1. ESTIMATING THE 6m TAGGER ACCEPTANCE Thomas Schörner-Sadenius, UHH ZEUS Collaboration meeting DESY, 27 February 2006

2. DESY, 27 February 2006TSS: 6m Tagger2 REPETITION Correlation of 6mT x position and spectrometer energy Use correlation of x position and spectrometer energy to take into account all dipole effects in the lepton’s path to the tagger.  Sample consists ~exclusively of Bethe-Heitler events. Idea Reasonable x range on tagger surface  BH acceptance 5.4-9.6 GeV. Acceptance This line for acceptance (tagger not well calibra- ted?) e + vs e - Rather large shift in acceptance (next slide).

3. DESY, 27 February 2006TSS: 6m Tagger3 FIT EXAMPLE

4. DESY, 27 February 2006TSS: 6m Tagger4 DIFFERENCES e + /e – seem to be rather large Test PRC proposal (R. Graciani) suggested smaller difference – 1.5 GeV versus 2.5 GeV at high tagger energies – 1 GeV versus 1.5 GeV at low tagger energies. PRC Apply method for runs with electrons and positrons  large difference in energy range visible.  will have big effect on tagger acceptance as function of Q 2 and E’.

5. DESY, 27 February 2006TSS: 6m Tagger5 ANGLES WITH Z AXIS lead to shifts in x,y position on surface No change in energy acceptance – electron slowly falls out of tagger surface  effect on acceptance via Q 2. Y angle X angle Change in x position also leads to varying energy acceptance. Result for x Calculate Q 2 from angles and calculate acceptance as function of Q 2 and E.  but quadrupole GI? e–e– e+e+

6. DESY, 27 February 2006TSS: 6m Tagger6 EFFECT OF GI QUADRUPOLE Use matrix formalism from linear optics Quadrupole Matrix With x,x’ position and tangens of angle to z axis, p momentum, g magnet strength (known). (this is for focusing plane, use hyperbolic functions in defocusing plane). GI magnet Focusing in y plane, defocusing in x, strength and position known  Calculate effect on position and thus on acceptance (next slide).

7. DESY, 27 February 2006TSS: 6m Tagger7 RESULT Tagger acceptance as function of Q 2 and E log 10 (Q 2 /GeV 2 ) E’/GeV Acceptance e – log 10 (Q 2 /GeV 2 ) E’/GeV Acceptance e + Desirable – Cross-check with newly implemented 6mtagger reconstruction. – Use of reconstruction in next Mozart release (now only offline). – Efficiency determination for electrons on tagger surface (Tim) (Estimate: almost 100% efficiency for large part of the acceptance).

8. DESY, 27 February 2006TSS: 6m Tagger8 COMPARISON with PRC proposal Again Effect of different spectrometer energy spectra visible.

9. DESY, 27 February 2006TSS: 6m Tagger9 RESULTING VALUES in histogram files /afs/desy.de/user/s/schorner/public/final.eplus.hbook 111 acceptance in finest binning in log 10 Q 2 (80 bins from –10 to -1) and E (22 bins from 4-15 GeV) 44110 acceptance in coarser bins (Q 2 : 36 from –9 to –1, E: 22 from 4 to 15 GeV) 44112 1-acceptance in same bins 74110 acceptance in still coarser bins (Q 2 : 24 from –9 to –1, E: 11 from 4 to 15 GeV) 741121-acceptance in same bins 84110 acceptance in even still coarser bins (Q 2 : 18 from –9 to –1, E: 11 from 4 to 15 GeV) 84112 1-acceptance in same bins

10. DESY, 27 February 2006TSS: 6m Tagger10 CROSS-CHECK Using full matrix formalism for all magnet elements Problem GG magnet designed for 30 GeV electrons. Our 5-10 GeV are no small deviation from this nominal value,  linear approximations don’t work  as effect we get large dependance on position of tagger wrt to beam line  not simply feasible. Approximately similar – but large uncertainties.