M. Posocco

The ZEUS barrel and rear muon detector

Abstract Design, construction and performance characteristics of the ZEUS barrel and rear muon detector are presented.

Measurement of the proton electromagnetic form factor near threshold in the time-like region

The rate of the reaction pp→e+e− has been measured in liquid hydrogen for antiprotons at momentum values between 150 and 300 MeV/c. New precise values of the proton electromagnetic form factor in the time-like region have been obtained assuming |Ge|=|Gm| in the investigated region. The q2 dependence of the form factor close to threshold is found to have a steeper slope than indicated by existing calculations based on vector dominance models.

Precise determination of the electromagnetic form factor of the proton in the time-like region up to s = 4.2 GeV2

Abstract The s dependence of the proton form factor in the time-like region has been determined up to s=4.2 GeV2, assuming the validity of the |Ge| = |Gm| = |G| hypothesis. Data were taken in a dedicated experiment performed at the LEAR antiproton ring at CERN, increasing by one order of magnitude the available statistics on the proton form factor near threshold in the time-like region. Our result consist of cross section measurements of the p p → e + e − reaction for different beam momenta in the kinematical r 3.6⩽s⩽4.2 GeV2. The observed s dependence of the form factor close to threshold differs appreciably from the one suggested by previous experiments.

A large solid angle magnetic detector for precision studies of e.m. processes in low-energy p interactions

The detector presented is designed to measure the proton e.m. form factors by measuring e+e− pairs produced in pp annihilations at low energy or at rest. In this paper the apparatus is described in detail, with emphasis on how to achieve a suppression factor of about 1010 of the hadronic background.

Drift time measurements in limited streamer tubes

Abstract We have investigated the performances of drift time techniques applied to limited streamer tubes. A resolution of ∼ 150 μm in the coordinate across the wire is found and a way to solve the left-right ambiguity is presented.

A measurement of the pp→π+π− reaction for 158⩽p(p)⩽275 MeV/c

Abstract A measurement of the total cross section for the reaction p p → π+π− has been performed for seven values of the incident momentum between 158 and 275 MeV/c. The values obtained, if compared with previous results at higher momenta, agree with a 1/s dependence. The differential cross section sssumed over the whole incident momentum range has also been measured and the result of a fit by Legendre polynomials is given.

Four-layer aerogel Cherenkov counter

Abstract A 4-layer design of aerogel threshold counters using two refractive indices was suggested for the particle identification in the forward region of the BaBar detector. Three prototypes filled with the high quality aerogel produced in Novosibirsk were tested at T10 beam at CERN. Monte Carlo code was developed for the simulation of the light collection in aerogel counters. Monte Carlo results based on measured PTFE reflection coefficient and aerogel absorption and scattering lengths are in agreement with experiment.

Extensive tests of Hybryd Photon Detectors (HPD) used to collect Cherenkov light

Abstract The principle of operation of a newly developed proximity focused Hybrid Photon Detector is described. The HPD characteristics, performance and calibration are reported. Results from beam tests of aerogel threshold counters read out by HPD and the particle identification performance are presented.

A scintillator based muon system with SiPM readout for the SuperB detector

The existing muon detectors for high-energy physics experiments are mainly made of gas chambers such as Resistive Plate Chambers, Limited Streamer Tubes or Multi Wire Proportional Chambers. With the increasing luminosity of the new accelerators and the increment in dimensions of the experiments the development of a new detection technique, which is robust, cheap and capable to sustain high particle rate, is mandatory. We present the technology proposed for the Super B muon system. The detector is based on MINOS style extruded scintillators coupled to wavelength shifting fibers. The light readout is done by means of Silicon Photomultiplier devices. We report the R&D results on prototypes that can be operated either with binary readout, measuring only one coordinate, or with a TDC readout that can measure both the coordinate at the same time with adequate precision. Efficiency and time resolution will be discussed for different prototype geometry as well as the main operational issues related to the photodetectors, like stability, noise rate and neutron damage. A full-scale prototype with the same geometry designed for the SuperB experiment is under construction in our lab and it will be tested with a muon/pion beam at FNAL next fall. The structure optimization has been studied using a GEANT4 Monte Carlo simulation and the expected muon identification performances have been evaluated with a neural network algorithm, we present preliminary results of the optimization and its implication for the SuperB muon system.

The BaBaR drift chamber project

The BaBar Drift Chamber is now under construction. We review its design, the progress in the construction of the components, the plan for assembly and stringing and we present test results obtained with a prototype exposed at SLAC to cosmic rays. We also report on projected dE/dx performance from beam tests done with a chamber with a different cell design.