high precision tof: belle experience and besiiiidlab/presentations/besiii_tof_v1.3.pdf ·...

High Precision Time-Of-Flight: Belle Experience and Future R&D

Gary S. VarnerUniversity of Hawai

,i

BESIII Meeting, IHEP5 June 2002

1Gary S. Varner, BESIII Meeting at IHEP, June 2002

Presentation Outline

• Belle Experience– Performance– GEANT understanding– Care and feeding– Limitations

• BESIII Application– Previous R&D– Precision Time Encoding– Time Walk Correction

• Summary– Action items and opportunities for joint

development


Belle Detector


PID Cross-section


TOF Counter (1 of 64)

• High B-field Operation• Hamamatsu R6680 Fine Mesh PMTs

– 24 stages– 2000 mesh/in.– G>3x106 in 1.5T field

• TSC radius = 118 cm• TOF radius = 120 cm


Result First!


Current Belle TOF Members

N. Gabyshev, H. Kichimiα,β and J. YashimaHigh Energy Accelerator Research Organization (KEK), Tsukuba Japan

J.W. Namβ, Y.I. Choi, D.W. Kim and J.H. KimSungkyunkwan University, Suwon Korea

B.C.K. Casey, M. Jones, S.L. Olsen, M. Peters,J.L. Rodriguez, G. Varner and Y. Zheng

University of Hawai’i, Honolulu, HI USA

J. ZhangUniversity of Tsukuba, Tsukuba Japan

T.H. Kim and Y.J. KwonYonsei University, Seoul Korea

α Belle TOF Leader β Primary authors for recent study[5]


Understanding Performance

• While basic Belle TOF performance good:– Wanted to understand limitations– Acceptance and Trigger efficiency– Nuclear/hadronic interactions– Higher Luminosity prediction

• Full GEANT simulation:– Full simulator [NIM A479 (2002) 117].– Accurate modeling of secondaries– Detector response and readout chain– Adjust parameters where required– Include beam background– Results submitted to NIM:

J.W.Nam et. alhep-ex/0204030


Detector Input Parameters

~ 300 cmAtten. Length

Polyvinyl tolueneBase

425 nmλ Max. Emission

~2.5 nsPulse Width

2.1 nsDecay Time

0.9 nsRise Time

1.58Refractive index

1.032Density

TOF scintillator (BC408)

6 ns (FWHM)Pulse Width

39mm (effective)Photocathode Dia.

4.5 nsFall Time

3.5 nsRise Time

0.6e- collection

~21%Q.E.

320 ps (rms)Transit Time Spread

FM PMT (R6680)


Energy Deposition

Deposition in steps along path length:– One γ per 100 eV– Isotropic angular distribution


Scintillation Photon Timing

• τ1 = 0.9 ns

• τ2 = 2.1 ns

• τ3 = 14.2 ns

• R = 0.27

Slow component*

*NIM A292 (1990) 329


Photon Propagation

Simplification 1:

Simplification 2:

2.79ns


Additional Modifiers

θ

“collection factor” ~ 60%

Rangle = cos θi

Average efficiency over all θ: 66%

B=0T B=1.5T

<q.e.> ~ 21%


PMT Response

tpe = ttraj + temit + tpro + tTT

2.0 GeV/c µ-, z=0

Vi(t)PMT Gain

τ = 6ns

Transit Time: (5.5 +/− 0.31) ns

r.m.s. Transit Time Spread

Q-V conv.


Readout Electronics

50mV150mV

• In addition, introduce timing uncertainty– Gaussian parameterization, 45ps width

• t0 determination, discrim/system noise, TS quantization/RF jitter, fudges


TDC Distributions

• Nice agreement– Requires timing

uncertainty

• 45 ps

Time (ns)Data [solid]

• Higher order z-dependent effects not shown


ADC Distributions

• Simulated charge distribution much narrower than data

– Requires modification

– Scaled Poisson distribution:

Width scale parameter=2 for best data match

Poisson distributed r.v.<N> = npe


Time Walk Comparison

Overall, good agreement

Large scatter in both simulation and data for large pulse heights


Degradation Modeling

“unholy Trinity”

Pile-up

Accidentals

Overflow


Degradations Reproduced!

Data,BackgroundData limitedFor >100kHz

Fixed,GeometricInefficiency


Simulation Summary

Always room for improvement

ps

Reproduces tails


Care and Feeding: Manpower

• Jorge Rodriguez– CLEO Cal. Expertise

– Original T0

• Karim Trabelsi– Backward Kalman

– “EXT”,Σ path– Tracking group

• Mike Peters– RecTOF

– Combining statistics (1-4 dof)

• Mike Jones– Daily monitoring

– Always finding problems

• H. Kichimi– TOF leader

– Constant attention

• And many others!!• In particular many students

who are based at KEK continually monitoring laser/Cal data


Collision Point/Timing Stability

Experiment 19Experiment 17T0 [ns]

T0 [ns]

T0 [ns]

200ps jump!

Run number Run number

• Run-by-run T0


Care and Feeding: monitoring

Charge dependence!


Limitations (1)

• Intrinsic Performance:– Tough to get– Beam tests don’t require

sustained operation– Hadronic Calibration!

• Very important – details omitted due to space limitations

• Much work, no fundamental understanding

• Velocity dependent (dE/dx?) fudge• Systematic, so no SQRT(2) • May be TWC technique dependent

– Sad history of underperformance:

• CLEO, CPLEAR, BESII, …

– Error Budget!!


Limitations (2)

DIRC + MDC


Expectations? (1)

• Q: what does this mean for BESIII TOF?BESIII

Spec. guess? Spec.RF/BCO <35 ps 35 ps <35 ps

uncorrected t=0 ? ? within runDiscrim. Overdrive ? ? could be calibrated

Beam bunch length 2.5 mm 8.3 ps 50 ps 15 mmTime Encoding <20ps 22 ps ?

(~42 ps)TOTAL < 40 ps ~45 ps < 45 ps ? looks difficult

Belle

• GEANT/full simulator contribution:

σ2fin 100ps – “known” ~ “physics” 40ps

(Belle detector/KEKB environment dependent)

• In summary, can parameterize:


Expectations? (2)

• Must minimize irreducible Systematics

40 45 50 55 60 65 7050

6580

0.0

20.0

40.0

60.0

80.0

100.0

120.0

Total Resolution (ps)

Systematic Error (ps)

Intrinsic resolution (ps)

100.0-120.080.0-100.060.0-80.040.0-60.020.0-40.00.0-20.0


Time Stretcher Concept

• In a pipelined/MTDC DAQ need a reference T0

– Map ~25ps desired lsb onto MTDC 0.5 ns (HPTDC 0.1ns ? [7])

• In principle, improve by the stretch factor


Time Stretcher Module

• Designed

with LRS

– R&D 100 Award

VIPA StandardModule

16 Channels/1 per DC

Stretch factor20x

RF clockReference


TS + MTDC Performance

• ~20ps jitter

σ = 22.5ps+50ps

-50ps


Monolithic Time Stretcher (MTS1)

Detailed SPICE Simulations to be

Presented @ High LWorkshop in August16/32 LV

TTLor LVDS inputs

• Target to use with HPTDC – Common development w/Belle High L upgrade

LVDS outputsto HPTDC

Specifications underdiscussion (with BESIII input),

could submitprototype August/Sept.

Chip shown Is previous

Ramp converter


Time Walk Correction

• Reasonable functional form– But can do better?

Pile-up

tFixed threshold

V

T0

Twc

ADCGate

Q

Sensitive to “3 Effects”

• Many ideas: e.g. direct digitization at high speed?


STRAW2 Chip Self-Triggered Recorder Analog Waveform (STRAW)

32 (16) Channels of256 deep SCA buckets

Optimized for RF inputMicrostrip 50Ω

Follow-on to the ATWDChip (LBL)

Target input Bandwidth:>700MHz

-LL and HL (adj.) for each channel

Sampling Rate:1-2GSa/s (adj.)

-Multiplicity triggerfor LL hits

On-chip ADC:12-bit, >2MSPS

Primary application:Askaryan-effect RFUHE cosmic detectors External option:

MUXed Analog out

Sampling Rates>~8GSa/s possiblew/ 0.25µm process

8192 analog storage cells

Die:~2.5mm2

Self-Triggering:

SubmissionDate: 15 July


Summary

• Desired TOF system performance challenging

• Two specific areas for R&D:– Encourage further, detailed simulation to obtain

more realistic performance estimate

– Joint development of precision timing encoding (also needed for Belle high Luminosity upgrade)

• Plans– HPTDC Evaluation board

– Monolithic Integrated Time Stretcher (MTS1)

– STRAW2 Submission mid-July


References[1] Belle collaboration, Letter of Intent for a study of CP violation in B Meson decays, KEK Report 94-2, April 1994.[2] Belle collaboration, Technical Design Report for a study of CP violation in B Meson decays, KEK Report 95-1, March 1995.[3] KEKB B-factory Design Report, KEK Report 95-7, June 1995.[4] H. Kichimi et. al, Nucl. Instr. And Meth. A325 (1993) 451.

[5] J.W. Nam et. al, A Detailed Monte-Carlo Simulation for the Belle TOF System, submitted to Nucl. Instr. And Meth., hep-ex/0204030.[6] H. Kichimi and G. Varner, Design of TOF Front End Electronics, Belle Note #138, August 1996.

[7] M. Mota HPTDC Test Report v.1 (unpublished). [8] G. Varner et. al, A time expanding multihit TDC for the Belle Time-Of-Flight detector at the KEK B-factory, Proceedings of the Sixth International Conference on Electronics for Particle physics, P17, May 1997.[9] H. Kichimi et. al, Nucl. Instr. And Meth. A453 (2000) 315.

[10] Belle collaboration, Nucl. Instr. And Meth. A479 (2002) 117.


Background: HPTDC Testing

σ100ps = 75.9ps

σ25ps = 69.8ps

Better for logicclock turned off

σ500ps ~ 330psFor LRS 1877S

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