Minimum bias vertex distribution for 1998/99 e-p

data and reweighting routine

Measuring the minimum bias vertex distribution.

Ricardo Gonçalo, 21/3/2000

Fitting the vertex distribution.

Tests of the routine...Use VTXZCORR version 6.3 now available, and send comments.

Problems with old reweighting.

21-3-2000 Vertex reweighting for 98/99 e- data

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Method to measure a Minimum Bias Vertex Distribution

(A. Quadt & O. Ruske, ZN 98-36)

• Divide the CTD into three overlapping regions.

• Apply cuts to Neutral Current events in these regions. Cuts are based on geometry of CTD/CAL to have constant efficiency in each region.

• Measure e with CAL hit and optimum h with CTD.

Z (cm) Ee,min (GeV) E-Pz (GeV) rad,max hadronic

Region 1 [-100, -40] 16 35 - 65 2.65 0.5 – 1.57Region 2 [-50, 50] 18 35 - 65 2.81 0.85 – 2.24Region 3 [40, 100] 15 35 - 65 2.89 1.57 – 2.63

21-3-2000 Vertex reweighting for 98/99 e- data

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Problems with old reweighting:

Q2 range in MC sample

Problem in normalization of regions

Bias in regions 1 and 3 (RCAL/FCAL)

Bias in Wodarczyk’s method for Z > 50 cm

21-3-2000 Vertex reweighting for 98/99 e- data

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Changes to old method

In reg. 2 and 3 e had to be raised to match MC Q2 range + in reg. 3 e>2.69 to eliminate bias (dead material?) h was raised to have more stereo hits in optimum hadronic tracks

Regions normalised with 1/Eff; Eff calculated using flat vertex MC

21-3-2000 Vertex reweighting for 98/99 e- data

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Independent minimum bias method used for tests

(M. Wodarzcyk)

• Guarantee that there are always good tracks: either electron or hadrons.

e

h Ee E-pZ

90°-151.8° 27.5°-90° > 10 GeV 35-65 GeV

Problem: Not using electron seed vertex low efficiency for Z > 50 cm (hadronic tracks)

21-3-2000 Vertex reweighting for 98/99 e- data

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Efficiency determination with flat vertex MC

Good enough to get vertex distribution

More flat vertex Monte Carlo on the way

Still some bias in region 1 ?

21-3-2000 Vertex reweighting for 98/99 e- data

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Fit to data vertex distribution

2/ndf = 88.7/73 …not bad !

Fitted 5 gaussians to 98/99 data min. bias vertex distribution

Satellite pairs is constrained but not distance from main peak

Neglected Z<-88cm and Z>82cm in fit but points still used to get reweighting factors

Shapes of 98 MC generated vertex and 98/99 data min. bias vertex

21-3-2000 Vertex reweighting for 98/99 e- data

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Comparison with Wodarczyk’s method

Good agreement (except for Z < -85 cm). For Z>50 cm Wodarczyk’s points should not be taken into account.

For -50<Z<-40 two methods are now within 2 or better.

21-3-2000 Vertex reweighting for 98/99 e- data

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Reweighting routine VtxZCorr version 6.3

• Can be used to reweight distributions found in 1998/99 Monte Carlo generated with 1997 vertex distribution.

VtxZCorr63(zvertex,toyear,weight,errcode)

Input:

zvertex Z coordinate of “true” vertex of the generated event.

toyear year of data taking to which the MC is being reweighted (1998, 1999 or 9899).

Output:

weight statistical weight of the event in the distributions.

errcode 0 means OK, 1 means Error.

21-3-2000 Vertex reweighting for 98/99 e- data

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Chris test of the reweighting with SFEW cuts

Essentially OK, but MC overshoots data for Z<-60 cm and Z>70 cm

21-3-2000 Vertex reweighting for 98/99 e- data

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Comparison of reweighted/unreweighted

MC to 98/99 data in bins of Z - Q2DA

21-3-2000 Vertex reweighting for 98/99 e- data

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Comparison of reweighted/unreweighted MC

to 98/99 data in bins of Z - e

Points at high e low Q2 lower Q2 MC needed?

Test best done with MC generated with new distribution

21-3-2000 Vertex reweighting for 98/99 e- data

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Fits to X and Y minimum bias vertex distributions

•X and Y vertex obtained from same selection as Z vertex.

• Normalization between regions as for the Z vertex

X vertex: mean = -0.0243 0.0005 cm

= 0.1192 0.0005 cm

Y vertex: mean = 0.0448 0.0004 cm

= 0.0899 0.0003 cm