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Radiative Bhabhas in the IFR
Nick Blount David Strom

Babar Collaboration Meeting December 7, 2004


Table of Contents
3. Software used 4. Predicted Bhabha rate 5. Plots of radial distribution of hits in forward endcap, with fits 6. Back of the envelope calculation of neutron hits in the IFR 7. Conclusions 8. Future Plans
Babar Collaboration Meeting December 7, 2004


Software and Runs Used
· Release: 15.7.1 · Package: PepBkgMon V00-00-02 · Simulation: Bhabha_generic_1deg.tcl
­ Uses Bhwide event generator ­ For angles greater than 1 degree in Bhabha rest frame

· Data: Run 44218 (January background run)
Babar Collaboration Meeting December 7, 2004


Predicted Bhabha rate
· The Born level differential cross section for Bhabhas is[1]: ds/dW=a2/2s [(1+cos4 q/2 )/sin4 q/2-2(cos4 q/2 / sin2 q/2 )+(1+cos2 q/2 )/2] · For small angles, this is approximately ds/dq=32pa2/sq3, for a 1/q3 distribution · Using a=1/137 and s=10.582, ds/dq=18.6/q3nb · This gives a Bhabha rate of 29kHz for q>10 at 1033cm2

Babar Collaboration Meeting December 7, 2004


Data Cont.: Radial Plots

· · · · ·

Note: Bhwide is a wide angle Bhabha simulator and is probably inaccurate for angles less than 10 degrees No noise: with noise added the noise dominates the hits from the Bhabhas Simulation scaled assuming 29kHz rate Data: Rate=10.113/Theta3 Chisq=2.084 Simulation: Rate=5.383/Theta3 Chisq=1.483
Babar Collaboration Meeting December 7, 2004


Neutron Calculation
· Using 1 neutron/5GeV (from Monday MDI meeting), .14 Amps/hour lost in each beam, 1-2 MeV neutrons, the predicted rate of interactions in the 2mm of gas in an IFR layer is roughly 94kHz. · This is comparable to the noise rate in the IFR

Babar Collaboration Meeting December 7, 2004


Details and Conclusions
· Angular distribution of Bhabhas in the IFR looks reasonable · Comparison with data consistent with significant backgrounds from Bhabhas

Babar Collaboration Meeting December 7, 2004


To Do
· Migrate to Release 16, PepBkgMon V00-01-17 · Produce more noiseless Bhabha MC · Look into different event generators (Bhlumi, BbBrem, fix Bhwide small angle bug) · Re-run simulation with extended detector model · Start looking at predicted neutron rate from MC

Babar Collaboration Meeting December 7, 2004


Bibliography
1. Hep-ex 9910066v2

Babar Collaboration Meeting December 7, 2004


Homework Problem Details
· · · · · Beam loss: .2A each beam over 1.4 hours Turn Period: 7.336E-6 sec Beam Energies: LER 3.1, HER 9.0 Neutron rate: 1/5GeV Cross Sections for 1-2 MeV neutrons:
­ C=1.8b, Ar=1.3b, F=2.7b, H=3.3b

· Gas: 65.5% Ar, 4.5% Isobutane, 30.0% Freon · Intermediate Numbers: · Beam loses 2.2E10GeV/s. Interaction Length=10.4g/cm2=3940cm
Babar Collaboration Meeting December 7, 2004