Searches for new physics at ATLAS

Transcription

1 1 Searches for new physics at ATLAS Gökhan Ünel U.C. Irvine On behalf of the ATLAS collaboration ICPP 2011 Istanbul

2 Outline 2 LHC has been giving us data at ever increasing pace. Lint =1 fb reached as of 17 th June 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

3 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

4 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

5 di-jet Resonances arxiv: 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

6 di-jet Limits 6 95% C.L. Limits (TeV) Observable Expected Observed Exited quark q* m jj F Χ (m jj ) Randall-Meade quantum black hole for n=6 m jj F Χ (m jj ) Axigluon m jj Contact interaction Λ F Χ (m jj ) mjj : reconstructed invariant mass Fx : scale at which new physics appears

7 di-jet 2011 updates ATLAS-CONF Events s=7 TeV, L dt = 163 pb Data Fit q*(00) q*(1700) q*(2750) A [pb] 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 ATLAS Preliminary Reconstructed m jj [GeV] Resonance Mass [GeV] Observable Observed 95% C.L. Limits (TeV) Exited quark q* m jj 2.49 Axigluon m jj 2.67

8 di-lepton Resonances 8 ATLAS-CONF 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 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 ATLAS Preliminary L dt = 236 pb s = 7 TeV Z/ * Diboson tt W+Jets QCD Z (00 GeV) Z (1250 GeV) Z (1500 GeV) m ee [GeV] m µµ [GeV] electrons muons

9 di-lepton Limits 9 Previous lower Limits [TeV] assuming SM couplings W Z CDF D 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 C.L. M Z (SSM) > TeV -2 ee: L dt = 167 pb µµ: ATLAS Preliminary L dt = 236 pb Z Z M Z* > TeV (first limit on Z* mass) M [TeV] E6 Z Z N Z Z I Z S Z Mass limit (TeV)

10 di-leptons on contact Interactions arxiv: 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

11 di-leptons on W and W* 11 arxiv: 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

12 W and W* Limits recall other limits W Z CDF D CMS 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

13 W and W* 2011 updates 13 Events 6 Data ATLAS Preliminary W µ s = 7 TeV L dt = 205 pb W (500) W (00) W (1500) W Z ttbar Diboson ATLAS-CONF muon channel early 2011 data Lint=205 pb 3 m T [GeV] B [pb] NNLO theory Observed limit Expected limit 1 Expected ± 1 Expected ± & early 2011 combined 95% CL below 1.70 TeV ATLAS Preliminary W l ( ) s = 7 TeV, Ldt = 241 pb m W [GeV]

14 di-photons on RS Gravitons ATLAS-CONF 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 = C.L. (m G limits for coupling 0.01 and 0.1 by D0: 560 and 50 GeV CDF : 459 and 963 GeV)

15 ttbar Resonances ATLAS-CONF 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 > mj

16 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 < % C.L.

17 Fourth generation quarks ATLAS-CONF 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 95% C.L. 95% C.L limits by CDF: m d4 > 372 GeV and m u4 > 356 GeV

18 Leptoquark Searches arxiv: 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

19 Leptoquark Limits 19 1 st generation 2 nd generation 95% C.L. Lower limit on LQ

20 Susy Searches Squarks & Gluinos w/ final state: jets+met+ 0,1 leptons 1 lepton details in arxiv: lepton details in arxiv: no deviation from SM squarks and gluinos of equal mass are excluded below 815 GeV at 95% CL ATLAS-CONF

21 Squarks & Gluionos 2011 updates 21 Much better limits with Lint=165pb Still no sign of susy.. [GeV] m 1/ 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) [GeV] ± 1 D0 ~ g, ~ q, tan =3, µ<0, 2.1 fb CDF ~ g, ~ q, tan =5, µ<0, 2 fb m 0

22 Susy Searches -2 arxiv: 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 masses in GeV

23 Susy Searches Gluinos w/ final states : MET+ b-jets no excess, Limit 95%CL mgluino>590gev for msbottom<500gev arxiv: Neutralinos & squarks w/ final states: MET+ll opposite vs same&opposite signs no excess, Limit 95%CL msquark > [ ] GeV depending on specific susy model arxiv: arxiv:

24 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!

25 Backup slides 25

26 di-jet angular distribution 26 χ distribution is relatively flat for QCD Fraction of di-jets produced centrally versus total number of di-jets

27 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: v1 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

28 Leptoquarks searches arxiv: Leptoquarks particles that carry both lepton and baryon quantum numbers Leptoquark production from qqbar annihilation or gluon fusion (hep-ph/ v1) 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

29 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

30 di-lepton Resonances w/ 20 data arxiv: 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

31 di-lepton Limits w/ 20 data 31 Previous lower Limits [TeV] assuming SM couplings W Z CDF D CMS No evidence for resonance The e + e - /µ + µ - combined mass C.L. M Z (SSM) > TeV M Z* > TeV (first limit on Z* mass) E6 Z Z N Z Z I Z S Z Mass limit (TeV)

32 ttbar Resonances w/ 20 data ATLAS-CONF 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 > mj

33 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 < C.L.