共查询到20条相似文献,搜索用时 15 毫秒
1.
《The European Physical Journal A - Hadrons and Nuclei》1999,5(4):429-440
The experimental data on the interactions of 10.6A GeV gold nuclei in nuclear emulsions are analyzed with particular emphasis
of target separation interactions and study of critical exponents. Charged fragment moments, conditional moments as well as
two and three – body asymmetries of the fast moving projectile particles are determined in terms of the total charge remaining
bound in the multiply charged projectile fragments. Some differences in the average yields of helium nuclei and heavier fragments
are observed, which may be attributed to a target effect. However, two and three-body asymmetries and conditional moments
indicate that the breakup mechanism of the projectile seems to be independent of target mass. We looked for evidence of critical
point observable in finite nuclei by study the resulting charged fragments distributions. We have obtained the values for
the critical exponents γ, β and τ and compare our results with those at lower energy experiment (1.0A GeV data). The values
suggest that a phase transition like behavior, is observed.
Received: 2 July 1998 / Revised version: 26 March 1999 相似文献
2.
3.
Abstact: The composition of forward-going projectile spectator matter in fixed-target Pb+Pb collisions at 158 A · GeV at the CERN
SPS has been studied as a function of centrality. The data were measured with the NA49 veto calorimeter. We observe that forward-going
spectator matter in central collisions consists of 9 neutrons, 7 protons, and half a deuteron on average. At large impact
parameters most spectator nucleons are bound in fragments. The relative resolution of the average impact parameter derived
from the measurement of spectator neutrons is roughly 19% in the range from zero to half maximum impact parameters.
Received: 16 February 1998 / Revised version: 30 March 1998 相似文献
4.
D.V. Anchishkin A.M. Gavrilik N.Z. Iorgov 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):229-238
We propose and develop to some extent a novel approach, which allows to effectively describe, for relativistic heavy-ion
collisions, the empirically observed deviation from unity of the intercept λ (i.e. the measured value corresponding to zero
relative momentum p of two registered identical pions or kaons) of the two-particle correlation function C(p,K). The approach is based on the use of two versions of the so-called q-deformed oscillators and the corresponding picture of ideal gases of q-bosons. By these techniques the intercept λ is put into direct correspondence with the deformation parameter q. For fixed deformation strength, the model predicts particular dependence of the intercept λ on the pion pair mean momentum
K.
Received: 2 July 1999 / Revised version: 11 November 1999 相似文献
5.
6.
M. El-Nadi M.S. El-Nagdy A. Abdelsalam E.A. Shaat N. Ali-Mossa Z. Abou-Moussa Kh. Abdel-Waged A. M-Abdalla E. El-Falaky 《The European Physical Journal A - Hadrons and Nuclei》2001,10(2):177-181
Data on the multiplicity of secondaries in central events of 28Si (14.6 AGeV) and 32S (3.7 AGeV) interactions with AgBr emulsion nuclei have been compiled and studied. The dependence of the multiplicities of
the outgoing charged stripping particles on the number of interacting nucleons and therefore on the impact parameter, as indicated
by the target size, and consequently, on the degree of centrality is investigated. The resultant multiplicity distribution
of the produced pions for each studied case is fitted by both Negative Binomial (NB) and Poisson distributions. The NB distribution
is valid for most of the considered cases. The transparency of the target for a projectile was found to become more pronounced
as the incident energy increased.
Received: 20 June 2000 / Accepted: 17 January 2001 相似文献
7.
K. Wosińska J. Pluta F. Hanappe L. Stuttge J. C. Angelique B. Benoit E. de Goes Brennand G. Bizard J. Colin G. Costa P. Desesquelles O. Dorvaux D. Durand B. Erazmus S. Kuleshov R. Lednicky M. Marques Th. Materna K. Mikhailov G. Papatheofanous T. Pawlak A. Staranowicz A. Stavinskiy B. Tamain A. Vlasov L. Vorobyev 《The European Physical Journal A - Hadrons and Nuclei》2007,32(1):55-59
The measurement of the two-particle correlation function for different particle species allows to obtain information about
the development of the particle emission process: the space-time properties of emitting sources and the emission time sequence
of different particles. The single-particle characteristics and two-particle correlation functions for neutral and charged
particles registered in forward direction are used to determine that the heavy fragments (deuterons and tritons) are emitted
in the first stage of the reaction (pre-equilibrium source) while the majority of neutrons and protons originates from the
long-lived quasi-projectile. The emission time sequence of protons, neutrons and deuterons has been obtained from the analysis
of non-identical particle correlation functions. 相似文献
8.
《The European Physical Journal A - Hadrons and Nuclei》2009,40(1):45-59
We present the results of a study of charged-pion production in 12C + 12C collisions at incident beam energies of 1A GeV and 2A GeV using the HADES spectrometer at GSI. The main emphasis of the
HADES program is on the dielectron signal from the early phase of the collision. Here, however, we discuss the data with respect
to the emission of charged hadrons, specifically the production of mesons, which are related to neutral pions representing a dominant contribution to the dielectron yield. We have performed
the first large-angular-range measurement of the distribution of mesons for the 12C + 12C collision system covering a fairly large rapidity interval. The pion yields, transverse-mass and angular distributions are
compared with calculations done within a transport model, as well as with existing data from other experiments. The anisotropy
of pion production is systematically analyzed. 相似文献
9.
C. Beşliu A. Jipa D. Argintaru C. Argintaru R. Zaharia J. Gabriel Rican M. Iosif 《The European Physical Journal A - Hadrons and Nuclei》1998,1(1):65-75
The problem of the nuclear matter jets in nucleus-nucleus collisions at 4.5 A GeV/c is discussed. The global analysis of
experimental data, namely the sphericity tensor, is used to evidence such jets. The experimental results are compared with
those obtained in the same collisions for hydrodynamic flow and thrust. The experiments have been performed in the frame of
the SKM 200 Collaboration from JINR Dubna.
Received: 20 March 1997 / Revised version: 20 July 1997 相似文献
10.
A. Kozlov 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):836-841
The production of the low-mass dielectrons is considered to be a powerful tool to study the properties of the hot and dense
matter created in the ultra-relativistic heavy-ion collisions. We present the preliminary results on the first measurements
of the low-mass dielectron continuum in Au + Au collisions and the φ-meson production measured in Au + Au and d + Au collisions at
= 200GeV performed by the PHENIX experiment. 相似文献
11.
B. K. Srivastava 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):862-867
The study of correlations and fluctuations can provide evidence for the production of the quark-gluon plasma (QGP) in relativistic
heavy-ion collisions. Various theories predict that the production of a QGP phase in relativistic heavy-ion collisions could
produce significant event-by-event correlations and fluctuations in transverse momentum, multiplicity, etc. Some of the recent
results using STAR at RHIC will be presented along with results from other experiments at RHIC. The focus is on forward-backward
multiplicity correlations, balance function, charge and transverse-momentum fluctuations, and correlations. 相似文献
12.
A. Hombach W. Cassing U. Mosel 《The European Physical Journal A - Hadrons and Nuclei》1999,5(1):77-84
We study the mixing and the kinetic equilibration of projectile and target nucleons in relativistic heavy-ion collisions
in the energy regime between 150 AMeV and 2 AGeV in a coupled-channel BUU (CBUU) approach. We find that equilibrium in the
projectile-target degrees of freedom is in general not reached even for large systems at low energy where elastic nucleon-nucleon
collisions dominate. Inelastic nucleon excitations are more favorable for equilibration and their relative abundance increases
both with energy and mass. Experimentally, the projectile/target admixture can be determined by measuring the degree of isospin
equilibration in isospin asymmetric nuclear collisions. For one of the most promising systems currently under investigation,
96
44Ru +96
40Zr, we investigate the influence of the equation of state and the inelastic in-medium cross section.
Received: 23 September 1998 / Revised version: 3 December 1998 相似文献
13.
J. T. Mitchell 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):851-853
The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has made measurements of event-by-event fluctuations in
the charged-particle multiplicity as a function of collision energy, centrality, collision species, and transverse momentum
in several heavy-ion collision systems. It is observed that the fluctuations in terms of σ
2/μ
2 exhibit a universal power law scaling as a function of Nparticipants that is independent of the transverse momentum range of the measurement. 相似文献
14.
Antiproton (ˉp) and antilambda (ˉΛ) production has been measured for minimum bias in p+A collisions and central A1+ A2 collisions at the CERN-SPS by the collaborations NA35/49 and NA44. The measurements are extrapolated from rapidity distributions
to absolute minimum bias cross sections. It is shown that the ˉp cross sections divided by A1· A2 follow an exponential trend as a function of a characteristic length obtained from a Glauber type absorption model, while
the ˉΛ cross sections divided by A1· A2 are constant. The exponential trend also holds for ˉp production at the lower energies of the Brookhaven AGS. A discussion of the physics interpretation of the established trends
in terms of an effective absorption cross section is presented.
Received: 15 July 1999 / Revised version: 10 November 1999 相似文献
15.
K. Wi?niewski P. Crochet N. Herrmann A. Andronic R. Averbeck A. Devismes C. Finck A. Gobbi O. Hartmann K.D. Hildenbrand 《The European Physical Journal A - Hadrons and Nuclei》2000,9(4):515-519
The ratio of K- to K+-meson yields has been measured in the systems 96Ru + 96Ru at 1.69 A GeV, 96Ru+96Zr at 1.69 A GeV, and 58Ni+58Ni at 1.93 A GeV incident beam kinetic energy. The yield ratio is observed to vary across the measured phase space. Relativistic
transport-model calculations indicate that the data are best understood if in-medium modifications of the kaons are taken
into account.
Received: 30 November 1998 / Accepted: 20 December 2000 相似文献
16.
The growth rate for instabilities in an expanding parton plasma is investigated by using a quasiparticle transport model
including hadronization. The coupled Boltzmann equations for partons and pions with time dependent mean field masses and source
terms are solved in the Bjorken boost invariant picture. Hadronization modifies the known instability in the parton plasma
created by the mean field in two ways: In the beginning, hadronization increases the rate Γ of instability, but then Γ→ 0
when the hadronization is dominating the time evolution.
Received: 11 January 1999 相似文献
17.
A new process of a nuclear excitation to discrete states in peripheral heavy ion collisions is studied. High-energy photons
are emitted by the exited nuclei with energies up to a few tens of GeV at angles of a few hundred microradians with respect
to the beam direction. We show that a two-stage process, where an electron-positron pair is produced by virtual photons emitted
by nuclei and then the electron or positron excites the nucleus, has a large cross-section. It is equal to about 5 b for CaCa
collisions. On the one hand, it produces a significant γ-rays background in the nuclear fragmentation region but, on the other
hand, it could be used for monitoring the nuclear beam intensity at the LHC. These secondary nuclear photons could be a good
signal for triggering peripheral nuclear collisions.
Received: 14 December 2001 / Accepted: 22 January 2002 相似文献
18.
D. Ghosh A. Deb M. Mondal S. Bhattacharyya J. Ghosh 《The European Physical Journal A - Hadrons and Nuclei》2002,14(1):77-80
Self-affine multiplicity scaling is investigated in the framework of two-dimensional factorial moment methodology using the
concept of the Hurst exponent (H). Our investigation on experimental data of the target-evaporated slow particles emitted in 32S-AgBr interactions at 200 AGeV and 28Si-AgBr interactions at 14.5 AGeV reveals that a better power law behavior is exhibited in self-affine analysis than self-similar
analysis. This work shows a clear evidence of self-affine target fragmentation.
Received: 22 October 2001 / Accepted: 6 March 2002 相似文献
19.
K. A. Chikin V. L. Korotkih A. P. Kryukov L. I. Sarycheva I. A. Pshenichnov J. P. Bondorf I. N. Mishustin 《The European Physical Journal A - Hadrons and Nuclei》2000,8(4):537-548
There exist several proposals to use Weizsäcker-Williams photons generated by ultrarelativistic heavy ions to produce exotic particles in γγ fusion reactions. To estimate the background conditions for such reactions we analyze various mechanisms of meson production in very peripheral collisions of ultrarelativistic heavy ions at RHIC and LHC energies. Besides the γγ fusion they include also electromagnetic γA interactions and strong nucleon-nucleon interactions in grazing AA collisions. All these processes are characterised by low multiplicities of produced particles. The γA an d AA events are simulated by corresponding Monte Carlo codes, RELDIS and FRITIOF. In each of these processes a certain fraction of pions is produced close to the mid-rapidity regionthat gives a background for the γγ events. The possibility of selecting the mesons produced in the γγ fusion events via different p t cut procedures is demonstrated. 相似文献
20.
Identification of baryon resonances in central heavy-ion collisions at energies between 1 and 2 AGeV
《The European Physical Journal A - Hadrons and Nuclei》1998,3(4):335-349
The mass distributions of baryon resonances populated in near-central collisions of Au on Au and Ni on Ni are deduced by
defolding the pt spectra of charged pions by a method which does not depend on a specific resonance shape. In addition the mass distributions
of resonances are obtained from the invariant masses of (p, π±) pairs. With both methods the deduced mass distributions are shifted by an average value of −60 MeV/c2 relative to the mass distribution of the free Δ(1232) resonance, the distributions descent almost exponentially towards mass
values of 2000 MeV/c2. The observed differences between (p, π−) and (p, π+) pairs indicate a contribution of isospin I = 1/2 resonances. The attempt to consistently describe the deduced mass distributions
and the reconstructed kinetic energy spectra of the resonances leads to new insights about the freeze out conditions, i.e.
to rather low temperatures and large expansion velocities.
Received: 26 June 1998 / Revised version: 2 September 1998 相似文献