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GlueX Luminosity Limits

GlueX Collaboration Meeting, Newport News, May 8-10, 2008. GlueX Luminosity Limits. Richard Jones, University of Connecticut. Design luminosity Physics possibilities at higher luminosities Limiting factors in current design. Design Luminosity.

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GlueX Luminosity Limits

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  1. GlueX Collaboration Meeting, Newport News, May 8-10, 2008 GlueX Luminosity Limits Richard Jones, University of Connecticut • Design luminosity • Physics possibilities at higher luminosities • Limiting factors in current design

  2. Design Luminosity • Goal – produce sufficient samples of exclusive reations to be systematics-limited (maximum sensitivity to weak exotic waves) in amplitude analysis for key channels. • Translation – when that occurs depends on the final state, ie. specific backgrounds, PID demands, … • Rule of thumb: 107 events is sufficient for a decent PWA • Consider a hypothetical case: s = 50 nb BR = 30% e = 25% GlueX Collaboration Meeting, Newport News, May 8-10, 2008

  3. Design Luminosity • At Ibeam = 107g/s, it would take 57 khr (~ 20 years) to collect these statistics. • At Ibeam = 108g/s, it would take 6 khr (~ 2 years) to collect these statistics. • Result: 108g/s is sufficient to complete the hybrid spectroscopy program. But is it optimal ? g cm3 L = .071 x 30 cm x 6.0 1023x 10-33x Ibeam 1 g cm2 nb = 1.3 10-9 nb-1x Ibeam GlueX Collaboration Meeting, Newport News, May 8-10, 2008

  4. Design Luminosity • Define: tagger figure of merit • Factor that rescales the amount of run time needed to reach a given level of statistical error in a tagged histogram. • Reference for FOM shown is the GlueX tagged beam under nominal conditions at 9 GeV, but with no mistags. • Assumes detector identifies correct beam bucket 100% of the time. • Shows some gains up to 3 108 Hz. • Gains are only about 25% for factor 3 in backgrounds. GlueX Collaboration Meeting, Newport News, May 8-10, 2008

  5. Design Luminosity • For 25% more statistics, what do we lose? • x3 radiation damage in FCal • x3 accidentals in the TOF and Start • x3 pileup in the FDC, extra tracks, etc. • x3 in channel count in the microscope – $$$ • x3 in radiator thickness – reduced polarization GlueX Collaboration Meeting, Newport News, May 8-10, 2008

  6. Design Luminosity • If this argument was not made before, what was the basis of the design goal of 108g/s? • the intuitive criterion of 50% accidental tags • evidence from Monte Carlo simulation that detector backgrounds are going to preclude higher luminosities • FCal radiation damage – already an issue at 108 • TOF occupancy – within a factor of 3-5 of ceiling • FDC pileup and extra tracks – within factor of 3-5 GlueX Collaboration Meeting, Newport News, May 8-10, 2008

  7. Physics at Higher Luminosity • What physics might make this interesting? • inverse DVCS – looks feasible • threshold J/Y – statistically difficult • Cascade baryons – needs kaon PID GlueX Collaboration Meeting, Newport News, May 8-10, 2008

  8. Beam Limiting Factors • Tagging near the end-point • no polarization • no significant collimation • amorphous radiator – factor 100 more luminosity available (if untagged) • current tagger design has full coverage over 9-11.4 GeV, designed to run up to 50 MHz / GeV. • at 50 MHz / GeV in end-point region, detector backgrounds are comparable to nominal conditions with polarized beam at 108g/s. GlueX Collaboration Meeting, Newport News, May 8-10, 2008

  9. Detector Limiting Factors • FCal radiation damage • Inner blocks could be shielded, giving up low-angle g acceptance, ok for some physics. • FTOF occupancy • ditto. • FDC pile-up – will be ultimate limiting factor. • essential for just about any physics • no effective means to shield them GlueX Collaboration Meeting, Newport News, May 8-10, 2008

  10. Conclusions • Design luminosity is optimized for carrying out the hybrid spectroscopy program. • Nominal high-intensity running conditions are consistent with tagging at 50 MHz / GeV at the end-point. • The photon source will produce as much intensity as the experiment can handle in any scenario. • With a dedicated end-point tagger, one can tag effectively up to 250 MHz, provided the detector can trigger. • With 250 MHz on 11 < Eg < 12 GeV, detector background would be x5 nominal, probably an upper limit. • FDC pile-up will be the limiting factor – how to estimate it? GlueX Collaboration Meeting, Newport News, May 8-10, 2008

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