1. ESTIMATING THE 6m TAGGER ACCEPTANCE Thomas Schörner-Sadenius, UHH Hamburg, DESY 10 February 2006 Sorry for not being around – cought some funny form of flue … And thanks again to Tim for presenting things I had not time to properly explain to him.

2. DESY, 10 February 2006TSS: 6m Tagger2 REPETITION Correlation of 6mT x position and spectrometer energy Use correlation of x position in tagger as taken from rather rough tagger reconstruction and nicely calibrated spectrometer energy measurement to take into account all dipole effects.  Assuming for this more or less pure Bethe-Heitler (BH) sample with electrons under 180 o (Tim on validity of this assumption?). Idea Reasonable x range on tagger surface  BH acceptance 5.4-9.6 GeV. Acceptance This line for acceptance (tagger not well calibra- ted?) Next steps Photoproduction events with angle to beam axis, quadrupole effects.

3. DESY, 10 February 2006TSS: 6m Tagger3 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. Idea for y Idea for x Change in x position also leads to varying energy acceptance. Result for x tan  x energy Bethe-Heitler acceptance (see slide before) Change in acceptance indicated by 2 red lines. Calculate Q 2 from angles and calculate acceptance as function of Q 2 and E.  but quadrupole GI?

4. DESY, 10 February 2006TSS: 6m Tagger4 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. Result on next slide (veeery close to result shown WITHOUT quadrupole two weeks ago).

5. DESY, 10 February 2006TSS: 6m Tagger5 RESULT Tagger acceptance as function of Q 2 and E log 10 (Q 2 /GeV 2 ) E/GeV acceptance

6. DESY, 10 February 2006TSS: 6m Tagger6 RESULT different binnings in Q 2, E log 10 (Q 2 /GeV 2 ) E/GeV acceptance1-acceptance Acceptance can be provided as function of Q 2 and E in histogram, text file, …

7. DESY, 10 February 2006TSS: 6m Tagger7 PROJECTIONS on Q 2, E axis – limited use in this analysis Problem is that initial sample not really physical – only single bins in Q2 and E plane can be considered – but not the projections on the axes. (flatly generated distributions of E and tan  in ~arbitrarily limited regions). These projections only give feeling for behaviour of acceptance, especially for Q 2 distribution – naively expected to be flat for some range … E/GeVlog 10 (Q 2 /GeV 2 ) a.u.

8. DESY, 10 February 2006TSS: 6m Tagger8 RESULTING VALUES in histogram file In /afs/desy.de/user/s/schorner/public/final.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

9. DESY, 10 February 2006TSS: 6m Tagger9 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.

10. DESY, 10 February 2006TSS: 6m Tagger10 SUMMARY uncertainties, todos, … Wait for Tim’s result with sufficient statistics and reasonable Q 2 range  do both results agree (more or less)? In which format do the PILERS want the results? Some uncertainties: -- composition of sample to derive correlation between spectrometer energy and tagger x position -- active tagger surface – I was rather conservative – so it might be that the actual acceptance is systematically a bit larger … -- … (please see last talk two weeks ago).