Recent searches for new particles using 13 TeV data with ATLAS at the LHC

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1 Recent searches for new particles using 13 TeV data with ATLAS at the LHC Vivek Jain (on behalf of the ATLAS Collaboration) State University of New York, Albany MIAMI2015 Dec 19, 2015

2 Beyond the Standard Model Many questions unanswered by the SM: The vast gap between Planck and EW scales Is the Higgs mass light because of SUSY, vector-like (top) quarks, new interactions? Are there extra dimensions that cause gravity to be weak Is the Higgs a fundamental or composite particle? What makes up dark matter? Are there more than 4 forces? MIAMI Dec 19 Vivek Jain 2

3 Search for heavy particles becomes more sensitive with increasing Energy MIAMI Dec 19 Vivek Jain 3

4 Many models and often overlapping signatures take agnostic approach Need to understand SM processes to get handle on backgrounds All results on ATLAS Twiki MIAMI Dec 19 Vivek Jain 4

5 LHC & Detector performance in 2015 Improvements to ATLAS: a) Extra pixel layer at R ~ 33 mm very useful for tracking, vertexing, b-tagging b) Improved muon coverage, support services... Performance already very good in 2015 Will keep improving Use ~ fb -1 data collected at 13 TeV pp collisions Data mainly with 25 ns bunch spacing: L peak = 5.1e-33 cm -2 s -1 <μ> ~ 13. Use a various triggers MIAMI Dec 19 Vivek Jain 5

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7 Search for Supersymmetry From Naturalness, gluinos, 3 rd generation squarks, (and Higgsinos) could have lower masses than others In the early 13 TeV running, focus on particles produced in strong interactions and where S/B is expected to be high Today focus on gluino/sbottom searches - assuming R-parity conservation, i.e., LSP escapes misse T All analyses make use of control and validation regions to predict background and understand MC modelling In general, analyses have more than 1 signal region, which are separately optimized for different event characteristics MIAMI Dec 19 Vivek Jain 7

8 0 leptons + (2-6 jets) + MET ATLAS-CONF MIAMI Dec 19 Vivek Jain 8

9 Limits for 2-6 jets: Already more sensitive than Run-1 results Use simplified model to get these limits MIAMI Dec 19 Vivek Jain 9

10 1 lepton + jets + MET ATLAS-CONF Analysis split into two streams Hard lepton (pt > 35 GeV) larger mass difference between chargino and neutralino Soft lepton (pt > 7/6 GeV) targets Compressed models or small mass differences MIAMI Dec 19 Vivek Jain 10

11 Mild excess: Obsvd 10 events Fitted bkgd: 4.4±1.0 (MC prediction = 5.2) MIAMI Dec 19 Vivek Jain 11

12 2 leptons (Z)+ jets+ MET ATLAS-CONF Observe 21 events in ee+μμ Total exp. Background 10.3±2.3 mild excess ~ 2.2σ Very similar Signal Region as Run-1 which had 1.7/3σ excess in μμ/ee MIAMI Dec 19 Vivek Jain 12

13 3 leptons or 2 same-sign leptons + MET ATLAS-CONF MIAMI Dec 19 Vivek Jain 13

14 No excess MIAMI Dec 19 Vivek Jain 14

15 Multi b-quark final state ATLAS-CONF If 3 rd generation squarks, as hoped, are lighter than 1 st two generations, will have many b, t quarks in final state tttt final state can have isolated leptons & has more jets than bbbb final state MIAMI Dec 19 Vivek Jain 15

16 Sbottom ATLAS-CONF Targets small mass differences ε ~ 5-10% for SRA w/ sbottom=800 GeV, χ=1 GeV MIAMI Dec 19 Vivek Jain 16

17 Search for Exotic phenomena Here there are many models that can give rise to visible, overlapping signatures in the detector Take an agnostic approach MIAMI Dec 19 Vivek Jain 17

18 Di-jet resonances (W /Z, q*, Contact Interactions, arxiv: Quantum Black Holes (TeV-gravity)) Leading jet pt>440 GeV & Sub-leading jet > 50 GeV, m jj > 1.1 TeV y* = (y 3 -y 4 )/2 rapidity of outgoing partons, and tends to be large for QCD di-jet events, which are produced at small angles in the COM frame Comparison with Pythia8 MIAMI Dec 19 Vivek Jain 18

19 Dijets angular search χ = exp( y 3 -y 4 ) ~ (1+cosθ*)/(1-cosθ*) MIAMI Dec 19 Vivek Jain 19

20 Photon+Jet resonance (QBH, q*) γ, jet pt > 150 GeV ε for 3.5 TeV q* or QBH (from ADD) ~ 50% BH threshold mass scale = scale of Gravity MIAMI Dec 19 Vivek Jain 20

21 Multi-jets (thermal black holes/string balls) arxiv: Excluded region N jet 3, Jet pt > 50 GeV The three vertical lines are lower boundaries of Control, Validation and Signal regions Also, look at events with 4, 5, 6, 7 and 8 jets (SRs vary) Use bootstrap approach start with 6.5 pb -1 increase sample in steps of ~ 10x MIAMI Dec 19 Vivek Jain 21

22 Di-boson resonances (Heavy bosons, Composite Higgs, Bulk RS model) Run-1 had 2.5σ (global) excess at ~ 2 TeV in qqqq (WZ) JJ ATLAS-CONF llj ATLAS-CONF ννj ATLAS-CONF MIAMI Dec 19 Vivek Jain 22

23 Dileptons Z, LED, Contact Int (ATLAS-CONF ) Lepton + MET (W ) ATLAS-CONF MIAMI Dec 19 Vivek Jain 23

24 Dark Matter (W/Z + MET) ATLAS-CONF Data/expectation for V-mediated simplied model Limits on EFT models Excluded region MIAMI Dec 19 Vivek Jain 24

25 γγ resonances ATLAS-CONF Search optimized for high mass γγ pairs Both narrow & large width scalars studied 2.0σ (global) excess ~ 750 GeV Smaller excess at 1.6 TeV MIAMI Dec 19 Vivek Jain 25

26 Summary and Outlook Run-2 at collision energy of 13 TeV has started and we have collected ~4 fb -1 Upgraded detector is performing well No new effects have been observed as yet, but it is still early in Run-2 Plan to collect ~ 300 fb -1 by 2023 All latest results can be found on ATLAS Twiki MIAMI Dec 19 Vivek Jain 26

27 Backup MIAMI Dec 19 Vivek Jain 27

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29 S. Willocq MIAMI Dec 19 Vivek Jain 29

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31 Kado, Dec EOYE MIAMI Dec 19 Vivek Jain 31

32 Improvements in detector performance tracking muon All detector systems, object reconstruction working as expected MIAMI Dec 19 Vivek Jain 32

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34 B-tagging in Run2 vs. Run1 MIAMI Dec 19 Vivek Jain 34

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36 Some definitions M eff is scalar sum over N leading jets with pt jet > X + MET (may also include leptons) H T is the scalar sum of N jets + leptons MIAMI Dec 19 Vivek Jain 36

37 0 lepton, 2-6 jets For each Signal region MIAMI Dec 19 Vivek Jain 37

38 Use fitted background, using extrapolations from Control Regions and checks in validation regions, for setting limits In general, fitted background agrees very well with SM expectations SUSY 0leptons MIAMI Dec 19 Vivek Jain 38

39 SUSY: 0lepton jets CRγ for 4jt MIAMI Dec 19 Vivek Jain 39

40 SUSY: 1 lepton MIAMI Dec 19 Vivek Jain 40

41 1-lepton (SUSY) validation regions MIAMI Dec 19 Vivek Jain 41

42 SUSY I-lepton MIAMI Dec 19 Vivek Jain 42

43 Results for two models: x= ΔM(chargino, neutralino)/δm(gluino, neutralino) = ½ SUSY I-lepton Neutralino fixed to 60 GeV MIAMI Dec 19 Vivek Jain 43

44 0 SUSY MIAMI Dec 19 Vivek Jain 44

45 SUSY: 2-lepton (Z) MIAMI Dec 19 Vivek Jain 45

46 SUSY: 2SS or 3Lep MIAMI Dec 19 Vivek Jain 46

47 SUSY multi b-quark final states Results of the background-only fit in the validation regions. The tt normalisation is obtained from the fit to the control regions. The upper panel shows the observed number of events and the predicted background yield. The lower panel shows the pulls in each validation region. MIAMI Dec 19 Vivek Jain 47

48 Sbottom production - SUSY a) Signal region A: 2 b-jets further sub-divided into three sub-regions based on contransverse mass, m 2 CT(v1,v2) = [E T (v1)+e T (v2)] 2 [p T (v1)-p T (v2)] 2 Max. value = (m 2 (sb) m 2 (χ))/m(sb) b) Signal region B: Additional non-bjet from ISR for small mass diff. MIAMI Dec 19 Vivek Jain 48

49 Exotics dijet analysis MIAMI Dec 19 Vivek Jain 49

50 Exotics: MultiJet Tables are for step 4 Limit plot is for black hole MIAMI Dec 19 Vivek Jain 50

51 Exotics: Photon+Jet MIAMI Dec 19 Vivek Jain 51

52 Exotics: MultiJet Limit plot is for string balls MIAMI Dec 19 Vivek Jain 52

53 ννqq final state Exotics: qqqq Diboson Resonance MIAMI Dec 19 Vivek Jain 53

54 Dileptons: Exotics MIAMI Dec 19 Vivek Jain 54

55 Exotics Lepton + MET pt (e) > 65, pt(mu)>55 similar cuts on MET Veto if 2 nd lepton w/ pt > 20 MIAMI Dec 19 Vivek Jain 55

56 Dark Matter (W/Z + MET) EFT approach Simplified model MIAMI Dec 19 Vivek Jain 56

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59 gamma/gamma resonance MIAMI Dec 19 Vivek Jain 59