atlas b trigger

ATLAS B trigger

• Overview of B trigger• Di-muon algorithms • Performance (efficiency/rates)• Menu for 1031

• 2009 data taking experience

7/1/2010 1ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

ATLAS UK Meeting, Cambridge (Julie Kirk, RAL) 2

B physics at LHC

• High bb production cross section: ~500 µb

• ~ 1 in 100 p-p collisions → bb pair. • Impossible to write all these to disk

- we must select those of interest.

7/1/2010

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

7/1/2010

Overview of ATLAS trigger

<2.5 s

~40 ms

~4 s

HL

T

~2-3 kHz out

~200 Hz out

LEVEL 1 TRIGGER• Hardware based (FPGAs ASICs)• Uses coarse granularity calorimeterand 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

EVENT FILTER• Refines LVL2 selection using“offline-like” algorithms • Better alignment and calibration data available H

LT:

soft

war

e ba

sed

For B physics require L1 MUON triggerwith muon and tracking at HLT

Di-muon trigger strategies

L1_MU

L1_MU

Topological trigger2 L1_MU - confirm both at HLT

L1 di-muon keeps rate under control. Poor efficiency for lowest pT muons.

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)

L1_MUTrigDiMuon

Extrapolate to muonsystem and search for hits

In both cases make mass cuts. Vertex cuts and opposite charge are configurable.


Mass cuts (GeV)

DiMu 0.5 →

Jpsi 2.5-4.3

Upsi 8-12

Bmumu 4-7

Topological triggerL1_MU

L1_MU

L1_MUXL1_MUX

FastFast

CombComb

L2_muXL2_muX

IdScan_muonIdScan_muon

EF trackingEF tracking

EF_muXEF_muX

TrigMuonEFTrigMuonEF

L2_muXL2_muX

L2BmumuFexL2BmumuFex

L2_2muX_xxxxxxL2_2muX_xxxxxx

L2BmumuHypoL2BmumuHypo

L2_muXL2_muX

EF_muXEF_muX

EFBmumuFexEFBmumuFex

2muX_xxxxxx2muX_xxxxxx

EFBmumuHypoEFBmumuHypo

EF_muXEF_muX

HLT muon confirmationfor each muon individually

B trigger algorithms then combinethe 2 muons

Confirm each muon at HLT (use muon system and inner detector)

Combine 2 opposite sign muons and make mass and vertex chi2 cuts.


xxxxx = DiMu, Jpsimumu, Upsimumu, BmumuSame algorithms, different mass cuts

TrigDiMuon (di-muon in large RoI/FullScan)

L1_MUTrigDiMuon

Extrapolate to muonsystem and search for hits

ATLAS UK Meeting, Cambridge (Julie Kirk, RAL)

L1_MUXL1_MUX

IdScan / SiTrackIdScan / SiTrack

L2DiMuHypoL2DiMuHypo

L2_MUX_xxxxxxL2_MUX_xxxxxx

TrigDiMuonTrigDiMuon

L2_muXL2_muX


EFDiMuHypoEFDiMuHypo

MUX_xxxxxxxMUX_xxxxxxx

TrigMuonEFTrigMuonEF

L2_muX_xxxxxxL2_muX_xxxxxx

muX_xxxxxxxmuX_xxxxxxx

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”)

EF_muXEF_muX

7/1/2010 7xxxxx = DiMu, Jpsimumu, Upsimumu, BmumuSame algorithms, different mass cuts

L1 efficiency


pT of highest pT muon

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)

Jpsi pT

For J/ψ both triggers are efficientFor the two muons are well separated and only FullScan or topological triggers are efficient.

RoI half-sizeEfficiency FullScan RoI

Jpsi 76% 76%

Uspi 67% 0.6%

Mass spectra for summed signal + background (see Vato’s talk previously)

HLT efficiency (RoI vs. FullScan)

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.

Tag and probe - muon + track trigger

L1_MUMuon + track L1_MUXL1_MUX

IdScan / SiTrackIdScan / SiTrack

L2TrkMassHypoL2TrkMassHypo

L2_MUX_Trk_xxxL2_MUX_Trk_xxx

L2TrkMassFexL2TrkMassFex

L2_muXL2_muX


EFTrkMassHypoEFTrkMassHypo

MUX_Trk_xxxMUX_Trk_xxx

EFTrkMassFexEFTrkMassFex

L2_muX_Trk_xxxL2_muX_Trk_xxx

muX_Trk_xxxmuX_Trk_xxx

EF_muXEF_muX

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)


Plans for 1031 di-muon physics menuSignature Expected Rate (Hz)*

L2 EF

TrigDiMuon mu4_DiMu 1.78 0.22

mu4_Jpsimumu 1.56 0.22

mu4_Upsimumu 0. 0.

mu4_Bmumu 0.22 0.

mu4_DiMu_FS 6.92 1.34

mu4_DiMu_SiTrk

mu4_DiMu_MG

mu4_DiMu_SiTrk_FS

mu4_DiMu_MG_FS

Topological 2mu4_DiMu_noVtx

2mu4_DiMu 0.66 0.44

2mu4_DiMu_Jpsimumu 0.22 0.22

2mu4_DiMu_Upsimumu 0. 0.

2mu4_DiMu_Bmumu 0. 0.

2mu4_DiMu_SiTrk

Muon + track mu4_Trk_Jpsi

mu4_Trk_Jpsi_FS

mu4_Trk_Upsi_FS

• 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.

2009 running


Reminder of strategy for HLT commissioning:1. Initially no HLT online (do fast re-processing offline)2. Once HLT validated offline, turn on algorithms online BUT in passthrough mode (running and

decision stored) but no events discarded.3. 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)

Make sure we understand the effect of these cuts before we use them to reject events

For B trigger slice steps 1 and 2.BUT rather few events seen by algorithms.

Run 141811 – muon+track algorithm


Cut on track pT>3GeV so no track pairs.

L2_MU4_Trk_Jpsi_loose_FS

Histograms from B trigger algorithms

Number of tracksTrack pT

IDSCAN_BPhysics

Histograms fromL2 track reconstructionalgorithms

Number of tracks

Track pT

RoI based

FullScan

TrigDiMuon

7/1/2010 ATLAS UK Meeting, Cambridge (Julie Kirk, RAL) 15

mumu massAll track pairs

Run 141811

Run 142191

mumu massRequire 1 track matches L1 MU RoI

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.

atlas b trigger

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