Status of the Crystal Zero Degree Detector (czdd)

Transcription

1 Status of the Crystal Zero Degree Detector (czdd) Achim Denig1, Peter Drexler1, Brice 1, Leonard Koch2, Wolfgang Kühn2, Sören Lange2, Werner Lauth1, Yutie Liang2, Torben Rathmann1, Christoph Redmer1, Milan Wagner2 1 Johannes Gutenberg Universität Mainz 2 Justus-Liebig-Universität Gießen BESIII Physics & Software Workshop 24 September 2016 IHEP, Beijing

2 Outline I.Physics Motivations II.The crystal Zero Degree Detector III.Geant4 Simulations IV.Beam test on LYSO crystals 2

3 Physics Motivations 3

4 Physics motivations e - e γ ISR - e- q q q e+ e+ Annihiliation with ISR γγ collision q e+ Tagged ISR allows measurement of the total hadronic cross section as function of energy up to s at fixed accelerator energy. ISR photons and e± from 2γ processes peaked at θ = 0 and 180. Upgrade for existing Zero Degree Detector : -Scintillating crystal (less radiation damage). -New DAQ to provide real time event correlation. 4

5 The czdd 5

6 The czdd X Y Z ZDD ZDD Interaction Point (IP) BES beam structure (top view) IP Two calorimeters located at BESIII front ends (z=+/- 335cm). 2 blocks separated by a 1 cm gap. The gap limits radiative Bhabha (e+e- e+e-γ) contamination. Z Each block divided by 1x1x14 cm3 crystals. czdd front view 6

7 Materials in front of ZDD (top view) Side view IP Y-Type Crotch ISPB magnet ZDD 7

8 Septum bending magnet (ISPB) X Y ISPB bends outgoing beam line by about 39 mrad. Field : GeV e+ Curvature radius : ρ=15294 mm Fringe field extends 10 cm away from ISPB yoke. Z ZDD (75 cm) 8

9 Geant 4 simulations 9

10 Geant 4 implementation CZDD made of PbWO4 crystals Implementation of the beam pipe by L.Koch and Y.Liang. Uniform magnetic field in ISPB region added : By=-4160 G 10

11 Radiative Bhabha (e+e- e+e- nγ) : Simulation conditions Event Generator : Bhlumi ECMS=3.773 GeV 0.08 <θe+< 5 deg. IP e+ beam Undeviated outgoing beam (w. crossing angle) x=3.68 cm Without two beam pipes (Y-Type Crotch+ISPB+outgoing pipe+ window) : BesSim.FullBeamPipe = 0 BESIII detectors (MDC,EMC,TOF,MUC)+Central beam pipe + SCM solenoid + ZDD included With magnetic field (ISPB included) 11

12 Radiative Bhabha : Energy Spectrum 5% of events results in energy deposition. Half of the sample deposits 0<E 60 MeV. Energy is either deposited in left part (z<0) or right part (z>0) of the ZDD. 12

13 Effect of radiative processes Non radiative Bhabha events (e+e- e+e- ) deposits energy in ZDD only for 0.2<θ<1. Radiative Bhabha events deposit energy down to minimum scattering angle. Need for generating at zero angle. 13

14 Radiative Bhabha (e+e- e+e- nγ) : effects of beam pipe material Interaction rate with ZDD slightly enhanced by the beam pipe material Secondary interactions with the beam pipe increases the background. Larger energy deposition in low energy region ( 0<E<500 MeV). γisr with E<500 MeV contaminated by Bhabha events for Ψ(3773) run. 14

15 e+e- ppγisr : simulation conditions MC event generator : Phokhara Decay mode : ee ppγ ECM=3.773 GeV Born, no FSR <Θγ<0.689 (Polar angle acceptance of ZDD) 0.<Θhadron<180. ISPB magnetic field included. Beam pipe material included. ZDD Y-Type Crotch ISPB Beam pipe 15

16 e+e- ppγisr : Energy spectra Energy deposition for half of the sample. At best ~80% of ISR photon energy deposited Large fraction of events deposits small energy, even for E γ=1.4 GeV. Reconstruction of γisr is not possible with current ZDD design. Closed gap configuration might improve energy deposition, as γisr passes through less pipe material. 16

17 Beam test 17

18 Scintillating crystals PbWO4 LYSO Density (g/cm3) Radiation Length (cm) Moliere radius (cm) Decay time τ (ns) 6.5 (30.4) 40 Lightyield (ph/mev) 100(31) Fragile Optimal light yield at T=-25 C Expensive (x2 as PbWO4) Radioactive (~kbq) 18

19 Setup (1) Beam MAMI : 195 and MeV e- beam at 1kHz. 1x1 cm2 LYSO crystal read out by 4 SiPMs. SiPM : SensL C-series (6x6mm2). Acquisition triggered by a scintillator placed before the crystal. PMT e- Trigger (scintillator) Crystal+readout 19

20 Setup (2) Crystal Filter SiPM array Power supply Output signal (Single SiPM) Output signal (Sum) e- 20

21 QDC spectra (E=195 MeV) SiPM#4 SiPM#5 ΣSiPM SiPM#7 Energy=195 MeV Crystal : 1x1 cm2 Filter : T=0.25 SiPM voltage=26v SiPM#8 LG : 26 fc/channel HG : 200 fc/channel Clear but smeared peak visible for a single SiPM. 21

22 QDC spectra (E=855 MeV) SiPM#4 SiPM#5 ΣSiPM SiPM#7 Energy=855 MeV Crystal : 1x1 cm2 Filter : T=0.05 SiPM voltage=26v SiPM#8 LG : 26 fc/channel HG : 200 fc/channel Clear and tighter peak visible at higher energy. 22

23 Conclusions Summary ISPB magnetic field implemented. Radiative Bhabha : Few non radiative events hits ZDD at (relatively) wide angle. Energy deposition even for low scattering angle. Secondary particles from the beam pipe increases the background. ISR photon : Reconstruction not possible with current design. Beam test on LYSO : Clear signal observed with a single SiPM. Good energy resolution in energy range of interest (E~1 GeV). Prospect Implementation of the fringe field from ISPB. Closed-gap configuration BUT MC generator at very small angle scattering (possibly θ=0 deg) needed. Interaction rate comparison between background Bhabha and processes of interest (ISR, γγ) Beam test on a czdd prototype with LYSO crystals Implementation of ZDD simulation with LYSO material. Thanks for your attention. 23

24 Backup slides 24

25 Particle gun (γ) ZDD γ particle gun shot at crystal #104 with energy E=1.5 GeV Magnetic field disabled. No materials from the beam pipe. γ interacts with ZDD through pair creation (γ e+e-) Photons ends inside the ZDD. At best 80% of initial γ energy recorded. 25

26 Particle gun (e+) ZDD e+ particle gun shot at crystal #104 with energy E=1.5 GeV Magnetic field disabled. No material from the beam pipe. e+ interacts with ZDD crystals through brehmstrahlung ( e+ e+γ) Few positrons ends beyond ZDD region. At best 80% of initial γ energy recorded. 26

27 Radiative Bhabha : MC Truth final position (e+) ZDD ZDD e+ e+ e+ interacts mainly by Bremsstrahlung process. Most positrons are bended outward by the ISPB magnet. Few positrons ends in the ZDD. e+ 27

28 Babayaga NLO : Simulations conditions BabayagaNLO Born mode ECMS=3.773 GeV 0+ε<θ<180-ε (ε=0.08º) Beam Energy spread= GeV. IP Undeviated outgoing beam (w. crossing angle) x=3.68 cm Without two beam pipes (Y-Type Crotch+ISPB+outgoing pipe+ window) : BesSim.FullBeamPipe = 0 BESIII detectors (MDC,EMC,TOF,MUC)+Central beam pipe + SCM solenoid + ZDD included With magnetic field (ISPB included) 28

29 Bhabha : MC Truth final position (e+) ZDD ZDD Most positrons are bended outward by the ISPB magnet. Few positrons ends in the ZDD. 29

30 Bhabha : MC Truth energy spectrum 1% of events results in energy deposition Energy is either deposited in left part (z<0) or right part (z>0) of the ZDD. Only one of the two particles hit the ZDD! Particles depositing energy are emitted away from the beam direction (θ>0.20 degree) 30

31 Bhabha : Effect of beam pipe materials Material added : Y-type crotch, ISPB wall and outgoing beam pipe. Interaction of e+/e- with beam materials increase the interaction rate in ZDD. Energy deposition is very small for a majority of events. 31

32 Bhabha : Correlation between e+ and e- calculated hit e- hits the detector Both e+ and e- hits the detector e+ hits the detector 32

33 Bhabha : Correlation between e+ and e- calculated hit e+ hits top,right ZDD e- hits bottom, left ZDD e+ hits top,right ZDD e- hits top, left ZDD e+ hits bottom,right ZDD e- hits bottom, left ZDD e+ hits bottom,right ZDD e- hits top, left ZDD 33

34 Bhabha : Hit position extrapolated from IP θ>0.2 deg. 34

35 Bhabha kinematics e+ e- Without beam crossing angle e+ e+ e+ e- e- e- With beam crossing angle 35

36 Readout Trigger PMT Crystal e- beam 2x2 SiPMs x10 PreAmp Σ LED Oscilloscope Delay & Gate Dual Range Q-ADC : -100 pc/3850 chn -800 pc/3850 chn VME Delay ~120ns 36