Boogert and Miller; Luminosity Measurement questions; calorimeter-related. 1 Luminosity Measurement questions; calorimeter-related Stewart Takashi Boogert and David John Miller Department of Physics and Astronomy University College London 1. First order optimism (duplicates MDI session talk). 2. Forward tracking plus endcap calorimetry. 3. Smaller angle measurements. 4. Work planned.

Boogert and Miller; Luminosity Measurement questions; calorimeter-related. 2 First order studies* suggested can be measured to the required energy precision: ~1 in 10 3 for top-antitop threshold ~1 in 10 4 for WW threshold On that basis we have advertised  * Frary and Miller; DESY A, Y.Kurihara, talk at Munich workshop D.Cinabro, LCWS Sitges, proceedings p249, K.Moenig, LC-PHSM TESLA; 10s of MeV (Martinez, St. Malo) (TESLA TDR) First order optimism

Boogert and Miller; Luminosity Measurement questions; calorimeter-related. 3 Sources of Energy Spread Beamstrahlung Initial State Radiation BHWIDE Beamstrahlung CIRCE Machine spread  s/2E b  TESLA TDR parameters, with some angle cuts, 350 GeV zoom To make polarised positrons in TESLA, get  p/p ~ 0.15% for e -, < 0.05% for e+ (what is NLC spread?). Maybe tolerable for top threshold, if spread can be well measured. For W mass at  s = 161 GeV How to unfold 1 in 10 4 from spread of 1.5 in 10 3 ? Alternative e + source? Spike gives mass sensit- ivity

Boogert and Miller; Luminosity Measurement questions; calorimeter-related. 4 Reference process should: 1. be based on real events, to truly represent the physics samples. 2. have better statistics than the physics channels. 3. have energy resolution to match the mass resolution required. Measurement of Bhabha acollinearity in the endcap region ( milliradians) appears to meet all 3 criteria. Nothing else does (  rate ~ physics rates; Z  not so precise; etc. etc.) Basic Principle Bhabha acollinearity AA  Where but (we discuss questions about how beam effects can louse-up correlation between  A and  s in MDI session) p-p- p+p+, small  A

Boogert and Miller; Luminosity Measurement questions; calorimeter-related. 5 For small  A and Gaussian errors,, so with fixed angular resolution the error on  s blows up at small Bhabha scattering angle . But the Bhabha rate for millirads is already > 400 times the  rate. And above ~100 milliradians there is good forward-tracking (7 layers of pixels/Si in TDR) with calorimetric backing (CALICE endcap) Endcap best? TPC HCAL CALICE

Boogert and Miller; Luminosity Measurement questions; calorimeter-related. 6 For and against endcap TDR; resolution on  A from forward tracker, mrad.  degrees ~.25mrad CALICE in TDR (endcaps as good?) Is tracker angular resolution good enough? ~ 0.02 mrad (but/sin  for ) - fine for top threshold; - just OK for WW? But forward trackers are never 100% efficient. Rely on calorimeter to measure efficiency of tracker. Is calorimeter angular res- olution good enough? - just OK for top - not for WW

Boogert and Miller; Luminosity Measurement questions; calorimeter-related. 7 Need FTD plus CALICE Calorimeter, assumed to have 100% efficiency for high energy electrons. It surveys efficiency of tracker. Tracker has the resolution needed for acollinearity, but needs calorimeter to measure its efficiency. Tracker must have good internal survey, to ~ 25 microns over ~3 metres. Clean electron tracks used to survey calorimeter position scale (c.f. OPAL). BUT TPC cage and ends make electrons shower - may move calorimeter cluster position, spoil purely calorimetric acollinearity measurement (study starting)

Boogert and Miller; Luminosity Measurement questions; calorimeter-related. 8 What about LAT and LCAL? LAT is SiW; ~28 to ~83 millirad. (Zeuthen et al studying potential) Similar angular resolution to CALICE? No TPC structures in front to shower, but /sin  gives worse. Very high rates (needed at GigaZ). Theoretical Bhabha cross sections more reliable at small angles than in endcap. LAT favoured for absolute luminosity measurement (c.f. LEP and SLC). LCAL may be PbWO; ~5 to ~27 millirad. Serious backgrounds from pairs and gammas. Not a precision luminometer, but good instantaneous rates for tuning. Background asymmetries reflect bunch misalignment.

Boogert and Miller; Luminosity Measurement questions; calorimeter-related. 9 Work Planned A. Simulate realistic data samples of Bhabhas measured in forward tracker and endcap calorimeters (including machine pathologies mentioned in MDI talk). B. Reconstruct, and extract measured luminosity spectra (using unfolding - c.f. Blair and Poirer?). C. Compare with Monte Carlo truth from Guinea-Pig. D. Investigate effects on m t and M W. Please tell us what else we should be worrying about!