A RICH detector for CLAS12

CLAS12 European WorkshopFebruary 25-28, 2009- Genova, Italy

Evaristo Cisbani INFN Rome and ISSPatrizia Rossi

INFN- Laboratori Nazionali di Frascati

Hall BCentral Detector

Forward Detector

Hadron PID in CLAS12 BaselineGeV/c 1 2 3 4 5 6 7 8 9 10

/KTOF

LTCC

HTCC

/pTOF

LTCC

HTCC

K/pTOF

LTCC

• /K PID rely on LTCC performance in 3-5 GeV/c

• No K/p PID in 5-8 GeV/c

Ratio K/ ~ 0.1-0.15 If we assume a 10% inefficiency for Cerenkov rejection factor /k ~1:1

RICH detector

RICH detector

θC

€

cosθC =1

nβ⇒ cos−1 m2 + p2

np

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

r

L

2θ

θ(deg)

r(cm)= Ltanθ

38.4 79

K 36.4 73

p 30.3 58

P = 2 GeV/c L= 1m n=1.28 (liquid freon)

Good separation /K/p

Which RICH?

• Liquid Radiator (Freon)

–May cover up to 5 GeV/c–Relatively inexpensive (proximity focusing RICH)

•Aerogel + Gas Radiators

–May cover up to 10 GeV/c–Very expensive(cost Aerogel RICH ~ 5x Proximity Focusing RICH)

Location of the RICH

Replace part of LTCC:

- No impact on baseline design

- Nobody will probably complain

- Large space available (and to be covered!)

Replace HTCC:- Impact on baseline design

- Impact on tracking recontruction

Simulation done for LTCC

LTCC sector

~ 6.2 m2

entrance window

1 m depth

• A proximity Focusing RICH (~1 m2 surface) is working in Hall A and being used in the Transversity experiment

• Same RICH type used by ALICE experiment ( ~10 m2

surface)

Hall A Proximity RICH

Proximity Focusing RICH

The Proximity Focusing RICH consists of 3 basic components:

Cherenkov Liquid Radiator

The Radiator must be in a container (vessel) with UV transparent window (QUARTZ window)

The Photon Detector must detect and localize the photon that hits on a given surface: we assume a “pads like” detector

Gap (gas filled space)

Photon Detector

Hall A Proximity RICH

• The Freon vessel (radiator) is the most fragile component of the detector• The Freon pressure is partially compensated by the glued spacers• Quarz planarity and parallelism 0.1 mm

Evaporation facility

• CsI is evaporated on the pad panel in the evaporation chamber: 120h x 110r cm2 (vacuum 10-7 mbar)• The evaporation facility - cost ~ 0.5 M$ has been built by the INFN Rome group (now at Stony Brook University)

Hall A RICH: QE measurements (July ‘08)

25

25

~ 25% Quantum Efficiency has been measured

K/ rejection ~ 1/1000

F. Garibaldi et al. NIM A502 (2003)

Hall A RICH in Hypernuclear Exp. (2003-2005)

• Estimate the optimal radiator thickness

– Larger the thickness, higher the number of photons, higher the uncertainties on photon emission– Larger the thickness more challenging is the vessel technology (and more expensive the system)

• Estimate the optimal Gap length– Larger the gap, better the ‘focusing’, but larger must be the detection plane

Monte Carlo studies: purpose

Old GEANT3/Fortran/PAW based MonteCarlo framework the same used the for the development of the Hall A Proximity RICH but with different geometry and size!

Charged particles phase space at the LTCC-RICH entrance window assumed uniformly distributed with +/- 10 degree divergence

Use arcs as radiator and detector geometries (see next)

Limitation on photon production (~3000) old memory constraint. This becomes relevant for radiator thickness > 2.5-3.0 cmMain output parameter:k= mean error on Cherenkov angle

reconstruction of k and

Monte Carlo studies: framework

θCθCK

K-= (K+ )/2

Working Point

Assume:• Two radiators (only 1 simulated); one per sector• Detector span up to 2 sectors (detect photons from both radiators)• Radiator Polar acceptance: 5° ÷30° fix radiator size ~ 4 m2

• Max gap length = 80 cm

Not to scaleUnit: mm and degree

•Particles uniformely distributed in the phase space

•Black dots are charged particle positions at RICH entrance (the envelope is the radiator)

•Contour lines are positions at the detector level of all photons generated in the radiator

•The large arc is the detector surface (photons out of there are not detected)

•Geometry is rotated respect to the previous drawing … but represent basically the same idea

Monte Carlo Result: Example

x/y are not to scale

Points: MonteCarlo, Curves: analytical functions~ 1 mr difference C5F12 mandatory!

Geometry from the previous example

Radiator Type

C5F12 C6F14θCθC

n

Simulation with realistic phase space

To detemine the best photon detector size, ,K,p have been generated at the LTCC-RICH entrance window according with a realistic phase space distribution of reconstructed momenta and angles.

(GeV/c)

K- Separation

Radiator= 2 cm

Radiator= 1.5 cm

Radiator= 3 cm

• Radiator Thickness = 1.5, 2, 2.5, 3, 3.5 cm• Gap length = 80 cm• Pad/Pixel size = 0.75 cm

Angle reconstruction error vs:

100k events

K- Separation• Radiator Thickness = 2 cm• Gap length = 60, 80 cm• Pad/Pixel size = 0.75 cm

Gap Length= 60 cm

Gap Length= 80 cm

Separation at 5 GeV/c: 3 = 1/100 / 75% efficiency 1/10 / 95% efficiency

Angle reconstruction error vs:

100k events

Radiation thickness

Thickness (cm) X0 (%)

Entrance window

Al 0.05 0.5

Rohacell51 5 2

Al 0.05 0.5

Radiator

Neoceram 0.4 3

C5F12 2 10

Quartz 0.5 4

Gap

CH4 80 0.001

Photon Detector

Pad NEMAG10 0.08 0.4

GEM chamber 1 0.6

Total radiation thickness of the proposed RICH: ~20% X0

HBD @ Phenix

Replace MWPC with GEM Chamber faster, higher gain, stability at high rate

Photon Detector

Hall A RICH Factor Class12 RICH

Readout 95 4 380 (15%)

MWPC: Pads Planes 20 10 200 (8%)

MWPC: Parts (Macor Insulator) 15 10 150 (6%)

Freon (C6F14) 20 40 800 (33%)

Quartz+Neoceram 30 20 600 (24%)

Mechanical Structure 30 10 300 (12%)

Evaporation Fac. 500 1 500 (exist)

Freon Recirculation System 20 (?) 1.5 30 (?)

Total 210+520 2420+530

Class12/Hall ARadiator: 36-48 (min.-max. volume), 24 (surface)Detector: 13 (surface), 4 (chs)

GEM ~ 1.2 x MWPC k$(estimation from Lire, CHF, $ and Euro)

Costs - Very Preliminary!!

Monte Carlo simulations have been started to study the feasibility to replace 2 sectors of LTTC with a proximity focusing RICH detector

From very preliminary results it seems that: The best choice is to use Freon C5F12 but it must be cooled! (it evaporate at 29 C at STP !!)At present stage the Cherenkov angle resolution is not impressive

a careful analysis and design is required to improve both the performance and the detector size

orientation of radiator pad size…

work is in progress

Conclusions and outlook