H. Pernegger

Centrality dependence of charged-hadron transverse-momentum spectra in d+Au collisions at sqrt[s(NN)]=200 GeV.

We have measured transverse momentum distributions of charged hadrons produced in d+Au collisions at sqrt[s(NN)]=200 GeV. The spectra were obtained for transverse momenta 0.25<p(T)<6.0 GeV/c, in a pseudorapidity range of 0.2<eta<1.4 in the deuteron direction. The evolution of the spectra with collision centrality is presented in comparison to p+pmacr; collisions at the same collision energy. With increasing centrality, the yield at high transverse momenta increases more rapidly than the overall particle density, leading to a strong modification of the spectral shape. This change in spectral shape is qualitatively different from observations in Au+Au collisions at the same energy. The results provide important information for discriminating between different models for the suppression of high-p(T) hadrons observed in Au+Au collisions.

Charge-carrier properties in synthetic single-crystal diamond measured with the transient-current technique

For optimal operation of chemical-vapor deposition (CVD) diamonds as charged particle detectors it is important to have a detailed understanding of the charge-carrier transport mechanism. This includes the determination of electron and hole drift velocities as a function of electric field, charge carrier lifetimes, as well as effective concentration of space charge in the detector bulk. We use the transient-current technique, which allows a direct determination of these parameters in a single measurement, to investigate the charge-carrier properties in a sample of single-crystal CVD diamond. The method is based on the injection of charge using an α source close to the surface and measuring the induced current in the detector electrodes as a function of time.For optimal operation of chemical-vapor deposition (CVD) diamonds as charged particle detectors it is important to have a detailed understanding of the charge-carrier transport mechanism. This includes the determination of electron and hole drift velocities as a function of electric field, charge carrier lifetimes, as well as effective concentration of space charge in the detector bulk. We use the transient-current technique, which allows a direct determination of these parameters in a single measurement, to investigate the charge-carrier properties in a sample of single-crystal CVD diamond. The method is based on the injection of charge using an α source close to the surface and measuring the induced current in the detector electrodes as a function of time.

Pseudorapidity distribution of charged particles in d+Au collisions at sqrt[sNN]=200 GeV.

The measured pseudorapidity distribution of primary charged particles in minimum-bias d+Au collisions at sqrt[s(NN)]=200 GeV is presented for the first time. This distribution falls off less rapidly in the gold direction as compared to the deuteron direction. The average value of the charged particle pseudorapidity density at midrapidity is |eta|< or =0.6)=9.4+/-0.7(syst) and the integrated primary charged particle multiplicity in the measured region is 82+/-6(syst). Estimates of the total charged particle production, based on extrapolations outside the measured pseudorapidity region, are also presented. The pseudorapidity distribution, normalized to the number of participants in d+Au collisions, is compared to those of Au+Au and p+(-)p systems at the same energy. The d+Au distribution is also compared to the predictions of the parton saturation model, as well as microscopic models.

The evaporative cooling system for the ATLAS inner detector

This paper describes the evaporative system used to cool the silicon detector structures of the inner detector sub-detectors of the ATLAS experiment at the CERN Large Hadron Collider. The motivation for an evaporative system, its design and construction are discussed. In detail the particular requirements of the ATLAS inner detector, technical choices and the qualification and manufacture of final components are addressed. Finally results of initial operational tests are reported. Although the entire system described, the paper focuses on the on-detector aspects. Details of the evaporative cooling plant will be discussed elsewhere.

Radiation hardness studies of CVD diamond detectors

Abstract The inherent properties of diamond make it an ideal material for tracking detectors especially in the high rate, high radiation environments of future colliders such as the LHC. In order to survive in this environment, detectors must be radiation hard. We have constructed charged particle detectors using high quality CVD diamond and performed radiation hardness tests on them. The signal response of diamond detectors to ionizing particles is measured before and after irradiation. Diamond detectors have been exposed to 60 Co photons at Argonne National Laboratory, 300 MeV/ c pions at PSI, 500 MeV protons at TRIUMF and 5 MeV alpha particles at Los Alamos National Laboratory. The results show that CVD diamond is an extremely radiation hard material well suited for particle detector production.

The ATLAS Beam Conditions Monitor

The ATLAS beam conditions monitor is being developed as a stand-alone device allowing to separate LHC collisions from background events induced either on beam gas or by beam accidents, for example scraping at the collimators upstream the spectrometer. This separation can be achieved by timing coincidences between two stations placed symmetric around the interaction point. The 25 ns repetition of collisions poses very stringent requirements on the timing resolution. The optimum separation between collision and background events is just 12.5 ns implying a distance of 3.8 m between the two stations. 3 ns wide pulses are required with 1 ns rise time and baseline restoration in 10 ns. Combined with the radiation field of 10/sup 15/ cm/sup -2/ in 10 years of LHC operation only diamond detectors are considered suitable for this task. pCVD diamond pad detectors of 1 cm/sup 2/ and around 500 /spl mu/m thickness were assembled with a two-stage RF current amplifier and tested in proton beam at MGH, Boston and SPS pion beam at CERN. To increase the S/N ratio two back-to-back diamonds were read out by a single amplifier and the detectors inclined to 45 degrees. Limiting the bandwidth at the readout to 200 MHz provided further improvement; S/N ratio of nearly 10:1 could be achieved with MIPs. Amplifiers of the two stages were irradiated with protons and neutrons to 10/sup 15/ cm/sup -2/. Evaluating the irradiated electronics with silicon pad detectors, 20% degradation in S/N ratio was observed. Ten detector modules are being assembled and tested at CERN for their final installation into the ATLAS pixel support structure in the beginning of 2006.

A fast low-noise charged-particle CVD diamond detector

This work presents the design and test results of a charged-particle solid-state detector with ultrafast signal response based on polycrystalline chemical-vapor-deposition (pCVD) diamond as active detector material and a high-bandwidth RF amplifier. We tested the detector at the Indiana University Cyclotron Facility Bloomington, IN, in a proton beam with a kinetic energy ranging from 55 to 200 MeV. The detector signals showed an average pulsewidth of 1.38 ns, which enables single-particle counting at instantaneous rates approaching the gigahertz range. The detector operated with a signal-to-noise ratio of 7 : 1 for 200-MeV protons and a single-particle detection efficiency up to 99%.

Recent results from the RD42 Diamond Detector Collaboration

Abstract Diamond, as the hardest material known, has an extremely high binding energy suggesting that it will be a radiation hard material. Given that it is also a semiconductor, one is led to believe that diamond might perform well as a high resolution semiconductor tracking detector in very hostile radiation environments in which more conventional detectors would fail. In this paper we, the RD42 Diamond Detector Collaboration, review the progress that we have made in the development of chemical vapor deposition (CVD) diamond as a detector material, its radiation hardness, and the performance we have achieved with diamond tracking detectors.

Neutron irradiation of CVD diamond samples for tracking detectors

Abstract Diamond may make an excellent substrate for a tracking device in the near future, especially at colliders like LHC, where extreme running conditions are expected (high rates and high radiation levels). We report on neutron irradiation of several CVD-diamond samples at the ISIS facility (Rutherford Appleton Laboratory), which provides a fast neutron spectrum similar to that expected in a high luminosity collider experiment like CMS. We measured beam-induced currents and charge collection of diamonds exposed to fluences in excess of 10 15 n/cm 2 (peaking at 1 MeV), which should be the maximum value of the ten years total fluence at the design LHC luminosity. Physical hypotheses for the interactions of neutrons on CVD-diamond are proposed.

The data acquisition and calibration system for the ATLAS Semiconductor Tracker

The SemiConductor Tracker (SCT) data acquisition (DAQ) system will calibrate, configure, and control the approximately six million front-end channels of the ATLAS silicon strip detector. It will provide a synchronized bunch-crossing clock to the front-end modules, communicate first-level triggers to the front-end chips, and transfer information about hit strips to the ATLAS high-level trigger system. The system has been used extensively for calibration and quality assurance during SCT barrel and endcap assembly and for performance confirmation tests after transport of the barrels and endcaps to CERN. Operating in data-taking mode, the DAQ has recorded nearly twenty million synchronously-triggered events during commissioning tests including almost a million cosmic ray triggered events. In this paper we describe the components of the data acquisition system, discuss its operation in calibration and data-taking modes and present some detector performance results from these tests