies, and also would lead to large color opacity
effects in eA collisions at HERA energies. In particular, the leading twist contribution to the cross section of the coherent
J/ψ production off A≥ 12 nuclei at s
−2≥ 70 GeV is strongly reduced as compared to the naive color transparency expectations. The Gribov black body limit for F
2A(x,Q
2) is extended to the case of the gluon distributions in nuclei and shown to be relevant for the HERA kinematics of eA collisions.
Properties of the final states are also briefly discussed.
Received: 12 March 1999 相似文献
3.
V. L. Lyuboshitz V. V. Lyuboshitz 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):465-467
The coherent inelastic processes of the type a→b, which may take place in the collisions of hadrons and γ-quanta with nuclei at very high energies (the nucleus remains the same), are theoretically investigated. The influence of
matter inside the nucleus is taken into account by using the optical model based on the concept of refraction index. Analytical
formulas for the effective cross-section σ
coh(a→b) are obtained, taking into account that at ultrarelativistic energies the main contribution into σ
coh(a→b) is provided by very small transferred momenta in the vicinity of the minimum longitudinal momentum transferred to the nucleus. 相似文献
4.
The pseudo-rapidity distribution has been studied for 50 GeV/cπ
−-colliding with various groups of target nuclei in emulsion. These data are compared with the published data onp-A collisions. It is observed that leading component multiplicity inπ
−-Em collisions decreases withN
h
in highη-region. It is also observed that nearly 20% of the interactions proceed via single cluster formation at this projectile energy. 相似文献
5.
I.F. Ginzburg U.D. Jentschura V.G. Serbo 《The European Physical Journal C - Particles and Fields》2008,54(2):267-276
Delbrück scattering is the elastic scattering of a photon in the Coulomb field of a nucleus via a virtual electron loop. The
contribution of this virtual subprocess to the emission of a photon in the collision of ultra-relativistic nuclei, Z1Z2→Z1Z2γ, is considered. We identify the incoming virtual photon as being generated by one of the relativistic nuclei involved in
the binary collision and the scattered photon as being emitted in the process. The energy and angular distributions of the
photons are calculated. The discussed process has no infrared divergence. The total cross section obtained is 14 barn for
Au–Au collisions at the RHIC collider and 50 barn for Pb–Pb collisions at the LHC collider. These cross sections are considerably
larger than those for ordinary tree-level nuclear bremsstrahlung in the considered photon energy range, me⪡Eγ⪡meγ, where γ is the Lorentz factor of the nucleus. Finally, photon emission in electron–nucleus collisions, eZ→eZγ, is discussed
in the context of the eRHIC option. 相似文献
6.
S. Shi 《Indian Journal of Physics》2011,85(7):1137-1141
Elliptic flow allows us to probe early dynamics in high energy nuclear collisions. The υ
2 result of charged hadrons and identified hadrons [1,2] from 200 GeV Au+Au collisions at RHIC suggest that the matter with
partonic collectivity and thermalization has been formed in central collisions. In this analysis, we present preliminary results
of υ
2 for K
S
0 and Λ from 200 GeV Cu+Cu collisions. The partonic collectivity and thermalization assumption are tested in smaller Cu+Cu system
comparing with those from Au+Au collisions. 相似文献
7.
Ph. Cahuzac J. L. LeGouët P. E. Toschek R. Vetter 《Applied physics. B, Lasers and optics》1979,20(1):83-88
Laser induced nonlinear absorption profiles in a three-level system have been recorded to study the effect of elastic collisions
upon optical coherences. In our particular system, the signal is due to a pure double-quantum term, where we have separated
the effect of phase-interrupting collisions from the effect of velocity-changing collisions. Experimental results show that
the effect of velocity-changing collisions is very small, and that broadening of the signal is due to phase-interrupting collisions
mainly. We are able to determine the increase of the decay rate of the coherent superposition (the “coherence”) of two levels
of same parity [Dγ
13/dp=(6.5±1) MHz/Torr] and an upper limit for the mean velocity change (ũ≲5m/s). 相似文献
8.
M. Anikina L. Chkhaidze T. Djobava V. Garsevanishvili L. Kharkhelauri 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):139-145
The light front analysis of π− mesons in He(Li,C), C-Ne, C-Cu and O-Pb collisions is carried out. The phase space of secondary pions is divided into two
parts in one of which the thermal equilibrium assumption seems to be in a good agreement with the data. Corresponding temperatures
T are extracted and their dependence on (A
P·A
T)1/2 is studied. The results are compared with the predictions of the Quark-Gluon String Model (QGSM). The QGSM satisfactorily
reproduces the experimental data for light and intermediate-mass nuclei.
Received: 29 September 1999 相似文献
9.
The narrow NN-decoupled dibaryon resonance with a mass about 1956 MeV was reported in 2000 by DIB2γ Collaboration (JINR, Dubna) on the
basis of the measurement of the two-photon energy spectrum in the reaction pp → pp2γ at 216 MeV. The most probable quantum numbers J
P
= 1+ prevent the resonance from decaying into two protons due to the exclusion principle, while the pionic decays are impossible
energetically. The significance of this resonance (called d
1* (1956)) for the interpretation of a few other exclusive and inclusive reactions connected with the photon(s) production
in nucleon collisions with nucleons and nuclei at different energies is discussed. The importance is stressed of on-going
and planned studies of the elastic and inelastic Compton scattering on the lightest nuclei for collecting information on the
structure and dynamics of d
1* (1956) which can shed light on its nature. 相似文献
10.
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
11.
S. E. Chigrinov K. K. Gudima A. I. Kievitskaya V. A. Petlitsky 《Hyperfine Interactions》1993,77(1):149-159
In this paper, we present a model of calculation with respect to the interactions of high-energy nuclei with matter. Based
on this model, we obtain results on energy and angular spectra of the n- and π−-particles produced in collisions of deuterium and tritium nuclei at energiesT
d=1 GeV/nucleon with light targets such as Li, Be. We have also estimated the production yields of neutrons and π−-mesons in targets of various radii, as well as mean energies of these these particles. Summarizing, we find that the lithium
target of radiusR=10−12 cm for which the energy cost επ to produce one π−-meson is estimated as 6.7 GeV/π for a d-beam and 5.3 GeV/π for a t-beam is the most preferred pion-production target. 相似文献
12.
G. Pichler M. Motzkus S. L. Cunha K. L. Kompa R. R. B. Correia P. Hering 《Il Nuovo Cimento D》1992,14(10):1065-1073
Summary We have carried out parallel studies of the quenching process in Na(3p)+H2 collisions and the possible reactive process in Na(3p)+H2 (v
″=1,2,3) collisions. Rich CARS spectra which were obtained at H2 pressure of 100 mbar and oven temperature of 600 K indicate the presence of vibrationally excited H2 and photochemically produced NaH molecules. Temporal resolution of NaH CARS lines was employed in order to rule out competing
collisional processes. We make use of resonantly enhanced CARS methods which enabled us to achieve very high sensitivity for
NaH detection.
Paper presented at the ?XI European CARS Workshop?, Florence, Italy, 23–25 March, 1992. 相似文献
13.
T. Ishii M. Asai A. Makishima I. Hossain P. Kleinheinz M. Ogawa M. Matsuda S. Ichikawa 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):15-19
Nuclei in the neutron-rich Ni region have been studied by γ-ray spectroscopy. Gamma-rays emitted from isomers, with T
1/2 > 1 ns, produced in heavy-ion deep-inelastic collisions were measured with an isomer-scope. The nuclear structure of the
doubly magic 68Ni and its neighbor 69,71Cu is discussed on the basis of the shell model. Future experiments for more neutron-rich Ni nuclei are also viewed.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
14.
The multiplicity dependence of inclusive spectra of identified hadrons (π, K,
, K
S
0
, and Λ) produced in high-energy
p and pp collisions is studied. Analysis of experimental data on high-p
T hadron cross sections obtained at the Tevatron and RHIC is performed in the framework of z scaling. Independence of the scaling function ψ(z) on the multiplicity density dN
ch/dη is established. The multiplicity density measured in nucleon-nucleon collisions reaches much higher values than the corresponding
quantity [1/(0.5N
p)]dN
ch/dη obtained in heavy-ion collisions. Its influence on particle production reveals properties of self-similarity and fractality.
The relation between the scaling variable z and thermodynamic quantities (“heat capacity” and “temperature”) of the medium associated with the produced inclusive particle
is discussed. Search for z-scaling violation in
p and pp collisions at very high multiplicities as an indication of new-physics phenomena is suggested.
The text was submitted by the authors in English. 相似文献
15.
《The European Physical Journal C - Particles and Fields》2009,61(4):853-858
The J/ψ azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158
GeV/nucleon. Various physical mechanisms related to charmonium dissociation in the medium created in the heavy ion collision
are expected to introduce an anisotropy in the azimuthal distribution of the observed J/ψ mesons at SPS energies. Hence, the measurement of J/ψ elliptic anisotropy, quantified by the Fourier coefficient v
2 of the J/ψ azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining
the anomalous J/ψ suppression observed in Pb-Pb collisions. We present the measured J/ψ yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier
coefficient v
2 as a function of the collision centrality and of the J/ψ transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy
detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed
in five centrality or p
T sub-samples. The extracted v
2 values are significantly larger than zero for non-central collisions and are seen to increase with p
T. 相似文献
16.
17.
A. B. Voitkiv 《Journal of Experimental and Theoretical Physics》1997,85(6):1074-1080
Ionization of hydrogen and helium atoms is studied for the case of “soft” collisions with highly charged fast ions with v≲Z≪v2 and v≫v
0, where Z is the ion charge, v is the collision velocity, and v
0∼1 is the characteristic velocity of the electron in the ground state of the atom. Analytical expressions are derived for
the singly and doubly differential cross section for ionization of a hydrogen atom accompanied by the ejection of a slow electron
v
e≲v
0, where v
e is the velocity of the ejected electron with respect to the recoil ion). The results are generalized to the case of single
ionization of helium. It is shown that soft collisions provide the main contribution to the hydrogen ionization cross section
and for all practical purposes determine the cross section for single ionization of helium. The asymmetry in the angular distribution
of the ejected slow electrons and the properties of momentum exchange in such collisions are discussed. Finally, a formula
for the cross section for single ionization of helium is proposed.
Zh. éksp. Teor. Fiz. 112, 1966–1977 (December 1997) 相似文献
18.
We propose the enhancement of Λ
c yield in heavy ion collisions at RHIC and LHC as a novel signal for the existence of diquarks in the strongly coupled quark-gluon
plasma produced in these collisions as well as in the Λ
c
. Assuming that stable bound diquarks can exist in the quark-gluon plasma, we argue that the yield of Λ
c would be increased by two-body collisions between [ud] diquarks and c quarks, in addition to normal three-body collisions among u, d and c quarks. A quantitative study of this effect based on the coalescence model shows that including the contribution of diquarks
to Λ
c
production indeed leads to a substantial enhancement of the Λ
c
/D ratio in heavy ion collisions. 相似文献
19.
Vi-Nham?Tram Fran?ois?Arleo 《The European Physical Journal C - Particles and Fields》2009,61(4):847-852
Interpreting the J/ψ suppression reported in nucleus–nucleus collisions at SPS and RHIC requires a quantitative understanding of cold nuclear-matter
effects, such as the inelastic rescattering of J/ψ states in nuclei or the nuclear modification of parton densities. With respect to our former Glauber analysis, we include
in the present work the new PHENIX d–Au measurements, and we analyze as well all existing data using the EPS08 nuclear parton densities recently released. The
largest suppression reported in the new PHENIX analysis leads in turn to an increase of σ
J/ψN from 3.5±0.3 to 5.4±2.5 mb using the PDF of the proton. The stronger x-dependence of the G
A
/G
p
ratio in EPS08 as compared to e.g. EKS98 shifts the cross section towards larger values at fixed-target energies (x
2∼0.1), while decreasing somehow the value extracted at RHIC (x
2∼10−2). 相似文献
20.
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