Production and test of sPHENIX W/SciFiber electromagnetic calorimeter blocks in China

The sPHENIX experiment is a new generation of large acceptance detectors at the relativistic heavy ion collider at Brookhaven National Laboratory,with scientific goals focusing on probing the strongly interacting Quark–Gluon plasma with hard probes of jets,open heavy flavor particles,andγproduction.The EMCal detector,which covers the pseudo-rapidity region of|η|≤1.1,is an essential subsystem of sPHENIX.In this study,we focused on producing and testing EMCal blocks covering a pseudo-rapidity of|η|∈[0.8,1.1].These,in conjunction with the central pseudo-rapidity EMCal blocks,significantly enhance the sPHENIX physics capability of the jet andγparticle measurements.In this paper,the detector module production and testing of sPHENIX W-powder/scintillating fiber(W/ScFi)electromagnetic calorimeter blocks are presented.The selection of the tungsten powder,mold fabrication,QA procedures,and cosmic ray test results are discussed.

Equalization for the low-response cells of the AMS-02 electromagnetic calorimeter

Purpose Performing precision equalization on the low-response detection units of electromagnetic calorimeter(ECAL),it is essential for precision energy measurements of Alpha Magnetic Spectrometer(AMS-02).Methods Cosmic helium nuclei are used instead of protons to perform the equalization.During the equalization,temperature effects are analyzed and corrected to improve the accuracy.Results The results of helium equalization are consistent with proton equalization,and the precision of helium equalization is about 1.5%.Conclusions The precision of helium equalization is better than that of proton equalization,which provides a reliable alternative to ECAL on-orbit equalization.

Correction of PMT position effect for a lead-scintillating fiber electromagnetic calorimeter

The position effect of the photoelectron multiplier tube （PMT） of the electromagnetic calorimeter （ECAL） of Alpha Magnetic Spectrometer-02 （AMS-02） has been studied with beam-test data. The reconstructed deposited energy in a layer versus incidence position in the cell can be described by Gaussian distribution, maximum and minimum value can be obtained when the particle passes across the center and the edge of a cell respectively. The distribution can be used to correct the effect of incidence position on energy reconstruction. Much better energy resolution was acquired be got with the correction, for 100 GeV electrons, energy resolution improved from 3% to 2%.

Angular reconstruction of a lead scintillating-fiber sandwiched electromagnetic calorimeter

The Neighbor Cell Deposited Energy Ratio （NCDER） is a new method that is proposed to reconstruct incidence position in a single layer for a 3-dimensional imaging electromagnetic calorimeter （ECAL）. This method was applied to reconstruct the ECAL test beam data for the Alpha Magnetic Spectrometer-02 （AMS-02）. The results show that this method can achieve an angular resolution of 7.36±0.08°/√E＋0.28±0.02° in the determination of the photon＇s direction, which is much more precise than that obtained with the commonly-adopted Center of Gravity （COG） method （8.4±0.1°/E＋0.8±0.3°）. Furthermore, since it uses only the properties of electromagnetic showers, this new method could also be used for other type of fine grain sampling calorimeters.

Improvements on the particle identification with dead cell and side leakage corrections for the electromagnetic calorimeter of the Alpha Magnetic Spectrometer

Background The electromagnetic calorimeter(ECAL)of the Alpha Magnetic Spectrometer(AMS-02)measures the energy of electrons/positrons and separates them from protons.Currently,there are five dead cells in the ECAL which affect the reconstructed energy of particles.The particle identification power of the ECAL decreases when particles pass through these dead cells or close to the ECAL border.Purpose To improve the ECAL particle identification for particles pass through these dead cells or close to the ECAL border.Methods An improved ECAL particle identification estimator using the electromagnetic shower shape is developed with dead cell and side leakage corrections.Results For events passing through dead cells,with this new estimator,the proton rejection power is improved by a factor of 2.2 and positron purity is improved from 31 to 50%in the energy range of 500–800 GeV.Conclusion The new estimator works well for event passing through dead cells or close to the ECAL border.

On-orbit equalization of the electromagnetic calorimeter of the Alpha Magnetic Spectrometer

Purpose The Alpha Magnetic Spectrometer(AMS-02)will continuously collect data for the lifetime of the International Space Station(ISS).On-orbit equalization must be performed to ensure the accuracy of the AMS energy measurement(~1%)by the electromagnetic calorimeter(ECAL).Methods The equalization is performed using the most probable value(MPV)of the cosmic-ray proton minimum ionizing particle(MIP).Kalman filter technique is used to improve the precision.Results The precision of the equalization with proton MIP is(7.206±0.003)%and improved to(2.388±0.002)%after the Kalman filter.From the toy Monte Carlo(MC)simulation,the error of the energy reconstruction is about 1.4%and 0.5%due to the 7.2%and 2.4%equalization accuracy,respectively.Conclusion About 1.4%error due to~7%equalization precision does not match the AMS requirement.With the improvement from the Kalman filter,the energy reconstruction error from the equalization is reduced to 0.5%,which can fulfill the AMS requirement.

Improvement of cosmic-ray protonmeasurement with the electromagnetic calorimeter of the Alpha Magnetic Spectrometer

Purpose The energy response of protons measured by electromagnetic calorimeter(ECAL)of Alpha Magnetic Spectrometer(AMS-02)shows disagreement between Monte Carlo(MC)simulation and data.Therefore,using the response matrix from MC to apply the energy unfolding,which is crucial for cosmic-ray proton spectrum measurement,is unreliable.As a result,cosmic-ray proton spectrum measured by ECAL based on raw MC would be different from the published results(based on the momentum measurement)by AMS-02.The purpose is tuning the response matrix to agree with data.Methods The independent energy measurement by AMS-02 magnetic spectrometer provides in-flight calibration for ECAL.The distributions of proton energy measured by ECAL in MC are corrected after the calibration.Results The proton spectrum based on the tuned response matrix is consistent with the published one.Conclusions The matrix tuning is effective for the energy unfolding for cosmic-ray proton spectrum measurement.

Improvement in the 3D shower shapes description in the Monte Carlo simulation for a lead-scintillating fiber electromagnetic calorimeter

Background The lead-scintillating fiber electromagnetic calorimeter(ECAL)of the Alpha Magnetic Spectrometer measures the energy of positrons/electrons and separates them from hadrons.The electromagnetic shower shapes from Monte Carlo(MC)simulation and data show disagreement.Purpose Tuning the MC to make the shower shapes from MC and data agree with each other.Methods The tuning is based on a 3D electromagnetic shower model.Results After tuning,the electromagnetic shower shapes are well described by MC up to TeV.As a result,the output of ECAL electron/proton separation estimator,ECAL BDT,shows thatMCand data are in good agreement.The proton rejection power of the ECAL BDT trained with MC electron samples is improved by a factor of 5 at∼800 GeV compared to the one trained with data.

S tudy on Doped Fluoride Glasses for Scintillation Applications

This paper studies the properties of fluoride glasses for use in particle calorimeters or in optical fibers. The effects of major and minor impurities in manufacturing process and ultimately on the glass properties have been investigated. Glasses in a range of compositions have been made and tested in the form of small samples as well as larger blocks of size 2×3×14 cm 3. Results of measurements on these materials, using a high energy particle beam, are presented.

Geant4 application for efficiency simulation of PbF2 based calorimeters

Purpose This study aims to create a new tool for fast computer simulations allowing one to design advanced electromagnetic calorimeters with the required properties.The application must calculate the calorimeter efficiency and measure the particles'energies,momenta and interaction time to detect the particles.This application should become the basis for a new technology of positron emission tomography.Methods To solve the problem,a new C++application based on Geant4 simulation toolkit has been developed.To monitor the response of calorimeters to different types of primary particles,we used different auxiliary Geant4 classes.In addition,we compare the simulation results for the detectors of three different setups,taking into account the detection of both electrons and gamma-quanta,and analyze their efficiency.To evaluate the capability of calorimeters to work under radiation load,we use an experimentally measured transmission function of radiation-damaged PbF_(2).Results Three calorimeter setups exploiting PbF_(2)were simulated with a new C++application based on Geant4.We showed that such type of calorimeter has an energy resolution of 4.1%√E^(e+)[GeV]and good linearity of response for GeV positrons measurements.The efficiency of such structures is found to be approximately 20%for gamma photons’detection.The multilayered structure based on gamma-quanta detection has been proven to be more efficient.It was shown that for the total ionizing dose of 30 krad the Cherenkov light yield decreases by up to two times for 14 cm long PbF_(2)crystals,while for the shorter ones(2.5 and 1.5 cm)this effect is almost negligible.Conclusions We present a new user application in Geant4 for fast simulation of complex structures designed for detection of different high-energy neutral and charged particles.Simulation of calorimeter interaction with 10^(3) of 3 GeV positrons takes 20 min on usual laptop,while for 105511 keV gamma photons it takes 1 min on average.This application allows one to evaluate the efficiency of electromagnetic calorimeters exploiting lead fluoride crystals.Our results pave the way for advanced particle energy measurements,including those used in rapidly developing medical applications such as positron emission tomography,single-photon emission computed tomography etc.

Cosmic-ray helium nuclei measurement with the calorimeter of the Alpha Magnetic Spectrometer

Purpose The distributions of energy responses of helium measured by the electromagnetic calorimeter(ECAL)of Alpha Magnetic Spectrometer(AMS-02)in Monte-Carlo do not agree with those in real data,thus using energy response matrix obtained from Monte-Carlo to measure the cosmic ray helium spectrum is not correct.Therefore,the spectrum measured with ECAL based on raw Monte-Carlo would be different from the real one.The purpose is to correct the response matrix to measure helium spectrum with ECAL.Methods The energy measured by ECAL of AMS-02 provides in-flight correction for the energy response matrix in Monte-Carlo.Results The spectrum based on corrected response matrix is consistent with the AMS collaboration published result.Conclusions It is feasible to measure helium spectrum with ECAL with corrected energy response matrix.

Absolute photon energy calibration for the BESⅢ EMC

The absolute energy calibration with photons from π0＇s for the BESⅢ EMC is discussed. Using 3 million hadronic events, the preliminary results are presented. Precision of about 1% in the photon energy measurement is obtained from crossing check using photons in ψ（2S）→γχc1,2（1P）.