ATLAS B trigger

1. ATLAS B trigger Overview of B trigger Di-muon algorithms Performance (efficiency/rates) Menu for 1031 2009 data taking experience ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

2. B physics at LHC • High bb production cross section: ~500 µb • ~1 in 100p-p collisions → bb pair. • Impossible to write all these to disk - we must select those of interest. ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

3. B physics at ATLAS • ATLAS has a wide ranging B-physics programme covering SM and NEW physics: • QCD tests (beauty and onia production cross-sections, polarization effects) • CP violation (e.g. B→ J/ψ) • Rare decays (e.g. B→, B→(X)) • B-hadron production and decay properties (e.g. Bc production and decays, Λb polarization) • B hadron decays into hadronic final states (e.g. Bs→Dsπ, Bs→Dsa1) • B physics trigger slice includes triggers for all these different types of event: • Di-muon trigger to cover: • J/ψ→, J/ψ’→ • → ’, ’’ region • rare exclusive decays (B→(X)) • rare semi-leptonic decays (B→K0*, etc.) • Muon + JET/EM RoI for hadronic (Bs→Ds(π)X), EM B decays (J/ψ→ee, B→γX). • Plus low pT single and di-muon triggers which are used for commissioning and efficiency measurements. For early data mainly interested in these ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

4. Overview of ATLAS trigger <2.5 ms ~2-3 kHz out ~40 ms HLT ~200 Hz out ~4 s • LEVEL 1 TRIGGER • Hardware based (FPGAs ASICs) • Uses coarse granularity calorimeter • and muon information • Identifies Regions Of Interest (ROI) for • further processing • LEVEL 2 TRIGGER • Full detector granularity • Confirm LVL1 trigger • Combine info from different • detectors in RoIs around LVL1 HLT: software based • EVENT FILTER • Refines LVL2 selection using • “offline-like” algorithms • Better alignment and • calibration data available For B physics require L1 MUON trigger with muon and tracking at HLT

5. L1_MU Topological trigger 2 L1_MU - confirm both at HLT L1 di-muon keeps rate under control. Poor efficiency for lowest pT muons. L1_MU RoI based single L1 muon triggers Open large RoI around L1 muon to find other muon/track. Rates may be high. Better efficiency for low pT muons. Can also use entire inner detector (FullScan) TrigDiMuon L1_MU Extrapolate to muon system and search for hits Di-muon trigger strategies In both cases make mass cuts. Vertex cuts and opposite charge are configurable. ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

6. L2_muX L2_muX L2BmumuFex L2BmumuHypo L2_2muX_xxxxxx Topological trigger HLT muon confirmation for each muon individually B trigger algorithms then combine the 2 muons L1_MU L2 L1_MUX L1_MU Fast IdScan_muon Comb EF L2_muX EF_muX EF_muX Confirm each muon at HLT (use muon system and inner detector) Combine 2 opposite sign muons and make mass and vertex chi2 cuts. EFBmumuFex EF tracking EFBmumuHypo TrigMuonEF 2muX_xxxxxx EF_muX xxxxx = DiMu, Jpsimumu, Upsimumu, Bmumu Same algorithms, different mass cuts ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

7. TrigDiMuon (di-muon in large RoI/FullScan) L1_MUX L2 IdScan / SiTrack L2_muX TrigDiMuon L2DiMuHypo L2_MUX_xxxxxx L2_muX_xxxxxx EF_muX • Track reconstruction (IdScan or SiTrack) in large region around L1 muon RoI. • Match one track to L1 RoI. • Extend tracks to muon system and search for hits to find second muon. • Combine 2 muons and make mass cuts. • Optionally can first confirm muon at HLT in muon RoI . Reduces rate at which need to run track reconstruction. (“muX”) • Can also run in FullScan mode (“_FS”) TrigDiMuon EF EF tracking L1_MU TrigMuonEF EFDiMuHypo Extrapolate to muon system and search for hits muX_xxxxxxx MUX_xxxxxxx xxxxx = DiMu, Jpsimumu, Upsimumu, Bmumu Same algorithms, different mass cuts ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

8. L1 efficiency J/ψ→μ(2.5)μ(2.5) L1_MU4 (open road, now called L1_MU0) efficient down to low pT. MU6 OK but would lose some low pT events – worse for Upsilon. Using L1_2MU4 much lower efficiency (particularly loses low pT Jpsi/Upsilon) pT of highest pT muon Jpsi pT ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

9. HLT efficiency (RoI vs. FullScan) Mass spectra for summed signal + background (see Vato’s talk previously) For J/ψ both triggers are efficient For  the two muons are well separated and only FullScan or topological triggers are efficient. RoI half-size

10. Comments on strategy • Best trigger is FullScan – particularly for Upsilon where the muons are well separated • RoI based TrigDiMuon trigger is as good for J/psi • L1 di-muon based trigger will be useful at higher luminosity but has only ~50% efficiency c.f. single L1 muon triggers. • Plan to use FullScan if resources allow (current studies show still OK at 10^31). Turn it off when necessary. • For J/psi still have RoI based single L1 trigger • For Upsilon will have to then use topological trigger.

11. Tag and probe - muon + track trigger L1_MUX L2 IdScan / SiTrack L2_muX L2TrkMassFex L2TrkMassHypo L1_MU L2_MUX_Trk_xxx L2_muX_Trk_xxx • For tag-and-probe studies want no muon requirement on second muon. Could use single muon “mu4/6” but heavily prescaled (6% J/ψ). • New trigger, similar to TrigDiMuon but no attempt to match second track with muon hits. • One track is tag (matched to L1 RoI) other is probe (no muon requirement). • To control rate/background have tight mass cuts (for Jpsi 2.85-3.35 GeV) Muon + track EF EF_muX EF tracking EFTrkMassFex EFTrkMassHypo muX_Trk_xxx MUX_Trk_xxx ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

12. Plans for 1031 di-muon physics menu • Primary physics triggers • Supporting triggers (efficiency measurement etc.) • Commissioning triggers (alternative reconstruction algorithms for testing – eventually decide on one of IdScan/SiTrack, TrigMuonEF/TrigMuGirl) Expect that we can run only 1 of RoI or FS (limited resources: execution time and AOD size). Other one is disabled . This menu assumes we are using RoI, can easily be flipped by changing prescales Rates from Trigger Rate Group using Enhanced Min Bias 10TeV, 15.3.0.2 Low stats (1 event=0.22Hz) – need real running to decide final strategy. ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

13. 2009 running • Reminder of strategy for HLT commissioning: • Initially no HLT online (do fast re-processing offline) • Once HLT validated offline, turn on algorithms online BUT in passthrough mode (running and decision stored) but no events discarded. • Use HLT actively • In B trigger slice loosened the triggers as much as possible: • No muon slice confirmation used in single-L1 muon triggers • No opposite sign cut • No vertex chi2 cuts • Use open mass window “DiMu” triggers • For muon+track trigger have loosened mass windows (same as other algorithms) – this gives a backup for TrigDiMuon (where the track extrapolation to MS needs commissioning) • Commissioning: • So far mostly via monitoring histograms (online and Tier0) • Allow us to check that algorithms are working as expected. • Online : histograms are produced in the trigger steering and the HLT algorithms during execution (L2 and EF). Histogram all quantities used to cut on. • Tier0 : histograms produced from the trigger objects in the bytestream data. Should be same as online histograms – checks integrity of trigger objects. Also compare objects at different levels (L2/EF/offline) For B trigger slice steps 1 and 2. BUT rather few events seen by algorithms. Make sure we understand the effect of these cuts before we use them to reject events ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

14. Track pT Run 141811 – muon+track algorithm IDSCAN_BPhysics Histograms from L2 track reconstruction algorithms Track pT Number of tracks RoI based L2_MU4_Trk_Jpsi_loose_FS Histograms from B trigger algorithms FullScan Number of tracks Cut on track pT>3GeV so no track pairs. ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

15. TrigDiMuon mumu mass Require 1 track matches L1 MU RoI mumu mass All track pairs Run 141811 Run 142191 ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

16. Summary • We have a flexible trigger for B physics at ATLAS. (Discussed di-muon triggers here, also MU+EM and MU+JET) • Different algorithms will allow us to collect data from earliest running through to high luminosity rare decay searches. Experience with low luminosity will determine strategy for higher luminosity (RoI vs. FullScan) • Commissioning started with 2009 data. Setup new chains with loosened cuts but we saw few triggers. Need more data to produce reference histograms and fully check algorithms. • Will continue during 2010 when we hope to see many onia events.