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Trigger for Run 8 Rates, Yields, Backgrounds… Debasish Das Pibero Djawotho Manuel Calderon de la Barca Analysis Meeting BNL October 16, 2007

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Prospects for in Run 8 p+p –30 pb-1 sampled luminosity Run 6: 9.2 pb -1 sampled, S/B~ 1 : 2.31 Physics goals: –Improved yield (stat. error can go down by ~2) –pT spectrum? Needs Seff~80, or ~450 counts (S eff ~40 in |y|<0.5). dAu –minbias = 2.2 b. –rare processes: = pp x (2·197) –peak: L = 30x10 28 cm -2 s -1, rate = 660 kHz (pileup!!) –L Delivered: 120 nb -1 –L Sampled: Fast Detectors : 60 nb -1 Slow Detectors : 30 nb -1 –Physics goals: Yield, R dAu pT integrated Needs counts in |y|<0.5

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(Final?) Numbers from 2006 Trig ID S = 175 B = 405 S eff = 31.1 S eff = 5.58 ε ϒ = dy=2.0 Ldt = pb-1 BR × dy/dσ = pb –Note: signal above in dy=2 –in dy=1; S=87.5, S eff = 16

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Upsilon Estimates for Run 8 What can we get? BR x d /dy = GeV. Efficiency : Geometrical Acceptance: 26% L0 Efficiency : 93% L2 Efficiency : 86% Offline electron pair efficiency : 47% –Total =9.4%, use ~10% Yields: –pp: 30 pb -1 x 91 pb x 10% = 273 ’s –dAu: 60 nb -1 x 91 pb x (2·197) 0.95 x 10% = 160 ’s With how much bandwidth? pp Rejection – Run 6: 10 Hz / 550kHz rejection factor : –Trigger rate Run 8 pp : 1.5 MHz/55000 = 27 Hz peak Au Au Run 7 : 10 Hz / 25kHz ( =235) –rejection factor : 2500 Assumption: rejection decreases linearly with increasing dAu = 17 –estimated rejection factor : –Trigger rate Run 8 dAu : 660 kHz/51000 = 13 Hz peak

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Options to decrease rate Focus on p+p case (27 Hz is the most bandwidth requested!) –Reductions in p+p can be carried over to d+Au case. Raising Cluster Energy of High-energy electron –Advantage: Rate goes down quickly with higher E. –Disadvantage: So does the efficiency… Hits low-pt hardest. Cutting tighter on opening angle –Advantage: efficiency does not drop dramatically –Disadvantage: Rate does not decrease dramatically either Hits high-pt hardest Vertex cuts? –Almost the same as a prescale. –Some Differences: For previous runs, tight vertex could help with Brems. of electrons With low material in 2008, Brems. not so much of an issue. It can still help with analysis offline, tracks will be close to center, many hits.

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Upsilon L2 parameters Algorithm ParameterSet ISet IISet III i0 L0 ADC threshold??? i1 L2 clustering seed threshold i2 CTB macthing000 i3 Use ZDC vertex z information000 i4 Tower per EMC cluster333 f0 Higher energy electron threshold44.55 f1 Lower energy electron threshold f2 Minimum invariant mass66.57 f3 Maximum invariant mass15 f4 Maximum cos(theta)

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Raising “f0” (E of leading-e) For 4

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Estimate Signal Reduction Plot is for Et of tower at L0 Cluster energy at L2 should show similar dependence. Take value at 4.5 GeV to be baseline (~ threshold used in Run VI and Run VII) Calculate reduction in signal relative to 4.5 GeV. Calculate S eff = S/(2*(B/S)+1) to compare.

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Estimate Reduction in Rate Rejection depends exponentially with Et –See blue lines Slope is independent of multiplicity –Minbias & Central Au+Au have same slope Use fit to rejection to estimate rate reduction Caveat: –Rate reduction does not equal offline background. –Rate: photons and electron combinations –Offline background: electron combinations –Assume offline background also decreases, but with half the slope.

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E threshold, Rate Reduction EEff.Rej.Rate Red. RateS red.B red.S eff S eff %27 Hz100% %12 Hz80%71% %6 Hz57%50% %4 Hz39%35%

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pt vs Cos( ) With good cos( ) determination, at cos(q) 6 GeV. Issue is resolution.

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From 2006 Offline data Nominal cut has been at cos( )=0 S eff drops linearly with cos( ) –How much tighter can we live with?

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cos( ), Rate Reduction cos( ) SBRate Red. Rate S eff %27 Hz %25.4 Hz %23 Hz (??)2281%21.9 Hz6.2 (??) %17.8 Hz5.5

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Other possibilities? Vertex cut? –VPD needed, available in run 8? –Run 8 is low material, so no issue with Bremsstrahlung –Slightly preferable to prescale, EMC design has projective geometry to z=0 –Better E resolution for single tower. –Caveat: normalization needs a mb trigger (prescaled) with identical vertex cut.

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Conclusions Raising E threshold on high energy cluster. –f0=5.5 GeV, rate goes to 12 Hz S eff ~6.5, S eff ~42.7 in |y|<0.5 Can get enough counts for pt spectrum? –More reduction is not desirable because impacts low pT. cos( )~-0.3 –Additional reduction possible (~10-20% rate reduction) –Impacts high-pT part. Run 8 trigger can work with slightly tighter cuts.

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