Searches using displaced leptons or jets J. Antonelli with input from M. Flowerdew, P. Pais, R. Rosten, H. Russell 1
I’ve spoken with authors from ~all of the relevant searches, here are some general musings resulting from those conversations • These searches are new ! ~6 of the 7 searches in this talk have only been done once • Signature-driven searches have a lot more design choices to make • You don’t know what your signal is and you don’t know what your backgrounds are! • Arguably a waste of resources to target a single model • Potential overlap with existing searches is tougher to evaluate • Lots of trial and error - this can lead to some “artifacts” that limit sensitivity • Getting these analyses approved by the collaboration is a struggle - Most reviewers don’t have a good frame of reference • These searches are great at finding software bugs in the “standard” code subset of the choices we all had to make: -use half of the event or all of it? -use standard algorithms (more robust) or homemade ones (more efficient)? -level of background to target? -simple event selection (more inclusive) or complex (less background)? -what lifetimes to target? - huge implications on search strategy! J. Antonelli UMass Workshop, Nov 13 2
Pros and cons of displaced lepton and jets compared to other LL signatures Pros: Cons: 1. The SM has lots of leptons and jets 1. The SM has lots of leptons and jets -they are well understood objects -higher backgrounds than other displaced signatures 2. There exist accepted reconstruction 2. There exist accepted reconstruction and ID algorithms and ID algorithms -easy path to reducing backgrounds -they probably won’t work for your signal 3. Leptons are good for triggering 3. Jets are hard to trigger on -dimuon triggers below 20 GeV -dijet triggers around 500 GeV in 2015 menu in 2015 menu 4. Can access lower signal lifetimes -compared to HSCP, Disappearing track, i.e. Simone’s “direct searches” J. Antonelli UMass Workshop, Nov 13 3
List of Run 1 displaced lepton searches CMS ee/ μμ CMS e μ ATLAS ee/e μ / μμ /l+DV arxiv:1411.6977 arxiv:1409.4789 arxiv:1504.05162 EXO-14-12 CMS Simulation [ cm ] t ˜ ˜ t → be b µ beamspot tt → ~ d 0 tt → [ ~ d 0 [ y x z -1 19.7 fb (8 TeV) 2 10 [cm] CMS τ Stop c 2 ± σ expected 1 10 ± σ expected Expected limit Observed limit 1 Excluded region -1 10 400 500 600 700 800 M [GeV] ~ t J. Antonelli UMass Workshop, Nov 13 4
Displaced e μ CMS Simulation Preliminary CMS Simulation Preliminary (8 TeV) (8 TeV) 1 1 reco reco mu ele 0.9 0.9 ∈ ∈ 0.8 0.8 • Goal to keep search as general as possible and 0.7 0.7 lepton reco. 0.6 0.6 0.5 0.5 simple to understand efficiencies 0.4 0.4 0.3 0.3 as a function of d 0 • Didn’t aim for background-free search 0.2 0.2 0.1 0.1 0 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 • QCD MC didn’t identify it as major background muon d [cm] electron d [cm] 0 0 • Complicated flavor composition of background CMS Simulation Preliminary CMS Simulation Preliminary (8 TeV) (8 TeV) 1 1 mu sel ele sel ∈ ∈ 0.9 0.9 • Factorized cuts to avoid null background counts 0.8 0.8 0.7 0.7 lepton selection 0.6 0.6 • Found cuts hidden in particle flow, triggers 0.5 0.5 efficiencies 0.4 0.4 • Simple event selection → simple recasting 0.3 0.3 as a function of p T 0.2 0.2 0.1 0.1 0 0 0 200 400 600 800 1000 0 200 400 600 800 1000 muon p [GeV] electron p [GeV] T T planned for run 2: remove deltaR & OS cuts, link to study improved muon trigger/reco ε μ (Run 2) ε μ (Run 1) J. Antonelli UMass Workshop, Nov 13 5
Displaced ee/ μμ • Measured displaced tracking efficiency by using cosmics • Background estimation leveraged symmetry in background • Presented limits with acceptance factored out planned for run 2: remove vertex constraint, join forces with Run 1 displaced e μ team, expand to more final states J. Antonelli UMass Workshop, Nov 13 6
Displaced ee/e μ / μμ /l+DV • Additional level of tracking needed • Couldn’t run on entire triggered dataset • No isolation requirement on leptons! • Electron systematics were a sticking point • No good source of displaced leptons • Used control sample of K S0 decays • Need to slowly unblind • Efficiency depends on a lot of parameters • No efficiency model so far (studies ongoing) planned for run 2: improvements in seeding of displaced track reconstruction 4 mm displacement on vertex can maybe be relaxed J. Antonelli UMass Workshop, Nov 13 7
List of Run 1 displaced jet searches CMS displaced dijet ATLAS displaced jets ATLAS displaced jets in tracker in ID/MS in HCAL arxiv:1411.6530 arxiv:1504.03634 arxiv:1501.04020 -1 18.5 fb (8 TeV) ) [pb] CMS q -1 10 q 95% CL limits: m = 1000 GeV → m = 150 GeV H X (X m = 350 GeV X 2 Exp. limits ( ± 1 σ ) XX) B -2 10 → (H σ -3 10 2 1 10 10 X c [cm] τ J. Antonelli UMass Workshop, Nov 13 8
Displaced dijets in tracker • H T trigger reduced sensitivity to SM Higgs portal • Validated vertex reconstruction with K S sample • Used complex multivariate discriminants instead of material veto planned for Run 2: jet-tagging algorithms -maximize lifetime coverage -remove need for dijet vertexing -a lot of interest! -N.B. non “refresh” analyses will take longer -1 17 pb (8 TeV) candidates / 0.6 cm CMS 4 10 Data Simulation 3 10 + = 0 s K 2 10 Data / Sim 1.1 1 0.9 0 10 20 30 40 50 60 0 arxiv:1503.05923 K transverse decay length [cm] s J. Antonelli UMass Workshop, Nov 13 9
Displaced jets in ID/MS • Used same displaced re-tracking dataset as displaced DV search • Needed to write MS tracklet reconstruction algorithm • Different trigger strategies depending on signal model • Used zero-bias data event overlaid on background instead of simulated pileup • Recasting is very model dependent, found two legs were not independent possibilities for run 2: combine with HCAL jets and and DV search, use long-lived hadron gun to estimate efficiency, displaced muons will be in the standard reco! J. Antonelli UMass Workshop, Nov 13 10
Displaced jets in HCAL • Considered both trackless jet (ECAL or HCAL) and low-EMF jet (HCAL) • Found search feasibility was much better with the extra background rejection from an H/E cut • Multiple jets will still create one HCAL cluster! • Timing cut to reduce cosmic background may be tighter than needed • Some efficiency loss for high mass signals planning for run 2: pileup removal will be key because of track isolation in trigger, combine with ID/MS analysis to have additional categories (ID/HCAL, MS/HCAL, etc.) J. Antonelli UMass Workshop, Nov 13 11
Run 2 outlook / conclusion We’ve been through a lot of trial and error! Some Run 1 searches ended up being somewhat over-engineered (hindsight is 20/20) In Run 2, results should come significantly faster Some limitations are unavoidable from detector technology, but much improvement is being made on the software side Now that the many displaced objects have been validated, make way for combinations! (ATLAS has a head-start in this respect) J. Antonelli UMass Workshop, Nov 13 12
fin J. Antonelli UMass Workshop, Nov 13 13
ATLAS Displaced dilepton search parameters Triggers: Mu50 Eta1.07 Photon120 Diphoton40 J. Antonelli UMass Workshop, Nov 13 14
ATLAS Displaced lepton in DV search parameters J. Antonelli UMass Workshop, Nov 13 15
CMS Displaced e μ search parameters Trigger: HLT Mu22 Photon22 CaloIdL J. Antonelli UMass Workshop, Nov 13 16
CMS Displaced ee/ μμ search parameters ee trigger: HLT Photon36 R9Id85 OR CaloId10 Iso50 Photon22 R9Id85 OR CaloId10 Iso50 μμ trigger: L2DoubleMu23 NoVertex 2Cha Angle2p5 J. Antonelli UMass Workshop, Nov 13 17
ATLAS HCAL jet search parameters L1 Trigger: narrow jet (tau seed) p T > 40 GeV L2: log 10 ( E H / E EM ) > 1.2, no pointing tracks L3: anti-k T jet, p T > 35 GeV J. Antonelli UMass Workshop, Nov 13 18
ATLAS displaced jet in ID/MS search parameters Jet E T + E T miss trigger: o ffl ine jet p T > 120 GeV, E T miss > 200 GeV Independent muon ROI trigger J. Antonelli UMass Workshop, Nov 13 19
CMS displaced dijet search parameters J. Antonelli UMass Workshop, Nov 13 20
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