LHCb

Abstract:

Inclusive photoproduction of D*± mesons has been measured for photon-proton centre-of-mass energies in the range 130 < W < 28OGeV and photon virtuality Q2 < IGeV2. The data sample used corresponds to an integrated luminosity of 37 pb-1. Total and differential cross sections as functions of the D* transverse momentum and pseudorapidity are presented in restricted kinematical regions and the data are compared with next-to-leading order (NLO) perturbative QCD calculations using the "massive charm" and "massless charm" schemes. The measured cross sections are generally above the NLO calculations, in particular in the forward (proton) direction. The large data sample also allows the study of dijet production associated with charm. A significant resolved as well as a direct photon component contribute to the cross section. Leading order QCD Monte Carlo calculations indicate that the resolved contribution arises from a significant charm component in the photon. A massive charm NLO parton level calculation yields lower cross sections compared to the measured results in a kinematic region where the resolved photon contribution is significant.

Abstract:

DELPHI results are presented on the inclusive production of the neutral mesons ρ0, f0(980), f2(1270), K2*0(1430) and f2′(1525) in hadronic Z0 decays. They are based on about 2 million multihadronic events collected in 1994 and 1995, using the particle identification capabilities of the DELPHI Ring Imaging Cherenkov detectors and measured ionization losses in the Time Projection Chamber. The total production rates per hadronic Z0 decay have been determined to be: 1.19 ± 0.10 for ρ0; 0.164 ± 0.021 for f0(980); 0.214 ± 0.038 for f2(1270); 0.073 ± 0.023 for K2*0(1430); and 0.012 ± 0.006 for f2′(1525). The total production rates for all mesons and differential cross-sections for the ρ0, f0(980) and f2(1270) are compared with the results of other LEP experiments and with models. © 1999 Elsevier Science B.V. All rights reserved.

Abstract:

The shapes of jets with transverse energies, EjetT, up to 45 GeV produced in neutral- and charged-current deep inelastic e+p scattering (DIS) at Q2 > 100 GeV2 have been measured with the ZEUS detector at HERA. Jets are identified using a cone algorithm in the η-φ plane with a cone radius of one unit. The jets become narrower as EjetT increases. The jet shapes in neutral- and charged-current DIS are found to be very similar. The jets in neutral-current DIS are narrower than those in resolved processes in photoproduction and closer to those in direct-photon processes for the same ranges in EjetT and jet pseudorapidity. The jet shapes in DIS are observed to be similar to those in e+e- interactions and narrower than those in p̄p collisions for comparable EjetT. Since the jets in e+e- interactions and e+p DIS are predominantly quark initiated in both cases, the similarity in the jet shapes indicates that the pattern of QCD radiation within a quark jet is to a large extent independent of the hard scattering process in these reactions.

Abstract:

Charged particle production in neutral current deep inelastic scattering (DIS) has been studied using the ZEUS detector. The evolution of the mean multiplicities, scaled momenta and transverse momenta in Q2 and cursive Greek chi for 10 < Q2 < 5120 GeV2 and cursive Greek chi > 6 × 10-4 has been investigated in the current and target fragmentation regions of the Breit frame. Distributions in the target region, using HERA data for the first time, are compared to distributions in the current region. Predictions based on MLLA and LPHD are inconsistent with the data.

Abstract:

The DIS diffractive cross section, dσdiffγ*p→XN/dMx, has been measured in the mass range Mx < 15 GeV for γ*p c.m. energies 60 < W < 200 GeV and photon virtualities Q2 = 7 to 140 GeV2. For fixed Q2 and Mx, the diffractive cross section rises rapidly with W, dσdiffγ*p→X N (Mx, W, Q2)/dMx ∝ Wadiff with adiff = 0.507 ± 0.034 (stat) +0.155-0.046 (syst) corresponding to a t-averaged pomeron trajectory of ̄αℙ = 1.127 ± 0.009 (stat) +0.039-0.012 (syst) which is larger than ̄αℙ observed in hadron-hadron scattering. The W dependence of the diffractive cross section is found to be the same as that of the total cross section for scattering of virtual photons on protons. The data are consistent with the assumption that the diffractive structure function FD(3)2 factorizes according to cursive greek chiℙFD(3)2(cursive greek chiℙ, β, Q2) = (cursive greek chi0//cursive greek chiℙ)nFD(2)2(β, Q2). They are also consistent with QCD based models which incorporate factorization breaking. The rise of cursive greek chiℙFD(3)2 with decreasing cursive greek chiℙ and the weak dependence of FD(2)2 on Q2 suggest a substantial contribution from partonic interactions.