ESTIMATING THE 6m TAGGERACCEPTANCE

Thomas Schörner-Sadenius, UHH

Hamburg, DESY10 February 2006

                

Sorry for not being around – cought some funny form of flue …

And thanks again to Tim forpresenting things I had not time

to properly explain to him.

DESY, 10 February 2006 TSS: 6m Tagger 2

REPETITIONCorrelation of 6mT x position and spectrometer energy

Use correlation of x position in tagger as taken from rather roughtagger reconstruction and nicely calibrated spectrometer energymeasurement to take into account all dipole effects.

Assuming for this more or less pure Bethe-Heitler (BH) sample with electrons under 180o (Tim on validity of this assumption?).

Idea

Reasonable x range on tagger surface BH acceptance 5.4-9.6 GeV.Acceptance

This line foracceptance(tagger notwell calibra-ted?)

Next steps Photoproduction events with angle to beam axis, quadrupole effects.

DESY, 10 February 2006 TSS: 6m Tagger 3

ANGLES WITH Z AXISlead to shifts in x,y position on surface

No change in energy acceptance – electron slowly falls out of tagger surface effect on acceptance via Q2.

Idea for y

Idea for x Change in x position also leads to varying energy acceptance.

Result for x

tanx

energyBethe-Heitler

acceptance (seeslide before)

Change in acceptanceindicated by 2 red lines.

Calculate Q2 from anglesand calculate acceptanceas function of Q2 and E. but quadrupole GI?

DESY, 10 February 2006 TSS: 6m Tagger 4

EFFECT OF GI QUADRUPOLEUse matrix formalism from linear opticsQuadrupole

Matrix pg

xx

xx

Mxx

GI

,cossin

sincos0

0

0

0

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).

DESY, 10 February 2006 TSS: 6m Tagger 5

RESULTTagger acceptance as function of Q2 and E

log10(Q2/GeV2)

E/GeVacceptance

DESY, 10 February 2006 TSS: 6m Tagger 6

RESULTdifferent binnings in Q2, E

log10(Q2/GeV2)

E/GeV

acceptance 1-acceptance

Acceptance can be providedas function of Q2 and E in

histogram, text file, …

DESY, 10 February 2006 TSS: 6m Tagger 7

PROJECTIONSon Q2, E axis – limited use in this analysis

Problem is that initial sample not really physical – only single bins in Q2 and Eplane 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 forQ2 distribution – naively expected to be flat for some range …

E/GeVlog10(Q2/GeV2)

a.u.

DESY, 10 February 2006 TSS: 6m Tagger 8

RESULTING VALUESin histogram file

In /afs/desy.de/user/s/schorner/public/final.hbook

• 111 acceptance in finest binning in log10Q2 (80 bins from –10 to -1)and E (22 bins from 4-15 GeV)

• 44110 acceptance in coarser bins (Q2: 36 from –9 to –1, E: 22 from 4 to 15 GeV)

• 44112 1-acceptance in same bins

• 74110 acceptance in still coarser bins (Q2: 24 from –9 to –1, E: 11 from 4 to 15 GeV)

• 74112 1-acceptance in same bins

• 84110 acceptance in even still coarser bins (Q2: 18 from –9 to –1, E: 11 from 4 to 15 GeV)

• 84112 1-acceptance in same bins

DESY, 10 February 2006 TSS: 6m Tagger 9

CROSS-CHECKUsing full matrix formalism for all magnet elements

0

012 xx

MMMMxx

DriftGGDriftGI

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.

DESY, 10 February 2006 TSS: 6m Tagger 10

SUMMARYuncertainties, todos, …• Wait for Tim’s result with sufficient statistics and reasonable Q2 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).