Yaping Wang

First results on the hybrid photodiode tube

Abstract The performance of a new breed of light detectors based on a photocathode followed by a planar silicon diode working in the bombarding mode is reported. This detector was developed by the LAA project in order to produce a fast light detector capable of covering a span of the more than 4 orders of magnitude of linearity required by the scintillating fibre and lead (“spaghetti”) calorimeter. Linear signals from single, to more than 10 6 photoelectrons per pulse were measured. The general characteristics of this detector are reported here.

Electron, pion and multiparticle detection with a lead/scintillating-fiber calorimeter

Abstract We report on the performance of a fine-grained 13-ton lead/scintillating-fiber calorimeter, in particular on its response to electrons, pions and multiparticles (reaction products from pions interacting in a target upstream of the detector). The detector signals were studied for particles in the energy range 5–150 GeV. The energy resolution was measured to be 12.9% √E for electrons, plus a constant term dependent on the angle θ Z between the particles direction and the fiber axis. This term, which is 1.2% for θ z = 3°, is shown to be due to anomalous sampling in the early shower stage. It is greatly reduced when only electrons entering the detector in the lead are considered. A 1.7 X 0 thick preshower detector, installed 12 cm in front of the calorimeter, only affected the signal linearity for electrons at low energy. The effect on the energy resolution was negligible. Single pions were detected with an energy resolution of ∼ 30%/√ E plus a constant term, which turned out to be mainly due to the effects of light attenuation in the fibers. Knowing the impact point of the particles, these effects could be efficiently removed for single pions. For jets (multiparticles), the effects of light attenuation are much less important, leading to considerably better on-line energy resolutions. The e π signal ratio was measured to range from 1.03 at 80 GeV to 1.10 at 5 GeV, for a detector with an effective radius of 49 cm. After correcting for the instrumental effects, we found the intrinsic e h value of this detector (with our particular choice of fibers and sampling fraction) to be 1.15±0.02. Detailed results are given on the detector performance (energy resolution, e π signal ratio, e/jet signal ratio) as a function of the lateral detector size and as a function of the jet multiplicity.

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.

Localizing particles showering in a Spaghetti Calorimeter

We report on the performance of a fine-grained 13-ton compensating lead/scintillating-fiber calorimeter, and in particular on its capability of localizing the particles that produce showers in it. The RMS position resolution was found to be 1.7 mm for electromagnetic showers and 5.1 mm for hadronic showers at 80 GeV, averaged over a tower with an effective radius of 39 mm. Pion-pion separation through analysis of the energy deposit pattern was achieved in more than 95% of the cases for distances down to 8 cm at 80 GeV. Because of the good lateral position resolution, detailed information on the longitudinal shower development could be obtained, with the help of tracking information, when single particles entered the (longitudinally unsegmented) detector at a small angle with respect to the fiber axis. This information made it possible to eliminate the effects of light attenuation in the fibers on the hadronic energy resolution and allowed e/π separation at the 10−4 level.

Detection of muons with a lead/scintillating-fiber calorimeter

Abstract We report on an experimental study of the signals from high-energy (5–225 GeV) muons traversing a 9.5 interaction lengths deep electromagnetic/hadronic calorimeter consisting of lead and scintillating plastic fibers, constructed at CERN in the framework of the LAA project. The muons lose on average between 2.6 GeV (at 5 GeV) and 8.8 GeV (at 225 GeV) in this process. This energy loss can be measured with a precision of a fraction of a GeV in most of the events. Accuracy in the energy loss measurements is important since the rms spread in the energy loss of muons traversing this calorimeter is not smaller than ∼6% at any energy. The nominal calibration constants, derived from the calorimeter response to electromagnetic showers, are found to be incorrect for the muon signals. On average, these calibration constants are between 40% (for low energy muons) and 15% (high energy) too high. The fiber bunches sticking out of the back plane of the calorimeter for readout purposes cause the muon signals to be position dependent. This can cause an anomalous enhancement of the muon signal of up to 35%. A moderate position resolution of ∼ 1 cm is sufficient to correct for this effect. The e/mip ratio was found to be 0.72±0.03.

On muon production and other leakage aspects of pion absorption in a lead/scintillating-fiber calorimeter

Abstract We report on an experimental study of longitudinal leakage phenomena in hadronic shower development. Pions in the energy range of 10–150 GeV were sent into a lead/scintillating-fiber calorimeter with a thickness of 9.6 nuclear interaction lengths. The average fraction of the energy leaking out at the back of this calorimeter ranges from 0.04% at 10 GeV to 0.4% at 150 GeV. This leakage has a very small effect on the hadronic energy resolution. We measured the probability of the creation of escaping muons in the shower development process. This probability ranges from 0.2% at 10 GeV to 2.1% at 150 GeV. Assuming that these muons are produced from π- or K-decay, we find an exponentially decaying muon spectrum with a typical momentum of 2.8 GeV/ c , at 80 GeV incident energy. Also the rates at which hadrons and soft neutrons escape from the calorimeter are measured. Within the acceptance of the leakage calorimeter, neutrons are observed about 10 times as often as muons. Escaping hadrons dominate muons for shower energies above 20 GeV. The experiments were performed at CERN in the framework of the LAA project.

STAR upgrade program and future physics

In this paper, we will present STARs future plan in terms of both the detector upgrade and physics measurement to study matter with colour degrees of freedom. We will first discuss the status of the newly installed Heavy Flavor Tracker and Muon Telescope Detector, and their physics prospect in 2014-2016. We will then describe the proposed detector upgrades for the second phase of Beam Energy Scan program in 2018-2019 to study the QCD phase diagram. Finally we will present STARs plan with detector upgrades in the forward directions for the anticipated pp/pA physics program in 2021-2022 and ep/eA in 2025+. The upgraded STAR experiment will be in an excellent position to perform precision measurements of the partonic structures of the nucleon and nuclei.

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 ηs 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.