ATLAS : highlights from the first run and prospects for 2011
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Transcript of ATLAS : highlights from the first run and prospects for 2011
F.Gianotti, Evian, 8/12/2010
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RecordedDelivered ~ 93.6%
pp
RecordedDelivered ~ 94.6%
PbPb
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%
Fraction of good quality data (heavy-ion 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%
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April:1st W
May: 1st Z
June: first topcandidates
July: first searchesbeyond Tevatron
August: more searchesbeyond Tevatron
September: updatedHiggs projections for 2011
October: highest mass di-jet event (3.7 TeV)
November: jet “quenching” in HI
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Excellent agreement with Standard Model Error dominated by 11% luminosity uncertainty
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
Z μμMC
First W lν and Z ll measurements
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Top-quark: the heaviest (and most intriguing …) elementary particle observed so far
e,μ
ν
Di-lepton channeltt bW bW blν blν
The most spectacular ATLAS candidate
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In the full data sample recorded this year, ATLAS has ~ 700 top-antitop events only ~ 8 times less than CDF or D0
First top measurementsat √s = 7 TeV(mtop= 172 GeV)
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ET jet1 ~ 670 GeV
ET jet2 ~ 610 GeV
First limits beyond the Tevatron reach : from dijet final states
Highest mass dijet in our data: Mjj =3.7 TeV
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Standard Model: χ distribution ~ flat Quark sub-structures: excess at low χ
Look for deviations from QCD in themeasured di-jet angular distributions
Look for di-jet resonances in the measured M(jj) distribution
ATLAS: Λ > 3.4 TeVATLAS: M (q*) > 1.5 TeV ~ 0.5 TeV beyond the Tevatron limits€
χ =exp (| y1 − y2 |) = 1 + cosϑ *
1 - cosϑ *
q* qgExploration of the TeV scale started in earnest
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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
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An asymmetric dijet event with a “quenched jet”
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Asymmetry A j = ET1 - ET2
ET1 + ET2
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Where are we today ?
W ✔Z ✔
top ✔
Next to come … ?
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SUSY ( ˜ q , ˜ g pairs), m ~ 0.7 TeV
Z’ m= 1.5 TeV
W’ m= 1.5 TeV
Higgs, mH~120 GeV
Single-top
Jets ✔
WW, ZZ, WZ
Known SMprocesses
DISCOVERIES !By increasing difficulty: Z’, W’, SUSY, Higgs
Candidate ZZ event
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Would indicate existence of new (small scale) forces (in addition to the known four) Present Tevatron limits: ~ 1 TeV
W’ lν, Z’ ll
ATLAS discovery reach at 7 TeV(very preliminary more in Chamonix)
45 pb-1 1 fb-1 5 fb-1
W’ 1.2 TeV 2 TeV 2.4TeV Z’ -- 1.5 TeV 2 TeV
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
ATLAS discovery reach(very preliminary more in Chamonix)
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Supersymmetry ˜ q ̃ q , ˜ q ̃ g , ˜ g ̃ g
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
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2011 (2012): the year(s) of the Higgs ?
Higgs in ATLAS
… and of the “race” with Tevatron …
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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-1 analyzable 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 GeVMost 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
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2011
2014
LEPexcluded
Tevatronexcluded
Tevatron
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If the Higgs is not there LHC needs ~ 2.5 fb-1 to compete with Tevatron for exclusiondown to lowest masses
Expected Higgs mass coverage (GeV) Here LHC means ATLAS and CMS combined(very preliminary)
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 ≥ 1143 σ evidence ~115, 150-180 130-450 127-500 123-530 ≥ 1145 σ discovery --- 152-174 150-176 138-220 120-570
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
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ATLAS Control Room, 20 November 2009
A fantastic year, exceeding all expectations !!
CONCLUSIONS
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 …)
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Spares
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~ 10-45 tracks with pT >150 MeV per vertexVertex z-positions : −3.2, −2.3, 0.5, 1.9 cm (vertex resolution better than ~200 μm)
Event with 4 pp interactions in the same bunch-crossing
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)