Concept for a RICH detector for the CBM experiment at the future accelerator facility

FAIR at GSI in Darmstadt

Claudia Höhne - GSI Darmstadt, GermanyCBM collaboration

Claudia Höhne 5th International Workshop on RICH Counters 2004

Outline

• context of the RICH detector

• CBM @ FAIR

• CBM physics

• requirements for RICH detector

• design of RICH detector

• mirrors

• photodetector

• radiator

• simulations

• summary - outlook - future plans

Claudia Höhne 5th International Workshop on RICH Counters 2004

SIS 100 TmSIS 300 TmU: 35 AGeV p: 90 GeV

Facility for Antiproton and Ion Research

„next generation“ accelerator facility:

• double-ring synchrotron

• simultanous, high quality, intense primary and secondary beams

• cooler/ storage rings (CR, NESR, HESR)

Ion and Laser induced plasmas: High energy density in matter

Compressed Baryonic Matter

Cooled antiproton beam: hadron spectroscopy

Structure of nuclei far from stability

CBM @ FAIR

Claudia Höhne 5th International Workshop on RICH Counters 2004

nuclei

hadronic phase

SPS

RHIC

lattice QCD : Fodor / Katz, Nucl. Phys. A 715 (2003) 319

SIS300

dilute hadron gas dense baryonic medium

Investigation of the phase diagram of strongly interacting matter

• high T, low B

top SPS, RHIC, LHC

• low T, high B

SIS

• intermediate range ?

low energy runs SPS, AGS

SIS 300 @ GSI !

Critical point?

Deconfinement?

Highest baryon densities

→ in medium properties of hadronsrestoration of chiral symmetry?

CBM physics

Claudia Höhne 5th International Workshop on RICH Counters 2004

CBM experiment

• tracking, vertex reconstruction: radiation hard silicon pixel/strip detectors (STS) in a magnetic dipole field

• electron ID: RICH & TRD (& ECAL) suppression 104

Compressed Baryonic Matter experiment

• hadron ID: TOF (& RICH)

• photons, 0, : ECAL

• high speed DAQ and trigger

Claudia Höhne 5th International Workshop on RICH Counters 2004

RICH detector in CBM

• radiator with high threshold (th > 40) → p,th ~ 5-6 GeV/c, 90% of e reached at 12-13 GeV/c

• sufficient radiator length for generation of Cherenkov photons (N >> 10), small radiation length, good UV transparency of radiator gas

• low material budget (holds for all detector parts) to minimize secondary interactions and in particular e+e- pairs from -conversion

• large, continuous mirror-surface with excellent optical properties

• fast photodetectors (107 Hz) with wide detection range, high qe, high granularity

• precise measurement of e+e- pairs from the decay of mesons within a large acceptance (-suppression ~ 103–104)

• improve /K separation at higher momenta (kaon ID by TOF quickly deteriorates above 4 GeV/c)

task of RICH detector

detector requirements

Claudia Höhne 5th International Workshop on RICH Counters 2004

RICH design

• 2.2m long gas radiatorgas vessel with beam pipe in the center

• 2 mirror and 2 photo-detector planes (vertically separated)

• mirror: Be+glass, R=450cm2 x (450cm x 175cm)

• photo-detector: PMT planeshielded by magnet yoke2 x (280cm x 140cm)

• support structures preferably from side

Claudia Höhne 5th International Workshop on RICH Counters 2004

RICH mirror (IHEP Protvino, Russia)

beryllium

glass

heater

High temperature (~600C)

• spherical mirror, R=450cm

• Be hexagons (3mm thick, maximum diameter 60cm, 1.3kg) covered with 0.5mm glass→ 1.25% of X0

• glass polishing, Al covering, SiO2 coating → 92% total reflectivity in wide wavelength range

• excellent optics, no degradation and radiator gas pollution due to long exposition in a radiation hard environment expected

production: assembly:

Claudia Höhne 5th International Workshop on RICH Counters 2004

RICH mirror

prototype available:

• optical surface roughness h = 1.6nm (after glass polishing, Al covering and SiO2 coating)→ diffuse reflection of only 12% of total for = 150nm

• image diameter of a point source D0 = 0.4mm (contains 95% of reflected light)

→ angular deviation from nominal curvature = 0.03mrad

Be plate for LHCb Be-mirror prototype

Claudia Höhne 5th International Workshop on RICH Counters 2004

PMTs (IHEP Protvino + Moscow Electrolamp)

PMT FEU-Hive

• K2CsSb photo-cathode, 25% quantum efficiency at = 410nm

• to be covered with transparanet WLS film (p-theraphenyl) → 22% qe for wide range

• ~90% geometrical efficiency

Claudia Höhne 5th International Workshop on RICH Counters 2004

PMT FEU-Hive

• external PMT diameter 6mm photo-cathode diameter 5mm → ~105 channels per detector plane

• length 6cm

• high voltage ~ 2kV

• effective number of dynodes 12

• amplification 106

→ effective operation in one-photoelectron regime

• power dissipation 40mW

• noise current ~ 3000 e-/s

• capacitance 10-15 pF

• dynamical range of signal charge Q = (0.25-25) 106 e-

• average signal time ~ 1ns

Claudia Höhne 5th International Workshop on RICH Counters 2004

radiator

• no window between radiator and photo-detectors: He, N2, CH4

fluorescence? CH4 as quenching gas in mixture?

• th > 40, UV transmittance, radiation length!

• ideal would be an easy handling (gas system)

n th c p,th th X0

He 1.000035 119.5 0.48° 16.7 GeV/c ~ 50nm 5300m

N2 1.000298 41 1.4° 5.72 GeV/c ~ 80nm 304m

CH4 1.000444 33.6 1.7° 4.68 GeV/c 145nm 650m

60%N2 + 40%CH4 1.000356 37.5 1.53° 5.25 GeV/c 145nm 386m

40%He + 60%CH4 1.0002804 42.2 1.36° 5.9 GeV/c 145nm 999m

Claudia Höhne 5th International Workshop on RICH Counters 2004

Simulation (GEANT3)

• CBM detector simulation framework GEANT 3, GEANT 4

• implementation of RICH detector

• Cherenkov properties of materials from HADES, literature

beam

2m3.

3m

4.7m

Gasbox: 250 m aluminum

• study basic properties of current detector concept

• prove feasibility of desired -suppression

• optimize geometrical design, optical layout

Claudia Höhne 5th International Workshop on RICH Counters 2004

rings() - polar angle, azimuth angle

• no diffusion at reflection

• no magnetic field, no multiple scattering

→ eccentricity for large

= 80o 60o 40o

20o

= 5o

10o 15o

20o 25o

30o 35o

one quarter of mirror/ photodetector:

Imaging properties of mirror

optimize optical design of detector!

Claudia Höhne 5th International Workshop on RICH Counters 2004

Single particles

radiator 40%He+60%CH4

• e/ separation (depending on radiator) up to 11-14 GeV/c

• identification from 5-7 GeV/c to 11-14 GeV/c

• diameter of ring 10.6-12 cm ≈ 17-20 PMTs diameter

• wide acceptance covered

single e- acceptance

Claudia Höhne 5th International Workshop on RICH Counters 2004

figure of merit

Cherenkov spectrum for N240%He + 60%CH4

min N N0 [cm-1] NPMT

120nm 33 292 25

200nm 23 204 18

250nm 15 138 11

300nm 11 93 8

N= 1.3 NPMT

Importance of continuation of the development of PMTs with large qe in the UV range!

Claudia Höhne 5th International Workshop on RICH Counters 2004

UrQMD event35 AGeV central Au+Au

about 40 rings/event:

• 33 electrons (~13 from primary vertex)

• 7 pions

• 0.1 muons

Claudia Höhne 5th International Workshop on RICH Counters 2004

UrQMD event

35 AGeV central Au+Auz-coordinates of track vertices for particles detected in RICH:

• target (z = 0cm) - 125m Au

• 7 STS – 2x100m, 5x200m Si (z = 5,10,20,40,60,80,100 cm)

• beampipe (z ~ 20-30 cm)

• magnet yoke (z ~110-140 cm)

optimize CBM detector layout to further suppress e+e- pairs from -conversion!

Claudia Höhne 5th International Workshop on RICH Counters 2004

misidentification

first estimation

• assume 100% ring finding, match closest track to a certain ring

• large number of charged tracks per event, additional information available from TRD, TOF

ideal tracking 1% momentum resolution

R

Claudia Höhne 5th International Workshop on RICH Counters 2004

summary - outlook - future plans

optimize detector layout (optics system!)

continue RICH R&D (radiator, mirror, PMT)

concept of RICH detector for the CBM experiment introduced

2006/2007 RICH prototype 2006/2007

2007/2008 beam tests of RICH prototype 2007/2008

2008/2009 final RICH design

2009/2010 RICH production

- 2012 installation, commissioning, beam!