499 research outputs found
Comparison of next-to-leading order calculations for jet cross sections in deep-inelastic
No full textA Measurement of the t dependence of the helicity structure of diffractive rho meson electroproduction at HERA
No full textThe helicity structure of the diffractive electroproduction of rho mesons, e + p --> e + rho + Y, is studied in a previously unexplored region of large four-momentum transfer squared at the proton vertex, t: 0 < t' < 3 GeV2, where t' = \t\ - \t\ min. The data used are collected with the HI detector at HERA in the kinematic domain 2.5 < Q(2) < 60 GeV2, 40 < W < 120 GeV No t dependence of the r(00)(04) spin density matrix element is found. A significant t dependent helicity non-conservation from the virtual photon to the rho meson is observed for the spin density matrix element combinations r(00)(5) + 2r(11)(5) and r(00)(1) + 2r(11)(1). These t dependences are consistently described by a perturbative QCD model based on the exchange of two gluons. (C) 2002 Elsevier Science B.V. All rights reserved
Limits on the decay-rate difference of neutral B mesons and on CP, T, and CPT violation in B0B0 oscillations
No full textUsing events in which one of two neutral B mesons from the decay of an Υ(4S) resonance is fully reconstructed, we set limits on the difference between the decay rates of the two neutral B mass eigenstates and on CP, T, and CPT violation in B0B0 mixing. The reconstructed decays, comprising both CP and flavor eigenstates, are obtained from 88 million Υ(4S)→BB̅ decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We determine six independent parameters governing oscillations (Δm,ΔΓ/Γ), CPT and CP violation (Rez,Imz), and CP and T violation (ImλCP,|q/p|), where λCP characterizes B0 and B0 decays to states of charmonium plus KS0 or KL0. The results are sgn(ReλCP)ΔΓ/Γ=-0.008±0.037(stat.)±0.018(syst.)[-0.084,0.068],|q/p|=1.029±0.013(stat.)±0.011(syst.)[1.001,1.057],(ReλCP/|λCP|)Rez=0.014±0.035(stat.)±0.034(syst.)[-0.072,0.101],Imz=0.038±0.029(stat.)±0.025(syst.)[-0.028,0.104].The values inside square brackets indicate the 90% confidence-level intervals. The values of ImλCP and Δm are consistent with previous analyses and are used as cross checks. These measurements are in agreement with standard model expectations
K-S(0) and Lambda(0) production studies in p(p)over-bar collisions at root s=1800 and 630 GeV
No full textWe present a study of the production of K-S(0) and Lambda(0) in inelastic p (p) over bar collisions at root s=1800 and 630 GeV using data collected by the CDF experiment at the Fermilab Tevatron. Analyses of K-S(0) and Lambda(0) multiplicity and transverse momentum distributions, as well as of the dependencies of the average number and \u3c p(T)\u3e of K-S(0) and Lambda(0) on charged particle multiplicity, are reported. Systematic comparisons are performed for the full sample of inelastic collisions, and for the low and high momentum transfer subsamples, at the two energies. The p(T) distributions extend above 8 GeV/c, showing a \u3c p(T)\u3e higher than previous measurements. The dependence of the mean K-S(0)(Lambda(0)) p(T) on the charged particle multiplicity for the three samples shows a behavior analogous to that of charged primary tracks
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Development of Photon Detectors for a Fast Focusing DIRC
No full textWe report progress in developing a Focusing DIRC with very good timing resolution. This basic detector development has been motivated by a possible upgrade of the very successful BaBar DIRC particle identification detector for a future Super B-factory. We have built a single bar full size prototype, which aims to reduce the chromatic error by precise timing, and to remove the effect of bar thickness with a focusing mirror. This paper describes the design of the prototype, and systematic studies of the timing resolution and position response for single photons for two 64-pixel detectors: (a) Hamamatsu Flat Panel PMTs, and (b) Burle MCP-PMTs. To test the prototype, we have developed new electronics for {approx}300 pixels capable of measuring a single electron timing resolution to {approx}100ps. We also report on a first measurement of aging with the MCP-PMT
Limits on the decay-rate difference of neutral B mesons and on CP, T, and CPT violation in oscillations
No full textUsing events in which one of two neutral B mesons from the decay of an Y(4S) meson is fully reconstructed, we determine parameters governing decay (\Delta\Gamma_d/\Gamma_d), CP and T violation (|q/p|), and CP and CPT violation (Rez,Imz). The results, obtained from an analysis of 88 million Y(4S) decays recorded by BABAR, are -- sgn(Re(lambdaCP))\Delta\Gamma_d/Gamma_d = -0.008 +- 0.037 +- 0.018 -0.084, 0.068 ] |q/p| = 1.029 +- 0.013 +- 0.011 [ 1.001, 1.057 ] Re(lambdaCP)/|lambdaCP| Rez = 0.014 +- 0.035 +- 0.034 [ -0.072, 0.101 ] Imz = 0.038 +- 0.029 +- 0.025 [ -0.028, 0.104 ]. -- The values inside square brackets indicate the 90% confidence-level intervals. These results are consistent with Standard Model expectations
Measurement of the CKM matrix element |V(ub)| with B ---> rho e nu decays
No full textWe present a measurement of the branching fraction for the rare decays B-->rhoenu and extract a value for the magnitude of V-ub, one of the smallest elements of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix. The results are given for five different calculations of form factors used to parametrize the hadronic current in semileptonic decays. Using a sample of 55x10(6) B (B) over bar meson pairs recorded with the BABAR detector at the PEP-II e(+)e(-) storage ring, we obtain B(B-0-->rho(-)e(+)nu)=(3.29+/-0.42+/-0.47+/-0.55)x10(-4) and \V-ub\=(3.64+/-0.22+/-0.25(-0.56)(+0.39))x10(-3), where the uncertainties are statistical, systematic, and theoretical, respectively
Energy flow and rapidity gaps between jets in photoproduction at HERA
No full textDijet events in photon-proton collisions in which there is a large pseudorapidity separation ## > 2.5 between the two highest E T jets are studied with the H1 detector at HERA. The inclusive dijet cross sections are measured as functions of the longitudinal momentum fractions of the proton and photon which participate in the production of the jets, x # respectively, ##, the pseudorapidity separation between the two highest E T jets, and , the total summed transverse energy between the jets. Rapidity gap events are defined as events in which E T is less than E T , for E T varied between 0.5 and 2.0 GeV. The fraction of dijet events with a rapidity gap is measured differentially in ##, x # . An excess of events with rapidity gaps at low values of E is observed above the expectation from standard photoproduction processes. This excess can be explained by the exchange of a strongly interacting colour singlet object between the jets. To be submitted to Eur. Phys. J. C. Adloff , V. Andreev , B. Andrieu , T. Anthonis , V. Arkadov , A. Astvatsatourov A. Babaev , J. Bahr , P. Baranov , E. Barrelet , W. Bartel , P. Bate , J. Becker A. Beglarian , O. Behnke , C. Beier , A. Belousov , T. Benisch , Ch. Berger T. Berndt , J.C. Bizot , J. Boehme , V. Boudry , W. Braunschweig , V. Brisson H.-B. Broker , D.P. Brown , W. Bruckner , D. Bruncko , J. Burger , F.W. Busser A. Bunyatyan 12,34 , A. Burrage , G. Buschhorn , L. Bystritskaya , A.J. Campbell J. Cao , S. Caron , F. Cassol-Brunner , D. Clarke , C. Collard , J.G. Contreras 7,41 Y.R. Coppens , J.A. Coughlan , M.-C. Cousinou , B.E. Cox , G. Cozzika , J. Cvach J.B. Dainton , W.D. Dau , K. Daum 33,39 , M. Davidsson , B. D..
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