Susan Watts

Precise determination of the lifetime of the charmed baryon Λc

Abstract We present the final result on the measurement of the lifetime of the Λ c -baryon from a sample of Λ c -decays obtained in the NA32 experiment at the CERN SPS using silicon microstrip detectors and charge-coupled devices for vertex reconstruction. We observe a total of 160 Λ c in five different decay modes. A sample of 101 unambiguous decays of Λ c →pK − π + (and charge conjugate) above a background of 7 events is used for the Λ c mass and lifetime measurement. The mean Λ c lifetime is determined to be 1.96 −0.20 +0.23 ×10 −13 s and the Λ c mass to be 2285.8±0.6±1.2 MeV/ c 2 .

Lifetime measurement of Ds mesons

We have observed a sample of 21 unambiguous decays of Ds mesons into KKπ hadronically produced in the NA11 and NA32 experiments at the CERN SPS using high resolution silicon microstrip detectors. We measure the mean lifetime and the mass of the Ds meson to be (3.3±0.61.0)x10−13 s and 1972.7 ± 1.5 ± 1.0 MeV/c2, respectively.

A-dependence study of inclusive ϑ production

TheA-dependence of the inclusive ϑ meson cross-section is measured using two target materials, beryllium and tantalum, in the kinematic range 0<xF<0.3 andpT2<1 GeV2. Parametrizing the cross-section with δ(A)=δ(A=1)Aα, yields α=0.90 ±0.02 and α=0.86±0.02 for production of ϑs with 120 GeVπ+ andp-beams respectively.

Lifetimes of charged and neutralD mesons

We have measured the lifetimes of hadronically produced charged and neutralD mesons using silicon microstrip detectors and an active silicon target in the NA32 spectrometer at the CERN SPS. We obtainτD± = (10.9±1.51.9)·10−13s andτD(−)10 = (4.2±0.5)·10−13s based on 59 and 90 fully reconstructed decays respectively, giving a ratioτD±/τD(−)10 of 2.6 ±0.5.

A study of λ+c decays into pK−π+, pK−π+π0and pK−π+π0π0

Abstract In the CERN NA32 experiment a high-resolution silicon vertex detector and a purely topological approach were used to collect a clean sample of λ + c decays into pK − π + with or without additional neutral particles. We study the subresonant structure of the λ c + peak obtaining BR (λ c + → p K ∗0 (892)) = 0.35 −0.07 +0.06 ±0.03 with respect to the total λ c + → pK − π + decay. We also determine branching ratios for some channels with neutral decay products, namely BR( λ c + → pK − π + π 0 ) = 0.73±0.12±0.05 and BR( λ c + → pK − π + π 0 π 0 = 0.16±0.07±0.03, again with respect to the total λ c + → pK − π + decay.