Jochen Schwiening, SLAC RICH2002, Nestor Institute, Pylos, June 2002 DIRC DIRC - - T T HE HE P P ARTICLE ARTICLE I I DENTIFICATION DENTIFICATION S S YSTEM FOR YSTEM FOR B B A A B B AR AR Outline: • DIRC Concept and Design • Operational Issue Highlights – details in second DIRC talk, Sunday. • Detector Performance – Detector Resolution – Photon Yield • Physics Application Examples Jochen Schwiening Jochen Schwiening RICH2002, Nestor Institute, Pylos, June 2002
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DIRC - T HE P ARTICLE I DENTIFICATION S YSTEM FOR B A B AR
DIRC - T HE P ARTICLE I DENTIFICATION S YSTEM FOR B A B AR. Outline: • DIRC Concept and Design • Operational Issue Highlights – details in second DIRC talk, Sunday. • Detector Performance – Detector Resolution – Photon Yield • Physics Application Examples. - PowerPoint PPT Presentation
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Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
DIRCDIRC - - TTHEHE P PARTICLEARTICLE I IDENTIFICATIONDENTIFICATION
S SYSTEM FORYSTEM FOR BBAABBARAR
DIRCDIRC - - TTHEHE P PARTICLEARTICLE I IDENTIFICATIONDENTIFICATION
S SYSTEM FORYSTEM FOR BBAABBARAR
Outline:
• DIRC Concept and Design
• Operational Issue Highlights– details in second DIRC talk, Sunday.
• Detector Performance – Detector Resolution
– Photon Yield
• Physics Application Examples
Jochen SchwieningJochen Schwiening
RICH2002, Nestor Institute, Pylos, June 2002
Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
a Stanford Linear Accelerator Centerb CEA-Saclay, c LPNHE des Universités Paris 6 et Paris 7d LAL, Universite Paris Sude Ecole Polytechnique, LPNHEf Lawrence Berkeley National Laboratoryg University of California, Santa Barbarah Colorado State Universityi University of Cincinnati
Novel RICH detector used for the first time in BABAR
DIRC combines with dE/dx from drift chamber and vertex detector
(mostly in the 1/2 region) ashadronic particle identification
system for BABAR.
Novel RICH detector used for the first time in BABAR
DIRC combines with dE/dx from drift chamber and vertex detector
(mostly in the 1/2 region) ashadronic particle identification
system for BABAR.
BABAR-DIRC CBABAR-DIRC COLLABORATIONOLLABORATION
The BABAR-DIRC Collaboration
I.Adam,a R.Aleksan,b D.Aston,a D. Bernard,e G.Bonneaud,e P.Bourgeois,b F. Brochard,e D.N.Brown,f J.Chauveau,c J.Cohen-Tanugi,c M.Convery,a S.Emery,b
S.Ferrag,e A.Gaidot,b T.Haas,a T.Hadig,a G.Hamel de Monchenault,b C.Hast,d A.Höcker,d R.W.Kadel,f J.Kadyk,f M. Krishnamurthy,h H. Lacker,c G.W.London,b
Covering all B Decays at BABAR requires Particle Identification (PID) up to 4.2 GeV/c momentum.
Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
• A charged particle traversing a radiator with refractive index n with v/c> 1/n
emits Cherenkov photons on cone with half opening angle cos c = 1/n.
• If n>2 some photons are always totally internally reflected for 1 tracks.
• Radiator and light guide: Long, rectangular Synthetic Fused Silica (“Quartz”) bars (Spectrosil: average <n()> 1.473, radiation hard, homogenous, low chromatic dispersion;144 bars: 4901.73.5 cm3, polished to surface roughness <5Å (rms); square to better than 0.3 mrad.)
• Square radiator bar magnitude of c
preserved during internal reflections.Typical DIRC photon:
400 nm, ~ 200 bounces,~ 10-60 ns propagation time,~ 5 m path in quartz.
DIRC PDIRC PRINCIPLERINCIPLE I I
Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
• Only one end of bar instrumented; mirror attached to other (forward) end.
• Spectrosil wedge glued to readout end reduces required number of PMTs by ~ factor 2 and improves exit angle efficiency for large angle photons .
• Photons exit from wedge into expansion region (filled with 6m3 pure, de-ionized water).(<nwater ()> 1.346, Standoff distance 120 cm, outside main magnetic field; shielding: B 1 Gauss)
• Pinhole imaging on PMT array (bar dimension small compared to standoff distance).(10,752 traditional PMTs ETL 9125, immersed in water, surrounded by hexagonal “light-catcher”,transit time spread ~1.5nsec)
• DIRC is a 3-D device, measuring: x, y and time of Cherenkov photons.
• PMT / radiator bar combination plus track direction and location from tracking
define cc tpropagation of photon.
~<
DIRC PDIRC PRINCIPLERINCIPLE II II
Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
PEP-II accelerator schematic and tunnel viewPEP-II accelerator schematic and tunnel view
3.1 GeV positrons on 9.0 GeV electrons
center of mass energy M(4S) =10.58 GeV/c2
= 0.56
THE SLAC PEP-II B-FACTORY
Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
BABAR layoutInstrumented Flux Return19 layers of RPCs 1.5 T Solenoid
Silicon Vertex Detector5 layers of double sided silicon strips
e– (9.0 GeV)
e+ (3.1 GeV)
THE BABAR DETECTOR
Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
DIRC thickness: 8 cm radial incl. supports19% radiation length
at normal incidenceDIRC radiators cover:
94% azimuth, 83% c.m. polar angle
THE DIRC IN BABAR
BABAR-DIRC Timeline:
November 1998: installed SOB and one bar box, PMTs in water;
April 1999: BABAR moves into beamline, added 4 more bar boxes;
November 1999: all 12 bar boxes installed, start of first physics run.
Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
DIRC ODIRC OPERATIONALPERATIONAL E EXPERIENCEXPERIENCE: I: ISSUESSSUES
• Calibration constants stable to typically rms < 0.1ns per year.
• No problems with water or gas systems.
The two most significant operational issues that have emerged during three+ years of running:
• Sensitivity of the DIRC to machine background interacting in the SOB(primarily DAQ issue)
• Concerns about PMT longevity due to PMT window degradation.
For more details on DIRC operations, see talk in Sunday session.For more details on DIRC operations, see talk in Sunday session.For more details on DIRC operations, see talk in Sunday session.For more details on DIRC operations, see talk in Sunday session.
DIRC is Stable and RobustDIRC is Stable and Robust
Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
DIRC ODIRC OPERATIONALPERATIONAL E EXPERIENCEXPERIENCE: P: PHOTONHOTON Y YIELDIELD
Concern: stability of photon yield
• PMT directly immersed in purified water since 1998;• observed front glass corrosion in October 1999;• no direct experience with maintaining high (>0.999)
radiator reflection coefficient for 10 years.
Detailed study of photon yield using:• LED pulser calibration,• PMT aging tests,• comparison of photon yield in real Bhabha and di-muon events separately for every radiator bar (box).
Consistent result:1-2% photon yield loss per year.
very minor impact on PID performanceover 10 year lifetime of DIRC.
barbox number
phot
on y
ield
cha
nge
per
year
(%
)
Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
Luminosity (1033/cm2s)
max
imum
sca
ler
rate
(kH
z)
Succession of lead shielding installed in 2000 and 2001.
Current shielding configuration “background safe” through 2002.
New TDC chips to be installed during shutdown Fall 2002:
<5% deadtime at 2.5MHz rate.
Thanks to lead shielding, PMT rates acceptable even above design lumi.
DIRC ODIRC OPERATIONALPERATIONAL E EXPERIENCEXPERIENCE: B: BACKGROUNDSACKGROUNDS
PMT Rate vs. Luminosity shows that lead shielding essential in protecting DIRC from
few MeV photon accelerator induced background (radiative Bhabhas etc).
DIRC TDC1: ~5% inefficiency at 250 kHzSpring 2000
Fall 2000
Spring 2001
Jochen Schwiening, SLACRICH2002, Nestor Institute, Pylos, June 2002
DIRC “Ring” images:
• limited acceptance for total internal reflection,