Time of Flight Counter

BESIII International Review Sep. 16, 2002

Heng Yuekun hengyk@mail.ihep.ac.cn

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!