ESTIMATING THE 6m TAGGERACCEPTANCE

Thomas Schörner-Sadenius, UHH

ZEUS Collaboration meetingDESY, 27 February 2006

                

DESY, 27 February 2006 TSS: 6m Tagger 2

REPETITIONCorrelation 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 foracceptance(tagger notwell calibra-ted?)

e+ vs e- Rather large shift in acceptance (next slide).

DESY, 27 February 2006 TSS: 6m Tagger 3

FIT EXAMPLE

DESY, 27 February 2006 TSS: 6m Tagger 4

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 Q2 and E’.

DESY, 27 February 2006 TSS: 6m Tagger 5

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.

Y angle

X angle Change in x position also leads to varying energy acceptance.

Result for x

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

e– e+

DESY, 27 February 2006 TSS: 6m Tagger 6

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 (next slide).

DESY, 27 February 2006 TSS: 6m Tagger 7

RESULTTagger acceptance as function of Q2 and E

log10(Q2/GeV2)

E’/GeVAcceptance e–

log10(Q2/GeV2)

E’/GeVAcceptance 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).

DESY, 27 February 2006 TSS: 6m Tagger 8

COMPARISON with PRC proposal

Again Effect of different spectrometerenergy spectra visible.

DESY, 27 February 2006 TSS: 6m Tagger 9

RESULTING VALUESin histogram files

/afs/desy.de/user/s/schorner/public/final.eplus.hbook/afs/desy.de/user/s/schorner/public/final.eplus.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, 27 February 2006 TSS: 6m Tagger 10

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.