First physics with the ATLAS and CMS experiments Niels van Eldik on behalf of the ATLAS and CMS collaborations
Content Status of the LHC and the ATLAS and CMS experiments Event production rates First physics with the LHC Summary 2
>Y>.2#G%')?CI&)?B#5%)Z#,2UKT >Y>.2#G%')?CI&)?B#5%)Z#,2UKT ::*#4I(33F3?4)%('*#B%HHI&4)%O?#:ZP3%43# SA+,.#T# %('F%('* :F%('!"#$%&'())%*##+,-./01*#2(34(5*#0670876001 6 <6D6#3N:?I4('BN4)%'C#!"!#$ 6V#WE#A./#I%'C# B%:(L?3#X;8"D#> A-,Q#T# ::*#XF:ZP3%43*#,/FO%(L&)%(' pp collisions at s = 14 TeV: Linitial ~ few x 10 33 cm -2 s -1, Ldesign= 10 34 cm -2 s -1 Heavy ions (e.g. Pb-Pb at s ~1000 TeV) S>ASU#&'B##,2U#T S>ASU#&'B##,2U#T C?'?I&L#:NI:(3? C?'?I&L#:NI:(3? -?I?T# S>ASU#&'B#,2U
ATLAS and CMS CMS ATLAS lepton ID or tracking 4
Detector performance SYSTEM ATLAS CMS INNER TRACKER EM CALO HAD CALO MUON SYSTEM MAGNETS Silicon pixels + strips TRT particle ID (e/π) B=2T σ/p T ~ 4x10-4 p T 0.01 Pb-liquid argon σ/e ~ 10%/ E Uniform longitudinal segmentation Fe-scint. + Cu-liquid argon σ/e ~ 50%/ E 0.03 Air-core toroids σ/pt ~ 10% at 1 TeV standalone Inner tracker in solenoid (2T) Calorimeters in field-free region Muon system in air-core toroids Silicon pixels + strips No particle identification B=4T σ/p T ~ 1.5x10-4 p T 0.005 PbWO 4 crystals σ/e~2.5% E no longitudinal segmentation Cu-scint. (> 5.8 l +catcher) σ/e ~ 100%/ E 0.05 Fe σ /p T ~ 5% at 1 TeV combining with tracker Solenoid 4T Calorimeters inside the field 5
Proton-proton cross section and LHC production rates LHC is a W, Z and top factory small statistical errors can search for rare processes large samples for studies of systematic effects Tevatron LHC Process σ (nb) Events on tape ( Ldt=100 pb -1 ) Min Bias 10 8 ~10 13 bb 10 7 ~10 12 Inclusive jets pt>200 GeV 100 ~10 7 W lν 15 ~10 6 Z ll 1.5 ~10 5 tt µ + X 0.8 ~10 4 6
LHC start up 2009 Machine plans for 2009/2010 2008 7
Minimum bias events Events from inelastic scattering often revered to as minimum bias events. expect an average of 2 inelastic interactions per bunch crossing at initial luminosity: large background to hard interactions at the LHC. Minimum bias events not well modelled at LHC energies extrapolating existing measurements to LHC energies reveal differences of about 50% between different models measurement of cross section important to understand hard interactions 8
Measurement of charged particle production in di-jet events Particle multiplicity can be obtained from the region transverse to the leading jet Measurement to be used to tune simulation Multiplicity of charge particles with pt > 0.5 GeV and η < 1 in the region transverse to the leading jet UE tuning Leading Jet φ Toward φ < 60 o Transverse o 60 < φ < 120 o Away φ > 120 o Transverse different Prediction models difference 9
QCD Jets with high transverse energy High cross-section (~10 events/1 pb -1 with ET > 1 TeV) can rapidly probe QCD at the TeV scale,-.$/"($1&)0020"1(')30 background to most searches: accurate reconstruction and calibration essential high ET region sensitive to new physics Main error on cross section comes from jet energy scale expect 10% initially from test beam studies will improve to about 1% using (Z/γ+jet, W jj in ttbar) <==%4>4+3* 2)30%<=%/@ 9< %"67(&)3 45-10
Z/W cross section measurement Large cross section at LHC allows for an early measurement Leptonic final states provide a very clean signature Theoretical uncertainties on the crosssection of the hard process very small (~1%) cross section measurement a direct test of QCD and PDF uncertainties Z ll very important to understand and improve the detector calibration and performance Z mass constraint can be use to calibrate the detector energy and momentum scale, trigger performance and reconstruction efficiencies 11
Top production and decay at the LHC!"# $"# %&'()!*+,'-'$""'#!!"ν, µν, == ))'./012'3)1)43 (5678'!!9)':'$"";+ <$, H =(FF$G-'&",+) (BC'D, @$I$J/*?$ H K/>+F/#*",+) (EF'D, @$" L$ν L$MJ/*?N$"O/Nµ H.+F/#*",+)$ (G'D, @$Q" L$Qν L$QJ/*?! Semi-leptonic decay channel golden channel 12
First top mass measurement σ )) 6K0#<H#?(A#))# HL HL# H=ν HMM JNOJP#<A>=%;%'&AF L"Q>AR>AR> 4 jets p T > 40 GeV <8$#+ 47 2 jets M(jj) ~ M(W) Isolated lepton p T > 20 GeV!"#$%&"'(%)"*+,-$&%"!. T W+n jets (Alpgen) + combinatorial background NO b-tag!! E T miss > 20 GeV Top signal observable in early days without using b-tagging expect 100 ± 20 events for 50 pb -1 Excellent sample to: commission b-tagging and study jet energy scale understand detector performance 13
Improving the performance of the analysis: applying b-tagging Background can be significantly reduced using b-tagging will move to b-tag analyses as soon as possible Background composition changes: jet combinatorics from top becomes more and more important 1 b-tag 2 b-tags + signal - combinatorial background - background processes + signal - combinatorial background - background processes 14
Heavy Higgs: possible early discovery H 4l: narrow mass peak, small background GAAHAH#!<H)#IJK FE L?A@#AM?A@%CA') XY&)#&K(Q)#)YA#=2#-%TT3 H WW lνlν: counting measurement (no mass peak) E0 E!!! "#$%&'('%)*+,-./01 E#JK FE J(@#O8P#,"<"#AM4BQ3%(' R#JK FE J(@#Rσ H%34(SA@D (SA@#JQBB#&BB(5AH#C&33#@&'TA &234%5% ))µµ E0 FE :;<:=#>#,2=?@AB%C%'&@D!"#$%&'(')*+',#- YA@A#H%34(SA@D#A&3%A@#5%)Y# Here discovery easier with T(BHF?B&)AH#- [[# UB gold-plated H ZZ 4l 67%)18%9::#%; C - I$ANL 9 15
Light Higgs: more difficult Three complementary channels with similar small significance! γγ different production and decay modes different backgrounds different detector performance requirements calibration of electromagnetic calorimeter for H γγ b-tagging for tth efficiency of jet reconstruction over η < 5 for qqh qqττ mh ~ 115 GeV, 10 fb -1 : S/ B ~ 4 (ATLAS) note that all three channels require a very good understanding of the detector performance E]=90*#F]G900*#E7 F]6 ""! ""##$ #%ν#&&## b b E]=>*#F]G>*#E7 F]6"6 ''!$ ''ττ τ H τ E]=0*#F]=0*#E7 F]6": 16
Early surprises... A very narrow Z resonance decaying into two leptons is predicted by several extensions of the Standard Model (here shown Sequential Standard Model) 7%KF <7 For MZ ~ 1 TeV an early discovery would be possible. The ultimate reach of the LHC would be a mass of about 5 TeV with 300 fb -1 Mass (TeV) Selected events (per fb -1) L for discovery 1 ~160 ~70 pb -1 1.5 ~30 ~300 pb -1 2 ~7 ~1.5 fb -1 17
Super symmetry General characteristics of R-parity conserving SUSY: sparticles produced in pairs and lightest SUSY particle (LSP) stable large amount of missing transverse energy coloured sparticles are copiously produced and cascade down to the LSP with emission of many hard jets and sometimes leptons Generic SUSY signatures are E T miss + multi-jets (and multi-leptons) 18
A typical SUSY event selection Large missing ET (MET): O(> 200 GeV) ( LSP) MET challenging to control at startup at least 3 hard jets ( cascade decays) N leptons (according to investigated topology) growing N: reduces QCD background angular or event shape variables for background rejection top background probably the most challenging Main backgrounds: tt+jets, W+jets, Z+jets, QCD (multijet) 19
SUSY discovery potential (msugra) 20
What to expect from the first collision data (1-100 pb -1 at 14 TeV)? Understand detector performance in situ in the LHC environment Perform first physics measurements understanding minimum bias events measure QCD jet cross-section measure W, Z cross-section observe a top signal improve knowledge of particle density functions with W/Z and maybe discover low mass SUSY up to ~1 TeV discover a Z up to masses of ~1 TeV... 21
After several years of data taking The LHC will explore in detail the highly-motivated TeV-scale with a direct discovery potential up to masses up to 5 TeV if there is new physics, the LHC is likely to find it it will say the final word on the SM Higgs mechanism and many TeV predictions it may add crucial pieces to our knowledge of fundamental physics 22