F Combley’s research while affiliated with The University of Sheffield and other places

Data taken with the ALEPH detector at LEP1 have been used to search for gamma gamma production of the glueball candidates f(0)(1500) and f(j)(1710) via their decay to pi(+)pi(-). No signal is observed and upper limits to the product of gamma gamma width and pi(+)pi(-) branching ratio of the f(0)(1500) and the f(j)(1710) have been measured to be Gamma (gamma gamma --> f(0)(1500)) . BR(f(0)(1500) --> pi(+)pi(-)) < 0.31 keV and Gamma (gamma gamma --> f(j)(1710)) . BR (f(j)(1710) --> pi(+)pi(-)) < 0.55 keV at 95% confidence level.

The decay is reconstructed with J/ψ→e+e− or μ+μ− and K0S→π+π−. From the full ALEPH dataset at LEP1 of about 4 million hadronic Z decays, 23 candidates are selected with an estimated purity of 71%. They are used to measure the CP asymmetry of this decay, given by sin2β in the Standard Model, with the result . This is combined with existing measurements from other experiments, and increases the confidence level that CP violation has been observed in this channel to 98%.

Using a sample of about 1.46 million hadronic Z decays collected between 1991 and 1993 with the ALEPH detector at LEP, the energy distribution of the B0 and B± mesons produced at the Z resonance is measured by reconstructing semileptonic decays B → ℓνℓD(X) or . The charmed mesons are reconstructed through the decay modes D0 → K−π+, D0 → K−π+π−π+, D+ → K−π+π+ and . The neutrino energy is estimated from the missing energy in the lepton hemisphere. Accounting for B∗ and B∗∗ production, the shape of the scaled energy distribution xE(b) for mesons containing a b quark is compared to the predictions of different fragmentation models. The mean value of xE(b) is found to be 〈xE(b)〉 = 0.715 ± 0.007(stat) ± 0.013(syst).

Measurements of the subjet structure of quark and gluon jets in hadronic Z decays are presented. The analysis is based on one million hadronic events recorded by the Aleph detector. Roughly symmetric three-jet events are selected with a coarse jet-resolution cut-off, y1. Gluon jets are identified with a purity of 94.6% in those events where evidence of long-lived heavy-flavour hadrons in the other two jets is found. The jets are then analyzed using a smaller cut-off y0 (< y1) so that subjets are resolved. The properties of the jets (subjet multiplicities (Nq), (Ng) and rates Rng(q) for n = 1, 2, 3, 4) are determined and are found to be in good agreement with the expectations of perturbative QCD as long as the subjet resolution parameter y0 is sufficiently large to keep non-perturbative effects small. In particular, the ratio , which to leading order in QCD is given by the ratio of colour factors , is measured to be 1.96 ± 0.15 for y0 = 2 · 10−3, but falls to 1.29 ± 0.03 for y0 = 1.6 · 10−5.

The branching fraction for D0 → K−π+ is measured with the statistics collected by ALEPH from 1991 to 1994. The method is based on the comparison between the rate for the reconstructed , D0 → K−π+ decay chain and the rate for inclusive soft pion production at low transverse momentum with respect to the nearest jet. The result is B(D0 → K−π+0 = (3.90 ± 0.09 ± 0.12)%

A lower limit is set on the Bs0 meson oscillation parameter Δms using data collected from 1991 to 1994 by the ALEPH detector. Events with a high transverse momentum lepton and a reconstructed secondary vertex are used. The high transverse momentum leptons are produced mainly by b hadron decays, and the sign of the lepton indicates the particle/antiparticle final state in decays of neutral B mesons. The initial state is determined by a jet charge technique using both sides of the event. A maximum likelihood method is used to set a lower limit of Δms. The 95% confidence level lower limit on Δms ranges between 5.2 and ps−1 when the fraction of b quarks from Z0 decays that form Bs0 messons is varied from 8% to 16%. Assuming that the B0s fraction is 12%, the lower limit would be ps−1 at 95% confidence level. For xs = ΔmsτBs, this limit also gives xs > 8.8 using the B0s lifetime of τBs = 1.55 ± 0.11 ps and shifting the central value of τBs down by 1σ.

The lifetimes of theB 0 andB + mesons have been measured with theAleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991–1994. In the first of three methods, semileptonic decays ofB 0 andB + mesons were partially reconstructed by identifying events containing a lepton with an associatedD*− or$\bar D^0$ meson. The second method used fully reconstructedB 0 andB + mesons. The third method, used to measure theB 0 lifetime, employed a partial reconstruction technique to identifyB 0→D*−π +X decays. The combined results are\begin{gathered} \tau _0 = 1.55 \pm 0.06 \pm 0.03 ps, \hfill \\ \tau _ + = 1.58 \pm 0.09 \pm 0.03 ps, \hfill \\ \tfrac{{\tau _ + }}{{\tau _0 }} = 1.03 \pm 0.08 \pm 0.02. \hfill \\ \end{gathered} .