Searches using displaced leptons or jets

Transcription

1 Searches using displaced leptons or jets J Antonelli with input from M Flowerdew, P Pais, R Rosten, H Russell

2 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 3 2

3 Pros and cons of displaced lepton and jets compared to other LL signatures Pros: The SM has lots of leptons and jets -they are well understood objects 2 There exist accepted reconstruction and ID algorithms -easy path to reducing backgrounds 3 Leptons are good for triggering -dimuon triggers below 20 GeV in 205 menu Cons: The SM has lots of leptons and jets -higher backgrounds than other displaced signatures 2 There exist accepted reconstruction and ID algorithms -they probably won t work for your signal 3 Jets are hard to trigger on -dijet triggers around 500 GeV in 205 menu 4 Can access lower signal lifetimes -compared to HSCP, Disappearing track, ie Simone s direct searches J Antonelli UMass Workshop, Nov 3 3

4 5 QCD Multi-jet Background Estimation 52 Z/g! tt Background Estimation 53 Other Backgrounds Systematic Errors Results 7 Event Yields 72 Limit-Setting Procedure 73 Limits 74 Discussion and outlook Summary Event Displays List of Run displaced lepton searches 6 7 CMS ee/μμ arxiv:46977 EXO-4-2 CMS eμ 8 arxiv: A CMS Simulation ATLAS ee/eμ/μμ/l+dv arxiv: ! be bµ Introductionttand Theoretical Motivation d~0 [cm] t t! be bµ beamspot of a new boson with a mass of roughly 26 GeV The discovery tt! be bµ 0 whose properties are, to-date, consistent with a stan[, d~2], tt! be bµ [cm]~ 0 dardd[cm] model (SM) Higgs boson, has underscored the importance of investigating models that are designed to account for the mathematical inconsistencies that are consequences of introducing the Higgs potential y x Stop cτ [cm] z 97 fb- (8 TeV) For this search, the most relevant of these unsolved issues 2 0 CMS ± 2 σexpected ± σexpected Expected limit Observed limit 0 Excluded region M ~t [GeV] J Antonelli UMass Workshop, Nov 3 4

5 (8 TeV) ele reco mu reco CMS Simulation Preliminary lepton reco efficiencies as a function of d (8 TeV) CMS Simulation Preliminary muon d0 [cm] CMS Simulation Preliminary (8 TeV) ele sel Goal to keep search as general as possible and simple to understand Didn t aim for background-free search QCD MC didn t identify it as major background Complicated flavor composition of background Factorized cuts to avoid null background counts Found cuts hidden in particle flow, triggers Simple event selection simple recasting 09 mu sel Displaced eμ lepton selection efficiencies as a function of pt electron d0 [cm] CMS Simulation Preliminary (8 TeV) muon p [GeV] T planned for run 2: remove deltar & OS cuts, Signal/Background Separation improved muon trigger/reco in Lepton Impact Parameter electron p [GeV] T link to study Displaced Global M εμ (Run 2) εμ (Run )!4 B2G Meeting Dec 9 J Antonelli UMass Workshop, Nov 3! Muon reconstruction efficiency as a function 5 the direct decay stop b + µ (with muon

6 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 displaced eμ team, expand to more final states J Antonelli UMass Workshop, Nov 3 6

7 Displaced ee/eμ/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 KS 0 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 3 7

8 List of Run displaced jet searches σ(h XX) B2(X qq) [pb] CMS displaced dijet in tracker arxiv:46530 ATLAS displaced jets in ID/MS arxiv: ATLAS displaced jets in HCAL arxiv: fb- (8 TeV) CMS 0-95% CL limits: mx = 50 GeV mh = 000 GeV mx = 350 GeV Exp limits (± σ) X cτ [cm] J Antonelli UMass Workshop, Nov 3 8

9 Displaced dijets in tracker HT trigger reduced sensitivity to SM Higgs portal Validated vertex reconstruction with KS 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! -NB non refresh analyses will take longer - K0s candidates / 06 cm 7 pb (8 TeV) CMS 04 Data Simulation 03 + = Data / Sim K0s arxiv: transverse decay length [cm] J Antonelli UMass Workshop, Nov 3 9

10 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 3 0

11 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 3

12 Run 2 outlook / conclusion We ve been through a lot of trial and error! Some Run 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 3 2

13 fin J Antonelli UMass Workshop, Nov 3 3

14 ATLAS Displaced dilepton search parameters Triggers: Mu50 Eta07 Photon20 Diphoton40 J Antonelli UMass Workshop, Nov 3 4

15 ATLAS Displaced lepton in DV search parameters J Antonelli UMass Workshop, Nov 3 5

16 CMS Displaced eμ search parameters Trigger: HLT Mu22 Photon22 CaloIdL J Antonelli UMass Workshop, Nov 3 6

17 CMS Displaced ee/μμ search parameters ee trigger: HLT Photon36 R9Id85 OR CaloId0 Iso50 Photon22 R9Id85 OR CaloId0 Iso50 μμ trigger: L2DoubleMu23 NoVertex 2Cha Angle2p5 J Antonelli UMass Workshop, Nov 3 7

18 ATLAS HCAL jet search parameters L Trigger: narrow jet (tau seed) pt > 40 GeV L2: log 0 (E H /E EM ) > 2, no pointing tracks L3: anti-kt jet, pt > 35 GeV J Antonelli UMass Workshop, Nov 3 8

19 ATLAS displaced jet in ID/MS search parameters Jet ET + E T miss trigger: offline jet pt > 20 GeV, E T miss > 200 GeV Independent muon ROI trigger J Antonelli UMass Workshop, Nov 3 9

20 CMS displaced dijet search parameters J Antonelli UMass Workshop, Nov 3 20