J. M. Butler

Search for the decay b→Xsμ+μ−

Abstract We have searched for the flavor-changing neutral current decay b → X s μ + μ − in p p collisions at s = 1.8 TeV with the DO detector at Fermilab. We determine the 90% confidence level limit for the branching fraction to be B ( b → X s μ + μ − ) −4 . We argue that this limit is more stringent than the best published limit on this decay rate.We have searched for the flavor-changing neutral current decay b ->s mu+ mu- in p pbar collisions at sqrt(s) = 1.8 TeV with the DO detector at Fermilab. We determine the 90% confidence level limit for the branching fraction to be B(b ->X_s mu+ mu-)<3.2 x 10^{-4}. We argue that this limit is more stringent than the best published limit on this decay rate.

Production and commissioning of a large prototype Digital Hadron Calorimeter for future colliding beam experiments

A new detector technology is being developed for future colliding beam experiments that is based on the use of fine-grained calorimetry, to optimize the use of Particle Flow Algorithms (PFAs) in measuring hadronic jets. Instead of traditional tower geometry and energy summation from many sampling layers, the new approach measures energy deposition in 1 cm2 cells on each sampling layer using discriminators. Jets are reconstructed using hit patterns from each layer, combined with information from inner tracking and the electromagnetic calorimeter. We have built a 480,000 channel prototype detector that is based on Resistive Plate Chambers (RPCs) to demonstrate this concept. The development is part of the CALICE Collaboration. The readout system uses a 64-channel custom integrated circuit called DCAL to record hits from each cell and apply a global timestamp. The chips mount directly on sophisticated front-end boards that are not only an integral part of the charge collection of the detector chambers, but also incorporate digital signal transmission, clock and control, and power and ground. The readout of data is serial, multiplexed into high-speed serial streams and sent to a “back-end” VME system for time-sorting and higher-level triggering. The system can be operated with an external trigger or be self-triggered, and can produce trigger signals from the front-end chips. The construction, installation, and commissioning of this prototype system is now complete. We have begun a measurement program using a test beam at Fermilab. An overview of the system is described. Experiences in building this large prototype system are reported. Results from the test beam are presented.

tt̄ production cross section in pp̄ collisions at √s = 1.8 TeV

Results are presented on a measurement of the t (t) over bar pair production cross section in p (p) over bar collisions at roots=1.8 TeV from nine independent decay channels. The data were collected by the D empty set experiment during the 1992-1996 run of the Fermilab Tevatron Collider. A total of 80 candidate events is observed with an expected background of 38.8+/-3.3 events. For a top quark mass of 172.1 GeV/c(2), the measured cross section is 5.69+/-1.21(stat)+/-1.04(syst) pb.Results are presented on a measurement of the ttbar pair production cross section in ppbar collisions at sqrt{s} = 1.8 TeV from nine independent decay channels. The data were collected by the Dzero experiment during the 1992-1996 run of the Fermilab Tevatron Collider. A total of 80 candidate events are observed with an expected background of 38.8 +- 3.3 events. For a top quark mass of 172.1 GeV/c^2, the measured cross section is 5.69 +- 1.21 (stat) +- 1.04 (sys) pb.

Design, Construction and Commissioning of the Digital Hadron Calorimeter - DHCAL

A novel hadron calorimeter is being developed for future lepton colliding beam detectors. The calorimeter is optimized for the application of Particle Flow Algorithms (PFAs) to the measurement of hadronic jets and features a very finely segmented readout with 1 × 1 cm2 cells. The active media of the calorimeter are Resistive Plate Chambers (RPCs) with a digital, i.e. one-bit, readout. To first order the energy of incident particles in this calorimeter is reconstructed as being proportional to the number of pads with a signal over a given threshold. A large-scale prototype calorimeter with approximately 500,000 readout channels has been built and underwent extensive testing in the Fermilab and CERN test beams. This paper reports on the design, construction, and commissioning of this prototype calorimeter.

Limits on [Formula Presented] and [Formula Presented] couplings from [Formula Presented] boson pair production

The results of a search for W boson pair production in pp collisions at √s=1.8TeV with subsequent decay to eμ, ee, and μμ channels are presented. Five candidate events are observed with an expected background of 3.1±0.4 events for an integrated luminosity of approximately 97pb -1 . Limits on the anomalous couplings are obtained from a maximum likelihood fit of the E T spectra of the leptons in the candidate events. Assuming identical WWγ and WWZ couplings, the 95% C.L. limits are -0.62<Δκ<0.77 (λ=0) and -0.53<λ<0.56 (Δκ=0) for a form factor scale Λ=1.5TeV.

Limits on anomalous [Formula Presented] and [Formula Presented] couplings

Limits on the anomalous WWγ and WWZ couplings are presented from a simultaneous fit to the data samples of three gauge boson pair final states in pp collisions at √s=1.8TeV: Wγ production with the W boson decaying to eν or μν, W boson pair production with both of the W bosons decaying to eν or μν, and WW or WZ production with one W boson decaying to eν and the other W boson or the Z boson decaying to two jets. Assuming identical WWγ and WWZ couplings, 95% C.L. limits on the anomalous couplings of -0.30<Δκ<0.43 (λ=0) and -0.20<λ<0.20 (Δκ=0) are obtained using a form factor scale Λ=2.0TeV. Limits found under other assumptions on the relationship between the WWγ and WWZ couplings are also presented.