babar dirc in solid - thomas jefferson national...
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BaBar DIRC in SoLIDBaBar DIRC in SoLID
P. Nadel-Turonski, Z. Zhao, C. Hyde ...P. Nadel-Turonski, Z. Zhao, C. Hyde ...
SoLID bi-weekly meeting, January 15, 2013SoLID bi-weekly meeting, January 15, 2013
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Emerging opportunity
1. BaBar DIRC suddenly becomes available in December 20121. BaBar DIRC suddenly becomes available in December 2012
2. SoLID with K ID up to 902. SoLID with K ID up to 90°° offers unique phy offers unique physics opportunitiessics opportunities
3. JLab would become main US center for Cherenkov technology3. JLab would become main US center for Cherenkov technology
• SuperB (next generation BaBar) canceled in Italy
• JLab can get the DIRC from SLAC – if needed for a good project
• He target outside, unpolarized (and longitudinal) targets inside solenoid
• High-pT SIDIS (→ Alexei's slides)
• Hard exclusive reactions with kaons and leptons (J/ψ, TCS)
• Spectroscopy (Ξ, Ω, etc)
• Funding SoLID would become a step toward a future EIC
• Other prospective EIC technologies could also be incorporated into SoLID– e.g., high-resolution (10-20 ps) TOF at forward angles
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• Charged particle traversing radiator with refractive index n with β = v/c > 1/n emits Cherenkov photons on cone with half opening angle cos θc = 1/βn(λ).
• For n>√2 some photons are always totally internally reflected for β ≈ 1 tracks.
• Magnitude of Cherenkov angle conserved during internal reflections
• Photons exit radiator into expansion region, detected on photon detector array.
• DIRC is intrinsically a 3-D device, measuring: x, y, and time of Cherenkov photons,defining θc, φc, tpropagation of each photon.
DIRC principle
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The synthetic fused silica (quartz) bars
Bar box: 12 bar boxes in BABAR12 long (4.9m) bars per box150μm air gap between barsdry nitrogen flow
Long bar: 4 short (1.225m) bars Mirror on forward end Wedge on readout end
BABAR-DIRC bars were polished to 5 Å rms, non-squareness < 0.25 mrad
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The DIRC in BaBar
DIRC thickness: 8 cm radial incl. supports19% radiation length
at normal incidenceDIRC radiators cover:
94% azimuth, 83% c.m. polar angle
DIRC photon detection array:10,752 PMTs ETL 9125
Low energy photons from accelerator hit Standoff Box.
Background rates in 300 ns window:
0.1-0.3 MHz per PMT (GHz per box)
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Event reconstruction
Calculate unbiased likelihood for signals to originate
from e///K/p track or from background:
Likelihood: Pdf(θc) x Pdf(Δt) x Pdf(Nγ)
Example: comparison of real event to simulated response of BABAR DIRC to e/π/K/p.
300 nsec trigger window 8 nsec t window (~500-1300 background hits/event) (1-2 background hits/sector/event)
Time resolution important for background suppression
Pdf = Probability distribution function
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Focusing DIRC (FDIRC) at SLAC
Photodetector:
12 arrays of 6*8 MaPMTs (HPK H8500) → 18,432 pixels.
Readout Electronics:
TDC/ADC information for every photon.
Bottom line:
Conservative, robust design;
10x better timing resolution than BABAR DIRC;
25x smaller expansion volume than BABAR DIRC;
Cherenkov angle determined from 2D spatial coordinates;
Time primarily used to correct chromatic dispersion.
Could be made cheaper (mineral oil instead of quartz)and momentum coverage could be extended
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Cherenkov angle (θc) resolution
• Extending π/K separation from 4 to 6 GeV/c requires σθ ~ 1 mrad (vs 2.4 in BaBar – a 58% reduction).
BaBar (3σ)
EIC?
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PID as a function of θc resolution
• Extending 3σ π/K separation from 4 to 6 GeV/c requires σθ ~ 1 mrad (vs 2.4 in BaBar – a 58% reduction).
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Improving the θc resolution
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Example 1 – DIRC and SoLID „as is“
Z. Zhao
• Illustrates the maximum coverage of the DIRC bars
• In reality it would be preferable to increase the DIRC radius leaving more room for
– polarized targets
– e/π Cherenkov (blue)
• Thinner and longer calorimeter in barrel would be preferable
– reoptimization of GEMs
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Example 2 – DIRC partially retracted
Z. Zhao
• Illustrates the DIRC in maximally retracted position
– Optimization of e/π Cherenkov and calorimeter would give more coverage
• Inner radius adjusted to 1 m (80% azimuthal coverage)
– Plenty of space for He target
• Cryotargets and longitudinally polarized target can be placed just inside the solenoid
– PID up to 90° in lab frame!
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Summary
Adding the BaBar DIRC to SoLID open new physics opportunities Adding the BaBar DIRC to SoLID open new physics opportunities
Re-using a very expensive detector makes SoLID more appealingRe-using a very expensive detector makes SoLID more appealing
• High-pT SIDIS, exclusive reactions, spectroscopy
Need to think in detail about integration of the DIRC with SoLIDNeed to think in detail about integration of the DIRC with SoLID
• JLab could become a center for imaging Cherenkov technology in the US
• SoLID could become the basis for the development of a future EIC detector
• Could invite expert from SLAC for collaboration meeting in February
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Backup
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BaBar
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GlueX detector
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BCAL for GlueX