Increasing Field Integralbetween Velo and TT

S. Blusk

Sept 02, 2009

SU Group Meeting

Introduction• Recall, for the Upgrade, we will read out the full detector at

40 MHz.• Need to quickly reject uninteresting events and select B

events.– MinBias:B event ~ 200:1, but can exploit:

• “Large” B mass large q2 B tracks have larger pT, on average

• Tracks from Min Bias events peak at lower pT, but do have tails out to larger pT.

– Exploit in trigger by requiring N tracks at “high” pT.(cut value to be tuned, but roughly expect ~ 1-2 GeV)

– Also, require that they do not point back to one of the primary interactions. (only want to do this check for a small subset of the tracks)

– Goal: To use TT to get a quick estimate of each particle’s pT. Aim for 10% resolution, in reNeed sufficient

TT in LHCb

Four layers of silicon X1, U(+5o), V(-5o), X2 ~200 um pitch: hit~50 m

A view from inside the magnet

TTBeampipe (10 mrad)

Bellows Flanges

IT-1

OT1

Efficiency “Turn on” for pT>1 GeVvs pT resolution

1/p / (1/p) = 10%

1/p / (1/p) = 20%

1/p / (1/p) = 30%

E.g:With ~10% resolution in1/pT, almost no trackswith pT<0.7-0.8 GeV would pass trigger.

With 30% resolution,~6-7% of tracks at pT<0.5 GeV would be accepted.

67% have pT<0.5 GeV91% have pT<1 GeV 96% have pT<1.5 GeV

Min Bias at 5 TeV

Efficiency “Turn on” for pT>1.5 GeVvs pT resolution

E.g:With ~10% resolution in1/pT, almost no trackswith pT<1.0 GeV would pass trigger.

With 30% resolution,~2% of tracks at pT<0.5 GeV would be accepted.

Momentum Resolution for VeloTT tracks

• Run Standard MC (5 TeV)• Form VeloTT tracks from ALL VELO-3D tracks

– Default would only make VeloTT tracks with VELO 3D tracks that don’t make long tracks

• Shift Magnetic Field upstream by 50 cmand do the same.– Puts more field integral between Velo & TT

• We do the Kalman Track Fit– Assume that track fit can be done relatively fast, ala

the current HLT2 scheme with parameterized materialdescription.

Comparison of pT Resolutions

For comparison, long trackshave a resolution of 0.5%

By shifting the field by ~50 cmupstream, we get about a factorof 2 improvement in pT resolution.

10% resolution attainableby moving the magnet…

Issues

• If we were to move the magnet upstream,might lose some acceptance on outer edges– TT would be more “inside the magnet”– I think we can get adequate coverage though– If you’ve seen a silicon detector inserted into

the bore of CDF, CLEO… you know what “tight space” means!

Summary

• Reduce pT uncertainty by ~ 2X by moving magnet 50 cm upstream

• Other things to do:– Remove RICH-1 from “default” and “shifted”– Simulation at – 25 cm– Look at rejection power after pT cuts and IP

cuts at different luminosities.– …