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ATLAS Highlights and Prospects 2011: Advances in Particle Physics

Explore ATLAS's achievements in the first run and upcoming prospects for 2011, from jet "quenching" to top quark measurements, driving the search for new physics and Higgs boson discovery.

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ATLAS Highlights and Prospects 2011: Advances in Particle Physics

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  1. ATLAS: highlights from the first run and prospects for 2011

  2. PbPb pp Recorded Delivered Recorded Delivered ~ 93.6% ~ 94.6% Fraction of good quality data (heavy-ion run) Fraction of good quality data (full pp run) •  Used for analysis: 80-85% of delivered luminosity • with first-pass processing • hope to improve to > 85% after data reprocessing • Cfr: Tevatron experiments: ~ 80% •  Used for analysis: 80-85% of delivered luminosity • with first-pass processing • hope to improve to > 85% after data reprocessing • Cfr: Tevatron experiments: ~ 80%

  3. November: jet “quenching” in HI August: more searches beyond Tevatron October: highest mass di-jet event (3.7 TeV) September: updated Higgs projections for 2011 July: first searches beyond Tevatron June: first top candidates April:1st W May: 1st Z

  4. First W  lν and Z  ll measurements Z  μμ MC In the full data sample recorded this year, ATLAS has: ~ 250k W μν, eν events ~ 23k Z  μμ, ee events  50 times less than CDF or D0 • Excellent agreement with Standard Model • Error dominated by 11% luminosity uncertainty

  5. Top-quark: the heaviest (and most intriguing …) elementary particle observed so far Di-lepton channel tt  bW bW  blν blν The most spectacular ATLAS candidate e,μ ν pT(μ)= 51 GeVpT(e)=66 GeVpT (b-tagged jets) =174,45 GeV ETmiss= 113 GeV, Secondary vertices: distance from primary vertex: 4mm,3.9mm vertex mass : ~2 GeV,~ 4GeV

  6. First top measurements at √s = 7 TeV (mtop= 172 GeV) In the full data sample recorded this year, ATLAS has ~ 700 top-antitop events  only ~ 8 times less than CDF or D0

  7. First limits beyond the Tevatron reach : from dijet final states Highest mass dijet in our data: Mjj =3.7 TeV ET jet1 ~ 670 GeV ET jet2 ~ 610 GeV

  8. Look for di-jet resonances in the measured M(jj) distribution Look for deviations from QCD in the measured di-jet angular distributions • Standard Model: χ distribution ~ flat • Quark sub-structures: excess at low χ Exploration of the TeV scale started in earnest q*  qg ~ 0.5 TeV beyond the Tevatron limits ATLAS: M (q*) > 1.5 TeV ATLAS: Λ > 3.4 TeV

  9. First direct observation of “jet quenching” in heavy-ion collisions One of main goals of high-energy HI collisions: recreate “plasma of free quarks and gluons” “quark-gluon plasma” that (we think) permeated the Universe ~ 10 μs after Big Bang Jets produced in HI collisions would be “quenched” by interacting with the (dense) plasma  expect asymmetric dijets final states • First asymmetric • dijet events • observed by ATLAS • on 8 November • (first day of Pb-Pb • stable beam collisions) • paper submitted • for publication in • Physical Review Letters • on 25 November

  10. An asymmetric dijet event with a “quenched jet”

  11. Where are we today ? Next to come … ? Candidate ZZ  event Jets ✔ W ✔ Z ✔ top ✔ Known SM processes Single-top WW, ZZ, WZ Higgs, mH~120 GeV DISCOVERIES ! By increasing difficulty: Z’, W’, SUSY, Higgs W’ m= 1.5 TeV Z’ m= 1.5 TeV

  12. W’  lν, Z’  ll • Would indicate existence of new (small scale) forces (in addition to the known four) • Present Tevatron limits: ~ 1 TeV 45 pb-1 1 fb-1 5 fb-1 W’ 1.2 TeV 2 TeV 2.4TeV Z’ -- 1.5 TeV 2 TeV ATLAS discovery reach at 7 TeV (very preliminary  more in Chamonix) • Our present best candidate for Universe's dark matter (SUSY’s neutralino) would be • produced in the cascade decays of squarks and gluinos. • Tevatron (exclusion) reach: ~ 450 GeV 1 fb-1 2 fb-1 5 fb-1 √s=7 TeV 0.7 TeV 0.8 TeV 1 TeV √s=8 TeV 0.8 TeV 0.9 TeV 1.1 TeV ATLAS discovery reach (very preliminary  more in Chamonix)

  13. 2011 (2012): the year(s) of the Higgs ? … and of the “race” with Tevatron … Higgs in ATLAS

  14. What do we know today ? • Theory: mH < 1 TeV • Present experimental exclusion: mH > 114.4 GeV (LEP), 158 < mH < 175 GeV (Tevatron) • Favoured region (electroweak data  consistency of Standard Model): mH < 158 GeV •  114.4-158 GeV is the “hottest” region (although higher masses cannot be excluded) • Tevatron luminosity projections: • “Analyzable” by CDF, D0 (i.e. good data quality): ~ 80% of delivered • Today: ~ 9 fb-1 delivered  up to ~ 7 fb-1 analyzed by CDF, D0 • Delivered per year: ~ 2.5 fb-1 ~ 2 fb-1analyzable • 2011: ~ 12 fb-1 delivered  10 fb-1 analyzable • 2014 (if run extended by 3 more years): ~ 20 fb-1 delivered  ~ 16 fb-1 analyzable The Tevatron-LHC complementarity Most difficult region at LHC: mH ~ 114-115 GeV Most difficult region at the Tevatron: mH ~ 135 GeV For mH ~ 115 GeV: best channel at LHC: H  γγ best channel at the Tevatron: WH, ZH with H  bb • Note: • Tevatron analyses very sophisticated (combinations of many decay modes, neural • networks with huge number of input variables, etc.) • LHC projections: very conservative  ATLAS and CMS can do better than shown here • Tevatron: no discovery (5σ) reach (not even if extended by 3 years); max 3σ evidence

  15. Tevatron excluded LEP excluded 2014 Tevatron 2011

  16. Here LHC means ATLAS and CMS combined (very preliminary) Expected Higgs mass coverage (GeV) • Tevatron LHC LHC LHC LHC • 10 fb-1(end 2011) 1 fb-1 7 TeV 1 fb-1 8 TeV 2.5 fb-1 8 TeV 5 fb-1 8 TeV • 95% CL exclusion 114-185 123-550 120-570 114-600 ≥ 114 • 3 σ evidence ~115, 150-180 130-450 127-500 123-530 ≥ 114 • 5 σ discovery --- 152-174 150-176 138-220 120-570 If the Higgs is not there  LHC needs ~ 2.5 fb-1 to compete with Tevatron for exclusion down to lowest masses • If the Higgs exists: • Need 5 fb-1 to compete with Tevatron for 3σ evidence around mH ~ 115 GeV, • but has better sensitivity at higher masses (above ~ 120 GeV) already with 1-3 fb-1 • Discovery (5σ) over full allowed mass region requires ~ 7 fb-1 at 8 TeV Note on 8 TeV vs 7 TeV: -- same reach with ~20% less luminosity -- for same luminosity, extend low-mass reach down by ~ 3 GeV

  17. CONCLUSIONS ATLAS Control Room, 20 November 2009 A fantastic year, exceeding all expectations !! • 2011: the year of first discoveries ? Z’, W’, SUSY, surprises … ? • The Higgs is within reach in the next 1-2 year(s), but the “race” with • the Tevatron will be tough (GeV by GeV, fb-1 by fb-1 …)

  18. Spares

  19. Max peak luminosity: L~ 2 x 1032 cm-2s-1 • average number of pp interactions per bunch-crossing: up to 4 • “pile-up” (~ 80% of the events have > 1 pp interaction per crossing) Event with 4 pp interactions in the same bunch-crossing ~ 10-45 tracks with pT >150 MeV per vertex Vertex z-positions : −3.2, −2.3, 0.5, 1.9 cm (vertex resolution better than ~200 μm)

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