LHCb

Abstract:

Correlations between pions from different Ws in e⁺e^- → W⁺W^- events are studied using data collected by the DELPHI detector at LEP running at a centre-of-mass energy of 172 GeV in 1996. At the present level of statistics, no enhancement of the correlation function above that expected from a pair of uncorrelated W's is observed at small values of the four- momentum difference of the pions. © 1997 Published by Elsevier Science B.V.

Abstract:

The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from Z⁰ decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at energies between 14 GeV and 91 GeV. A large scaling violation is observed, which is used to extract the strong coupling constant from a fit using a numerical integration of the second order DGLAP evolution equations. The result is αs(Mz) = 0.1241^+0.006-0.007(exp) ±0.009(theory) where the first error represents the experimental uncertainty and the second error is due to the factorization and renormalization scale dependence. © 1997 Elsevier Science B.V.

Abstract:

In a sample of 3.02 million hadronic Z⁰ decays collected by the DELPHI detector, 270 J/ψ → l⁺l^- candidates have been selected. A search for fully reconstructed B^±c mesons has yielded one B^±c → J/ψ π^± candidate, no B^±c → J/ψ l^± Vl candidates, and one B^±c → J/ ψ π⁺ π^- π^± candidate, consistent with expected background in each channel. The following 90% confidence level upper limits are determined: Br(Z⁰ → B^±c X) × Br(B^±c → J/ψ π^±) < (1.05 to 0.84) × 10^-4 and Br(Z⁰ → B^±c X) × Br(B^±c → J/ψ l^± Vl) < (5.8 to 5.0) × 10^-5, where the ranges quoted correspond to the range of predicted B^±c lifetimes from 0.4 to 1.4 ps, and Br(Z⁰ → B^±c X) × Br(B^±c → J/ψ π⁺ π^- π^±) < 1.75 × 10^-4, constant over the range of predicted B^±c lifetimes. © 1997 Elsevier Science B.V.

Abstract:

Using the ZEUS detector at HERA, we have studied the reaction e+p → e+X for Q2 > 5000 GeV2 with a 20.1 pb-1 data sample collected during the years 1994 to 1996. For Q2 below 15000 GeV2, the data are in good agreement with Standard Model expectations. For Q2 > 35000 GeV2, two events are observed while 0.145 ± 0.013 events are expected. A statistical analysis of a large ensemble of simulated Standard Model experiments indicates that with probability 6.0%, an excess at least as unlikely as that observed would occur above some Q2 cut. For x > 0.55 and y > 0.25, four events are observed where 0.91 ± 0.08 events are expected. A statistical analysis of the two-dimensional distribution of the events in x and y yields a probability of 0.72% for the region x > 0.55 and y > 0.25 and a probability of 7.8% for the entire Q2 > 5000 GeV2 data sample. The observed excess above Standard Model expectations is particularly interesting because it occurs in a previously unexplored kinematic region. © Springer-Verlag 1997.

Abstract:

In 1996 LEP ran at a centre-of-mass energy of 161 GeV, just above the threshold of W-pair production. DELPHI accumulated data corresponding to an integrated luminosity of 9.93 pb^-1, and observed 29 events that are considered as candidates for W-pair production. From these, a cross-section for the doubly resonant e⁺e^- → WW process of 3.67^+0.97-0.85 ± 0.19 pb has been measured. Within the Standard Model, this cross-section corresponds to a mass of the W-boson of 80.40 ± 0.44(stat.) ±0.09(syst.) ±0.03(LEP) GeV/c². Alternatively, if m^w is held fixed at its current value determined by other experiments, the observed cross-section is used to obtain limits on trilinear WWV(V ≡ γ, Z) couplings. © 1997 Elsevier Science B.V.