E - 94 -107

RICH detector status report

- Why

- How

- Were we are

E-94-107 - High Resolution 1p shell Hypernuclear Spectroscopy F. Garibaldi, S. Frullani, J. LeRose, P. Markowitz, T. Saito

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

forward angle&very good very good PIDPIDare needed to be able to get reasonable counting rates and unambiguous kaon identification in order to clean up the huge background

Kaon Identification through Aerogels:

AERO1 n=1.015

AERO2 n=1.055

p

k

KAONS = AERO1•AERO2

p k

All events

Hypernuclei -> smaller scattering angle -> higher background --> something else is needed

Contamination of pion and proton on the K signal with different PID systems, for the counting rates of two levels (10-2 Hz and 10-4 Hz)

Process Rates

signal (e,e’K) 10-4 – 10-2

accidentals

(e,e’)(e,pi)(e,e’)(e,p)(e,e’)(e,k)

1001000.1

RICH

0

without RICH with RICH

Cos =1/n / = tg N = p.e. per ring

/sqrt(N)

- n fixed by the momentum(2GeV/c)

C6 F14, transparent down to 160 nm

- compact (~ 50 cm)

- relatively thin (18% X0)

- 310 x 1820 mm2

- quarz window 5 mm

15 mm300 nm

€

Many parameters affect the detector performances (# p.e.)

- quartz transparency in the v.w. region of interest (160 - 220 nm)

- freon purity to not absorb the emitted Cherenkov light

- freon purity circuit + continuously monitoring

- CsI photocathode

- evaporation + on line QE absolute measurement

- QE is strongly affected by oxygen and moisture

- Careful handling of photocathodes after evaporation

- Continuous monitoring of gas “purity”

CERN tests

11/01 !! 7 GeV/C p beam

Argon CH4 (25/75)

2photocathodes

Romeand CERN

Equal performances

N = ~ 12N = ~ 12Can be be

extrapolated

to ~ 1414 with CH4

Evaporation system

110 cm

120 cm

Photocathode

UV source box

PMT Collection chamber

Rotating mirror (CaF2)

Movement system

10-6 mbar vacuum, 2 nm/s CsI deposition at T = 60 ºC (CERN experts indications). Vacuum - heating conditions start 15 –24 h before evaporation. A post -evaporation heat treatment is done for 12 hours.

Crucible bars

Evaporation layout

§ PhotoCathode– crucibles plane distance: 42 cm§ 4 μ m Ni– 1μ m Au support§ :0.8 ,crucible quantity g weight each one

~320 ( corresponding to nm thickness expected )and measured

.Pos X .Pos Y#1:Source 2.5 53.15#2:Source 61.5 53.15#3:Source 61.5 -12.85 [ ]:y cm 66#4:Source 2.5 -12.85

. [ ]:Ep min nm 286 [ ]:x cm 59. [ ]:Ep max nm 387

.:diff 26.1%

0,0

1Source 2Source

3Source4Source

Crucibles positions

1 3 57

911

13S1

S5

S90

50

100

150

200

250

300

350

400

350-400

300-350

250-300

200-250

150-200

100-150

50-100

0-50

Thickness (nm)

Expected thickness

64,40

3PD

Reference QE

0

0.05

0.1

0.15

0.2

0.25

150 160 170 180 190 200 210 220

Wavelength (nm)

QE (%)

CERN

Jlab

Jlab Cosmic tests June 03

Extrapolating to =0 and taking into account the geometric inefficiency and false triggers (cosmics): > ~ 12 p.e. (as at CERN)

2200 V

G~ 2.5 x 105

A0=26

Probably underestimated (protons below threshold, random coincidences etc.)

The detector has been tested succesfully at CERN Novembre 2000 (12 p.e.(14-15 with CH4)) 2 photocathode evaporated respectively at CERN and ROME

---> same result !(the best CERN had obtained with the same gas mixture)

After trasportation, mechanical problems(a. w. to photocatode distance)

lower gain --> lower # p.e.(Difficult to measure, difficult to fix) fixed July 2002 right gain back, but-wait for freon-Radiator accident-Fixed, but still some leak ->quench

--> lower gain (lower #p.e.)

Neverthless increasing HV (2100 to 2200V) gain back p.e 10-12 (very difficult to estimate with cosmic, conservative)

Fixing freon leakage ==> 12-14 p.e.(look at possible moisture contamination!)

detector ready end ofJuly-spare radiator-spare f.e. electronics-3 spare radiators to be evaporated by end of July

Slow control status to be checked (kaon meeting should be good (Jlab task)

DAQ integration (see Bodo)

Software - C++ code written by Guido being tested with CERN data for comparison with CERN (report next kaon mee.- improving the tracking (minimizing the angle error) using FPP?

Detector ready to be installed when needed - decision driven by Hall A installation schedule

(eventual “last” evaporation not to be anticipated)

- only test missing: hight rate behaviour on Jlab beam

- the CERN experience (the only one available) says that we should not have problem but no tests are possible with a continuous beam) (type of problem: charging up of photocathode (CsI))

- F.Piuz (Pilos proceedings): 24 hours with 6.4X10-10 Coulomb/mm2/s

- in our case (Hall A, our experiment at 250 KHz we have 2 x 10-13 coulomb/mm2/s

Conclusions