Results are presented on two-jet and three-jet cross sections, measured in the UA1 experiment at the CERN Super Proton Synchrotron (SPS) pp̄ Collider, at the highest available subprocess cms energies ( s ̂ >150 GeV ). Precise measurements of the two-jet angular distribution are consistent with previous results but show significant scale-breaking effects. The three-jet Dalitz plot and the three-jet angular distributions show evidence for final- and initial-state bremsstrahlung processes, in agreement with the leading-order QCD predictions. A comparison of the yield of wide-angle three-jet events with the yield of two-jet events at smaller scattering angles gives for the strong interaction coupling constant: α s ( K 3J K 2J )=0.16±0.02±0.03 at Q 2 ≈4000 GeV 2 , where the factor K 3J K 2J may plausibly be assumed to be close to unity.
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Inclusive cross sections and longitudinal momentum distributions are presented for γ rays produced in K − p and K + p interactions at 32 GeV/c in the 4.5 m Mirabelle hydrogen bubble chamber at the Serpukhov accelerator. The average longitudinal and transverse momentum of neutral pions and the average π 0 multiplicity ▪ 〈 n π 0〉 are estimated. It is found that 〈 n π 0〉 is an increasing function of the number of charged prongs.
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We compare high-transverse-momentum (P⊥) inclusive π0 production from π−, K−, p, and p¯ beams, at 100 and 200 GeV/c, for center-of-mass (c.m.) angles ranging from 2° to 115° and P⊥<4.5 GeV/c. The ratio σ(pp→π0X)σ(πp→π0X) decreases with increasing P⊥, and changes dramatically with c.m. angle. Also, the ratios σ(K−p→π0X)σ(π−p→π0X) and σ(p¯p→π0X)σ(pp→π0X) are approximately constant. These measurements are consistent with a theoretical viewpoint in which constituents of the incident hadrons undergo a hard-scattering subprocess.
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A series of semi-inclusive deep-inelastic scattering measurements on deuterium, helium, neon, krypton, and xenon targets has been performed in order to study hadronization. The data were collected with the HERMES detector at the DESY laboratory using a 27.6 GeV positron or electron beam. Hadron multiplicities on nucleus A relative to those on the deuteron, R_A^h, are presented for various hadrons (\pi^+, \pi^-, \pi^0, K^+, K^-, p, and \bar{p}) as a function of the virtual-photon energy \nu, the fraction z of this energy transferred to the hadron, the photon virtuality Q^2, and the hadron transverse momentum squared p_t^2. The data reveal a systematic decrease of R_A^h with the mass number A for each hadron type h. Furthermore, R_A^h increases (decreases) with increasing values of \nu (z), increases slightly with increasing Q^2, and is almost independent of p_t^2, except at large values of p_t^2. For pions two-dimensional distributions also are presented. These indicate that the dependences of R_A^{\pi} on \nu and z can largely be described as a dependence on a single variable L_c, which is a combination of \nu and z. The dependence on L_c suggests in which kinematic conditions partonic and hadronic mechanisms may be dominant. The behaviour of R_A^{\pi} at large p_t^2 constitutes tentative evidence for a partonic energy-loss mechanism. The A-dependence of R_A^h is investigated as a function of \nu, z, and of L_c. It approximately follows an A^{\alpha} form with \alpha \approx 0.5 - 0.6.
PI+ multiplicty ratio (Helium/Deuterium) as a function of NU.
K+ multiplicty ratio (Helium/Deuterium) as a function of NU.
P multiplicty ratio (Helium/Deuterium) as a function of NU.
The inclusive π0 production cross-section and the η/π0 ratio have been measured inpp collisions at\(\sqrt s= 63 GeV\) at the CERN Intersecting Storage Rings in the rapidity range 2.00<y<2.75. The π0 cross-section exhibits a strongy-dependence and falls more steeply as a function ofpT, compared with the cross-section measured aty∼0. We find a value of 0.46±0.07 for the η/π0 ratio with no significantpT dependence over the range 2.0<pT<4.0 GeV/c.
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Direct photon and neutral-pion production have been measured inpp collisions at the CERN ISR for 30<\(\sqrt s \)<63 GeV and transverse momenta up to 12 GeV/c. The direct photon signal relative to neutral-pion production increases withpT and shows little\(\sqrt s \)-dependence. Results are reported from a variety of running conditions, and details are given on the method of analysis and on the evaluation of systematic errors for the inclusive cross-section of single-photon and neutral-pion production.
The inclusive cross-section for π0 production near 90° inpp collisions at the CERN Intersecting Storage Rings has been studied for thepT range 3<pT<16GeV/c at four different centre-of-mass energies (\(\sqrt s = 30.6\), 44.8, 52.7, and 62.8 GeV). In this experiment the two photons from the π0→yy decay were resolved and measured separately forpT values up to 10 GeV/c. Results indicate an agreement with thepT−8 behaviour for the lower values ofpT and a slower decrease of the cross-section for the higher values ofpT. The high-pT data deviate from the scaling expressionpT−nF(xT), which holds for the lowerpT values (pT<8GeV/c).
USING RETRACTED GEOMETRY.
USING SUPER-RETRACTED GEOMETRY.
USING SUPER-RETRACTED GEOMETRY.
We report on double-differential inclusive cross-sections of the production of secondary protons, charged pions, and deuterons, in the interactions with a 5% nuclear interaction length thick stationary carbon target, of proton and pion beams with momentum from \pm 3 GeV/c to \pm 15 GeV/c. Results are given for secondary particles with production angles between 20 and 125 degrees. Cross-sections on carbon nuclei are compared with cross-sections on beryllium, copper, tantalum and lead nuclei.
The measured deuteron to proton ratios for each of the 8 GeV Proton, PI+ and PI- beams for the angular range 20 to 30 degrees.
The measured deuteron to proton ratios for each of the 8 GeV Proton, PI+ and PI- beams for the angular range 30 to 45 degrees.
The measured deuteron to proton ratios for each of the 8 GeV Proton, PI+ and PI- beams for the angular range 45 to 60 degrees.
An improved measurement of the average b hadron lifetime is performed using a sample of 1.5 million hadronic Z decays, collected during the 1991–1993 runs of ALEPH, with the silicon vertex detector fully operational. This uses the three-dimensional impact parameter distribution of lepton tracks coming from semileptonic b decays and yields an average b hadron lifetime of 1.533 ± 0.013 ± 0.022 ps.
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We describe a search for psi(3770) decay to two-body non-DDbar final states in e+e- data produced by the CESR collider and analyzed with the CLEO-c detector. Vector-pseudoscalar production of Rho0Pi0, Rho+Pi-, OmegaPi0, PhiPi0, RhoEta, OmegaEta, PhiEta, RhoEtaPrime, OmegaEtaPrime, PhiEtaPrime, Kstar0 K0bar, and Kstar+K- is studied along with that of BOnePi (BOne0Pi0 and BOne+Pi-) and Pi+Pi-Pi0. A statistically significant signal is found for PhiEta, at an excess cross section of (2.4 +- 0.6) pb [Gamma_{PhiEta} (psi(3770)) =(74 +- 16)Mev], and a suggestive suppression of Pi+Pi-Pi0 and RhoPi. We conclude with form factor determinations for OmegaPi0, RhoEta, and RhoEtaPrime.
Cross sections at 3.671 and 3.773 GeV.
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