Questions to Signature & Performance Groups

• Possibilities for tightening/adding selection cuts: comparison of online and offline selection cuts:

– cuts that could be tightened online? – cuts that could be moved online? (e.g. Mass cuts, Decay length cuts, Primary vertex requirements, Secondary

vertex requirements...)? – online cuts that are too tight?

• Sources of inefficiency: – Causes? Plans to address these?

• Planned/possible changes to algorithms? :– What changes are planned? What changes are possible? – Do you plan to make changes exploiting L2-EF merger? What changes could be made?

• What is the effect of planned/possible changes on HLT resource usage - ROS request rate and CPU usage:

e.g. increased RoI size, increased use of full-event information, change to slower algorithms. – Plans to limit/reduce HLT resource usage? e.g. 2-step L2 tracking for Tau trigger

• Input on questions to physics groups: • issues from threshold increase c.f. Multi-object or topological triggers.

Aim of questions is to collect input on plans/possibilities for improving online algorithms and selections

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• What follows is a short summary provided by Signature coordinators. • Full answers are attached to Twiki: TriggerWorkshop2012

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e/gamma: Tightening of selection cuts and adding new cuts

Cuts that could be tightened online? - The EF selection uses same identification cuts as applied offline. => hence not easy to identify cuts to tighten without losing efficiency

-A bottom up approach in collaboration with the offline will be needed• Photon triggers mostly loose identification, tighter identification is often used offline=> Could move to tighter photons. Specific background-enriched (loose) support triggers would be needed.- Could also investigate calorimeter isolation for the photon selections- Some analysis cuts could be investigated online e.g. W transverse mass cut => need physics group input

NOTE: need a low pT diphoton trigger (Higgs). i.e. there must be a di-photon trigger with ~30GeV threshold and leaving some room for cut reversal.

Paul Bell for e/gamma signature & performance groups

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e/gamma: Sources of inefficiency• Electrons:

• largest sources of inefficiency due to tracking and track-calorimeter matching. • Few percent for e24vhi_medium1, no big, single source remains • Will investigate these by continuing event-by-event loss studies.

• Photon triggers are ~100% efficient for offline tight photons. - Remaining sources of inefficiency relate to inherent differences between L2, EF and offline:

- different tracking algorithms and tunes at L2, EF wrt offline.- use of the GSF track refitting offline, not applied at EF.

- At L2 selection based on calorimeter only-cuts are kept very loose to minimise losses=> Improved shower shape resolutions would allow tighter cuts early on in the trigger chains.

Summary: use of algorithms and calibration closer to the offline will be critical to minimise the losses and allow further rate reduction.

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e/gamma: Planned or possible changes• Offline electron identification will probably move from a cut based method to MVA(ultimate scenario may see different tunes for different values of mu in a single run. ) need same algorithm online

We should use topological triggers at L1 to reduce rates and keep the performance high. - At HLT we should explore more multi-object triggers with topological cuts, while keeping some multi-purpose triggers, with higher thresholds, to cover a wide phase space.

Other Comments

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Muon Responses1) Tightening of selection cuts and addition of new cutsSingle isolated muon: Both pT and track isolation cuts are already well optimized wrt offline

Possible new cuts? > 90% of triggered events contain indeed offline muon Only the handle to reduce rates is to suppress real muons from QCD by isolation requirement, or, to raise pT threshold• Possible new cuts

-- Higher pT threshold -- Tighter track isolation + ptCone30 + Absolute value cut

-- Addition of calo isolation

34 GeV with loose isolation• Cuts: pT 24 34 GeV, ptCone20/pT < 0.12 sameExpected EF rate reduction: 56% 29 GeV with tight isolation:

• Cuts: pT 24 29 GeV• pTCone20/pT < 0.12 pTCone30 < 1 GeV

Expected EF rate reduction: 52% (+ calorimeter isolation: not yet studied)

Kunihiro Nagano for Muon signature and performance groups

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Muon Responses• Asymmetric di-muon with EF FS (single L1 muon)

* Current cuts pT : ’18 GeV’, ‘8 GeV’ Offline: pT > 20 GeV, 10 GeV * Possible new cuts: -- L1_MU15 L1_MU20 -- Add track iso. to leading-pT muon

mu24i_mu8_EFFS Cuts: pT 18 24 GeV add ptCone20/pT < 0.12 Expected EF rate reduction: 51%

Highly recommend to move to use mu24i_mu8_EFFS instead of mu24i (for processes that include >=2 muons)

• Topological di-muon (requires 2 L1 RoIs) * Current cuts pT : ’13 GeV’, ‘13 GeV’ Offline: pT > 15 GeV, 15 GeV * Possible new cuts -- Addition of track isolation to leading-pT muon -- Efficiency loss if we have to change L1 seed from L1_2MU10 to 2MU11 + ~5-7% inefficiency for a single muon at barrel In this case, 2MU10_MU11 could be an option (not yet studied)

2mu14i Cuts: pT 13 14 GeV add ptCone20/pT < 0.12 Expected EF rate reduction: 53%

2mu14i_L12MU10_MU11 Same as 2mu14i but is seeded from 2MU10_MU11

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Muon Responses - 3

• RoI-seeded triggers (e.g. single isolated muon, topological di-muon) * Inefficiency mainly comes from L1: RPC ~ 30%, TGC ~10%, mainly due to limited chamber coverage etc. + RPC plans to integrate some chambers (in the ‘feet’ region) which are not used for now into the trigger. Geometrical coverage expected to increase by ~3%. (Trigger efficiency increase will be similar or less.)

* Inefficiency at HLT is typically: + ~2% at L2 (~1% by muFast, ~1% by muComb), + <1% at EF L2 has improved with newTrigL2MuonSA (from 2012 period C), muFast efficiency increased by ~1% at barrel, muComb efficiency increased by ~1% at endcap. (as the seed from muFast improves)

+ Improvements on L2 algorithms to recover the remaining inefficiencies (pattern rec failure at muFast, ID-MS matching failure at muComb) planned in LS1

Sources of inefficiency

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TauTightening of selection cuts?• L1 isolation could be tightened.• Single tau threshold proposed for 1034 is too high• Multi-object trigger + topological requirements is the way to go

Topological & combined triggers• Could add topological cut dEta(tau,tau)

• Combining with a jet trigger will save a lot, but careful study is necessary.• Sources of inefficiency:

– Mainly L2 energy resolution

Soshi Tsuno, Phillip Urquijo for Tau signature & performance groups

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Feedback from the jet trigger group M.Campanelli, M.Tamsett for Jet signature and Jet/MET performance Groups

Groups of triggers:

Inclusive jets (EF_j360_a4tchad) Multijets (EF_4j65_a4thad_L2FS) Total Energy (EF_j170_HT700) Fat jets (EF_j360_a10tchad)

Each group shares our rate (about 40 Hz) ~equally

Tightening of selection cuts:

• Only option is cleaning (already there at L2, too late for EF this year)• but only reduces rates by few %, only relevant for pathological cases (eg hot cells)

Are there cuts only applied offline that could be moved online?

• Only possibility is Jet Vertex Fraction (JVF) - currently studying this option• Cuts like dijet mass or angular separation only useful for specific cases

Are there online cuts too tight and need to be loosened? No.

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Sources of inefficiency:

Multijets:• the square shape of the sliding window is causing some inefficiencies

basically solved by the use of L1.5• Difference in jet algorithm at L2 causes small inefficiencies

moving to anti-kt for L2 as well

Other methods to reduce rates apart from rising thresholds:

• We are already using some topological triggers. • Inclusive measurements obviously need inclusive triggers, but they can be prescaled• More complex final states do benefit from combined triggers

deployed according to the requests form the physics groups• L1Cal will have a topological module, allowing cutting on jet directions at L1.

We are starting to study HLT chains based on this possibility.• Some form of pileup offset subtraction: could be <mu> and BCID dependent

• could compute jet area based offsets depending on measured ambient energy per event• running anti-kT on the full event at full L2/EF calorimeter granularity

• ideally build topo-cluster and topo-towers as soon as possible• Better calibration: The addition of nMCM at L1 will mean L1Calo can apply a hadronic

specific calibration => sharpen threshold, some additional rejection at L1.5.

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B-jet

1) Tightening of selection cuts and addition of new cutsPropose to add Jet Vertex Fraction : offline value 0.5Expected rate reduction: Difficult to estimate as it depends on pileup and jet-item multiplicity

2) Sources of inefficiency (in our case this is mainly a problem of extra light-jet efficiency)• Different b-tagging algorithms and sec. vert. Algorithms from offline• Fix planed : could give factor 1.5/2 rejection increase, estimated from offline • No track-jet algorithm currently used online (we run on all tracks in RoI)• 0.2 RoI w.r.t 0.4 offline jets

Planed changes:• use of JetVertex Fitter information • porting of offline vertexing tools online • porting of offline b-tagging algorithms • use of a larger RoI in combination with track-jet algorithm

Carlo Schiavi, Lorenzo Feligioni for B-Jet signature and flavour tagging performance groups

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METAllen Mincer for MET signature & JET/MET performance groups

A few comments about the other triggers:• Not yet clear that XS triggers will have any signal efficiency for large mu. Need to study.• Have not found a way to make TE triggers useful. Studies of ETXS show that this variabledoesn't help when there is large variation in mu, as is the case for large <mu>.

Tightening of selection cuts and addition of new cuts:• Given turn-on curves for existing algos, increasing MET threshold results in loss of physics.Sources of Inefficiency• Main sources:

– poor MET resolution of the L1 trigger-towers sums– fake MET due to pileup determines the minimum threshold

• At EF level: if have to revert to cell sums (rather than clustering): poorer resolution will degrade efficiency.

4. Planned or possible changes:• calibration at L2: unlikely to give large changes.• Tuning of noise thresholds: possibly different values in forward region

– Could reducing rates without severely impacting efficiency.• At EF level: not clear can run the current cluster algorithm with higher pileup.

– coarser granularity might allow the cluster formation time to stay within limits in 2015.• Missing HT algorithms need to be investigated, but for XE and XS type triggers.• Investigate moving online improvements from offline: e.g. using tracking and primary vertex

information to reduce the pileup contribution in the calorimeter sums.