rich status report claudia höhne, gsi for the cbm rich group bergische universität wuppertal...

RICH Status Report

Claudia Höhne, GSI for the CBM RICH group

Bergische Universität Wuppertal (BUW), GermanyGSI, GermanyHochschule Esslingen (HSE), GermanyPNPI Gatchina, St. Petersburg, RussiaPusan Natl. University (PNU), Korea

2 15th CBM collaboration meeting, GSI, April 2010 C. Höhne

particle beam

electron

photodetector radiator

gas VUV-mirror

target

Cherenkovlight

photomultipliers, e.g. MAPMT H8500

glass mirrors

RICH detector for CBM

aim: electron identification for momenta below 8-10 GeV/c .... maybe use also for additional -suppression in K-id at higher p

concept: gaseous RICH detector: stable, robust, fast rely to a large extend on components from industry

radiator: CO2, pion threshold 4.65 GeV/c


CBM RICH working group


Outline

• Photodetector

• wavelengthshifter films for enhanced UV-photon detection

• first studies of crosstalk for WLS covered MAPMT

• application techniques

• new testsetup at Wuppertal lab for q.e. measurements

• Mirror

• mirror samples, mirror mount design

• Prototype

• Pusan RICH prototype

• Plans for large, scalable prototype, gas system

• Summary

Photodetector


Photodetector

• use MAPMT (e.g. H8500-03) from Hamamatsu

• readout with current n-XYter adopted: single photon counting achieved!

[Ham

amat

su P

hoto

nics

]

GSI testbeam Sep ‘09

• aim at large number of hits on ring

→ investigate means to increase q.e.• UV extended window• Super-/ ultra bialkalkali photocathodes• wavelength-shifter films


WLS films

Wavelength shifting films – principle and application

• Organic molecules absorbing in the short (UV) wavelength region• Strong fluorescence in visible region• Application via evaporation, spin coating/ dip coating

Example: p-Terphenyl

[P. Koczon et al, submitted to NIMA]

p-terphenyl (PT)


WLS-films (II)

• basic studies performed in cooperation with CERN, paper submitted to NIMA

• p-terphenyl (PT): gain factor of 1.7 for borosilicate glass window of PMT, for UV window 1.3 estimated

• rather insensitive on filmthickness if > 0.8 µm

[P. Koczon et al, submitted to NIMA]


• GEANT4 simulation (P. Solevi, ETH Zürich): photons generated isotropically in 0.8µm thick p-terphenyl layer on top of 1.5mm thick borosilikate window

• photons distributed around generation point with =2.1mm at photocathode (distribution well described by gaussian)

• degradation of resolution expected!

[P.

Koc

zon

et

al.,

sub

mitt

ed

to N

IM A

]

Degradation of position resolution?

0.8 µm PT

1.5 mm PMT glass

photocathode


Degradation of position resolution? (III)

first investigations with H8500-03 (one half covered with PT)

• pinhole mask: enlight center of one pixel only

• fraction of hits in neighbouring pixels

~16% no WLS

~31% w WLS

• consistent with Hamamatsu specification, WLS simulation

• approx. factor 2 more crosstalk with WLS

• further measurements planned/ started at GSI (J. Eschke), Wuppertal group

[P. Koczon, GSI]


Simulation studies

• analytic calculation with simulation input: degradation of pixel resolution from 1.7 mm () to 2.3 mm

• implement WLS coverage in CbmRoot, consider additional collection efficiency of photoelectrons in electron optics (maybe on 70% level)

• momentum-integrated ring finding efficiency for electrons embedded in central Au+Au collisions at 25 AGeV

no WLSWLS (PT) coverage

• resolution degradation no problem

• higher efficiency due to larger number of photons (~30%)

with WLS

[S. Lebedev, GSI and JINR]

13 …………21 hits/ring


WLS films (III)

• application technique, mechanical stability of films?

• so far evaporated films used• homogenous coverage• minor formation of crystals• not stable against scratches

• test dip coating• larger mechanical stability due to

additional binder

[M. Dürr, HS Esslingen]


WLS films (IV)

340 360 380 400 420 4400

5

10

15

20

25

excitation = 280 nm

WLS-films / p-terphenyl

Inte

nsi

ty [

106 c

ou

nts

]

Wavelength [nm]

evap.

100 µg/cm2

sample 4 sample 5 sample 7 sample 8

first explorative studies:

• comparable fluorescence intensity seen to evaporated films!

• improve on homogeneous coverage, investigate formation of crystals, influence of binder…?

25 mm



New Lab at Wuppertal

[J. Kopfer for University of Wuppertal group]


New Lab at Wuppertal (II)



Measurement of absolute Q.E.

→ characterization of H8500 family, further investigation of WLS films,….


Mirror


Mirrors

Companies possibly to cooperate with

• Flabeg, Germany (mirrors)

• Compas, Czech Republic (mirrors)

• Siso, France (coating)

• SLO - Olomouc, Czech Republic (Auger Experiment, contact via Uni Wuppertal)

1st trial: Flabeg

test coating for reflectivity measurements o.k., D0 not so good (substrates not polished)

2nd trial: Compas

first results delivered early last year

installed in PNU-RICH 2


Mirrors presented last year

photography

dimensions:

Size: R = 300 mmglass: d = 3 mmRadius: r0 = 3000 mm

coating:

Al: d = 80 nmMgF2: d = 30 nm

• Mirrors broke when the company tried to cut quadratic tiles and/ or lost shape after cutting• Mirror mount rather complicated

Compas mirrors



New samples

(a) Coated mirror, size adjusted for PNU-RICH2

Specifications:

Size: A = 20 x 20 cm2

glass: d = 6 mmRadius: r0 = 3000 mm

coating:

Al + MgF2, not yet specified

Compas mirrors (II)

Simulations in CbmRoot: larger mirror thickness well tolerable!



New samples

(b) uncoated mirror

Size: D = 60 cmglass: d = 4 mmRadius: r0 = 3000 mm

Compas mirrors (III)

Proposed for delivery soon:

glass: d = 6 mmRadius: r0 = 3000 mmcoating Al+MgF2

2 samples: round (D=60 cm), rectangular (40x40 cm2)

next steps: same type of samples with 5 mm and 4 mm thickness→ systematically study distortions from cutting, stability



Measurement of Radius of curvature – D0 (still simplified setup, to be upgraded)

r0 = 2970 mm D0 ~ 2-3 mmonly slight distortions outside of center

10 m

m

10 mm25 cm

mirror

• measurement

sensitivity x 8

CCD

Point source

mirror

radius of curvature (2 x f)

Compas mirrors (IV)



Mirror mount

• mirror mount design at PNPI Gatchina, St. Petersburg

three mirror mounts allow enough freedom for mirror adjustment

detailed considerations how to achieve necessary degress of freedom

[V. Nikulin for PNPI-RICH group]


Mirror mount (II)

Trapezoid mirror tiles Hexagon mirror tile (for comparison)

• investigation (simulation) of influence of placement of mirror mounts on additional distortions on D0 for mirror + mount



Mirror mount (III)

Tilt angle of the tile is -20 degrees

example: calculation of additional D0 due to mirror distortions (mount, gravity) for right-angled mount: D0 = 0.37 mm



Mirror mount (IV)

Max. deformation

[microns]

Spot diameter D0(95%), [mm]

right-angled triangular mount (3 mm), trapezoid

65 2.0

right-angled triangular mount (6 mm), trapezoid

5.4 0.37

acute-angled triangular mount (6mm), trapezoid

6.3 0.53

acute-angled triangular mount (6mm), hexagon

2.0 0.22

Simulation results of optical response

• thicker mirrors (6 versus 3 mm) shows an increase in stability/ focal quality by an order of magnitude

• no large difference between different mirror mount options

• no large difference between rectangular and hexagonal shape



Mirror inhomogenity (D0) in simulations

• D0 is diameter of light spot in which 95% of the light intensity are reflected back; assume gaussian distribution of intensity spot → D0 ~ 2∙2

• Compas mirror: D0 = 2.3 mm → ~ 0.6 mm

• additional D0 component from mount well tolerable

s_mirror : irregularity of mirror

[S. Lebedev, GSI and JINR]


Next steps

• mirror mounts ready to be tested with first mirror sample!

[V. Nikulin for PNPI-RICH group; M. Dürr, HSE]

RICH prototypes


RICH prototype Pusan

• RICH prototype produced in Pusan, tested in 60 MeV electron beam at Pohang

• no ring structure seen in event integrated displays

[Pusan RICH group]


Mirror of Pusan RICH

• mirror sample from FLABEG installed in Pusan RICH (lower surface inhomogeneity, less focussing quality)

• D0 approx. 5mm → expect somewhat distorted/ widened ring image

20 m

m

25 mm

CCD

Point source

mirror

radius of curvature (2 x f)



On-site measurement: focussing properties ok!

laser diode

mirror f

detector plane

parallel beam

15 m

m

28 mm

sensitivity / 7.5

Mirror of Pusan RICH



Simulations of RICH prototype Pusan

• implementation of Pusan RICH with mirror and PMT plane in CbmRoot including concrete wall and Pb collimator

• including: absorption of photons in gas, chromatic dispersion, reflectivity of mirror, q.e. of PMT (H8500 and H8500-03)

nice ring structure seen for 6 GeV electron beam even with measured mirror distortion

[Pusan RICH group]


Simulations of RICH prototype Pusan (IV)

MC RICH Points

Without multiple scattering

• problem: Pohang delivers 60 MeV electron beam: multiple scattering in air and radiator!

→ no ring image seen in event integrated MAPMT signals because rings are smeared all over the PMT-plane

[Pusan RICH group]


Simulations of RICH prototype Pusan (VI)

simulation

• experimental setup: no possibility to trigger on single electrons!

• too high beam current (1nA in approx. 1µs bunch)• not yet enough electronics channels available for readout of 2(-4)

MAPMTs

data

→ improve beam conditions (select single electrons)

→ upgrade readout (n-XYter)

→ once running: test gas system specifications[Pusan RICH group]


CBM RICH prototype

plan for a larger RICH prototype with “real” modules for the final CBM-RICH:

• 2x2 mirror module with mounts: test effect of mirror distortions, test mirror adjustment, tiles of 40x40 cm2

• 3x3 or 4x4 MAPMT supermodule: test different H8500 versions, test WLS coverage, develop concept for electronics integration, PMT module mounting (7x7 would match mirror size)

• simplified gas system, to be extended/ upgraded later

~1.9 m~1 m

~1.

5 m

→ scalable to the full RICH detector


Path towards a complete RICH prototype (III)

• gas system proposal from PNPI Gatchina, start with simplified version (open system, less controls,…)

RICH

Prototype

H2OO2

Dryer

Purifier

Bubbler

Analyzers TT1 PT1

BP

PIT 2

SV2

SV1 PIDController

PT2

PIT 1

BV1

BMV1

SV3

MFC

FI1

FI2PR1BPR1

Fresh CO2 Compressor Abbreviations:

TT-temperature transmitterPT-pressure transmitterPIT-pressure indicating transmitterBP-barometric pressureSV-solenoid valvePR-pressure regulatorBPR-back pressure regulatorBV-bypass valveBMV-bypass manual valveMFC-mass flow controllerFI-flow indicator

• closed circuit gas system

• components can be reused for RICH gas system later



Summary

• Photodetector

• further investigations of wavelengthshifter films for enhanced UV-photon detection: degradation in resolution, application technique

• new testsetup at Wuppertal lab for q.e. measurements

• Mirror

• new mirror samples available (proposed), mirror mount design

• Prototype

• better understanding of Pusan RICH prototype

• Plans for large, scalable prototype, gas system

rich status report claudia höhne, gsi for the cbm rich group bergische universität wuppertal...

Documents

cbm collaboration meeting

uv window

hhnecbm rich

koczon et

gaseous rich detector

films principle

enhanced uvphoton

nimapterphenyl pt