Multiplicity and pseudorapidity distributions of charged particles from32S induced heavy ion interactions at 200A GeV

Multiplicity and pseudorapidity distributions have been measured for³²S+Al, Cu, Ag and Au at 200A GeV. The widths of the pseudorapidity distributions increase from central to peripheral collisions. The main contribution is assumed to come from the increasing fraction of charged particles stemming from the fragmentation of the target for peripheral collisions as compared to central collisions. On the average 170–180 charged particles per unit of pseudorapidity are attained for the most central³²S+Au events at the maximum of the distribution. The target dependence of the yield of charged particles for central collisions is investigated. In the target rapidity region the yield is directly proportional to the target mass. The transverse energy per charged particle has been studied as a function of centrality and pseudorapidity. The experimental results are compared to the results from the Monte-Carlo model VENUS 3.11 which includes rescattering among secondaries. A comparison between different centrality triggers is made.     

Strange meson enhancement in PbPb collisions

The NA44 Collaboration has measured yields and differential distributions of K⁺, K⁻, π⁺, π⁻ in transverse kinetic energy and rapidity, around the center-of-mass rapidity in 158 A GeV/c Pb+Pb collisions at the CERN SPS. A considerable enhancement of K⁺ production per π is observed, as compared to p+p collisions at this energy. To illustrate the importance of secondary hadron rescattering as an enhancement mechanism, we compare strangeness production at the SPS and AGS with predictions of the transport model RQMD.     

Spectra of negative particles and photons in collisions of p−W and16O−W at 200 GeV/u

p _⊥ spectra of negative particles were measured for p?W and¹⁶O?W collisions at 200 GeV/u in the rapidity range 0.9<y<1.9. Within the systematic errors of 20% the spectra are identical in the range 0.05<p _⊥<2.0 GeV/c. The p?W and¹⁶O?W spectra exhibit an exponential shape forp _⊥ >250 MeV/c. This is consistent with previous p?A data, but there is a significant excess above this exponential at lowerp _⊥. Photon spectra were measured using a conversion method. Theirp _⊥ distribution agrees in shape with the sum of known hadronic γ-sources.     

Determination of strange quark suppression in hadronic vacuum

We study the forward-backward rapidity correlation slope in \(\bar p\) p interactions at high energies. We show that the measurement of this slope in different rapidity intervals, yields direct information on multiple-scattering. It turns out that the particles produced in inelastic rescattering are concentrated neary=0. This is a key feature of the multi-chain dual parton model, and leads to a simple explanation of the main features of multi-hadron production at very high energies, such as the energy dependence of the height and shape of the rapidity distribution, approximate K.N.O. scaling etc. We also show that the large values of the forward-backward correlation slope measured at ISR and SPS, are obtained in the model using the standard idea of short-range order in a single inelastic collision.     

Baryon number transport in high-energy nuclear collisions

Recent SPS data on the rapidity distribution of protons inp+S,p+Au and S+S collisions at 200 AGeV and preliminary Pb+Pb collisions at 160 AGeV are compared to HIJING and VENUS calculations as well as to predictions based on the Multi-Chain Model (MCM). The preliminary Pb data suggest that a linear dependence of the proton rapidity shift as a function of the nuclear thicknes, as first observed inp+A reactions, may apply up to Pb+Pb reactions. The observed rapidity dependence of produced hyperons in bothp+A and A+A reactions however cannot be explained in terms of such models without introducing additional non-linear effects.     

Prospects for new physics observations in diffractive processes at the LHC and Tevatron

We study the double-diffractive production of various heavy systems (e.g. Higgs, dijet, and SUSY particles) at LHC and Tevatron collider energies. In each case we compute the probability that the rapidity gaps, which occur on either side of the produced system, survive the effects of soft rescattering and QCD bremsstrahlung effects. We calculate both the luminosity for different production mechanisms, and a wide variety of subprocess cross sections. The results allow numerical predictions to be readily made for the cross sections of all these processes at the LHC and the Tevatron collider. For example, we predict that the cross section for the exclusive double-diffractive production of a 120 GeV Higgs boson at the LHC is about 3 fb, and that the QCD background in the decay mode is about 4 times smaller than the Higgs signal if the experimental missing-mass resolution is 1 GeV. For completeness we also discuss production via or WW fusion. Received: 7 November 2001 / Revised version: 11 December 2001 / Published online: 25 January 2002     

Competition between neutron-proton rescattering and deuteron break-up in (d, np) reactions

Existing final-state interaction (FSI) theories predict observable rescattering effects in low-energy nuclear reactions with three or more particles in the final state. Obvious yields which could be attributed to this effect have only been reported in (d, np) reactions. However,n-p rescattering might be confused with the neutron-proton FSI following deuteron break-up since both contribute strongest at low relative neutron-proton energies. We have re-examined the (d, np) reactions on¹²C and⁴⁰Ca in a kinematically complete experiment making special effort to try to distinguish between rescattering and then-p FSI. Data have been taken within and outside the reaction plane at different bombarding energies. Attempts to simultaneously fit the detailed shapes of the proton spectra and the azimuthal angularn-p correlations with theoretical predictions in a consistent way were unsuccessful forboth reaction mechanisms. Improvements in the fits at particular energy and angle combinations were always at the expense of the agreement at other angles or energies. Therefore it must be concluded from our analysis that on the basis of calculations available at present the contributions fromn-p rescattering and deuteron break-up cannot be distinguished in a conclusive manner in the (d, np) experiments performed to date.     

W Boson Pair Production in Association with the Photon in Proton - Proton Collisions at LHC Energies

The vector bosons production at the Large Hadron Collider makes it possible to investigate in detail the basic structure of electroweak interactions. Besides the LHC with a good accuracy will be measure production of weak bosons (pp → W⁺W⁻). The production of weak bosons with photon (pp → W⁺W⁻γ) provides an increasingly powerful handle at higher center-of-mass energies. We present phenomenological results for WWγ production in proton-proton interaction at the Large Hadron Collider. In this paper, we calculate the total and differential cross sections. We consider the dependence of differential cross section distributions on transverse momentum and rapidity particles, which are produced in the final state (W⁺ and W⁻). We consider several important distributions, which are included in the search for new physics at the Large Hadron Collider. The results for transverse momentum distributions, rapidity distributions and total cross section are presented.

     

Universal Schwinger cocycles of current algebras in (D+1)-dimensions: Geometry and physics

We discuss the universal version of the Schwinger terms of current algebra (we call it the universal Schwinger cocycle) forp=3 (herep denotes the class of the Schatten idealI _p , which is related to the (D+1) space-time dimensions byp=(D+1)/2) in detail, and give a conjecture of the general form of the cocycle for anyp. We also discuss the infinite charge renormalizations, the highest weight vector and state vectors forp=3. Last, we give brief comments on the problems caused by the difficulties to construct the measure of infinite-dimensional Grassmann manifolds.     

Net baryon density in Au+Au collisions at the relativistic heavy ion collider

We calculate the net-baryon rapidity distribution in Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) in the framework of the parton cascade model (PCM). Parton rescattering and fragmentation leads to a substantial increase in the net-baryon density at midrapidity over the density produced by initial primary parton-parton scatterings. The PCM is able to describe the measured net-baryon density at RHIC.     

The nature of the vectorial photoelectric effect in the threshold energy region

Summary An immediate correlation has been proved to exist between the vectorial photoelectric effect and electronic surface structure modified due to adsorption. Experimental studies were performed for Cs overlayers on W(110) and Si(111) faces using visible exciting photons with energies below those of both bulk and surface plasmons. Considerable (more than 20 fold) growth of the effect was observed forp-polarized light in the vicinity of threshold as the light frequency approached the position of the maximum of local density in the surface-state band. A special case of the vectorial photoelectric effect forp-polarized light has been found in the absence of bulk photoemission excited bys-polarized light. Our results prove that the anomalous vectorial photoelectric effect is caused by the normal electric vector component of thep-polarized light under appropriate conditions for the particular photoemission enhancement on the surface. The effect can be related to optical absorption by the surface-state band and to subsequent electron emission into the vacuum, the normal electric vector component of thep-polarized light being essential for both processes.     

High Energy Unequal-nuclei Collisions and Relaxation Time in Fokker Plank Equation

In this paper,the time evolution of high energy heavy ion collisions is described by Fokker-Planck Equation.The rapidity distribution of the final state particles is analysed with this model for ¹⁶O and ³²S particles beams of 200AGeV.The relaxation time for various systems are determined.Results comparable to the usual empirical data are obtained.     

Growth, percolation, and correlations in disordered fiber networks

This paper studies growth, percolation, and correlations in disordered fiber networks. We start by introducing a 2D continuum deposition model with effective fiber-fiber interactions represented by a parameterp which controls the degree of clustering. Forp=1 the deposited network is uniformly random, while forp=0 only a single connected cluster can grow. Forp=0 we first derive the growth law for the average size of the cluster as well as a formula for its mass density profile. Forp>0 we carry out extensive simulations on fibers, and also needles and disks, to study the dependence of the percolation threshold onp. We also derive a mean-field theory for the threshold nearp=0 andp=1 and find good qualitative agreement with the simulations. The fiber networks produced by the model display nontrivial density correlations forp<1. We study these by deriving an approximate expression for the pair distribution function of the model that reduces to the exactly known case of a uniformly random network. We also show that the two-point mass density correlation function of the model has a nontrivial form, and discuss our results in view of recent experimental data on mss density correlations in paper sheets.     

A New Version of the Fast Multipole Method for Screened Coulomb Interactions in Three Dimensions

We present a new version of the fast multipole method (FMM) for screened Coulomb interactions in three dimensions. Existing schemes can compute such interactions in O(N) time, where N denotes the number of particles. The constant implicit in the O(N) notation, however, is dominated by the expense of translating far-field spherical harmonic expansions to local ones. For each box in the FMM data structure, this requires 189p⁴ operations per box, where p is the order of the expansions used. The new formulation relies on an expansion in evanescent plane waves, with which the amount of work can be reduced to 40p²+6p³ operations per box.     

Electronic structure of hydrogen and muonium in Al,Mg and Cu

The electronic structure of hydrogen and muonium in simple metals is investigated. The spherical solid model potential is used for the discrete lattice and the Blatt correction for lattice dilation. The proton and muon are kept at the octahedral sites in the fcc and hcp lattices and self-consistent non-linear screening calculations are carried out. The scattering phase shifts, electronic charge density, effective impurity potential, self-energy, charge transfer, residual resistivity and Knight shift are calculated. The spherical solid potential changes the scattering character of impurity. The phase shifts are found slowly converging. The scattering is more prominent in Al than in Mg and Cu. The virtual bound states of proton and muon are favoured in all the three metals. The calculated value of residual resistivity for CuH is in good agreement with the experimental value. The results for Knight shift forμ ⁺ in Cu and Mg are in reasonable agreement with the experimental values while those forμ ⁺ in Al are lower than the experimental value. The analytical expressions for effective impurity potential and electronic charge density are suggested.     

High order moments of the\bar p p multiplicity distribution in the dual parton model

The first four moments of the \(\bar p\) p multiplicity distribution are computed in the framework of the dual parton model at ISR, SPS collider and Tevatron energies, and for different rapidity intervals. Our results exhibit a striking dependence of the various moments on the size of the rapidity interval which is characteristic of the nature of the rescattering chains in the dual parton model. They also show a violation of KNO scaling throughout the considered energy range. Our results indicate that only light clusters (consistent with known resonances) are produced at all energies.     

Subthreshold antiproton andK − production in heavy ion collisions

Subthreshold ¯p andK ^– and energetic ^– production was studied in Ne + NaF, Cu, Sn and Bi, and in Ni + Ni collisions with incident energies between 1.6 and 2 GeV/u. The measured cross sections indicate a dominant contribution of baryonic resonances. This is also consistent with a generalized scaling behaviour of the cross sections with the energy available in the collision and the energy necessary to produce particles as observed with Ne induced reactions. Deviations from scaling especially pronounced in the Ni-Ni system will be discussed in terms of absorption effects. The flat slope of the excitation function for ¯p production can be related to a reduced production threshold caused by a reduction of the antiproton mass in the dense and heated medium by about 100—150 MeV/c². A similar in-medium mass reduction is also indicated forK ^– mesons. An increased ¯p reabsorption probability for the heavier systems is concluded from the comparison of the ¯p yields in Ne + NaF, Ne + Sn and Ni + Ni collisions.Dedicated to Professor Klaus Dietrich on the occasion of his 60th birthday.     

Photon-exchange processes at hadron colliders as a probe of the dynamics of diffraction

The rich structure of photon-exchange processes at hadron colliders is studied. We discuss central vector meson production , W production and production. Each process has distinct, and large, soft pp rescattering effects, which can be directly observed by detecting the outgoing protons. This allows a probe of the optical density of the proton, which plays a crucial role in the evaluation of the rapidity gap survival probabilities in diffractive-like processes at hadron colliders. We note that an alternative mechanism for production is odderon, instead of photon, exchange; and that the ratio of odderon to photon contributions is enhanced (suppressed) for vector meson production. Received: 1 February 2002 / Revised version: 4 April 2002 / Published online: 22 May 2002     

J/<Emphasis Type="Italic">ψ</Emphasis> production measurements by the PHENIX experiment

Quarkonia suppression is considered to be one of the key probes of the Quark Gluon Plasma (QGP) created in heavy ion collisions. The PHENIX experiment has measured J/ψ production in a variety of colliding systems. Measurements made in p+p collisions show good agreement with pQCD predictions and serve as baseline for other systems at the same collision energy. The cold nuclear matter contribution to the suppression is constrained through measurements in d+Au collisions. In Au+Au, the suppression observed at mid rapidity is smaller than that at forward rapidity, a tendency opposite to what is expected from the higher gluon density at mid rapidity. The results will be presented and discussed in this article.