10,539 research outputs found
A Study of Two- and Four-Fermion Production in E
No full textIn e + e \Gamma collisions at a centre-of-mass energy of about 161 GeV, slightly above the W + W \Gamma production threshold, the production of final states that do not involve real or virtual W bosons has been measured. In hadronic and leptonic 2-fermion final states cross-sections and leptonic forward-backward asymmetries have been obtained, both including and excluding the dominant production of radiative flZ 0 events. We have measured R b , the ratio of the number of bb to all multihadronic events at 161 GeV, and compared it to the result obtained at 130--136 GeV. In addition, 4-fermion final states of the type ` + ` \Gamma qq and ` + ` \Gamma ` 0+ ` 0\Gamma have been searched for. All results agree well with the Standard Model expectations. In a model-independent fit to the Z 0 lineshape, the hadronic cross-section presented here provides a complementary constraint on the size of the Z 0 -Photon exchange interference term compared to that afforded by LEP-..
Soft And Semi-Hard Hadronic Compared To
No full textMultiparticle production in soft and semi-hard hadronic collisions is reviewed in terms of correlations, where possible in comparison to e + e \Gamma and lepton-hadron collisions. Important differences are listed between these types of collision, but models based on QCD can be tuned to describe most of the observations in all three. Recent decisive data force these models to an increased convergence. 1. INTRODUCTION The aim of our game is a unified description of multiparticle production in hadron-hadron, lepton-hadron and e + e \Gamma collisions. In this game, particle production is assumed to proceed in two steps, excitation of a colour field and hadronization of the quarks and gluons produced in this field. The excitation is supposed to be of a hard scattering type in lh and e + e \Gamma collisions, but soft or at most "semi-hard" in normal (low p T ) hh collisions. Hadronization is seen as a soft process in all three. The aim is still hidden in the fog of non-perturbat..
Measurement of the production cross section of prompt J/ψ mesons in association with a W± boson in pp collisions at p s = 7 TeV with the ATLAS detector
No full textThe process pp → W±J/ψ provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions in the colliding protons. Using the 2011 ATLAS dataset of 4.5 fb-1 of p s = 7TeV pp collisions at the LHC, the first observation is made of the production of W± + prompt J/ events in hadronic collisions, using W± → μ and J/ψ → μ+μ-. A yield of 27.4±7.5 -6.5 W± + prompt J/ψ events is observed, with a statistical significance of 5.1. The production rate as a ratio to the inclusive W± boson production rate is measured, and the double parton scattering contribution to the cross section is estimated
Four-Fermion Production in E
No full textFour-fermion events have been selected in a data sample of 5.8 pb \Gamma1 collected with the aleph detector at centre-of-mass energies of 130 and 136 GeV. The final states ` + ` \Gamma q¯q, ` + ` \Gamma ` + ` \Gamma , ¯q¯q, and ¯` + ` \Gamma have been examined. Five events are observed in the data, in agreement with the Standard Model predictions of 6:67 \Sigma 0:38 events from four-fermion processes and 0:14 + 0:19 \Gamma 0:05 from background processes. (Submitted to Physics Letters B) See following pages for the list of authors The ALEPH Collaboration D. Buskulic, I. De Bonis, D. Decamp, P. Ghez, C. Goy, J.-P. Lees, A. Lucotte, M.-N. Minard, J.-Y. Nief, P. Odier, B. Pietrzyk Laboratoire de Physique des Particules (LAPP), IN 2 P 3 -CNRS, 74019 Annecy-le-Vieux Cedex, France M.P. Casado, M. Chmeissani, J.M. Crespo, M. Delfino, I. Efthymiopoulos, 20 E. Fernandez, M. Fernandez-Bosman, Ll. Garrido, 15 A. Juste, M. Martinez, S. Orteu, C. Padilla, I.C. Park, ..
Very high energy cosmic gamma rays from radio and x-ray pulsars
No full textThis thesis is concerned with the detection of very high energy cosmic gamma-rays from isolated pulsars and X-ray binary sources using the atmospheric Cerenkov technique. A general introduction to gamma ray detection techniques is followed by adscription of the properties of atmospheric Cerenkov radiation and a discussion of the principles of the atmospheric Cerenkov technique. The Mark I and Mark II gamma-ray telescopes operated in Dugway, Utah by the University of Durham between 1981 and 1984 are briefly described. There follows a discussion of the results from observations at many different wavelengths of Cygnus X-3. This object was observed by the Durham group between 1981 and 1983 in Dugway Utah and also in Durham during autumn 1985. The detection in the Dugway data of the 4.8 hr X-ray period and the possible detection of a19.2 day intensity variation are considered. The discovery of a 12.59 ms pulsar in data taken on Cygnus X-3 in 1983 is described. Evidence is presented which suggests this periodicity is also present at a weaker level in earlier data and also in the data taken in Durham in 1985.Results from observations of PSR1937+21 , PSR1953+29and six radio pulsars , are presented. The design and construction of the Mark III telescope, now operating in Narrabri , N.S.W. , is described in detail. Preliminary results from observations with the Mark III telescope of three objects, LMC X-4, the Vela pulsar and CentaurusX-3, are presented, with particular reference to periodicities inherent in the sources. An observation of the supernova in the Large Magellanic Cloud is discussed. A brief discussion of the mechanisms by which V.H.E. gamma-rays may be produced in isolated pulsars and X-ray binary pulsars is given, followed by a description of the future prospects for the Mark III and Mark IV telescopes
Study of Z Boson Pair Production in e
No full textWe report on a study of ZZ production in e + e \Gamma annihilation at center-of-mass energies near 183 GeV and 189 GeV. Final states containing quark and lepton pairs, (qq` + ` \Gamma , qq, and ` + ` \Gamma ` + ` \Gamma ), and the all-hadronic final state (qqqq) are considered. In all states with at least one Z boson decaying hadronically, lifetime and event-shape tags are used to identify bb final states. At p s = 189 GeV the cross section was measured to be 0:76 +0:14 \Gamma0:13 (stat.) +0:06 \Gamma0:05 (syst.) pb, consistent with the Standard Model prediction. At p s = 183 GeV the 95% C.L. upper limit is 0:56 pb. Limits on anomalous ZZfl and ZZZ couplings are derived. DISCLAIMER: This note describes preliminary results of the OPAL Collaboration. 1 Introduction The study of the process e + e \Gamma ! ZZ has recently become possible since LEP now operates at centerof -mass energies above the threshold for on-shell Z boson pair production. In the Standar..
Single Hadron Spectrum in [Gamma]-[Gamma] Collisions: The QCD Contribution to Order [Alpha]s and the Non Perturbative Background
No full textAurenche P, Douiri A, Baier R, Fontannaz M, Schiff D. Single Hadron Spectrum in [Gamma]-[Gamma] Collisions: The QCD Contribution to Order [Alpha]s and the Non Perturbative Background. Zeitschrift für Physik C: Particles and fields. 1985;29(3):423-437
Measurement of the D+/- production asymmetry in 7 TeV pp collisions
No full textThe asymmetry in the production cross-section \sigma of D+/- mesons, A_P = (\sigma(D+) - \sigma(D-))/(\sigma(D+) + \sigma(D-)), is measured in bins of pseudorapidity \eta and transverse momentum p_T within the acceptance of the LHCb detector. The result is obtained with a sample of D+ -> K_S pi+ decays corresponding to an integrated luminosity of 1.0 fb^-1, collected in pp collisions at a centre of mass energy of 7 TeV at the Large Hadron Collider. When integrated over the kinematic range 2.0 K_S pi+ decay is negligible. No significant dependence on \eta or p_T is observed
A Study of the Fragmentation of Quarks in
No full text: Deep inelastic scattering (DIS) events, selected from 1993 data taken by the H1 experiment at HERA, are studied in the Breit frame of reference. The fragmentation function of the quark is compared with those of e + e \Gamma data. It is shown that certain aspects of the quarks emerging from within the proton in e \Gamma p interactions are essentially the same as those of quarks pair-created from the vacuum in e + e \Gamma annihilation. The measured area, peak position and width of the fragmentation function show that the kinematic evolution variable, equivalent to the e + e \Gamma squared centre of mass energy, is in the Breit frame the invariant square of the four-momentum transfer. We comment on the extent to which we have evidence for coherence effects in parton showers. S. Aid 13 , V. Andreev 24 , B. Andrieu 28 , R.-D. Appuhn 11 , M. Arpagaus 36 , A. Babaev 26 , J. Baehr 35 , J. B'an 17 , Y. Ban 27 , P. Baranov 24 , E. Barrelet 29 , R. Barsch..
An Interaction region for Gamma-Gamma and Gamma-Electron collisions at TESLA/SBLC
No full textLinear colliders offer unique opportunities to study gamma-gamma (, gamma-electron () interactions. Using the laser backscattering method one can obtain gg, ge colliding beams with an energy and luminosity comparable to that in collisions. This work is a part of the Conceptual Design of TESLA/SBLC linear colliders describing a second interaction region for gg, ge collisions. We consider here possible physics in high energy , collisions, conversion, requirements to lasers, collision schemes, attainable luminosities, backgrounds, possible lasers, optics at the interaction region and other associated problems
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