E. O'Brien

Two pion correlations in Au + Au collisions at 10.8-GeV/c per nucleon

Two-particle correlation functions for positive and negative pions have been measured in Au+Au collisions at 10.8GeV/{ital c} per nucleon. The data were analyzed using one- and three-dimensional correlation functions. From the results of the three-dimensional fit the phase space density of pions was calculated. It is consistent with local thermal equilibrium. {copyright} {ital 1997} {ital The American Physical Society}

Search for strange quark matter in high-energy heavy-ion collisions

Abstract We have initiated a search for strange quark matter in the products of 14.6 GeV/ c per nucleon 28 Si collisions with nuclei, utilizing the apparatus of E-814 at Brookhaven National Laboratorys AGS. We report the first results of this search, which is sensitive to particles with charge-to-mass ratios between 0.1 and 0.3 (GeV/ c 2 ) −1 that are produced within approximately ±0.5 units of the center of mass rapidity.

A monolithic preamplifier-shaper for measurement of energy loss and transition radiation

A custom monolithic circuit has been developed for the Time Expansion Chamber (TEC) of the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). This detector identifies particles by sampling their ionization energy loss (dE/dx) over a 3 cm drift space and by detecting associated transition radiation (TR) photons. The requirement of being simultaneously sensitive to dE/dx and TR events requires a dual-gain system. We have developed a compact solution featuring an octal preamplifier/shaper (P/S) IC with a split gain stage. The circuit, fabricated in 1.2 /spl mu/m CMOS process, incorporates a trans-impedance preamplifier and a 70 ns unipolar CR-RC/sup 4/ shaper with ion tail compensation and active DC offset cancellation. Digitally selectable gain, peaking time, and tail cancellation as well as channel-by-channel charge injection and disable can be configured in the system via a 3-wire interface. The 3.5/spl times/4.5 mm/sup 2/ die is packaged in a fine pitch 64-pin PQFP. Equivalent input noise is less than 1500 rms electrons at a power dissipation of 30 mW per channel. On a sample of 2400 chips, the DC offset was 2.3/spl plusmn/3 mV rms without trimming. A chamber-mounted TEC-PS Printed Circuit Board (PCB) houses four P/S chips, on-board calibration circuit, and 64 analog differential line drivers which transmit the shaped pulses to crate-mounted flash ADCs 7 m apart. An RS-422 link provides digital configuration downloading and read back, and supplies the calibration strobe. The 24.6 cm/spl times/9.5 cm board dissipates 8.5 W.

A study of wire chambers with highly segmented cathode pad readout for high multiplicity charged particle detection

Investigations of interpolating cathode pad readout have been carried out for high-multiplicity, two-dimensional position-sensitive detection of minimum ionizing particles and heavy ions. A detector configuration representing only 0.6% of a radiation length and covering an area of 26 cm by 16 cm, with over 1000 readout channels, has been developed. In a prototype chamber using this technique, a resolution of less than 1090 mu m (RMS) for 5.4-keV X-rays and differential nonlinearity of +or-6% have been achieved. The technique has also been demonstrated for detectors of much larger area. Pad chamber and chevron pad types of detector have been built and used in the E814 heavy ion experiment at the Brookhaven National Laboratory Alternating Gradient Synchrotron. It is concluded that their ability to handle high particle multiplicity and provide unambiguous two-dimensional position information (1-3% readout node spacing along the wire direction) affords a very powerful detector technique. >

Transverse energy distributions in Si-nucleus collisions at 10 GeV/nucleon

Transverse energy distributions have been measured for collisions of 10 GeV/nucleon Si with targets of Al, Cu and Pb using a combination of a NaI wall and a uranium based sampling calorimeter. The measured cross sectionsdσ/dET anddET/dη are consistent with full stopping and an increase, with increasing values ofET, of energy flow into large angles.

A transition radiation detector which features accurate tracking and dE/dx particle identification

The authors describe the results of a test run involving a transition radiation detector (TRD) that can both distinguish electrons from pions with momenta greater than 0.7 GeV/c and simultaneously track particles passing through the detector. The particle identification is accomplished through a combination of the detection of transition radiation from the electron and the differences in electron and pion energy loss (dE/dx) in the detector. The dE/dx particle separation is most efficient below 2 GeV/c while particle ID utilizing transition radiation is effective above 1.5 GeV/c. Combined, the electron-pion separation is better than 5*10/sup 2/. The single-wire, track position resolution for the TRD is approximately 230 mu m.<<ETX>>

Baryon distributions in ultrarelativistic nucleus-nucleus collisions

We have measured distributions in transverse momentum and rapidity of protons from interactions of 14.6 GeV/nucleon28Si projectiles with targets of Al and Pb. The transverse momentum spectra exhibit a thermal shape with a rapidity dependent temperature parameter. For very central or violent collisions the proton rapidity distributions exhibit the large rapidity shifts and (for Si+Al) a peak at midrapidity as required for full stopping.

A many particle-tracking detector with drift planes and segmented cathode readout

The design and performance of a detector system for tracking charged particles in an environment of high track density and rates up to 1 MHz are described. The system operates in the forward spectrometer of the Brookhaven National Laboratory heavy ion experiment E814 and uses principles of general interest in high-rate, high-multiplicity applications such as at the Relativistic Heavy Ion Collider or the Superconducting Supercollider. The system is required to perform over a large dynamic range, detecting singly charged particles as well as fully ionized relativistic /sup 28/Si. Results on gas gain saturation, delta -ray suppression, and overall detector performance in the presence of a 14.6-GeV/nucleon /sup 28/Si beam and a 14-GeV proton beam are presented. >

Front-end electronics for PHENIX time expansion chamber

Front-end electronics (FEE) has been developed for the PHENIX time expansion chamber (TEC), a multi-wire tracking detector with over 20k readout channels. The FEE for the TEC consists of an analog preamplifier shaping amplifier circuit board, a digital front-end module circuit board plus ancillary support boards for timing, control and communication. Signals from each chamber wire are sampled (/spl sim/40 MHz), digitized, buffered, and then formatted as 64 channel serial data packets to be transmitted via 1 GHz optical link. Three custom ICs have been designed for this system: 1) octal preamplifier and shaping amplifier with tail cancellation and dual-gain for large dynamic range with full serial control of gain, shaping time and tail; 2) nonlinear 5 bit flash-ADC with 9 bit dynamic range; 3) digital memory unit for programmable delay and memory depth. The FEE has been installed, commissioned and operated in the PHENIX experiment at Brookhaven National Laboratory.

The pixel readout system for the PHENIX pad chambers

Abstract A new concept for two-dimensional position readout of wire chambers is described. The basic idea is to use a cathode segmented into small pixels that are read out in specific groups (pads). The electronics is mounted on the outer face of the chamber with a chip-on-board technique, pushing the material thickness to a minimum. The system described here, containing 210 000 readout channels, will be used to read out the pad chambers in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC).