ATLAS : highlights from the first run and prospects for 2011

F.Gianotti, Evian, 8/12/2010

F.Gianotti, Evian, 8/12/2010 2

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%


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


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


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


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)


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


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


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


An asymmetric dijet event with a “quenched jet”

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Asymmetry A j = ET1 - ET2

ET1 + ET2


Where are we today ?

W ✔Z ✔

top ✔

Next to come … ?

€

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


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


2011 (2012): the year(s) of the Higgs ?

Higgs in ATLAS

… and of the “race” with Tevatron …


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


2011

2014

LEPexcluded

Tevatronexcluded

Tevatron


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


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 …)


Spares



~ 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)

Documents

ATLAS : highlights from the first run and prospects for 2011