D. Acosta

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.

Results of prototype studies for a spaghetti calorimeter

In the framework of the LAA project, prototypes for a new type of calorimeter, intended for the detection of both electromagnetic (e.m.) and hadronic showers, muons and missing energy (e.g. neutrinos) at high-luminosity multi-TeV pp colliders, were tested. The detector consists of scintillating plastic fibres embedded in a lead matrix at a volume ratio 1:4, such as to achieve compensation. The optimization of the construction of the detector modules is described, as well as the performance concerning e.m. shower and muon detection and e/π separation. We used electron, pion and muon beams in the energy range 10–150 GeV for this purpose. n nFor the energy resolution of electrons we found 13%/trE, with a constant term of 1%. The signal uniformity was better than 3% over the total surface of projective modules. The signal linearity for e.m. shower detection was better than 1%, and the e/π separation was better than 5 × 10−4 for isolated particles. Channeling effects are negligible, provided that the angle between the incoming particles and the fibre axis is larger than 2°.

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.

Lateral shower profiles in a lead/scintillating fiber calorimeter

Abstract The lateral profile of the energy deposition in a prototype of a lead and scintillating fiber calorimeter, constructed in the framework of the LAA project at CERN, has been measured for both electromagnetic and hadronic showers in the energy range from 5 to 150 GeV. The distributions are well described by analytic functions whose parameters allow one to determine the radial scaling of the shower development. In the electromagnetic case, the data are compared to Monte Carlo calculations. Estimates of the lateral leakage outside of the detector are made as well as calculations of the average π 0 content of hadronic showers and event-to-event fluctuations in this electromagnetic component. A method is developed whereby knowledge of the hadronic shower profile can be used to determine the relative calibration constants of neighboring towers in such a calorimeter.

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.

The performance of a lead/scintillating-fiber calorimeter at LHC/SSC compatible gate widths

Abstract We report on an experimental study of the performance of a lead/scintillating-fiber calorimeter intended for the detection of leptons, hadrons, gammas and missing energy. In particular, the effects of reducing the charge collection time down to values that are relevant for experiments at the future proton-proton colliders LHC and SSC are investigated. The total calorimeter signal, the energy resolution, the e/π signal ratio, the signal linearity, the hadronic shower profile and the electron/pion separation capability of the detector are measured as a function of the charge collection time, ranging from 5 to 358 ns. The performance is practically unaffected down to ∼40 ns, even when unrealistically long signal cables are used and no signal shaping is applied. For shorter gates, we observe incomplete charge collection, a gradually deteriorating energy resolution, an increase in the e/π signal ratio and in the hadronic signal nonlinearity, a narrowing of the hadronic shower profile and a degradation of the electron/pion separation. However, even for gates as short as the LHC/SSC bunch-bunch spacing (∼ 15 ns), these effects are not unacceptably large. The experiments were performed in the framework of the LAA project at CERN.

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.

Effects of radiation damage on scintillating fibre calorimetry

Abstract We report on measurements of radiation hardness of plastic scintillating fibres to be used for fibre calorimetry. Fibres were irradiated with a 60 Co γ-source and the effects on the emission and on the attenuation of scintillation light in a number of different fibre types were studied. A Monte Carlo study that simulates radiation damage in a compensating lead/fibre calorimeter and predicts the impact on the performance is described. We infer from these results that with the best fibres that are presently commercially available the effects on calorimeter performance appear to be within acceptable limits up to 7Mrad doses deposited in the scintillator at the peak of the damage.

A Projective Geometry Lead Fiber Scintillator Detector

The Superconducting Super Collider (SSC), presently under construction near Dallas, Texas requires highly sophisticated particle detectors. The energy and particle flux at the SSC are more than an order of magnitude higher than the highest machine located at the Fermi National Accelerator near Chicago. An important element of particle detectors for the SSC is the calorimeter. It measures a particle’s energy by sampling its energy deposit in heavy material, such as (depleted) uranium or lead.