Marcel Vreeswijk (Nikhef/UvA-IoP) First Results of ATLAS at the LHC -- The rediscovery of the Standard Model-- Contents: Intro: The Standard Model Elementairy particles. Status LHC and ATLAS Physics results 2010

The Standard Model So, what have we been doing in 2010? Measuring ‘backgrounds’! Higgs mechanisme to generate mass! Higgs boson mass > 114 GeV Ultimate goal: detect the Higgs particle (not yet;need more data!)

Marcel Vreeswijk (Nikhef/UvA-IoP) CERN site LHC P+P at 7TeV 27km 60 ton He at 2K 4 big experiments this talk: ATLAS First year of running. (7TeV) high quality data 2010: ~35pb-1 In 2011: run at 7TeV or higher? >>10-fold luminosity? The LUMINOSITY represents the delivered number of proton collisions In addition: Pb+Pb collisions (not in this talk) atlas Large Hadron Collider (LHC)

Marcel Vreeswijk (Nikhef/UvA-IoP) LHC physics reach Production Cross-section of top quarks and W, Z bosons are measurable with 2010 data! Top, W,Z signals are important: 1.Standard candles for calibration 2.Background to new physics & Higgs searches M 5 T # events in 2010 Higgs Top quarks W,Z bosons Proton-Proton In reach in 2010 Higgs W, Z Promising final states: H  W + W -  2 leptons + EtMiss H  ZZ  4 leptons Also H  2 photons 7TeV in 2010 jargon: lepton=electron or muon N = L.  N = # collisions L = Luminosity  = cross-section

Marcel Vreeswijk (Nikhef/UvA-IoP) Inner detector (charged particle tracks) Calorimeter (energy all particles, but muons) Muon ‘Chambers’ ATLAS p Data rec. 93.5% #working channels >99%

Marcel Vreeswijk (Nikhef/UvA-IoP) Performance Inner Tracker 1 m Inner Tracker KsKs    Kaon discovery: 1947 Pixel detector (80M channels) Silicon strips (6M channels) TRT (350k channels) Operational for 97.5% Momentum measurement in magnetic field of 2T Resolution σ(pT)/pT = 0.05%pT ⊕ 1%

Marcel Vreeswijk (Nikhef/UvA-IoP) Performance Calorimeter electromagnetic: Liquid Argon sampling calorimeter. Resolution ~10%/sqrt(E) Granularity: eta x phi=0.025 x    since 1950 Rediscovery of the  0 8m

Marcel Vreeswijk (Nikhef/UvA-IoP) Di-jet physics

Marcel Vreeswijk (Nikhef/UvA-IoP) Di-jet invariant mass New energy domain. Highest Pt jet: 1.12 TeV Highest mass: 3.7 TeV Searches for new physics ongoing ATLAS published 3 papers on jet measurements pp jet

Marcel Vreeswijk (Nikhef/UvA-IoP) Performance Muons Physics signals show up! Muon system: 1200 Muon chamber 350k drift tubes (air core toroidal field 0.5T) Designed for TeV muons (not yet) Z boson ‘rediscovered’ Originally: 1983 at CERN Mass: GeV

Marcel Vreeswijk (Nikhef/UvA-IoP) Muon resonances ATLAS 2010   ? mass Published 2010 Z cross-section in new energy domain=7TeV

Marcel Vreeswijk (Nikhef/UvA-IoP)  Missing Transverse energy W boson ‘rediscovered’ Originally: 1983 at CERN Mass: 80.4 GeV

Marcel Vreeswijk (Nikhef/UvA-IoP) W boson production W decays to muon + (unseen) neutrino.  Missing transverse energy.  W q q’ g Transverse W mass:

Marcel Vreeswijk (Nikhef/UvA-IoP) Top pair (ttbar) production complicated events: 1.Many jets with 2 b-jets (can be ‘tagged’) 2.Electron or Muon 3.EtMiss  Standard candle  New physics may show up p p t t ttbar has two measurable decays modes:  single-lepton  di-lepton (mode is set by W decay) ttbar single-lepton Datum Basic prper. Europ. Topds! Last heaviest known particle Last before new

Marcel Vreeswijk (Nikhef/UvA-IoP) di-leptonic ttbar 2 b-tagged jets

Marcel Vreeswijk (Nikhef/UvA-IoP) ttbar More info on poster by Ido & Hegoi N. from Nikhef Van Tera naar 100evts selectie Speld hooi

Marcel Vreeswijk (Nikhef/UvA-IoP) ttbar: theory & experiment

Marcel Vreeswijk (Nikhef/UvA-IoP) Higgs in 2011 ? We have measured the ‘backgrounds’, now we are ready for the signal ! Conclusion The LHC and the ATLAS detector have demonstrated to be ready for the Standard Model Higgs or new physics See next talk by Paul de Jong!

Marcel Vreeswijk (Nikhef/UvA-IoP) BACKUP “We know everything about the Higgs boson except its mass” Λ (GeV) Higgs mass (GeV) Triviality Vacuum stability Limits on m h from theory Limits on m h from exper.

Marcel Vreeswijk (Nikhef/UvA-IoP) W boson cross section

Marcel Vreeswijk (Nikhef/UvA-IoP) Photon production (QCD compton) photons of hundreds of GeVs ! (Xray GeV)

Marcel Vreeswijk (Nikhef/UvA-IoP)

The Standard Model Ultimate goal: detect the Higgs particle (not yet…need more data!) So, what have we been doing in 2010? Measuring ‘backgrounds’! + Higgs boson to generate mass! Promising decay modes H  2 photons H  W+W-  2 leptons + EtMiss H  ZZ  4 leptons and much more….

Marcel Vreeswijk (Nikhef/UvA-IoP) The Standard Model Production Cross-section of top quarks and W, Z bosons are measurable with 2010 data! Top, W,Z signals are important: 1.Standard candles for calibration 2.Background to new physics & Higgs searches M 5 T # events in 2010 Higgs Top quarks W,Z bosons Proton-Proton In reach in 2010 Note: a proton=many quarks+gluons Higgs W, Z Promising final states: H  W + W -  2 leptons + EtMiss H  ZZ  4 leptons Also H  2 photons 7TeV in 2010 jargon: lepton=electron or muon

Marcel Vreeswijk (Nikhef/UvA-IoP) CERN site LHC P+P at 7TeV 27km 60 ton He at 2K 4 big experiments this talk: ATLAS First year of running. (7TeV) high quality data 2010: ~35pb-1 This year (2011): run at 7TeV or higher? >>10-fold luminosity? The LUMINOSITY represents the delivered number of proton collisions 3.2T botsingen 655k hi Pb=Pb

Marcel Vreeswijk (Nikhef/UvA-IoP) Z boson production  Do we understand Z production and its backgrounds?  First measurement ever at 7 TeV. Ook in e+e- Diagrammen Lin schaal? Datum Z massa 2Gev wordt 90GeV