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
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? MIAMI2015 - Dec 19 Vivek Jain 2
Search for heavy particles becomes more sensitive with increasing Energy MIAMI2015 - Dec 19 Vivek Jain 3
Many models and often overlapping signatures take agnostic approach Need to understand SM processes to get handle on backgrounds All results on ATLAS Twiki MIAMI2015 - Dec 19 Vivek Jain 4
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 ~3.2-3.6 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 MIAMI2015 - Dec 19 Vivek Jain 5
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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 MIAMI2015 - Dec 19 Vivek Jain 7
0 leptons + (2-6 jets) + MET ATLAS-CONF-2015-062 MIAMI2015 - Dec 19 Vivek Jain 8
Limits for 2-6 jets: Already more sensitive than Run-1 results Use simplified model to get these limits MIAMI2015 - Dec 19 Vivek Jain 9
1 lepton + jets + MET ATLAS-CONF-2015-076 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 MIAMI2015 - Dec 19 Vivek Jain 10
Mild excess: Obsvd 10 events Fitted bkgd: 4.4±1.0 (MC prediction = 5.2) MIAMI2015 - Dec 19 Vivek Jain 11
2 leptons (Z)+ jets+ MET ATLAS-CONF-2015-82 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 MIAMI2015 - Dec 19 Vivek Jain 12
3 leptons or 2 same-sign leptons + MET ATLAS-CONF-2015-078 MIAMI2015 - Dec 19 Vivek Jain 13
No excess MIAMI2015 - Dec 19 Vivek Jain 14
Multi b-quark final state ATLAS-CONF-2015-067 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 MIAMI2015 - Dec 19 Vivek Jain 15
Sbottom ATLAS-CONF-2015-066 Targets small mass differences ε ~ 5-10% for SRA w/ sbottom=800 GeV, χ=1 GeV MIAMI2015 - Dec 19 Vivek Jain 16
Search for Exotic phenomena Here there are many models that can give rise to visible, overlapping signatures in the detector Take an agnostic approach MIAMI2015 - Dec 19 Vivek Jain 17
Di-jet resonances (W /Z, q*, Contact Interactions, arxiv:1512.01530 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 MIAMI2015 - Dec 19 Vivek Jain 18
Dijets angular search χ = exp( y 3 -y 4 ) ~ (1+cosθ*)/(1-cosθ*) MIAMI2015 - Dec 19 Vivek Jain 19
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 MIAMI2015 - Dec 19 Vivek Jain 20
Multi-jets (thermal black holes/string balls) arxiv: 1512.02586 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 MIAMI2015 - Dec 19 Vivek Jain 21
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-2015-073 llj ATLAS-CONF-2015-071 ννj ATLAS-CONF-2015-068 MIAMI2015 - Dec 19 Vivek Jain 22
Dileptons Z, LED, Contact Int (ATLAS-CONF-2015-070) Lepton + MET (W ) ATLAS-CONF-2015-063 MIAMI2015 - Dec 19 Vivek Jain 23
Dark Matter (W/Z + MET) ATLAS-CONF-2015-080 Data/expectation for V-mediated simplied model Limits on EFT models Excluded region MIAMI2015 - Dec 19 Vivek Jain 24
γγ resonances ATLAS-CONF-2015-081 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 MIAMI2015 - Dec 19 Vivek Jain 25
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 MIAMI2015 - Dec 19 Vivek Jain 26
Backup MIAMI2015 - Dec 19 Vivek Jain 27
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S. Willocq MIAMI2015 - Dec 19 Vivek Jain 29
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Kado, Dec. 15 - EOYE MIAMI2015 - Dec 19 Vivek Jain 31
Improvements in detector performance tracking muon All detector systems, object reconstruction working as expected MIAMI2015 - Dec 19 Vivek Jain 32
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B-tagging in Run2 vs. Run1 MIAMI2015 - Dec 19 Vivek Jain 34
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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 MIAMI2015 - Dec 19 Vivek Jain 36
0 lepton, 2-6 jets For each Signal region MIAMI2015 - Dec 19 Vivek Jain 37
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 MIAMI2015 - Dec 19 Vivek Jain 38
SUSY: 0lepton + 2-6 jets CRγ for 4jt MIAMI2015 - Dec 19 Vivek Jain 39
SUSY: 1 lepton MIAMI2015 - Dec 19 Vivek Jain 40
1-lepton (SUSY) validation regions MIAMI2015 - Dec 19 Vivek Jain 41
SUSY I-lepton MIAMI2015 - Dec 19 Vivek Jain 42
Results for two models: x= ΔM(chargino, neutralino)/δm(gluino, neutralino) = ½ SUSY I-lepton Neutralino fixed to 60 GeV MIAMI2015 - Dec 19 Vivek Jain 43
0 SUSY MIAMI2015 - Dec 19 Vivek Jain 44
SUSY: 2-lepton (Z) MIAMI2015 - Dec 19 Vivek Jain 45
SUSY: 2SS or 3Lep MIAMI2015 - Dec 19 Vivek Jain 46
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. MIAMI2015 - Dec 19 Vivek Jain 47
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. MIAMI2015 - Dec 19 Vivek Jain 48
Exotics dijet analysis MIAMI2015 - Dec 19 Vivek Jain 49
Exotics: MultiJet Tables are for step 4 Limit plot is for black hole MIAMI2015 - Dec 19 Vivek Jain 50
Exotics: Photon+Jet MIAMI2015 - Dec 19 Vivek Jain 51
Exotics: MultiJet Limit plot is for string balls MIAMI2015 - Dec 19 Vivek Jain 52
ννqq final state Exotics: qqqq Diboson Resonance MIAMI2015 - Dec 19 Vivek Jain 53
Dileptons: Exotics MIAMI2015 - Dec 19 Vivek Jain 54
Exotics Lepton + MET pt (e) > 65, pt(mu)>55 similar cuts on MET Veto if 2 nd lepton w/ pt > 20 MIAMI2015 - Dec 19 Vivek Jain 55
Dark Matter (W/Z + MET) EFT approach Simplified model MIAMI2015 - Dec 19 Vivek Jain 56
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gamma/gamma resonance MIAMI2015 - Dec 19 Vivek Jain 59