Seaches fo log-lived paticles with displaced signatues at the LHC. Daniela Salvatore (INFN Cosenza) on behalf of the ATLAS and CMS Collaborations

Transcription

1 Seaches fo log-lived paticles with displaced signatues at the LHC Daniela Salvatore (INFN Cosenza) on behalf of the ATLAS and CMS Collaborations

2 Outline A review of the most recent results from ATLAS & CMS on the searches for Long-Lived Particles (LLP) with TeV data. These searches can be interpreted in terms of R-parity conserving or violating SUSY models, split SUSY, stealth SUSY and exotic scenarios like Hidden Valley. Observations are compatible with background expectations. Upper limits are set for the cross sections of the different decay modes. 2

3 ATLAS: displaced vetices axiv: , submited to PRD Searches for LLPs with lifetimes of the order of ps to ns, decaying at mm to tens of cm from the IP LLP decays observed as Displaced Vertices (DV) Di-lepton searches: DV formed by opposite charge μμ, ee, eμ Multitrack searches: a DV + high pt μ or e / jets / missing transverse energy (ETmiss) DV selection: mdv > 10 GeV, >= 5 tracks, > 4 mm distance from primary vertex (PV) DVs in dense material are vetoed. Retracking: Hits not associated with existing tracks. Looser requirements on track impact parameters nn More o ora 's talk n o s s r Pette! 3

4 ATLAS: displaced vetices axiv: , submited to PRD Expected background from accidental crossings and merged vertices Less than 1 event per channel No events observed in the signal region. Upper limits set on the number of LLP decays and cross section for the different channels to be interpreted in the context of: SUSY with R-parity violation (RPV), gauge mediated SUSY breaking scenarios (GMSB): LLP is the lightest neutralino. talk! s ' n o s s split SUSY: LLP is gluino. etter P a r o nn More o 4

5 ATLAS: LLPs in the Hadroic Caloimete PLB 743 (2015) LLPs decaying in the Hadronic Calorimeter (HCal) i.e. 2 to 4 m in the ATLAS barrel jets with large energy deposition in the HCal Isolated wrt Inner Detector (ID) Dedicated CaloRatio trigger based on this unique signature Signal: trackless jets Log10 (EHad / EEm) > 1.2 Hidden Valley (HV) scenario: SM scalar boson communicator Φ between SM and hidden sector LLPs are the valley pions πv 5

6 ATLAS: LLPs in the Hadroic Caloimete PLB 743 (2015) Observed events compatible with bkg expectations Multi-jets and cosmics Upper limits on σ (Φ) x BR (Φhs πvπv) Φ masses from 100 to 900 GeV 126 GeV included (exotic Higgs decays) πv masses from 10 to 150 GeV 6

7 ATLAS: displaced vetices in MS + ID PRD 92, (2015) Searches for LLP decaying in the Muon Spectrometer (MS) and Inner Detector (ID) Benchmark models: HV Φ communicator HV Z' communicator, decaying into hidden quark pair Stealth SUSY: DV in the ID: re-tracking, looser impact parameters DV in the MS: from MS segments isolated wrt ID. High number of MDT and RPC hits. Dedicated MuonRoICluster trigger R-parity conserving model. Two displaced gluons per gluino decay. 7

8 ATLAS: displaced vetices in MS + ID PRD 92, (2015) No events observed in the ID Vx + MS Vx and 2 ID Vx channel 2 observed events in the 2 MS Vx channel compatible with bkg. Upper limits (the most stringent to date) set on the three models, for different combination of masses for the communicators and LLPs. 100% BR assumed for LLP to fermion ~ ~ ~ pairs and S S G and S gg 8

9 ATLAS: Lepto Jets JHEP 11 (2014) 088 Hidden and visible sectors communicate through a dark photon γd. γd can decay to collimated pairs of e, μ, charged π (lepton jets LJ) far from the IP. LJs reconstructed from a simple clustering algorithm (muons and jet are combined into a 0.5 cone in (η,φ) space). Collimated μ and no jets in a narrow cone. All γd decaying to muon pairs. A cluster of 2 μ and 1 or 2 jets. 1 γd into muon pair, 1 γd into e/π pair. Only jets. Decay into e/π pair. 9

10 ATLAS: Lepto Jets JHEP 11 (2014) 088 Triggers: Multi-muon trigger for LJ 0 and LJ 1 Low electromagnetic fraction (EMF) CaloRatio trigger for LJ 2 Multi-jet and cosmics bkg reduced by: constraints on the impact parameter, track isolation around LJ direction, low EMF Observations consistent with bkg expectations. Limits on σ x BR for H 2γd + X and H 4γd + X for mh = 125 GeV, mγ = 400 MeV d Excluded cτ: mm and mm 10

11 CMS: LLPs into quak pais PRD 91, (2015) Search for a non-sm Higgs ( GeV) decaying into 2 scalar neutral LLPs X ( GeV). X decays in turn into quark pairs. Or events with a pair of squarks ( GeV) decaying into neutralinos ( GeV) and quarks. The LL neutralino decays in turns into quarks + muon. Dedicated displaced-jet trigger. Threshold on single jet pt and on the scalar sum of all transverse energies. At least 2 jets with constraints on associated track impact parameters. DV fitting in the tracker: at least one track from each of the two jets, m well separated from PV DV > 4 GeV Best di-jet candidates with higher track multiplicity. 11

12 CMS: LLPs into quak pais PRD 91, (2015) Observations compatible with bkg expectations. 1 (2) events depending on signal regions, optimized for X transverse decay distance more (less) than 20 cm. Upper limits set: on the mean number of events which could pass the selection requirements; on the production cross section (the most stringent to date). X channel: Proper decay lengths in the cm range ---> upper limits fb. Neutralino channel: Proper decay lengths in the 2 40 cm range ---> upper limits fb. 12

13 CMS: LLPs into di-leptos PRD 91, (2015) Search for final states including a pair of electrons or muons originating from a displaced vertex in the tracker. LLP can be a spin-0 boson X: H XX, X l+l H: GeV, X: GeV ~ 0, ~χ0 l+l- ν Or a neutralino from q~ qχ mq~: GeV, m~χ0: GeV Tracks are from an electron if in a ΔR < 0.1 cone wrt ECal deposits. Tracks are from a muon if matching a muon candidate in ΔR < 0.1. LL candidates from pairs e or μ: ee channel: 40 (25) GeV μ+μ- channel: 2 x 26 GeV 13

14 CMS: LLPs into di-leptos PRD 91, (2015) Constraints on impact parameters to reject prompt particles ( d0 /σd > 12) Efficiencies estimated for events with 1 or 2 LLP with re-weighted lifetimes from 200 μm to 200 m. Background from Drell-Yan dileptons. No observation either in the e or μ channel. Upper limits set on the cross section x BR for: The X boson channel The neutralino channel 14

15 CMS: coplementay LLPs into leptos CMS PAS EXO : Final states with 2 μ reconstructed in the muon chamber only. H XX μ+μ- and ~ q qχ~0, ~χ0 μ+μ- ν. Muons in the muon chamber must be isolated wrt silicon tracks (no overlap with previous analysis). No events observed in the signal region combined limits. PRL 114, (2015) Final states with opposite charge e + μ and large impact parameters ( cm). Results interpreted in the displaced SUSY context. ~ lk! LLP is the t b + lepton. on's ta More etters P a r o on N s 15

16 Coclusios ATLAS and CMS performed a large number of searches for long-lived particles with 2012 data at a center-of-mass energy of 8 TeV. Not covered in this talk: delayed photons (arxiv: v2 and CMS PAS EXO14-017), disappearing tracks (arxiv: v1 and arxiv: v2), multicharge LLP (arxiv: v1), stopped particles (arxiv: v3 and arxiv: v2). Depending on the signatures, no events have been found or observations are consistent with background expectations. MS vertices ϕ versus η position obtained from ATLAS 13 TeV data corresponding to an integrated luminosity of 78 pb -1 Run 2: exploiting higher energies to keep searching! 16

17 Back-up mateial 17

18 ATLAS: displaced vetices axiv: , submited to PRD a) and b) RPV c) GMSB d) split SUSY 18

19 ATLAS: displaced vetices in MS + ID PRD 92, (2015) 19

20 ATLAS: displaced vetices in MS + ID PRD 92, (2015) 20

21 ATLAS: Lepto Jets JHEP 11 (2014)

22 ATLAS 22

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