LHCb

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.

Abstract:

A search for stable or long-lived heavy charged particles in e⁺e^- interactions at energies of 130-136, 161 and 172 GeV has been performed using the data taken by the DELPHI experiment at LEP. The search is based on particle identification provided by the Time Projection Chamber and the Ring Imaging Cherenkov detector. Upper limits at 95% confidence level are derived on the cross-section for heavy long-lived pair-produced charge ±e and ±2/3e particles in the range of 0.4-2.3 pb for masses from 45 to 84 GeV/c². Within supersymmetric extensions of the Standard Model, long-lived charginos with masses from 45 to 84 (80) GeV/c² for high (low) sneutrino masses can be excluded at 95% confidence level. Left-handed (right-handed) long-lived or stable smuons and staus with masses between 45 and 68 (65) GeV/c² can be excluded at 95% confidence level. © 1997 Elsevier Science B.V.