triggering on isr events nicolas berger babar online/daq/trigger workshop december 2 nd, 2004
TRANSCRIPT
Triggering on ISR Events
Nicolas Berger
BaBar Online/DAQ/Trigger WorkshopDecember 2nd, 2004
ISR Signal• Look for events with
– high-E photon (E* = 3-5.3 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,
-0.75 < cos(*)< 0.93 and one of:– 1 track E/p < 0.7, p*>600 MeV/c OR– 2 tracks, E/p < 0.8, 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 BGFTwoProng with BGFIsr
s’ [GeV]
Eff
icie
ncy
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 Level Eff (%)
L1 99.97
L3 99.5
L3 Physics 99.4
BGF 97.2
MH, NH, ISR, 94.4
MH, NH, ISR 93.7
MH, ISR 93.0
ISR 90.1
Trigger/Filter Overall Performance
Events Passing:
L1L3L3 PhysicsBGFMultiHad, NeutralHad, ISR and MultiHad, NeutralHad and ISRMultiHad, ISRISR
s’ [GeV]
L1 Line Breakdown
s’ [GeV]
s’ [GeV]
+
L3 Breakdown
s’ [GeV]
s’ [GeV]
High L3OutEmc efficiency due to auxiliary clusters caused by interaction in EMC
0 +-
Filter Level Eff (%)
L1 99.96
L3 98.9
L3 Physics 98.9
BGF 97.4
MH, NH, ISR, 90.7
MH, NH, ISR 90.2
MH, ISR 90.2
ISR 89.6s’ [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!)
K0SK0
L
Filter Level Eff (%)
L1 99.97
L3 97.3
L3 Physics 96.0
BGF 71.8
MH, NH, ISR,
61.6
MH, NH, ISR 56.5
MH, ISR 56.3
ISR 56.0
Fails L3
Fails L3
Accounts for almost all of the overall efficiency dip at mass
e+e-
Filter Level Eff (%)
L1 99.95
L3 99.6
L3 Physics 99.5
BGF 57.4
MH, NH, ISR, 9.5
MH, NH, ISR 9.5
MH, ISR 9.1
ISR 7.8
• Almost completely removed by Bhabha Vetos
• Accounts for most of the dip in efficiency at mass.
Break-up by NGoodTracksLoose : NGTL=0
Filter Level Eff (%)
L1 99.0
L3 94.0
L3 Physics 93.6
BGF 58.4
MH, NH, ISR, 48.5
MH, NH, ISR 48.5
MH, ISR 47.5
ISR 47.5
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 NGTL : NGTL=1
Filter Level Eff (%)
L1 99.96
L3 98.0
L3 Physics 97.9
BGF 88.8
MH, NH, ISR, 86.3
MH, NH, ISR 86.2
MH, ISR 84.1
ISR 84.0
s’ [GeV]
Break-up by NGTL : NGTL=2
Filter Level Eff (%)
L1 99.99
L3 99.5
L3 Physics 99.5
BGF 98.7
MH, NH, ISR, 93.1
MH, NH, ISR 91.5
MH, ISR 90.4
ISR 90.2s’ [GeV]
BGFPhiGamma efficient on low-mass events for both KK and
Break-up by NGTL : NGTL=3
Filter Level Eff (%)
L1 100
L3 99.93
L3 Physics 99.93
BGF 99.7
MH, NH, ISR, 99.5
MH, NH, ISR 99.5
MH, ISR 99.4
ISR 92.5
s’ [GeV]
Break-up by NGTL : NGTL>4
Filter Level Eff (%)
L1 100
L3 99.99
L3 Physics 99.99
BGF 99.97
MH, NH, ISR, 99.96
MH, NH, ISR 99.96
MH, ISR 99.96
ISR 94,4
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!)