Flavio Gatti, PSI, 11 February , 2004 1

Genova/Pavia/Roma

Timing Counter: status @ january 2004

Flavio Gatti, PSI, 11 February , 2004 2

Genova/Pavia/Roma

Timing Counter Activities

• Timing resolution (Ge-Pv-Rm)• PMs characteristics in magnetic field(Ge-Pv) • APD for the counter (Ge)

• MC simulation activities(Pv-Rm)• Helium(Ge-Pv)

Flavio Gatti, PSI, 11 February , 2004 3

Genova/Pavia/Roma

Timing resolutionThe spread of the time distribution of the positron impact,T0, is

evaluated as: (T0) (TL- TR)]/2

where (TL- TR)] is the delay spread between the L and R PM------------------------------------------------------------------------- T0 =(TL+TR)/2 +L/(2Veff) (T0) [(TL+TR)/2] ; [(TL+TR)]= [(TL-TR)]

TLTR

T0

Flavio Gatti, PSI, 11 February , 2004 4

Genova/Pavia/Roma

Timing resolution Main parameters to be evaluated and matched in the TC:

1. Scintillation time, attenuation length, PM coupling2.PM’s Transit Time Spread, Quantum Efficiency, Gain3. Signal Slew Rate, Bandwidth and Noise4.Particle trajectory length(=light output) and its

spread High Luminosity Event, High Quantum Efficiency and PM

Collecting Area, High Slew Rate Signal (dV/dt), High S/N ratio, High Bandwidth.

PM TTS (FWHM) Typ. TTS Measured

R7761-70(1.5”) 350 ps 470 ps

R5924 (2”) 440 ps 650 ps

XP2020 UR (2”) 350 ps 350 ps

Flavio Gatti, PSI, 11 February , 2004 5

Genova/Pavia/Roma

Timing resolution measurements• First test(PSI-E5)- may 03: -BC404 (1X5x80 cm3) – light guides and 1”1/2 and 2”

Hamamatsu Fine Mesh PMs-passive beam collimation (6mm diameter)

-5 cm positron path length.-Analogic electronics - Double Threshold Discriminator-

MCA

2.35x (tL- tR)]/2= 124 ps FWHM

Scintillator

Light guide

248 ps FWHM(tL- tR)

Low Thr.

High Thr.

Delaycoinc

PM

Flavio Gatti, PSI, 11 February , 2004 6

Genova/Pavia/Roma

Timing resolution measurements• Last test (LNF-Frascati-Beam Test Facility –BTF-) January 04:Energy Range 25-800 MeV e- 25-550 MeV e+ Max. Repetition Rate 50 Hz Pulse Duration: ~ ns Current/pulse 1 to 1010 particles (Allowed Current 103 particles/second)Beam spot : x=2mm y=4mm (in the focus)• Further geometrical selection of 5mmx5mm spot by two scintillating fibers

with APD read-out. Time spread due to the spot size ~25ps.• Coincidence with “APD cross” and the LINAC trigger allow to reject most of

the bck. events.

beam

APD

APD

Scint. Fiber Spot SizeTime spread ~25ps

Flavio Gatti, PSI, 11 February , 2004 7

Genova/Pavia/Roma

Timing resolution measurements• BC404 and BC408 (2X5x80 cm3) directly coupled to 1.5” and

2” Hamamatsu Fine Mesh PMs• Digital electronic readout (CAMAC)

Beam

Approx. Beam Focus Position

APD Cross and Preamplifier

TC

BTF Beam line

Flavio Gatti, PSI, 11 February , 2004 8

Genova/Pavia/Roma

Timing resolution measurements1. 1,2,3 electron events are resolved in the charge spectrum2. (tL- tR) is selected in the 1e peak Our Best Results :

2.35x (tL- tR)]/2= 1042ps FWHM

1e2e

3e

Flavio Gatti, PSI, 11 February , 2004 9

Genova/Pavia/Roma

Timing resolution measurements

• We don’t see walk-effect (time/amplitude correlation).

The thresholds have been set to 0.5% of the average pulse height (3 V) at about 7 (rms noise level) from the baseline.

TDC Thr.

ADC off-line selection

Flavio Gatti, PSI, 11 February , 2004 10

Genova/Pavia/Roma

Timing resolution measurements

• The plastic slab acts as a light guide with Veff=12.6 cm/ns• The time resolution is proportional to the inverse of the

sqrt(path length)

2x (

di s

tan

ce f

rom

ce

nte

r ) [

c m]

Flavio Gatti, PSI, 11 February , 2004 11

Genova/Pavia/Roma

2” PM in Magnetic Field (Data presented in July 03)

2” PM 2” PM

Transit time spread respect to B=0

Magnetic field [ T ]Magnetic field [ T ]

Gain respect to B=0

0º

10º

20º

Note: no charge/amplitude corrected

Flavio Gatti, PSI, 11 February , 2004 12

Genova/Pavia/Roma

Timing resolution measurements• Conclusions:

– 2” PMs allow to obtain the target resolution– We are still limited by the number of

photoelectrons (light output from scintillator, quantum efficiency of PM, coupling scintillator-PM[2”], which has 39 mm dia. active area)

– In these tests there is no evidence of limits due to the electronics (slew rate, noise, …)

– No evidence of differences between BC404 and BC408

• To be done:– Geometrical arrangement that provide the same

efficiency of positron collection and same timing resolution in Magn. Field (see exe. in figures ->)

- Selection of 2” PMs with respect the Q.E. and gain may be needed.

– Improvements & fine tuning will be done in the next beam times

– Finalize the design of TC from now

50x20 mm

39x30 mm

Flavio Gatti, PSI, 11 February , 2004 13

Genova/Pavia/Roma

Guideline for Operation in Magnetic FieldImpact angles: 60º in the orthogonal

plane, 40º in the longitudinal plane

Magn. Field at radius 29<R<31 in figure.

Minimal CrossSection 39x30 mm 60º

PM section

PM activediameter

20º 20º8.5º

From COBRA center

105 cm

10º

25 cm

BB0.75 T 1.05 T

Reductio factor

Ext. PM Int. PM

Gain 12 @ 8.5º 5 @ 20º

35 @ 10º15 @ 20º

TTS 1.2* @ 8.5º1.2* @ 20º

1.8* @ 10º1.6* @ 20º

Expected Positron Path-Length: ~7cm (factor ~ 1.4)Geom. Matching Improv.: ~ 1.5Total increase of light yield:~ 2.1Better situation @ 30º PM tilt angleMC comparison of different config.

(Rotated Slab, ..) under study for further impr. (coincidence….)

*Note: data not corrected for time-walk effect

Flavio Gatti, PSI, 11 February , 2004 14

Genova/Pavia/Roma

Curved detector (triggering)

• Problem: curved thin scintillators orthogonal to the field• Proposal: 5mmx5mm scintillating fibers coupled with APD.

*APD high efficiency 95%*Optimal Matching of fibers/detectors*No relevant results published result on fast scintillator results ( 0.5 ns claimed)*Preliminary results in which we observed light pulses in plastic with Advanced Photonics

and Hamamatsu APDs are obtained in the last summer.

– November 03: received first batch of APDs selected for CMS – We made our selection, which is based on static parameters measurements (I-dark and

Gain vs Vbias, Vbkd…), in order to calculate the expected Signal/Noise at the working point.

Flavio Gatti, PSI, 11 February , 2004 15

Genova/Pavia/Roma

- detector (triggering)• We found good APDs with high S/N ratio that we tested at PSI and LNF (Frascati)

e- beam Pure e-beam

Flavio Gatti, PSI, 11 February , 2004 16

Genova/Pavia/Roma

- detector (triggering)• But, only about 10% of the selected APDs are good enough• Huge spread in dynamic parameters not predictable from static parameters [left

figure]• The CMS selection and conditioning of the first batch of APDs is not applicable to MEG

(we are working at few Volts from Vbkd – high gain- and we are interested to high slew rate and high S/N for timing purpose)

• For comparison new APDs from Hamamatsu have similar response[right figure] • More work is needed to better understand the correlation between static and dynamic

parameters of CMS APDs.

FromHamamatsu

from CMSselection

Flavio Gatti, PSI, 11 February , 2004 17

Genova/Pavia/Roma

Schedule

Beam Test

2002 2003 2004 2005

Test MilestoneAssemblyDesign Manufactoring

Design

Assembly

PMT Evaluation PMT procur.

Procur & Manuf.

2” Fine Mesh 19 dyn. R5924

APD Evaluation APD test APD procur.

5x5 mm APD Hmamatsu