Neutral strange particle production in proton-proton collisions at\sqrt s = 63 GeV

The inclusive cross section for the production ofK _s ⁰ mesons, Λ and \(\bar \Lambda\) particles in proton-proton interactions at \(\sqrt s = 63\) GeV is presented. The produced particles have been detected in the full phase space. Behaviour of the longitudinal and transversal depandences of the cross sections are discussed. The total production cross sections for _s ⁰ mesons and Λ particles was determined to \(\sigma _{{\rm K}_S^0 } = (25.5 \pm 1.4)\) mb andσ _Λ =(7.8±1.2) mb respectively. A strong energy dependence of the production cross sections is observed.     

Production of meson resonances as leading particles in jets in proton-proton collisions at\sqrt s = 62 GeV at the CERN ISR

The production of ρ(770)⁰,K ^*(892)⁰, \(\bar K^* (892)^0 \) andf ₂(1270) mesons as leading particles in hadron jets (<z>～0.7) has been measured in deep inelasticpp interactions at the CERN ISR at \(\sqrt s = 62\) GeV. The comparison of vector and pseudoscalar meson production at the same transverse momentum provides a rather model independent way to determine the fragmentation parameterV/P. We determine(V/P) _u,d =1.66±0.18±0.63 from the ρ/π ratio and(V/P) _s =0.90±0.13±0.27 from theK ^*/K ratio. For thef ₂(1270) production we findf ₂/ρ⁰=0.30±0.08.     

Double parton scattering inpp collisions at\sqrt s = 63 GeV

In a study ofpp collisions at \(\sqrt s = 63\) GeV with more than 29 GeV total transverse energy emitted into 1.8 units of rapidity in the central region, we have extracted a sample of 4-jet events and compared it with models of the two sources of 4-jet production: double bremsstrahlung and double parton scattering. The data cannot be described by bremsstrahlung alone, and we extract the fraction of 4-jet events attributed to double parton scattering for various definitions of the 4-jet sample. We determine the double parton scattering/2-jet yield ratio, and this leads to a determination of the proton radius. We discuss the implications of our observations for the general understanding of high-ΣE _T events.     

Contribution of single diffraction dissociation to highp T production in proton-proton collisions at\sqrt s = 62 GeV at the CERN ISR

The contribution of single diffraction dissociation to highp _T particle production has been determined with the split field magnet detector. For transverse momentap _T >2 GeV/c and production angles θ>10° it is found to be less than 5% for all types of trigger particles. Specifically, a diffractive origin of the large production cross section for highp _T protons can be excluded. The contributions found to highp _T production are found to be in good agreement with extrapolations of the relative particle yields from single diffraction dissociation observed in inelastic minimum bias events.     

Soft and hard interactions in p \bar p collisions at \sqrt s = 1800 and 630 GeV

We present a study of p $\bar p$ collisions at $\sqrt s = 1800$ and 630 GeV collected using a minimum bias trigger by the CDF experiment in which the data set is divided into two classes corresponding to “soft” and “hard” interactions. For each subsample, the analysis includes measurements of the multiplicity, transverse momentum (p _T ) spectrum, and the average p _T and event-by-event p _T dispersion as a function of multiplicity. A comparison of results shows distinct differences in the behavior of the two samples as a function of the center-of-mass (CM) energy. We find evidence that the properties of the soft sample are invariant as a function of CM energy.     

Multi-photon production in ee collisions at \sqrt{s} = 181-209 GeV

The process is studied using data collected by the OPAL detector at LEP between the years 1997 and 2000. The data set corresponds to an integrated luminosity of 672.3 pb^-1 at centre-of-mass energies lying between 181 GeV and 209 GeV. Total and differential cross-sections are determined and found to be in good agreement with the predictions of QED. Fits to the observed angular distributions are used to set limits on parameters from several models of physics beyond the Standard Model such as cut-off parameters, contact interactions of the type , gravity in extra spatial dimensions and excited electrons. In events with three photons in the final state the mass spectrum of photon pairs is investigated. No narrow resonance is found and limits are placed on the product of the production cross-section and branching ratio. Received: 22 July 2002 / Published online: 8 November 2002     

The influence of Bose-Einstein correlations on intermittency inp\bar p collisions at\sqrt s = 630 GeV

The influence of Bose-Einstein correlations on the rise of factorial moments is small in the 1-dimensional phase space given by the pseudorapidity η, where the 2-body correlation function is dominated by unlike-sign particle correlations. Contraily, the influence is dominant in the higher dimensional phase space. This is shown by using correlation integrals. They exhibit clear power law dependences on the four-momentum transferQ ² for all orders investigated (i=2–5). When searching for the origin of this behaviour, we found that the Bose-Einstein ratio itself shows a steep rise forQ ²→0, compatible with a power law.     

Photonic events with missing energy in \mathrme^+\mathrme^- collisions at \sqrt{s} = 189 GeV

Photonic events with large missing energy have been observed in collisions at a centre-of-mass energy of 189 GeV using the OPAL detector at LEP. Results are presented for event topologies consistent with a single photon or with an acoplanar photon pair. Cross-section measurements are performed within the kinematic acceptance of each selection, and the number of light neutrino species is measured. Cross-section results are compared with the expectations from the Standard Model process + photon(s). No evidence is observed for new physics contributions to these final states. Upper limits on and are derived for the case of stable and invisible . These limits apply to single and pair production of excited neutrinos (), to neutralino production () and to supersymmetric models in which and is a light gravitino. The case of macroscopic decay lengths of particle X is considered for , , when . The single-photon results are also used to place upper limits on superlight gravitino pair production as well as graviton-photon production in the context of theories with additional space dimensions. Received: 4 April 2000 / Published online: 27 November 2000     

Production of mesons and baryons at high rapidity and high p(T) in proton-proton collisions at square root[s] = 200 GeV

We present particle spectra for charged hadrons pi(+/-), K(+/-), p, and p[over] from pp collisions at square root[s] = 200 GeV measured for the first time at forward rapidities (2.95 and 3.3). The kinematics of these measurements are skewed in a way that probes the small momentum fraction in one of the protons and large fractions in the other. Large proton to pion ratios are observed at values of transverse momentum that extend up to 4 GeV/c, where protons have momenta up to 35 GeV. Next-to-leading order perturbative QCD calculations describe the production of pions and kaons well at these rapidities, but fail to account for the large proton yields and small p[over]/p ratios.     

Midrapidity neutral-pion production in proton-proton collisions at square root s = 200 GeV

The invariant differential cross section for inclusive neutral-pion production in p+p collisions at sqrt[s]=200 GeV has been measured at midrapidity (|eta|<0.35) over the range 1相似文献   

Single intermediate vector boson production in e + e - collisions * at \sqrt{s} = {}183-209 GeV

The production of single charged and neutral intermediate vector bosons in e ⁺ e^- collisions has been studied in the data collected by the DELPHI experiment at LEP at centre-of-mass energies between 183 and 209 GeV, corresponding to an integrated luminosity of about 640 pb^-1. The measured cross-sections for the reactions, determined in limited kinematic regions, are in agreement with the Standard Model predictions. Arrival of the final proofs: 21 November 2005     

Nuclear gluon shadowing via continuum lepton pairs inp+A collisions at\sqrt s = 200 A GeV

The dilepton spectra from open charm decay inp+A reactions at $\sqrt s = 200$ AGeV are proposed to constrain gluon shadowing in nuclei. We show that the required measurements are feasible at RHIC.     

Measurement of transverse single-spin asymmetries for Dijet production in proton-proton collisions at sqrt[s]=200 GeV

We report the first measurement of the opening angle distribution between pairs of jets produced in high-energy collisions of transversely polarized protons. The measurement probes (Sivers) correlations between the transverse spin orientation of a proton and the transverse momentum directions of its partons. With both beams polarized, the wide pseudorapidity (-1< or = eta < or = +2) coverage for jets permits separation of Sivers functions for the valence and sea regions. The resulting asymmetries are all consistent with zero and considerably smaller than Sivers effects observed in semi-inclusive deep inelastic scattering. We discuss theoretical attempts to reconcile the new results with the sizable transverse spin effects seen in semi-inclusive deep inelastic scattering and forward hadron production in pp collisions.     

Search for neutralino pair production at \sqrt{s} = 189 GeV

A search for pair-production of neutralinos at a LEP centre-of-mass energy of 189 GeV gave no evidence for a signal. This limits the neutralino production cross-section and excludes regions in the parameter space of the Minimal Supersymmetric Standard Model (MSSM). Received: 22 November 2000 / Revised version: 11 January 2001 / Published online: 15 March 2001     

Neutral pion production in d-Au collisions at \sqrt{s_{NN}} = 200 GeV

In this paper, preliminary results are presented on high inclusive neutral pion measurements in d-Au collisions at GeV in the pseudo-rapidity range . Photons from the decay are detected in the Barrel Electromagnetic Calorimeter of the STAR experiment at RHIC. The analysis of this first BEMC hadron measurement is described in detail. The results are compared to earlier RHIC findings. Furthermore, the obtained invariant differential cross sections show good agreement with next-to-leading order (NLO) perturbative QCD calculations. Arrival of the final proofs: 4 July 2005 PACS: 25.75.-q     

J/psi production from proton-proton collisions at square root of s=200 GeV

J/psi production has been measured in proton-proton collisions at square root of s=200 GeV over a wide rapidity and transverse momentum range by the PHENIX experiment at the Relativistic Heavy Ion Collider. Distributions of the rapidity and transverse momentum, along with measurements of the mean transverse momentum and total production cross section are presented and compared to available theoretical calculations. The total J/psi cross section is 4.0+/-0.6(stat)+/-0.6(syst)+/-0.4(abs) mu b. The mean transverse momentum is 1.80+/-0.23(stat)+/-0.16(syst) GeV/c.