Download - Time of Flight Counter BESIII International Review Sep. 16, 2002 Heng Yuekun [email protected]
Outline Functions and targetAnalysis of time res.Two options
TOF+TOF TOF+CCT
Scintillator and PMTStructure and installationElectronics introduction
Functions of TOFParticle ID:
2 K/ separation up to 1.0GeV/c
Give a fast trigger
Analysis of time res. (1)
1) :intrinsic time resolution of TOF Scintillator and PMT time performance Light transmit spread: scintillator length
Number of pes:light output: light output and thicknesss attenuation and length quantum efficiency
22exp
22222thresholdectselectronicpositionZlengthbunchtimebunchTOF
TOF
pePMTscinTOF Nc
Lnn
22
22
2
)1()
35.2
1(
deLNN aLLtpe )()( /
0
Analysis of time res. (2)2) :beam bunch center uncertainty
Phase stabilization of RF at storage ring:±1º, i.e.,5ps
Considering cable transmit and electronics: <20ps
3) :beam bunch length uncertaintybeam bunch length: 1.5cm, i.e., 50ps
Two bunches colliding: 35ps
4) :Z-position particle impact uncertaintyTransit time in the scintillator should be reduced and the res
olution is related to the hitting position determination. As MDC track reconstruction simulation: several mms, ~25ps
timebunch
lengthbunch
positionZ
Analysis of time res. (3)5) : electronics of time measurement
CERN HPTDC 25ps according to its design
6) : res. of expected time of flight in MDC Particle ID capability: measured time minus expecte
d time Expected time in MDC: 30 ps
tracking length: several mms momentum: 0.6%
selectronic
ectexp
Analysis of time res. (4)7) : threshold correction: ~10ps
High threshold(~250mv): to give trigger low threshold(~50mv): to measure time
threshold
.mV4~
ns3~ mV,250
5
1
,
ADC
tV
ttV
Vt
Vt
Vt
timerisesignal
hhthresholdhigh
thresholdlowl
timerise
signalh
htT(ns)
V(m
v)
V
thresholdhighV
thresholdlowV
lt
Analysis of time res. (5)
Table 3.6-1 Analysis of TOF time resolution
Item Barrel time reso. Endcap time reso.
Intrinsic time reso. of one TOF layer 80ps 80ps
Intrinsic time reso. of one CCT layer 100ps
Uncertainty from bunch length 15mm,35ps 15mm,35ps
Uncertainty from bunch time ~20ps ~20ps
Uncertainty from Z position 5mm,25ps 10mm,50ps
Uncertainty from electronics 25ps 25ps
Resolution of expected time of flight 30ps 30ps
Uncertainty from threshold correction 10ps 10ps
Total time reso. Of one layer of TOF 100~110ps 110~120ps
Total time reso. Of one layer of CCT 120ps
Total time reso. Of double layer of TOF 90ps
Non-TOF error totally is over 60ps, TOF intrinsic resolution is 80ps.
Two options Radius 81cm: 1.0GeV/c K/ time
difference is only ~280psTwo layers, two independent timesTwo options:
TOF+TOF TOF+CCT
CCT Principle Improve PID
increase time difference Threshold
Cerenkov radiation & Full reflection:
Under threshold, TOF layer give trigger
Fig. CCT operating principle.
Figure Momentum thresholdfor different particles in CCT.
Comparison of K/ sep. TOF+TOF TOF+CCT
Fig. K / separation for Double TOF Fig. K / separation for TOF+CCT
CCT Material Better UV
transmission KEK beam test
Quartz is best,but expensive
Plastic: 50-100ps
BC800: Trans. over 70% from 300nm to 400nm
Fig. Transmission spectra of BC800 and BC802
CCT Simu. Based on GEANT4 Number of pes VS positions: 20~150
3.6-14 Number of photoelectrons in right or left PMT versus hit position from CCT simulation.
CCT Simu.: δ-electrons Number of pes from
δ-electron is fewerthan that from pions:threshold useful
pes fromδ-electron: earlier for vertical particle
Fig.3.6-15 CCT simulation : comparison of hit time and photoelectron yield at the PMT for a 1.0GeV/c π and a δ-electron produced by π.
(a) π hits at 90° (b) π hits at 30°
Scintillator BC404 VS BC408:
more light output faster rise and decay times shorter attenuation length
Fig. KEK beam test, BC404’s time resolution is better ~10ps than BC408.
PMT R5924 It has 19 fine-mesh dynode stages and high gain.
It has high quantum efficiency for the light with 300nm
to 500nm wavelengths.
It has good timing performance: anode pulse rise time
is 2.5 ns, and transit time spread (FWHM) is 0.44ns.
Its length is only 50mm, very suited to our limited
space.
PMT: R5924Table The properties of PMT R5924
ITEM PROPERTIESDiameter 51mmCathode area 39mmSpectral Response Range 300~650nmWavelength of Maximum Response 42050nmSupply Voltage 2300V(Max.)Photocathode Material BialkaliCathode Quantum Efficiency at 390nm 22%Window Material Borosillicate glassWindow Shape Plano-planoDynode Structure Fine MeshNumber of Dynode Stages 19Gain 1.0107 at 0 Tesla
4.1106 at 0.5 Tesla2.5105 at 1 Tesla
Anode Pulse Rise Time 2.5 nsTransit Time 9.5 nsTransit Time Spread(FWHM) 0.44ns
BTOF DimensionPlaced between MDC and EMCR-direction space: 81cm-92.5cm
Scintillator Length: 2440mm
Coverage:~82%
Pieces: 88 /layer
Thickness: 50mm /layer
Fig. Assembly of barrel TOF.
BTOF installation
Fig. BTOF side view. To save space, the base of PMT housing is pentagon-shaped and the inner and outer layer is across. It has four screws to connect the scin.
ETOF structure and installation
Fig. TOF structure Fig. Installation of endcap TOF
Monitor systemAmplitude and time performance
monitor
Fig. TOF monitor system
Schedule
2001.4~2002.9 TOF preliminary design
2001.10~2003.6 CCT cosmic and beam tests; simulation of CCT and TOF
2002.11~2003.12 TOF prototype experiment 2004.1 Determining option: double TOF or TOF+CCT 2004.1~2005.1 Machining
2004.1~2004.5 Monitor system tests
2004.1~2004.5 Order PMTs
2004.6~2004.12 PMT checks
2004.9~2005.2 Order scintillator
2005.3~2005.6 Scintillator checks
2005.7~2005.12 TOF installation
2006.2~2006.6 BES commissioning
TOF comparison BESII BELLE BESIII Scintillator Size(mm) Light guard Rise Time Decay time FWHM Atte. Length
BC408 50x156x2800 yes 0.9ns 2.1ns 2.5ns 2.1m
BC408 40x60x2550 no 0.9ns 2.1ns 2.5ns 2.1m
BC404 50x(58~66)x2440 no 0.7ns 1.8ns 2.2ns 1.4m
PMT Quan. Effi. Gain Rise time Transit time Tra.TimeSpr.
R2495-05 20%
~2x106(0.4T)
- 8.5ns 0.17ns
R6680 -
3x106(1.5T) 3.5ns - 0.32ns
R5924 22%
~0.25x106(1T)
2.5ns 9.5ns 0.17ns
Inner radius 115cm 120cm 81cm Magnetic Field 0.4T 1.5T 1.0/0.4T Beam bunch 5cm 0.25cm 1.5cm T0 Pick up RF clock RF clock Readout elec. TAC+ADC TDC1877S HPTDC Intr. time res. 135ps 70~80ps 80ps(one layer) Total time res. 180ps ~100ps ~90ps(double layers) K/ separation 0.8GeV/c 1.2GeV/c 1.0GeV/c
TOF Elec. Intr. (1) Details, by Prof. AN Qi Tasks:
Time measurement : <25ps Charge measurement to correct time-wal
k: 4mv~4V, effective bit:10
Fast trigger signal
TOF Elec. Intr.(2)Block diagram of Front-End
Electronics HT: ADC gate; double end signal to
trigger LT: measure time
1: 3 spl i t 1: 3 spl i t
Leadi ng EdgeDi scri m. wi thl ow threshol d
Leadi ng EdgeDi scri m. wi th
hi gh threshol d
Leadi ng EdgeDi scri m. wi thl ow threshol d
Leadi ng EdgeDi scri m. wi th
hi gh threshol d
ADCADCHPTDC HPTDCMean Ti mer
PMT2PMT1 176 × Barrel TOF
L1 Tri gger L1 Tri gger
To Tri gger Modul e
gate gate
TOF Elec. Intr.(3) Time measurement: CERN HPTDC,
Very high reso. mode(25ps), no time stretcher High reso. mode(100ps) with time stretcher(1:4)
Charge measurement: Pulse Waveform Digitization: ATWD of 1GSPS
(analog transient waveform digitizer) Pulse amplitude measurement: integrator + FADC
Refer. Time: Use RF 500M Clock to generate a 40M refer. clock, w
hich is precisely synchronized with the beam collision time.
The End
Thanks a lot!