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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