Charged particle multiplicity distributions at 200 and 900 GeV c.m. energy

Multiplicity distributions of charged particles produced in non single-diffractive collisions between protons and antiprotons at centre of mass energies of 200 and 900 GeV are presented. The data were recorded in the UA5 streamer chambers at the CERN Collider, which was operated in a pulsed mode between the two energies. A new method to correct for acceptance limitations and inefficiencies based on the principle of maximum entropy has been used. Multiplicity distributions in full phase space and in intervals of pseudorapidity are presented in tabular form. The violation of KNO scaling in full phase space found by the UA5 group at an energy of 546 GeV is confirmed also at 200 and 900 GeV. The shape of the 900 GeV distribution in full phase space is narrower in the peak region than at 200 GeV but exhibits a pronounced high multiplicity tail. The negative binomial distribution fits data at 200 GeV in all pseudorapidity intervals and in small intervals at 900 GeV. In large intervals at 900 GeV, however, the negative binomial distribution. Fits to the partially coherent laser distribution are also presented as well as comparisons with predictions of the Dual Parton, the Fritiof and the Pythia models.     

Antiproton-proton cross sections at 200 and 900 GeV c.m. energy

Data on antiproton-proton cross sections at the c.m. energies 200 and 900 GeV are presented. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode in which the same beams were accelerated and decelerated between beam energies of 450 and 100 GeV. The properties of the machine determine the ratio of the luminosities at the two energies to about 1% and thus an accurate measurement of the ratioR of the inelastic cross sections could be made. We findR (=σ ⁹⁰⁰/σ ²⁰⁰)=1.20±0.01±0.02, where the first error is statistical and the second systematic. Interpolating existing data to estimateσ _ine1(200 GeV) this measurement ofR leads toσ _ine1(900 GeV)=50.3+0.4+1.0 mb. Using an extrapolated value ofσ _e1/σ _tot we estimate the total cross section at 900 GeV to be 65.3±0.7±1.5 mb. Both the inelastic and total cross sections are compatible with a ln² s dependence. Comparisons are made with different fits to the total cross section energy dependence.     

Photon production at c.m. energies of 200 and 900 GeV

We present data on photon production in non single-diffractivep \(\bar p\) -collisions at c.m. energies of 200 and 900 GeV. Besides the general properties of photon production, i.e. pseudorapidity distribution and average multiplicity, we also investigate photon-charged two-particle pseudorapidity and multiplicity correlations. We find for the average number of photons in non single-diffractivep \(\bar p\) -collisions 22.2±1.4±2.0 at 200 GeV and 41.4±2.1±3.5 at 900 GeV, where the first error is statistical and the second systematic. The analysis of photon-charged particle multiplicity correlations reveals strong positive correlations between the average number of photons and the number of simultaneously produced charged particles, as expected from FNAL and ISR studies and from our result at 546 GeV. We obtain for the correlation slope 0.95±0.08±0.11 at 200 GeV and 1.09±0.09±0.13 at 900 GeV (first error is statistical and the second systematic). The investigation of photon-charged two-particle pseudorapidity correlations shows that these correlations are of short range and compatible with the observed charged two-particle pseudorapidity correlations. These correlations and the results for the average number of photons as a function of the produced number of charged particles favour the conclusion that photon sources other than π⁰ s contribute significantly to the observed photon yield in non single-diffractivep \(\bar p\) -collisions. For example, if all photons are assumed to come from π⁰ s and η mesons, a η/π⁰ ratio of about 20% is inferred.     

Kaon production in\bar pp interactions at c.m. energies from 200 to 900 GeV

A detailed analysis ofK _s ⁰ production in \(\bar pp\) |<2.5 the average transverse momentum is found to be 0.53±0.07 GeV/c at 200 GeV and 0.62±0.08 GeV/c at 900 GeV, which is an increase with respect to data at c.m. energies below 60 GeV. TheK _s ⁰ production cross sections in inelastic collisions are 29±4 mb at 200 GeV and 63±6 mb at 900 GeV, showing an increase compared to lower energy data. The central kaon density is found to increase as a logarithmic function of energy. At 900 GeV, where statistics are sufficient to allow one to draw conclusions, the average transverse momentum is higher in events with large charged multiplicity than in events with low multiplicity.     

New scaling of charged particle pseudorapidity distributions at collider energies

A new scaling form is proposed for charged particle pseudorapidity (η) distributions on the basis of scaling in the mean hypothesis. Our new scaling accounts well the recent UA5 data of η distributions in various intervals of charged multiplicity for non single-diffractive events at energies \(\sqrt s = 200\) and 900 GeV. Similar scaling of inclusive η distributions is theoretically derived, and the validity of this scaling is assured in comparison with the data of ISR and collider energies.     

Scaling of pseudorapidity distributions at c.m. energies up to 0.9 TeV

New data are presented on charged particle pseudorapidity distributions for inelastic events produced at c.m. energies \(\sqrt s \) =200 and 900 GeV. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode. The rise of the central density ρ(0) at energies up to \(\sqrt s \) =900 GeV has been studied. A new form of central region scaling is found involving the densityρ _n (0) for charged multiplicityn, namely that the scaled central densityρ _n (0)/ρ(0) expressed as a function ofz=n/〈n〉 is independent ofs. Scaling in the fragmentation region holds to 10–20%, and the small amount of scalebreaking observed here could be accommodated within the framework suggested by Wdowcyk and Wolfendale to account for both accelerator and cosmic ray data.     

Parton rescattering effect on particle production in ultra-relativistic p+p collisions

The parton rescattering effect on the charged particle production in ultra-relativistic p+p collisions is studied by the parton and hadron cascade model PACIAE, based on PYTHIA. We have calculated charged particle pseudorapidity density at mid-rapidity and the pseudorapidity distribution in inelastic and non-single diffractive p+p collisions at $\sqrt{s}=200$ , 900, 5500, and 14000 GeV with the PYTHIA and PACIAE models. The calculated results for $\sqrt{s}=900$  GeV are well compared with the ALICE data. Comparing the PYTHIA results (without parton rescattering) with the PACIAE results (with parton rescattering), it turned out that the parton rescattering may play an important role and this effect increases with increasing CMS energy.     

Energy dependence of elliptic flow over a large pseudorapidity range in Au+Au collisions at the BNL relativistic heavy ion collider

This Letter describes the measurement of the energy dependence of elliptic flow for charged particles in Au+Au collisions using the PHOBOS detector at the Relativistic Heavy Ion Collider. Data taken at collision energies of square root of s(NN)=19.6, 62.4, 130, and 200 GeV are shown over a wide range in pseudorapidity. These results, when plotted as a function of eta(')=|eta|-y(beam), scale with approximate linearity throughout eta('), implying no sharp changes in the dynamics of particle production as a function of pseudorapidity or increasing beam energy.     

The C(α, X)11C cross sections at 1.59 and 4.19 GeV

The absolute cross sections for the production of ¹¹C by 1.59 GeV and 4.19 GeV α-particles incident on natural carbon have been measured to be 46.4 ± 1.3 mb and 42.5 ± 1.1 mb respectively. These results, together with data reported at other energies, indicate that the C(α, X)¹¹C cross section becomes approximately constant at a value of about 43 mb for energies above 3 GeV (750 MeV/n). A similar energy dependence is exhibited by the C(p, X)¹¹C reaction whose cross section has been measured previously over an extensive energy range. The C(α, X)¹¹C cross sections are found to be in good agreement with predictions of a semi-empirical model developed to describe nuclear fragmentation.     

Energy dependence of directed flow over a wide range of pseudorapidity in Au + Au collisions at the BNL Relativistic Heavy Ion Collider

We report on measurements of directed flow as a function of pseudorapidity in Au + Au collisions at energies of square root of SNN = 19.6, 62.4, 130 and 200 GeV as measured by the PHOBOS detector at the BNL Relativistic Heavy Ion Collider. These results are particularly valuable because of the extensive, continuous pseudorapidity coverage of the PHOBOS detector. There is no significant indication of structure near midrapidity and the data surprisingly exhibit extended longitudinal scaling similar to that seen for elliptic flow and charged particle pseudorapidity density.     

Cross section determination for the reaction K+p → K+pπ+π−π0 and K+π+π+π−n at 8.2 and 16 GeV/c

The cross sections for the reactions: (a) K⁺p → K⁺pπ⁺π^?π⁺ and (b) K⁺p → K⁺π⁺π⁺π^?n have been determined at 8.2 and 16 GeV/c with the following results:at 8.2 GeV/c: (a) 0.99 ± 0.07 mb, (b) 0.41 ± 0.04 mb;at 16 GeV/c: (a) 0.72 ± 0.05 mb, (b) 0.28 ± 0.05 mb.Using the available data at other energies, the cross-section dependence of these reactions on the incident momentum is discussed.     

Inclusive two-and three-particle rapidity correlations in high-energy hadron-nucleus collisions

Three-particle pseudorapidity correlations are investigated for relativistic secondaries from proton-nucleus interactions at 50, 67, 200 and 400 GeV/c and from pion-nucleus interactions at 50 and 200 GeV/c. The experimental data on two- and three-particle correlations are compared with quantitative predictions of current multiple scattering models of nuclear production. Within these models the influence of various factors on the magnitude of correlations is discussed and it is shown, in particular, that energy-momentum conservation plays an essential role at present accelerator energies.     

Soft QCD in ATLAS: Minimum bias and diffraction studies

We present measurements of charged particle production in proton-proton collisions at centre-of-mass energies of √s = 0.9, 2.36 and 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. Events were collected using a single-arm minimum bias trigger, charged tracks are measured with high precision in the inner tracking system. Minimum bias analysis uses data samples at all three energies, while diffractive events are studied using a sample of events at √s = 7 TeV. To study diffractive interactions, the events that have hits on exactly one side of the ATLAS detector were selected. The charged particle multiplicity, pseudorapidity and transverse momentum spectra are analyzed and compared to the predictions by various Monte Carlo models.     

Charged particle correlations in\bar pp collisions at c.m. energies of 200, 546 and 900 GeV

We present data on two-particle pseudorapidity and multiplicity correlations of charged particles for non single-diffractive \(p\bar p - collisions\) at c.m. energies of 200, 546 and 900 GeV. Pseudorapidity correlations interpreted in terms of a cluster model, which has been motivated by this and other experiments, require on average about two charged particles per cluster. The decay width of the clusters in pseudorapidity is approximately independent of multiplicity and of c.m. energy. The investigations of correlations in terms of pseudorapidity gaps confirm the picture of cluster production. The strength of forward-backward multiplicity correlations increases linearly with ins and depends strongly on position and size of the pseudorapidity gap separating the forward and backward interval. All our correlation studies can be understood in terms of a cluster model in which clusters contain on average about two charged particles, i.e. are of similar magnitude to earlier estimates from the ISR.     

Inclusiveπ° production in 360 GeVpp interactions using the european hybrid spectrometer

The intermediate and forward gamma detectors of EHS are used to reconstructπ°'s produced by 360 GeV/cpp interactions in the Rapid Cycling Bubble Chamber (RCBC). Using thepp forwardbackward symmetry, the inclusiveπ° production cross section is obtainedσ _π°=(132±11) mb. The averageπ° multiplicity is determined as a function of the charged particle multiplicity. The (1?x) dependence is given for differentp _T regions.     

Recent results from PHOBOS

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has delivered the collisions between Au nuclei at the highest center of mass energies achieved in the laboratory to date. PHOBOS is one of four experiments studying the these interactions. In this paper we will briefly describe the PHOBOS experiment, and discuss some of the current physics results obtained at $\sqrt {s_{NN} } = 56$ , 130 and 200 GeV: the systematic study of charged particle multiplicity as a function of pseudorapidity and centrality, measurements of antiparticle to particle ratios, and the hadron spectra as function of transverse momentum for both high and low pt.     

Diffraction dissociation in the reaction p+p→Λ°+K++p at the CERN ISR

The exclusive reaction pp→Λ°K⁺p has been studied at 0.1<?t_pp<0.6 GeV² and energies √s=45 GeV and 53 GeV at the CERN ISR. Diffractive excitation p→Λ°K⁺ occurs predominantly in the mass range M(Λ°K⁺)≈2.1 GeV and peaks at 1.7 GeV. The cross section for pp→Λ°K⁺p is 10±3μb for M(Λ°K⁺)<2.5 GeV, and the t_pp dependence is exp (bt) with b=7.0±0.5 GeV^?2.     

Measurement of theΞ - p elastic cross section at 102 and 135 GeV/c

TheΞ ^- p differential elastic cross section has been measured in the SPS hyperon beam at 102 and 135 GeV/c. In the range 0.012, thet distributions are found to be compatible with the formA exp(Bt) whereB is 7.7±0.4(GeV/c)^?2 at 102 GeV/c and 8.2 ±0.5(GeV/c)^?2 at 135 GeV/c. The corresponding total elastic cross sections areσ _el=4.9±0.7 mb andσ _el=5.6±0.9 mb, respectively. These results are compared with the predictions of phenomenological models.     

Neutral kaon production in K+p interactions at 32 GeV/c

The production of neutral kaons in the reaction K⁺p → Kⁿ + X is studied at the incident momentum of 32 GeV/c. Inclusive cross sections and single-particle distributions are presented and compared with the data at lower energies. The total inclusive cross section amounts to 7.9 ± 0.3 mb at 32 GeV/c and is significantly higher than at lower energies due to the rapid rise of multikaon production. The fraction of Kⁿ's coming from the decay of the K¹ resonances stays roughly constant with energy between 8.2 and 32 GeV/c. In the central and beam fragmentation regions the single-particle distributions reveal no energy dependence between the 16 and 32 GeV/c data in contrast with the behaviour at lower energies, while in the proton fragmentation region the data are compatible with the trend observed at lower energies and with theoretical expectations.