1 Searches for new physics at ATLAS Gökhan Ünel U.C. Irvine On behalf of the ATLAS collaboration ICPP 2011 Istanbul
Outline 2 LHC has been giving us data at ever increasing pace. Lint =1 fb reached as of 17 th June 2011. Limits from resonances dijets dileptons : Z & Contact IA dileptons : W bosons diphotons : Gravitons ttbar New particle searches 4th generation quarks Lepto-quarks Susy Searches Lint =1 fb
introduction: SM 3 Fermions as matter particles Quarks & Leptons Gauge group structure gauge bosons as force carriers EW Symmetry Breaking mass via Higgs bosons 3+1 space-time SM is like your old car: you like it but you also know it has problems... SM can not be the final theory: Hierarchy problem: δh ~ MH EW and Strong forces not unified Arbitrary fermion masses & mixings Arbitrary number of families Unknown source of baryogenesis
introduction: SM to BSM 4 Super Symmetry Fourth Family GUTs Gauge G Little Higgs 2HDMs Fermions as matter particles Quarks & Leptons new quarks Gauge group structure gauge bosons as force carriers new gauge bosons EW Symmetry Breaking mass via Higgs bosons new scalars new leptons new EWSB mchanism 3+1 space-time lepto-quarks new constituents composite models Dynamical Symmetry Breaking Technicolor new dimensions RS Model ADD Models
di-jet Resonances arxiv:13.3864 5 These 2 2 scattering processes are well described within SM sensitive to new phenomena Observables : Di-jet invariant mass Di-jet angular distributions of energetic jets relative to the beam axis Events with two highest p T jets recoiling back to back with rapidities, y 1 and y 2 No evidence for a bump in m jj X 2 test, p-value 0.88 Set exclusion limits
di-jet Limits 6 95% C.L. Limits (TeV) Observable Expected Observed Exited quark q* m jj 2.07 2.15 F Χ (m jj ) 2.12 2.64 Randall-Meade quantum black hole for n=6 m jj 3.64 3.67 F Χ (m jj ) 3.49 3.78 Axigluon m jj 2.01 2. Contact interaction Λ F Χ (m jj ) 5.72 9.51 mjj : reconstructed invariant mass Fx : scale at which new physics appears
di-jet 2011 updates ATLAS-CONF-2011-081 7 Events 4 3 2 s=7 TeV, L dt = 163 pb Data Fit q*(00) q*(1700) q*(2750) A [pb] 3 2 1 q* MC A (MRST) Observed 95% CL upper limit Expected 95% CL upper limit 68% and 95% bands ATLAS Preliminary L dt = 163 pb s = 7 TeV 1 significance 2 0-2 ATLAS Preliminary 00 2000 3000 4000 00 2000 3000 4000 Reconstructed m jj [GeV] -2 00 2000 3000 4000 Resonance Mass [GeV] Observable Observed 95% C.L. Limits (TeV) Exited quark q* m jj 2.49 Axigluon m jj 2.67
di-lepton Resonances 8 ATLAS-CONF-2011-083 Signature: Opposite charge, same flavor di-lepton (e + e - /µ + µ - ) Observable : invariant mass of di-lepton Backgrounds: Z/γ* (Drell-Yan), QCD, tt, di-boson (WW/WZ and ZZ)W+jets Signals : leptophobic Z (PYTHIA), Z* (CompHEP using CTEQ6L1) Events 5 4 3 2 1 ATLAS Preliminary L dt = 167 pb s = 7 TeV Data 2011 Z/ * QCD Diboson W+Jets tt Z (00 GeV) Z (1250 GeV) Z (1500 GeV) Events 5 Data 2011 4 3 2 1 ATLAS Preliminary L dt = 236 pb s = 7 TeV Z/ * Diboson tt W+Jets QCD Z (00 GeV) Z (1250 GeV) Z (1500 GeV) -2 80 0 200 300 00 2000 m ee [GeV] 80 0 200 300 00 2000 m µµ [GeV] electrons muons
di-lepton Limits 9 Previous lower Limits [TeV] assuming SM couplings W Z CDF 1.12 1.071 D0 1.0 1.023 B [pb] 1 s = 7 TeV Z ll Expected limit Expected ± 1 Expected ± 2 Observed limit Z SSM No evidence for resonance The e + e - /µ + µ - combined mass limits @95 C.L. M Z (SSM) > 1.407 TeV -2 ee: L dt = 167 pb µµ: ATLAS Preliminary L dt = 236 pb Z Z M Z* > 1.152 TeV (first limit on Z* mass) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 M [TeV] E6 Z Z N Z Z I Z S Z Mass limit (TeV) 1.116 1.142 1.150 1.203 1.230 1.259
di-leptons on contact Interactions arxiv:14.4398 g : coupling constant Λ: energy scale below which fermion constituents are bound g/λ 2 =1 and η LL, η LR, η RR =1 Use the same event selection as in heavy resonance searches Signal broad deviation from SM not a peak 95%C.L. Λ >4.9 TeV Λ + > 4.5 TeV
di-leptons on W and W* 11 arxiv:13.1391 Signature : High p T isolated lepton (e,µ) and large missing energy Observable : Transverse mass Backgrounds W l ν (irreducible) Drell-Yan, ttbar, di-boson QCD multi-jet, Cosmic rays (from data) Signal W (PYTHIA), W* (CompHep using CTEQ6L1) electron channel muon channel
W and W* Limits recall other limits W Z CDF 1.12 1.071 D0 1.0 1.023 CMS 1.58 1.14 12 e/µ combined result for W e/µ combined result for W* No evidence found Lower limits on W and W* are set at 95% C.L m W > 1490 GeV and m W* >1350 GeV
W and W* 2011 updates 13 Events 6 Data 2011 5 4 3 2 1 ATLAS Preliminary W µ s = 7 TeV L dt = 205 pb W (500) W (00) W (1500) W Z ttbar Diboson ATLAS-CONF-2011-082 -2 2 muon channel early 2011 data Lint=205 pb 3 m T [GeV] B [pb] NNLO theory Observed limit Expected limit 1 Expected ± 1 Expected ± 2-2 20 & early 2011 combined 95% CL below 1.70 TeV ATLAS Preliminary W l (20-2011) s = 7 TeV, Ldt = 241 pb 500 00 1500 m W [GeV]
di-photons on RS Gravitons ATLAS-CONF-2011-044 14 RS introduces an extra spatial dimension (ED) to resolve hierarchy problem TeV scales Plank scale Λ π = 1/ 8 M PI exp(k π r c ) (k=curvature, r c : ED radius) Massive graviton excitations Kaluza-Klein (KK) tower m G > 545 (920) GeV for k/m PI = 0.02 (0.1) @ 95 C.L. (m G limits for coupling 0.01 and 0.1 by D0: 560 and 50 GeV CDF : 459 and 963 GeV)
ttbar Resonances ATLAS-CONF-2011-087 15 Signature : (At least one W reconstructed leptonically): High pt isolated lepton (e,µ), jets and large missing energy Observable : Invariant mass of ttbar computed from the reconstructed objects in the final state Objects are not assigned to either of the t (i.e. no t reconstruction) Two methods to reconstruct ttbar: 4 hardest jets - four highest pt jets drmin method - as 4 hardest jet, but removes jet if ΔRlj > 2.5-0.015 mj
ttbar Limits 16 The observed cross section limits on σ Br(Z ttbar) ranges from 38 pb at M = 500 GeV to 2.2 pb at M=1300 GeV for leptophobic Z Exclude M gkk < 650 GeV @ 95% C.L.
Fourth generation quarks ATLAS-CONF-2011-022 17 Fourth generation is not excluded with the EW fit Pair production of Q 4 Ws decay leptonically Discriminating variables : H T and M collinear Main background : ttbar background H T > X-Y M coll. remove significant background while sacrificing a small fraction of events signal m Q4 > 270 GeV/c 2 @ 95% C.L. 95% C.L limits by CDF: m d4 > 372 GeV and m u4 > 356 GeV
Leptoquark Searches arxiv:14.4481 18 Observables: Leptoquark invariant mass or transverse mass depending on the lepton charge. Backgrounds : lljj : Z+jet and ttbar and lvjj : W+jets and ttbar Rejection: measured transverse energy: eejj eνjj
Leptoquark Limits 19 1 st generation 2 nd generation 95% C.L. Lower limit on LQ
Susy Searches Squarks & Gluinos w/ final state: jets+met+ 0,1 leptons 1 lepton details in arxiv:12.2357 0 lepton details in arxiv:12.5290 no deviation from SM squarks and gluinos of equal mass are excluded below 815 GeV at 95% CL ATLAS-CONF-2011-064 20
Squarks & Gluionos 2011 updates 21 Much better limits with Lint=165pb Still no sign of susy.. [GeV] m 1/2 600 550 500 450 400 350 300 250 200 150 MSUGRA/CMSSM: tan =, A = 0, µ>0 0 ATLAS 0 lepton 2011 combined int L = 165 pb, q ~ (600) Preliminary ~ q (00) s=7 TeV ~ q (1400) ~ g (00) Observed 95% C.L. limit Median expected limit CL s Observed 95 % C.L. limit CL s Median expected limit Reference point 20 data PCL 95% C.L. limit CMS 20 Razor,Jets/MHT LEP 2 ~ g (800) ~ g (600) 500 00 1500 2000 2500 [GeV] ± 1 D0 ~ g, ~ q, tan =3, µ<0, 2.1 fb CDF ~ g, ~ q, tan =5, µ<0, 2 fb m 0
Susy Searches -2 arxiv:13.1984 22 Stable hadronising Squarks and Gluinos (R-hadrons) slowly moving stable particles with final state: High pt track associated with energy depositions in the calorimeter. ATLAS also sought for neutral R-hadrons Aleph CDF CMS no excess observed 95%CL limits set sbottom stop gluino 294 309 586 masses in GeV
Susy Searches -3 23 Gluinos w/ final states : MET+ b-jets no excess, Limit set @ 95%CL mgluino>590gev for msbottom<500gev arxiv:13.4344 Neutralinos & squarks w/ final states: MET+ll opposite vs same&opposite signs no excess, Limit set @ 95%CL msquark > [450.. 690] GeV depending on specific susy model arxiv:13.6208 arxiv:13.6214
Conclusions 24 Very successful LHC run at 7 TeV so far. ~50 pb data is collected in 20 Many BSM scenarios studied with 20 and early 2011 data. No deviations from the SM found; yet. TeV scale limits were set : some world s best limits 2011 data taking is going very well : Lumi record set 2011 target reached more than 1fb already collected. Keep watching us for new results!
Backup slides 25
di-jet angular distribution 26 χ distribution is relatively flat for QCD Fraction of di-jets produced centrally versus total number of di-jets
About new heavy bosons 27 Many models predict additional new heavy gauge bosons beyond SM (W (*),Z (*) ) Sequential Standard Model (SSM) Same coupling to fermions as SM Width increases linearly with W /Z mass GUT E6 inspired Z Different model leads to specific Z states : arxiv:0801.4235v1 Z Z* New Chiral boson spin 1 bosons - W*, Z* Excited bosons Different couplings to fermions (magnetic moment type) Differential cross section for Z and Z* at 800GeV < M ll < 1200 GeV
Leptoquarks searches arxiv:14.4481 28 Leptoquarks particles that carry both lepton and baryon quantum numbers Leptoquark production from qqbar annihilation or gluon fusion (hep-ph/9808413v1) Many models predicts leptoquarks Quark and lepton sub-structure Theories seek GUT Extended technicolor LO search - LQ pair production e/µ for 1st/2nd LQ generation through lljj and lvjj
Susy Searches 29 Give up the (so far) observed spin asymmetry between matter and force carriers: partners for all SM particles solves Fine Tuning, DM.. problems SUSY not observed: sparticles heavy: broken symmetry Rich phenomenology (even with Rparity): large # of parameters: >0 in MSSM case R many SB options: MSSM, msugra, GMSB, AMSB.. Common properties: has 5 parameters cascade decays of sparticles to high pt objects, stable LSP escapes undetected: large ET miss. has 6 parameters Look for: jets + E T miss and leptons +jets + E T miss R #parameters=124 given in SN-ATLAS-2006-058
di-lepton Resonances w/ 20 data arxiv:13.6218 30 Signature: Opposite charge, same flavor di-lepton (e + e - /µ + µ - ) Observable : invariant mass of di-lepton Backgrounds: Z/γ* (Drell-Yan), QCD, tt, di-boson (WW/WZ and ZZ)W+jets Signals : Z (PYTHIA), Z* (CompHEP using CTEQ6L1) electrons muons
di-lepton Limits w/ 20 data 31 Previous lower Limits [TeV] assuming SM couplings W Z CDF 1.12 1.071 D0 1.0 1.023 CMS 1.58 1.14 No evidence for resonance The e + e - /µ + µ - combined mass limits @95 C.L. M Z (SSM) > 1.048 TeV M Z* > 1.152 TeV (first limit on Z* mass) E6 Z Z N Z Z I Z S Z Mass limit (TeV) 0.738 0.763 0.771 0.842 0.871 0.900
ttbar Resonances w/ 20 data ATLAS-CONF-2011-070 32 Signature : (At least one W reconstructed leptonically): High pt isolated lepton (e,µ), jets and large missing energy Observable : Invariant mass of ttbar computed from the reconstructed objects in the final state Objects are not assigned to either of the t (i.e. no t reconstruction) Two methods to reconstruct ttbar: 4 hardest jets - four highest pt jets drmin method - as 4 hardest jet, but removes jet if ΔRlj > 2.5-0.015 mj
ttbar Limits w/ 20 data 33 The observed cross section limits on σ Br(Z ttbar) ranges from 55 pb at M = 500 GeV to 2.2 pb at M=00 GeV Exclude M QBH < 2400 GeV @ 95 C.L.