arXiv subjects
Publications and source records attributed to H. Fischer.
A search for lepton flavor violating decays, \kmmp, \keep, \kpem, \kmep and \pizem, was performed using the data collected in E865 at the Brookhaven Alternating Gradient Synchrotron. No signal was found in any of the decay modes. At the 90% confidence level, the branching ratios are less than $3.0\times10^{-9}$, $6.4\times10^{-10}$, $5.2\times10^{-10}$, $5.0\times10^{-10}$ and $3.4\times10^{-9}$ respectively.
The experiment E865 at BNL places an upper limit on the branching ratio for the decay K+ -> pi+ mu+ e- of 3.9x10^-11 (90% C.L.). Along with with other results this yields a combined upper limit on this branching ratio of 2.8x10^-11. A new upper limit on the branching ratio for pi0 -> mu+ e- of 3.8x10^-10 (90% C.L.) is also established. The experiment and analysis are described.
The E885 collaboration utilized the 1.8 GeV/c K^- beam line at the AGS to accumulate 3 x 10^5 (K^-,K^+) events. Xi hypernuclear states are expected to be produced through the reaction K^- + ^{12}C -> K^+ + ^{12}_{Xi}Be. The measured missing-mass spectrum indicates the existence of a signal below the threshold for free Xi production. Although the resolution was not sufficient to resolve discrete hypernuclear states, the excess of events in the region of missing mass, kinematically inaccessible in free Xi production, is compared to theoretical prediction for ^{12}_{Xi}Be production.
A new TDC chip has been developed for the COMPASS experiment at CERN. The resulting ASIC offers an unprecedented degree of flexibility and functionality. Its capability to handle highest hit and trigger input rates as well as its low power consumption makes it an ideal tool for future collider and fixed target experiments. First front-end boards equipped with the F1 chip have been used recently at testbeam experiments at CERN. A functional description and specification for this new TDC chip is presented.
More than 400 $K^{+}\toπ^{+}μ^+μ^-$ events were observed in a rare $K^+$ decay experiment at the AGS. Normalized to the $K^{+}\toπ^{+}π^+π^-$ decay, the branching ratio is determined to be $(9.22 \pm 0.60 (stat) \pm 0.49 (syst))\times 10^{-8}$. This branching ratio and the $μμ$ mass spectrum is in very good agreement with the measurement of the $K^{+}\toπ^{+}e^+e^-$ decay, but deviates significantly from the previous measurement.
A new TDC-chip is under development for the COMPASS experiment at CERN. The ASIC, which exploits the 0.6 micrometer CMOS sea-of-gate technology, will allow high resolution time measurements with digitization of 75 ps, and an unprecedented degree of flexibility accompanied by high rate capability and low power consumption. Preliminary specifications of this new TDC chip are presented. Furthermore a FPGA based readout-driver and buffer-module as an interface between the front-end of the COMPASS detector systems and an optical S-LINK is in development. The same module serves also as remote fan-out for the COMPASS trigger distribution and time synchronization system. This readout-driver monitors the trigger and data flow to and from front-ends. In addition, a specific data buffer structure and sophisticated data flow control is used to pursue local pre-event building. At start-up the module controls all necessary front-end initializations.
A study has been performed of the reaction pbar p -> 4K using in-flight antiprotons from 1.1 to 2.0 GeV/c incident momentum interacting with a hydrogen jet target. The reaction is dominated by the production of a pair of phi mesons. The pbar p -> phi phi cross section rises sharply above threshold and then falls continuously as a function of increasing antiproton momentum. The overall magnitude of the cross section exceeds expectations from a simple application of the OZI rule by two orders of magnitude. In a fine scan around the xi/f_J(2230) resonance, no structure is observed. A limit is set for the double branching ratio B(xi -> pbar p) * B(xi -> phi phi) < 6e-5 for a spin 2 resonance of M = 2.235 GeV and Width = 15 MeV.
The reaction pbar p -> pbar p pi+ pi- has been studied with high statistics at CERN-LEAR with incident pbar momenta from 1.65 to 2.0 GeV/c by the JETSET (PS202) experiment. The aim of this paper is to search for narrow resonances decaying to pbar p. No evidence for such structures is found. In particular, an upper limit for the production of a 2.02 GeV state with a width of Gamma = 20 MeV, having been seen in other hadroproduction experiments, is established. Our results restrict the cross section for such a peak to be below 200 nb at the 95% confidence level.
The pbar p -> Ks Ks -> 4pi+/- cross section was measured at incident antiproton momenta between 0.6 and 1.9 GeV/c using the CERN Low Energy Antiproton Ring (LEAR). This investigation was part of a systematic study of in-flight antiproton-proton annihilations into two-neutral-meson final states in a search for hadronic resonances. A coarse scan of the pbar p -> Ks Ks cross section as a function of center-of-mass energy between 1.964 and 2.395 GeV/c^2 and a fine scan of the region surrounding the Xi(2220) are presented. Upper limits on the product branching ratio BR(Xi -> pbar p)BR(Xi -> Ks Ks) are determined for a wide range of mass and width assumptions based on the non-observation of the Xi(2220). A rise in the pbar p -> Ks Ks cross section is observed near 2.15 GeV/c^2, which is consistent with the f2(2150) resonance.