Hadron Multiplicities in Pb＋Pb Collisions at the Large Hadron Collider and Pomeron Loop Effects

We study the pseudo-rapidity distribution of hadron multiplicities of high energy Pb＋Pb collisions by using color glass condensate dynamics at LHC/ALICE in the fixed coupling case. It is found that after including the pomeron loop effects the charged hadron multiplicities at central rapidity are about 1500 for central Pb＋Pb collisions, which are significantly smaller than the saturation based calculations, ～ 1700 ÷ 2500 and compatible with that based on a study of multiplicities in the fragmentation region.     

158A GeV Pb+Pb反应中多粒子产生的双源统计模型分析

提出双源统计模型并用它研究了158A GeV Pb+Pb反应中多粒子产生.模型很好地描述了实验,同时给出一个合理清晰的物理图像.反应系统由一个热而小的内源和一个大而较凉的外源构成.外源具有类弹和类靶特征,内源具有反应中心区特征.在freeze-out时系统仍处于膨胀中.     

Central Pb+Pb collisions at 158 A GeV/c studied by \pi^-\pi^- interferometry

Two-particle correlations have been measured for identified from central 158 A GeV Pb+Pb collisions and fitted radii of about 7 fm in all dimensions have been obtained. A multi-dimensional study of the radii as a function of is presented, including a full correction for the resolution effects of the apparatus. The cross term of the standard fit in the Longitudinally CoMoving System (LCMS) and the parameter of the generalised Yano-Koonin fit are compatible with 0, suggesting that the source undergoes a boost invariant expansion. The shapes of the correlation functions in and have been analyzed in detail. They are not Gaussian but better represented by exponentials. As a consequence, fitting Gaussians to these correlation functions may produce different radii depending on the acceptance of the experimental setup used for the measurement. Received: 3 February 2000 / Published online: 18 May 2000     

Indications for the onset of deconfinement in Pb+Pb collisions at the CERN SPS

Particle production in central Pb+Pb collisions was studied with the NA49 large acceptance spectrometer at the CERN SPS at beam energies of 20, 30, 40, 80 and 158 GeV per nucleon. A change of the energy dependence is observed around 30A GeV for the yields of pions and strange particles as well as for the shapes of the transverse mass spectra. The energy dependence of fluctuations and correlations shows no structure. At present only a reaction scenario with onset of deconfinement is able to reproduce the measurements.     

Three-pion interferometry results from central Pb+Pb collisions at 158A GeV/c

Three-particle correlations have been measured for identified pi(-) from central 158A GeV Pb+Pb collisions by the WA98 experiment at CERN. A substantial contribution of the genuine three-body correlation has been found as expected for a mainly chaotic and symmetric source.     

Space-time evolution of the hadronic source in peripheral to central Pb+Pb collisions

Two-particle correlations of negative pions as a function of charged particle multiplicity are studied in Pb+Pb collisions at GeV per nucleon using the NA44 experiment at the CERN Super Proton Synchrotron(SPS). We find that the source size parameters increase with the charged particle multiplicity. However the slope of the source size parameters plotted as a function of charged multiplicity is slightly larger at high multiplicity than at low multiplicity. The value of is independent of charged multiplicity. For Pb+Pb collisions, is larger than and for all multiplicity intervals, whereas these three radius parameters were approximately equal in S+Nucleus collisions. The ratios () and () for Pb+Pb data show almost no dependence on charged multiplicity. The duration of pion emission is constant at 3.81.1 fm/c as a function of the charged multiplicity in Pb+Pb collisions. Effective volume (V) is also calculated as V=, assuming a cylindrically shaped source. We found, within the limited statistics, the effective volume rapidly increases at high multiplicity. Received: 17 July 2000 / Revised version: 3 November 2000 / Published online: 8 December 2000     

Hadronic expansion dynamics in central Pb+Pb collisions at 158 GeV per nucleon

Two-particle correlation functions of negative hadrons over wide phase space, and transverse mass spectra of negative hadrons and deuterons near mid-rapidity have been measured in central Pb+Pb collisions at 158 GeV per nucleon by the NA49 experiment at the CERN SPS. A novel Coulomb correction procedure for the negative two-particle correlations is employed making use of the measured oppositely charged particle correlation. Within an expanding source scenario these results are used to ext ract the dynamic characteristics of the hadronic source, resolving the ambiguities between the temperature and transverse expansion velocity of the source, that are unavoidable when single and two particle spectra are analysed separately. The source shape, the total duration of the source expansion, the duration of particle emission, the freeze-out temperature and the longitudinal and transverse expansion velocities are deduced. Received: 25 November 1997 / Published online: 24 March 1998     

Kaon production in S+nucleus and Pb+Pb collisions at CERN SPS

Charged and neutral kaon production in S-nucleus and Pb-Pb collisions has been measured at CERN in the NA35 and NA49 experiments, close to mid-rapidity. The production ofK ^± in S+S, Ag, Au at 200 GeV/nucleon was measured via their one-prong (kink) topology inside a Time Projection Chamber (TPC). The resulting charged kaon yields are in agreement with other measurements done in the same experiment. TheK ⁺/K ^? ratio was found to be 1.30±0.15 in central S+Au interactions. The production ofK _S ⁰ in Pb+Pb collisions was measured using the NA49’s large (Main) TPCs outside the magnetic field. The resulting yields are compatible with other measurements performed in the same experiment, within the quoted systematic errors. The preliminary rapidity distribution in Pb+Pb scales with the number of participants if compared to S+S collisions. From this we conclude that no further strangeness enhancement (relative to nucleon-nucleon collisions) is observed in going from S+S to Pb+Pb.     

Particle production in Pb+Pb collisions at the SPS

Experiment NA49 at the CERN SPS employs a large acceptance detector to study particle spectra, yields and correlations in nucleus-nucleus, nucleon-nucleus and nucleon-nucleon collisions. Preliminary results on pion, kaon, A and ā production in central Pb+Pb collisions at 40, 80 and 158 A·GeV beam energy are shown and compared to measurements at lower and higher energies.     

Suppression of high-p{T} neutral pion production in central Pb+Pb collisions at sqrt[S{NN}]=17.3 GeV relative to p+C and p+Pb collisions

Neutral pion transverse momentum spectra were measured in p+C and p+Pb collisions at sqrt[S{NN}]=17.4 GeV at midrapidity (2.3 less than or approximately equal eta{lab} less than or approximately equal 3.0) over the range 0.7 less than or approximately equal p{T} less than or approximately equal 3.5 GeV/c. The spectra are compared to pi{0} spectra measured in Pb+Pb collisions at sqrt[S{NN}]=17.3 GeV in the same experiment. For a wide range of Pb+Pb centralities (N{part} less than or approximately equal 300), the yield of pi{0}'s with p{T} greater than or approximately equal 2 GeV/c is larger than or consistent with the p+C or p+Pb yields scaled with the number of nucleon-nucleon collisions (N{coll}), while for central Pb+Pb collisions with N{part}greater than or approximately equal 350, the pi{0} yield is suppressed.     

Omega- and Omega+ production in central Pb + Pb collisions at 40 and 158A GeV

Results are presented on Omega production in central Pb+Pb collisions at 40 and 158A GeV beam energy. For the first time in heavy ion reactions, rapidity distributions and total yields were measured for the sum Omega(-) + Omega(+) at 40A GeV and for Omega(-) and Omega(+) separately at 158A GeV. The yields are strongly underpredicted by the string-hadronic UrQMD model but agree better with predictions from hadron gas models.     

Antideuteron production in 158A GeV/c Pb + Pb collisions

The invariant cross section as a function of transverse momentum for antideuterons produced in 158A GeV/c per nucleon Pb+Pb central collisions has been measured by the NA44 experiment at CERN. This measurement, together with a measurement of antiprotons, allows for the determination of the antideuteron coalescence parameter. The extracted coalescence radius is found to agree with the deuteron coalescence radius and radii determined from two particle correlations.     

The impact parameter dependence of the Pb + Pb K − MO spectrum

Molecular orbital X-rays are emitted during ion-atom collisions. The theoretical treatment, numerical results for the Pb + Pb system and a comparison with background radiation like NNB, SEB and γ-decay of Coulomb excited nuclei are presented.     

K-X-ray spectrum of the Pb + Pb quasimolecules

We present ab initio calculations of the quasimolecular K-X-ray spectrum from the Pb + Pb system, where both the Kd-hole amplitude and the radiation amplitude is calculated in first order perturbation theory. A comparison with the background radiation like NNB, SEB and γ-decay of excited nuclei shows that the molecular X-rays should be measurable up to X-ray energies corresponding to the characteristic K-line of the united superheavy atom.     

The effect of nuclear and Coulomb interactions on the nuclear shapes of two colliding208Pb nuclei

Using a complex energy density functional derived from the Reid soft-core potential, the changes in nuclear shapes of two colliding²⁰⁸Pb are investigated. At each separation distanceR, the total binding energy of the Pb + Pb system is minimized w.r.t. the quadrupole deformation and diffuseness parameters of nuclear densities. It is found that the nuclear shapes are strongly affected by the nuclear and Coulomb interactions. A sudden transition occurs from oblate to prolate shapes around R16.8fm and a smooth one from prolate to oblate shapes aroundR?11.76 fm.     

Energy dependence of proton and antiproton production in central Pb+Pb collisions from NA49

Recent results of the NA49 collaboration on the production of p and p̄ at midrapidity in central Pb+Pb collisions in the beam energy range 20–158 A  GeV are presented. The preliminary results for the rapidity distributions of p and p̄ at 40 A  GeV are also discussed. PACS 25.75.Dw     

Dynamics of superheavy system in 86Kr + 208Pb reaction

The dynamics of the excited superheavy system with Z = 118 in the reaction ⁸⁶Kr + Pb at E _Kr = 600 MeV has been investigated. The mass and kinetic energy of binary fragments were measured by the time-of-flight method. Double differential distributions of neutrons and α particles were measured in coincidence with fragments. Neutron and α-particle probes were used for determination of the fragmentation time scale. Evidence of the neck fragmentation was obtained from analysis of double differential α spectra. Properties of the α-particle neck fragmentation component are close to those known from the ternary fission of actinide nuclei, but the multiplicity is much larger. The total kinetic energy distribution of fragments tagged by neutrons or α particles shifts towards lower energies. Fragment yields in the symmetric region increase substantially when fragments are tagged by α particles.     

Interferometry of direct photons in central 208Pb + 208Pb collisions at 158A GeV

Two-particle correlations of direct photons were measured in central 208Pb+208Pb collisions at 158A GeV. The invariant interferometric radii were extracted for 100相似文献   

Event-by-event fluctuations of the Kaon-to-Pion ratio in central Pb+Pb collisions at 158 GeV per nucleon

We present the first measurement of fluctuations from event to event in the production of strange particles in collisions of heavy nuclei. The ratio of charged kaons to charged pions is determined for individual central Pb+Pb collisions. After accounting for the fluctuations due to detector resolution and finite number statistics we derive an upper limit on genuine nonstatistical fluctuations, which could be related to a first- or second-order QCD phase transition. Such fluctuations are shown to be very small.     

Pb2+离子在CaS中的发光特性与应用

研究了单掺Pb^2 和共掺Pb^2 、Eu^2 离子的CaS 发光材料的荧光性质。Pb^2 的发射光谱位于蓝区，Eu^2 的发射光谱位于红区，实验结果表明，Pb^2 对Eu^2 荧光发射有很强的敏化作用。Pb^2在紫区有较强的吸收，说明Pb^2 、Eu^2 共激活的CsS材料是一种适用于高原寒冷地区的农用薄膜转光剂。