) motivation, CKM mass resolution ) SELEX, three aspects ) radius distributions & tails

Radial Tail Resolution in the SELEX RICH

A. Morelos, P.Cooper, J.Mata, J.Engelfried

Using a 7 Million data sample of 600 GeV/c single track pion events, where the pion track is reconstructed upstream and downstream the SELEX RICH, a circle fit on the phototubes ring is performed. From the fit we get three parameters, the radius, and the center coordinates plus their statistical errors. Applying modest cuts on track and circle fit uncertainties we build the radius histogram distribution and count

the tail the events that fall outside 5 from the =1 radius, giving a fraction of 4x10-5 events outside the gaussian tails. This control of events

stablish the ability of using the RICH as velocity spectrometers for high precession search of the K+ + anti() experiments like CKM.

) motivation, CKM mass resolution

) SELEX, three aspects

) radius distributions & tails

) a look into simulation

) summary

outline

PNN1 PNN2

Número de planos prendidos Npl

500

4300

Beam Transition Radiation Detector BTRD

Ring Imaging Cherenkov

beam event at 600 GeV/c

Vector Drift Chambers VDC

Downstream track

M1 M2 RICH

Vertex

Vdc-a Vdc-b

Beam

Track existence

Select PMT´s around +- 1.27 cmFrom SELEX standard radius

ring fitsoft cuts on center and radius uncertainties

Mean radius dispersion by run

Dispersion 0.009 cm

radius 0.15 cm single track 0.18 cm multi-track

Single hit 0.55 0.47 cmin agreement

no track uncertainty

by run

Ring Radius distribution

upstream track existence dowstream track existence

5 tail (CKM < 3 x10-5)

upstream existence downstream existence

3 tail difference

A model for decay events in RICH

blindRich

blinddownstream existence

Events are left in the tails

“ C “ type: either close or opens the radius

A look into random PMT simulation

no PMT efficiencyno individual noise

“ C “ event like events

maximum angle between two consecutive PMT´s per event

( radians )

data broadness: improve lowering noise and better efficiency

radianradian

Summary

) downstream track existence eliminated decay events which were in the tail region

) With 5 tail analysis we are in a region of 3.9 x10-5 events, close to CKM requirements (less than 3 x10-5 )

) Still: a completely stand alone algorithm, work is being done, and include noise and efficiency per tube in simulation