Triggering on ISR Events Nicolas Berger BaBar Online/DAQ/Trigger Workshop December 2 nd, 2004

ISR Signal Look for events with –high-E photon (E* = GeV) –Recoiling hadronic system (charged or neutral) Produce qq continuum and 1 -- resonances (  …) Use s’ = inv. mass squared of Had system as reference

BG Filter Improvements 2 New filters in 2003 reprocessing: BGFIsr: Select ISR events –Require cluster with E*>2.5 GeV, < cos(  *)< 0.93 and one of: –1 track E/p 600 MeV/c OR –2 tracks, E/p 250 MeV/c OR –2 clusters, E > 100 MeV –Veto if tracks with E/p > 0.8 and p*>4 GeV/c –Veto on  topologies BGFRadTwoProng: Unbiased 2-prong sample for  efficiency studies. –2 tracks with p* > 250 MeV –Missing p* > 2 GeV, Pointing in EMC acceptance –Missing M < 2 GeV.

BG Filter Improvements BG Filter efficiency vs. s’ for different filter configurations, on  0   +  - MC Denominator = fiducial events BGFIsr gives significant improvement Only BGFMultiHadron with BGFNeutralHadron with BGFTau with BGFTwoProngwith BGFIsr  s’ [GeV] Efficiency

Trigger/Filter Overall Performance We use: – L3 Physics = (L3OutDch || L3OutEmc) – MH = BGFMultiHadron – NH = BGFNeutralHadron – ISR = BGFIsr –  = BGFPhiGamma Denominator = Events with >0 clusters with –E* > 3 GeV –|cos(  *)|<0.95 Filter LevelEff (%) L L399.5 L3 Physics99.4 BGF97.2 MH, NH, ISR,  94.4 MH, NH, ISR93.7 MH, ISR93.0 ISR90.1

Trigger/Filter Overall Performance Events Passing: L1 L3 L3 Physics BGF MultiHad, NeutralHad, ISR and  MultiHad, NeutralHad and ISR MultiHad, ISR ISR  s’ [GeV]

L1 Line Breakdown  s’ [GeV] +

L3 Breakdown  s’ [GeV] High L3OutEmc efficiency due to auxiliary clusters caused by  interaction in EMC

0  +-0  +- Filter LevelEff (%) L L398.9 L3 Physics98.9 BGF97.4 MH, NH, ISR,  90.7 MH, NH, ISR90.2 MH, ISR90.2 ISR89.6  s’ [GeV] BGFPhiGamma designed to pick up  K + K - but also works for low-mass    

 0   +  - Issue 1: Close Tracks Fails L1 Fails L3 (2 L3 tracks but misreconstructed)

 0   +  - Issue 2: Pion showers Fails BGF Doesn’t fire BGFIsr due to Bhabha veto

 0   +  - Issue 3: Interactions Fails L3, No IP tracks (We probably don’t want this event anyway!)

  K0SK0L  K0SK0L Filter LevelEff (%) L L397.3 L3 Physics96.0 BGF71.8 MH, NH, ISR,  61.6 MH, NH, ISR56.5 MH, ISR56.3 ISR56.0 Fails L3 Accounts for almost all of the overall efficiency dip at  mass

  e+e-  e+e- Filter LevelEff (%) L L399.6 L3 Physics99.5 BGF57.4 MH, NH, ISR,  9.5 MH, NH, ISR9.5 MH, ISR9.1 ISR7.8 Almost completely removed by Bhabha Vetos Accounts for most of the dip in efficiency at  mass.

Break-up by N GoodTracksLoose : N GTL =0 Filter LevelEff (%) L199.0 L394.0 L3 Physics93.6 BGF58.4 MH, NH, ISR,  48.5 MH, NH, ISR48.5 MH, ISR47.5 ISR47.5  s’ [GeV] BGF dominated by BGFIsr, requires 2 mips Low eff. At low s’, but not clear how useful these events are anyways.

Break-up by N GTL : N GTL =1 Filter LevelEff (%) L L398.0 L3 Physics97.9 BGF88.8 MH, NH, ISR,  86.3 MH, NH, ISR86.2 MH, ISR84.1 ISR84.0  s’ [GeV]

Break-up by N GTL : N GTL =2 Filter LevelEff (%) L L399.5 L3 Physics99.5 BGF98.7 MH, NH, ISR,  93.1 MH, NH, ISR91.5 MH, ISR90.4 ISR90.2  s’ [GeV] BGFPhiGamma efficient on low-mass events for both  KK and 

Break-up by N GTL : N GTL =3 Filter LevelEff (%) L1100 L L3 Physics99.93 BGF99.7 MH, NH, ISR,  99.5 MH, NH, ISR99.5 MH, ISR99.4 ISR92.5  s’ [GeV]

Break-up by N GTL : N GTL >4 Filter LevelEff (%) L1100 L L3 Physics99.99 BGF99.97 MH, NH, ISR,  MH, NH, ISR99.96 MH, ISR99.96 ISR94,4  s’ [GeV]

Conclusions ISR events are a challenge for the trigger The BaBar trigger performs well –Most of the events useful for physics are selected –For L1 and L3, benefit of the “inclusive” selection approach. –For BGF, more problems originally but modifications always possible (if willing to wait ~6 months!)