110315529
Characterization of a new charge sensitive preamplifier (CSP) for the electromagnetic calorimeters of the ALICE experiment
The ALICE calorimeters PHOS and EMCal (including its extension DCal) are based on Avalanche Photo-Diode (APD) photosensors with Charge Sensitive Preamplifiers (CSPs) for readout of the scintillating elements. A new CSP has been developed on the basis of the design of the PHOS CSP, but modified to meet the requirements of the EMCal and DCal. Modifications were made specifically for a different APD choice with different characteristics, and also with the goals of less noise, faster rise time, and reduced cost. This paper presents a detailed description of the new CSP features and the test results.
110710115
Readout electronics of the ALICE photon spectrometer
The photon spectrometer (PHOS) in the ALICE experiment at LHC is a PbWO4 crystal based electromagnetic calorimeter, dedicated to measuring photons, π°'s and η's over a broad pT range from about 100 MeV/c to 100 GeV/c with the best possible energy and position resolution. The front-end electronics of the PHOS is thus required to cover a large dynamic range, to achieve a timing resolution better than ~ 2 ns in order to discriminate against 1-2 GeV/c (anti-)neutrons, and to provide high pT trigger to select rare high pT events. In this paper, we present the full PHOS readout system, including the avalanche photo-diode, the low noise charge sensitive preamplifier, the 32 channel front-end electronics card, the trigger region unit and the trigger OR module. Results from PHOS commissioning with beam particles and cosmic rays will also be presented to address the performance of the PHOS readout electronics.
120815101
Front-end electronics of the ALICE photon spectrometer
Abstract The photon spectrometer (PHOS) in the ALICE experiment at LHC is dedicated to measuring photons, π 0 's and η 's in a broad p T range from about 100 MeV/ c to 100 GeV/ c , providing the best possible energy and position resolution in order to narrow the π 0 and η mass peaks and thus to increase the signal to background ratio. The front-end electronics (FEE) of the PHOS is thus required to cover a large dynamic range, to have a timing resolution better than ∼ 2 ns in order to discriminate against 1–2 GeV/ c (anti-)neutrons, and to provide high p T trigger to select rare high p T events. In addition, to equalize the gains of individual detector channels, it is desired that the PHOS FEE can regulate the bias voltage of APD. In this paper, we will present the performance and status of the 32-channel low noise front-end electronics for the PHOS with a dynamic range of 14 bits. Measurements with LED pulse at laboratory and results from beam test with the first PHOS module at T10 of the CERN PS show that its performance fulfills the PHOS requirements.
110697258
Front-end Electronics for the ALICE Calorimeters
Abstract The ALICE calorimeters PHOS and EMCal are based on Avalanche Photo-Diode (APD) photosensors with Charge Sensitive Preamplifiers (CSP) for readout of the scintillating elements. The amplified signals are read out via 32-channel shaper/digitizer front-end electronics (FEE) with 14-bit effective dynamic range. The electronics is based on second order shapers with dual gain for each channel, getting digitized by ALTRO chips. Each APD channel is equipped with an individual 10-bit APD gain adjustment and 2 × 2 channel clusters generate a 100 ns shaped analog sums output (Fast OR) for the associated Trigger Region Units (TRU). The Fast OR signals are generated by first order shapers with a dynamic range of 12-bit given by the ADC in the TRU cards. Board controller firmware in the FPGA provides local monitoring and configuration of all parameters via the ALICE DCS system. The signal to noise ratio for MIP at 215  MeV is ∼ 7 per channel with a noise level of 30 MeV at room temperature for a dynamic range of 80 GeV for PHOS, and the fast-OR RMS noise level is about 75 MeV for a dynamic range of 250 GeV for EMCal.
108590046
Hierarchical trigger of the ALICE calorimeters
Abstract The trigger of the ALICE electromagnetic calorimeters is implemented in 2 hierarchically connected layers of electronics. In the lower layer, level-0 algorithms search shower energy above threshold in locally confined Trigger Region Units (TRU). The top layer is implemented as a single, global trigger unit that receives the trigger data from all TRUs as input to the level-1 algorithm. This architecture was first developed for the PHOS high p T photon trigger before it was adopted by EMCal also for the jet trigger. TRU units digitize up to 112 analogue input signals from the Front End Electronics (FEE) and concentrate their digital stream in a single FPGA. A charge and time summing algorithm is combined with a peakfinder that suppresses spurious noise and is precise to single LHC bunches. With a peak-to-peak noise level of 150 MeV the linear dynamic range above threshold spans from MIP energies at 215 up to 50 GeV. Local level-0 decisions take less than 600 ns after LHC collisions, upon which all TRUs transfer their level-0 trigger data to the upstream global trigger module which searches within the remaining level-1 latency for high p T gamma showers (PHOS) and/or for Jet cone areas (EMCaL).
7991709
Measurement of inelastic, single- and double-diffraction cross sections in proton–proton collisions at the LHC with ALICE
Measurements of cross sections of inelastic and diffractive processes in proton–proton collisions at LHC energies were carried out with the ALICE detector. The fractions of diffractive processes in inelastic collisions were determined from a study of gaps in charged particle pseudorapidity distributions: for single diffraction (diffractive mass MX<200 GeV/c2) $\sigma_{\mathrm{SD}}/\sigma_{\mathrm {INEL}} = 0.21 \pm 0.03, 0.20^{+0.07}_{-0.08}$, and $0.20^{+0.04}_{-0.07}$, respectively at centre-of-mass energies $\sqrt{s} = 0.9, 2.76\mbox{, and }7~\mbox{TeV}$; for double diffraction (for a pseudorapidity gap Δη>3) σDD/σINEL=0.11±0.03,0.12±0.05, and $0.12^{+0.05}_{-0.04}$, respectively at $\sqrt{s} = 0.9, 2.76\mbox{, and }7~\mbox{TeV}$. To measure the inelastic cross section, beam properties were determined with van der Meer scans, and, using a simulation of diffraction adjusted to data, the following values were obtained: $\sigma_{\mathrm{INEL}} = 62.8^{+2.4}_{-4.0} (\mathrm{model}) \pm1.2 (\mathrm{lumi})$ mb at $\sqrt{s} = 2.76\ \mbox{TeV}$ and $73.2^{+2.0}_{-4.6} (\mathrm{model}) \pm2.6 (\mathrm{lumi})~\mbox{mb}$ at $\sqrt{s} = 7\ \mbox{TeV}$. The single- and double-diffractive cross sections were calculated combining relative rates of diffraction with inelastic cross sections. The results are compared to previous measurements at proton–antiproton and proton–proton colliders at lower energies, to measurements by other experiments at the LHC, and to theoretical models.
121485651
Aging test of a real-size high rate MRPC for CBM-TOF wall
A new kind of low-resistivity glass has been developed. Its volume resistivity is on the order of 1010 Ω cm and multi-gap resistive plate chambers (MRPCs), once assembled with it, can be operated at a charged particle flux in excess of 25 kHz/cm2, with very small charge build-up at the plates. This new technology has a wide range of application in high energy physics experiments such as FAIR-CBM, LHC-ATLAS or Jlab-SOLID, to mention some. In this paper we report on results related to its long-term behavior (aging). A 6 × 2-pad CBM module has been irradiated by X-rays at a mips-equivalent flux of 15 kHz/cm2, for 300 hours and for a released charge totaling 0.22 C (50 mC/cm2). Tested in an electron beam before and after exposure, no degradation of the detector performances could be appreciated. As expected, compared to common glass MRPCs, the newly developed high rate counter also responds faster to sudden irradiation.
121107871
Electron-pion discrimination with a scintillating fiber calorimeter
Abstract We report on an experimental study of a variety of techniques for discriminating between (isolated) electrons and pions in a lead and scintillating fiber calorimeter without longitudinal segmentation. Using information from the lateral shower development, from a pre-shower detector, from the time structure of the signals, or from a combination of these we measure pion rejection factors of up to several thousand while maintaining electron efficiencies of 95% or higher.
12149444
Observation of a Near-Threshold Enhancement in the p-anti-p Mass Spectrum from Radiative J/psi --> gamma-p-anti-p Decays
We observe a narrow enhancement near 2m{sub p} in the invariant mass spectrum of p{bar p} pairs from radiative J/{psi} {yields} {gamma}p{bar p} decays. No similar structure is seen in J/{psi} {yields} {pi}{sup 0} p{bar p} decays. The results are based on an analysis of a 58 million event sample of J/{psi} decays accumulated with the BESII detector at the Beijing electron-positron collider. The enhancement can be fit with either an S- or P-wave Breit Wigner resonance function. In the case of the S-wave fit, the peak mass is below 2m{sup p} at M = 1859{sub -10}{sup +3} (stat){sub -25}{sup +5} (sys) MeV/c{sup 2} and the total width is {Lambda} < 30 MeV/c{sup 2} at the 90 percent confidence level. These mass and width values are not consistent with the properties of any known particle.
31639934
New approach to background subtraction in low-energy neutrino experiments
We discuss a new method to extract neutrino signals in low-energy experiments. In this scheme the symmetric nature of most backgrounds allows for direct cancellation from data. The application of this technique to the Palo Verde reactor neutrino oscillation experiment allows us to reduce the measurement errors on the antineutrino flux from {approx}20% to {approx}10%. We expect this method to substantially improve the data quality in future low background experiments such as KamLAND and LENS. (c) 2000 The American Physical Society.
123179598
Bakelite RPCs for Digital Hadron Calorimeter
Abstract This paper presents the test results of Bakelite RPCs using readout pads with an area of 1 cm×1 cm and 1-bit resolution per pad (binary readout). The results include noise rate, detection efficiency and pad multiplicity as well as comparisons of different surface treatments for Bakelite plates. Pad multiplicity’s dependence on surface resistivity at the readout side is also reported. This study shows Bakelite RPCs can be used as the active elements of digital hadron calorimeter.