1 / 17

Study of energy resolution of PWO Crystal with cosmic muons

Study of energy resolution of PWO Crystal with cosmic muons. Alexander Toropin New York University. Introduction.

skah
Download Presentation

Study of energy resolution of PWO Crystal with cosmic muons

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Study of energy resolution of PWO Crystal with cosmic muons Alexander Toropin New York University

  2. Introduction • Scintillation light from each crystal in the MECO calorimeter will be collected by two APDs attached to the rear surface of the crystal. The use of two APD’s improves the energy resolution and, by comparison of the two signals, permits the rejection of nuclear counter effects. • It is possible to estimate the energy resolution by comparing the charges collected by the two APDs after the passage of a cosmic muon. • Lead tungstate crystals (PbWO4 ) and RMD (Radiation Monitoring Devices) and Hamamatsu APDs were used in the study. • New charge sensitive preamplifiers and shapers, both designed at NYU, were used. • The study was made at a temperature of -23oC. At this temperature, the light yield of the PWO crystal increases ~2.5 times and the gain stability and dark current performance of the APD improves considerably. Alexander Toropin NEW YORK UNIVERSITY

  3. Parameters of RMD APD • The parameters of one RMD APD used in the studies are shown in the plots. • Gain, gain stability, and dark current performance improve significantly with cooling. Alexander Toropin NEW YORK UNIVERSITY

  4. Crystal, APDs and setup schematic view • 3  3  14 cm3 PWO crystal • Large area (13mm x 13mm) APD from RMD inc. • Hamamatsu (5mm x 5mm) APD used by CMS. • Crystal / APD combinations are tested using cosmic rays. The crystal, APD, and preamplifier are cooled, increasing the crystal light yield and decreasing dramatically the APD dark current. Crystal / APD Test Arrangement Alexander Toropin NEW YORK UNIVERSITY

  5. Two Approaches to Resolution • The distribution in the difference between the APD signals after the passage of a cosmic muon provides a measure of the resolution at (approximately) the mean energy loss (~40 MeV). • The amplitude of an LED light source (430 nm) is adjusted to give a signal at the MPV (35 MeV) of the cosmic muon. The LED produces the same number of e-h pairs but without Landau Fluctuations.. Alexander Toropin NEW YORK UNIVERSITY

  6. RMD. Cosmic muons spectra at -23o C. 50 ns Shapers. Energy spectra from two RMD APDs. 50 ns shapers were used. Superimposed curves are fits to Landau distributions. MPV values from these plots were used to estimate the numbers of primary photoelectrons. Alexander Toropin NEW YORK UNIVERSITY

  7. RMD. Estimation of energy resolution. In the case of cosmic muons spectra, the energy resolution can be estimated as This value corresponds to MPV = 35 MeV of energy deposition in PWO crystal. Alexander Toropin NEW YORK UNIVERSITY

  8. Calculation of the number of primary e-h pairs using LED calibrated by cosmic rays The normalized total error in measured signal is is r.m.s. of signal amplitude , is excess noise factor, , - gain, - charge in number of electrons, r.m.s. of electronics noise. , From the plot of values as a function of is possible to estimate the number of primary photoelectrons. Alexander Toropin NEW YORK UNIVERSITY

  9. RMD. Numbers of primary photoelectrons. From these dependences, assuming F = 2, the numbers of primary e-h pairs for each APD per MeV of energy deposited in the crystal can be found Here 35 is the cosmic muon most probable value energy loss in the PWO crystal (MC simulation). Corresponding energy spectra for these APDs are shown on the next page. Alexander Toropin NEW YORK UNIVERSITY

  10. RMD. Estimation of energy resolution. Energy resolution of PWO crystal can be estimated from distributions of differences and sums of 2 APD signals. In the case of Gaussian distributions of LED signals energy resolution corresponding to the sum of two signals can be determined as and . Alexander Toropin NEW YORK UNIVERSITY

  11. RMD. Study with different shaping times. T = -23oC The Gain values were defined by using calculated numbers of primary photoelectrons from LED signals and taking into account electronics calibration coefficients. Alexander Toropin NEW YORK UNIVERSITY

  12. Hamamatsu. Study with different shaping times. T = -23oC. Alexander Toropin NEW YORK UNIVERSITY

  13. Hamamatsu. Energy resolution with 200 ns Shapers. On this picture are shown distributions of differences and sums of signals from 2 Hamamatsu APDs with 200 ns Shapers. Energy resolution in this case corresponding to 35 MeV of cosmic muons energy depositions in PWO crystal is Alexander Toropin NEW YORK UNIVERSITY

  14. Advanced Photonics APD. Advanced Photonics (AP) APD with sensitive area of diameter 16 mm was used to make comparison with RMD APD. RMD APD has sensitive area 13x13 mm2. Curves of Gain as a function of Bias Voltage for two different temperatures are shown below. Alexander Toropin NEW YORK UNIVERSITY

  15. Advanced Photonics APD. The cosmic muons spectrum and calibration plot for AP APD are shown on these pictures. In given test APD worked with gain M = 200 and electronics calibration coefficient was 26 V/pC. The number of primary photoelectrons can be estimated as Number of primary photoelectrons from calibration plot is Alexander Toropin NEW YORK UNIVERSITY

  16. Conclusions • RMD APDs. At the ~ 35 MeV energy loss of cosmic muons in the PWO crystal, the energy resolution is ~4.3 % for a shaping time of 50 nsec. For 100 MeV energy loss the resolution should be less by a factor of ~ (~2.5%). The energy resolution decreases only slightly with increasing shaping time, ~4.1 % at a shaping time of 200 nsec, implying that most of the light is already collected with the 50 ns shaper. • Hamamatsu APDs. The best value of energy resolution in the case of 35 MeV energy loss for Hamamatsu APD is ~7.6 % for 200 ns shaping time. The resolution depends strongly on the shaping time and for 50 ns shaping time is ~13.5 %. • For temperature –23oC, the ratio of the numbers of primary e-h pairs from the RMD and Hamamatsu APDs is approximately the ratio RMD(Area, QE) / Hamamatsu(Area, QE) = 5, where QE is the quantum efficiency of the APD for blue light (~430 nm). • The Advanced Photonics APD collects approximately the same amount of primary e-h pairs as does the RMD diode. It has ~20% larger area and, taking into account the result that if only one RMD APD is attached to the crystal it collects ~25% more e-h pairs, the Advanced Photonics APD does not show better results. Alexander Toropin NEW YORK UNIVERSITY

  17. Future plans • Prepare a matrix (3x3 or 4x4) of PWO crystals with cooling system to make study by BNL test beam. Alexander Toropin NEW YORK UNIVERSITY

More Related