Minimum bias vertex distribution for 1998/99 e - p data and reweighting routine é Measuring the minimum bias vertex distribution. Ricardo Gonçalo, 21/3/2000 éFitting the vertex distribution. éTests of the routine...Use VTXZCORR version 6.3 now available, and send comments. éProblems with old reweighting.

Vertex reweighting for 98/99 e- data 2 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.

Vertex reweighting for 98/99 e- data 3 Problems with old reweighting:  Q 2 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

Vertex reweighting for 98/99 e- data 4 Changes to old method  In reg. 2 and 3  e had to be raised to match MC Q 2 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

Vertex reweighting for 98/99 e- data 5 Independent minimum bias method used for tests (M. Wodarzcyk) Guarantee that there are always good tracks: either electron or hadrons.    Problem: Not using electron seed vertex  low efficiency for Z > 50 cm (hadronic tracks)

Vertex reweighting for 98/99 e- data 6 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 ?

Vertex reweighting for 98/99 e- data 7 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 82cm in fit but points still used to get reweighting factors Shapes of 98 MC generated vertex and 98/99 data min. bias vertex

Vertex reweighting for 98/99 e- data 8 Comparison with Wodarczyk’s method Good agreement (except 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.

Vertex reweighting for 98/99 e- data 9 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.

Vertex reweighting for 98/99 e- data 10 Chris test of the reweighting with SFEW cuts Essentially OK, but MC overshoots data for Z 70 cm

Vertex reweighting for 98/99 e- data 11  Comparison of reweighted/unreweighted MC to 98/99 data in bins of Z - Q 2 DA

Vertex reweighting for 98/99 e- data 12  Comparison of reweighted/unreweighted MC to 98/99 data in bins of Z -  e Points at high  e  low Q 2  lower Q 2 MC needed? Test best done with MC generated with new distribution

Vertex reweighting for 98/99 e- data 13 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 =  cm  =  cm Y vertex: mean =  cm  =  cm