Le démarrage du LHC Réunion du vendredi 12/09/2008

L’histoire du LHC est déjà longue ! 1984 : Premières réflexions sur l’après LEP 1992 : workshop d’Evian, remise des Letters of interest 1989 : Premières proto-collaborations expérimentales Fin 2000 : Fin du LEP Conception, test et production des éléments de détecteurs 02/1996 Approbation de la construction d’ATLAS et CMS (suivi par ALICE 02/1997, LHCb 09/1998) 16/12/1994 Approbation de la construction du LHC par le Conseil du CERN 2004 Début de l’intégration d’ATLAS Mai 2007 Installation du dernier aimant de la machine Début 2008 Mise en froid de l’anneau Tests cosmiques Maintenant Premières collisions

LHC et la conduite de projet Temps officiel restant avant la prise de données (années) Evolution du LHC Evolution du projet idéal (pente -1, pas de plateau) Date (année)

Cosmiques…

Premiers événements, vus de l’intérieur

Et maintenant ?

Peak luminosity a few 1031 cm-2 s-1 Integrated luminosity 10s of pb-1 Summary – aims for 2008 Commission machine to 5TeV Multiple bunches circulating in each ring (43) Moderate intensities (few 1010) Single beam lifetimes ~ 30h Injection optics (β*= 11 m in IR 1 & 5, β*= 10 m in IR 2 & 8) No squeeze No crossing angle Collisions Secondary aims Commission squeeze in 1 and 5 to 3m Commission squeeze in 8 to 6m Push intensities (156 bunches, high 1010) Tertiary aims Commission crossing angle Commission 75ns beams Realistically (1 and 5) 50 days of physics Peak luminosity a few 1031 cm-2 s-1 Integrated luminosity 10s of pb-1

Integrated luminosity 2-3 fb-1 Summary – aims for 2009 Commission high energy operation Aim for 7TeV (magnets will decide) 43 /156 bunch running to start (brief) 75ns running 25ns running High 1032 cm-2 s-1 is in reach 150 days for proton physics Efficiency for physics 40% Overall efficiency factor 0.2 Ion run ? Realistically (1 and 5) 150 days of physics Peak luminosity 1033 cm-2 s-1 Integrated luminosity 2-3 fb-1

Resulting plan for protons 2008 A Hardware commissioning To 5TeV Machine checkout Beam commissioning 5TeV 43/156 bunch operation Train to 7TeV No beam Beam 2009 B C Train to 7TeV Machine checkout Beam Setup 75ns ops 25ns ops I Shutdown No beam Beam

Hardware Commissioning Calendrier 2008 et 2009 Month Phase Days physics Efficiency factor Peak luminosity Delivered luminosity Jan Cooldown and Hardware Commissioning Machine checkout Feb Mar Apr May June Jul Aug Beam Commissioning Physics run Sep Oct Nov 50 0.1 5 1031 20 pb-1 Dec Shutdown 75ns Commissioning 150 0.2 1033 2.5 fb-1

Un peu de physique dans les prochains mois… QCD Saveurs lourdes Modèle Standard (W,Z) Quark top Phénomènes inattendus ?

LHC: physics roadmap Prepare the road to discovery: Understand/calibrate detector and trigger in situ using “candles” samples e.g. - Z  ee,  tracker, ECAL, muon chamber calibration and alignment, etc. - tt  bl bjj jet scale from Wjj, b-tag performance, etc. Understand basic SM physics at s = 14 TeV measure cross-sections for e.g. minimum bias, W, Z, tt, QCD jets (to ~20 %), start to tune Monte Carlo measure top mass  give feedback on detector performance Note : statistical error negligible with O(10 pb-1) Prepare the road to discovery: measure backgrounds to New Physics : e.g. tt and W/Z+ jets look at specific “control samples” for the individual channels: e.g. ttjj with j  b “calibrates” ttbb irreducible background to ttH  ttbb Look for New Physics potentially accessible in first year(s) e.g. Z’, SUSY, Higgs ?

Cross-sections and rates At luminosity 1032 cm-2 s-1 Inelastic: 107 Hz bb production: 104 Hz W ℓ: 1 Hz Z  ℓℓ: 0.1 Hz tt production: 0.1 Hz Tout d’abord, mesurer avec précision les sections efficaces Modèle Standard  permettra de s’assurer de la compréhension du détecteur et de la physique.

Minimum Bias Motivation: Interesting in its own right A necessary first step for precision measurements such as m(top) A key ingredient to modelling pile-up (already expected more or less on day-1) First events on which jet algs can be tested. Reminder: Models tuned to agree with the SpS and Tevatron can and do have very different predictions for LHC energies

Charged particle density at  = 0 (Only need central inner tracker and a few thousand pp events) LHC? Multiple interaction model in PHOJET predicts a ln(s) rise in energy dependence. PYTHIA suggests a rise dominated by the ln2(s) term. Vital for understanding : Detector backgrounds, Energy scales, Detector occupancy

Evenement sous-jacent Modelling of underlying event necessary tool for high pT physics Important ingredient for jet and lepton isolation, energy flow, jet tagging, etc Underlying event uncertain at LHC, depends on multiple interactions, PDFs, gluon radiation Look at tracks in transverse region w.r.t. jet activity <Nchg> No charged particles in transverse region: pT>0.5 GeV and |η|<1 model dependency Pythia tuned Phojet CDF data pT leading jet (GeV)

Evenement sous-jacent Pythia Select events with >1jets with ET>10 GeV, ||< 2.5 Look at tracks in transverse plane with pT>1GeV, ||<2.5 Study done using Ldt ~ 60 pb-1 at s = 14TeV Jet measurements of early data will extend considerably our knowledge of the UE

Jets Physics There should be an avalanche of jets already in 2008 1st measurement of jet cross sections! We will see jets above 1 TeV for the very first time! The beginning of discovery physics! LHC (s = 14 TeV) 10 events with Ldt = 20 pb-1 Tevatron

Forte statistique de jets disponible rapidement Tests de QCD non perturbative Compréhension des algorithmes de jets

Why PDFs are vital at LHC? On Hadron Colliders every Cross-Section calculation is a convolution of the cross-section at parton level and PDFs: PDFs are vital for reliable predictions for new physics signal (Higgs, Super- Symmetry, Extra Dimensions etc.) and background cross-section at LHC. [at CDF ΔσHiggs,SUSY (CTEQ) ~ 5%] pA pB fa fb x1 x2 X

How do we want to constrain PDFs? W total and differential cross sections theoretical calculations are very robust: known to NNLO in QCD pert. theory input E.W. param. known to high accuracy EXP.: Clean measurement Abundance of W’s (300M evt/y at LHC at low Lumi.) Main Theoretical uncertainty comes from PDFs Tevatron W± Symmetric Kinematic regime for LHC much broader than currently explored

Plot: Kramer; arXiv:hep-ph/0106120 Motivation for Onia study Detector commissioning Narrow resonances (J/, ) with clean signature (in muon channel)  invaluable for calibration of the trigger, tracking and muon systems Statistic : Express stream: ~ 15,000 J, ~25,000  Physics stream: ~ 50k-1M J’s and ’s Provide additional low-mass, low transverse momenta points for detector studies generally conducted with the W/Z Data: CDF PRL 79 572 Plot: Kramer; arXiv:hep-ph/0106120 Theoretical interest Production mechanism of quarkonium unexplained Important as testbed for QCD in both perturbative and non-perturbative regimes Once understood, quarkonium production is the perfect probe for determining low x gluon PDFs Quarkonia forms an important background for many other B-physics processes at LHC

B masses and lifetimes as test of ID performance Lifetime measurements provide a sensitive test of detector alignment. Accurate lifetime measurements are required for software validation such as the vertexing software. Using the J/ψ → μ μ trigger 3 early physics channels: 1. Inclusive bb → J/ψ X (High statistic but kinematic correction needed) 2. Exclusive B+ → J/ψ K+ (Low statistic + Full Reconstructable) 3. Exclusive Bd → J/ψ K0* Sufficient statistics can be accumulated in express stream for an inclusive lifetime measurement Within 10 pb-1, have enough statistics for measurements using fully reconstructed exclusive B-decays. Primary Vertex J/ψ X pT(B) Secondary Vertex Lxy

Z Production Zee Zee Z Some ingredients Use trigger and offline eff. from tag-and-probe Use only loose EM based electron selection plus isolation Data-driven background subtraction available Ldt=50pb-1: 27.1k Z, 0.23k bckgd events =201616(stat)72(syst)202(lumi) pb Z Some ingredients Use trigger and offline eff. from tag-and-probe Relies only on tracks in Muon Spectrometer (no isolation) Could use InDet tracks and ask for confirmation in Muon spectrometer Ldt=50pb-1: 25.7k Z, 0.1k bckgd evt =201616(stat)64(syst)202(lumi) pb Zee

(RE)-Découverte du Z Utilisation de Ze+e- pour étalonner le calorimètre électromagnétique Précision possible de 0.5% sur ~400 régions de 0.2 par 0.2 avec ~0.1 fb-1 Etude du bruit de fond QCD Avec coupures: ET>15 GeV, ||<2.5 Sans coupures L ~ 35 pb-1 G~2.2 GeV

W Production We W Some ingredients Trigger and offline efficiencies from tag-and-probe (Zee) Medium e-identification Missing ET > 25GeV Ldt=50pb-1: 227k W, 6.1k bckgd events =2052040(stat)1060(syst)2050(lumi) pb W Some ingredients Trigger and offline efficiencies from tag-and-probe (Z) Muon isolation in calo: ET (R<0.4) < 5 GeV Missing ET > 25GeV, some understanding needed Ldt=50pb-1: 300k W, 20k bckgd evt =2053040(stat)630(syst)2050 (lumi) pb

Top physics during commissioning Several months to achieve pixel alignment Study separation of top from background without b-tagging Use high multiplicity in final states High Pt cuts to clean sample Use kinematical features Even with a 5% efficiency 10evts/hour at 1033 Hadronic top: Three jets with highest PT W boson: Two jets in hadronic top with highest PT in reconstructed jjj C.M. frame W CANDIDATE TOP CANDIDATE

Top physics during commissioning m (topjjj) B S S/B = 0.45 S/B = 1.77 L=300 pb-1 m (topjjj) m(Wjj) |mjj-mW| < 10 GeV S : MC @ NLO B : AlpGen x 2 to account for W+3,5 partons (pessimistic) Expect ~ 100 events inside mass peak with only 300 pb-1 top signal observable in early days with no b-tagging and simple analysis W+jets background can be understood with MC+data (Z+jets)

Pour le moment, on a échappé à ca …

Backup

Minimum Bias Non-single diffractive evts, s ≈ 60-70 mb Soft interactions Low PT, low Multiplicity. Soft tracks: pTpeak~250MeV Approx flat distribution in h to |h|~3 and in f Nch~30; |h|<2.5 Rate: R~700kHz @ L=1031cm-2s-1, For dN/dh require ~10k What we would observe with a fully inclusive detector/trigger. First events where elaborate (jet) reconstruction algorithms can be tested

Parameter evolution and rates All values for nominal emittance, 10m * in points 2 and 8 All values for 936 or 2808 bunches colliding in 2 and 8 (not quite right) Parameters Beam levels Rates in 1 and 5 Rates in 2 and 8 kb N * 1,5 (m) Ibeam proton Ebeam (MJ) Luminosity (cm-2s-1) Events/ crossing 43 4 1010 11 1.7 1012 1.4 8.0 1029 << 1 Depend on the configuration of collision pattern 3 2.9 1030 0.36 156 6.2 1012 5 1.0 1031 9 1010 1.4 1013 5.4 1031 1.8 936 3.7 1013 42 2.4 1031 2.6 1031 0.15 2 1.3 1032 0.73 6 1010 5.6 1013 63 2.9 1032 1.6 6.0 1031 0.34 1 8.4 1013 94 1.2 1033 7 0.76 2808 1.1 1014 126 7.2 1031 7.9 1031 3.8 1032 0.72 5 1010 1.4 1014 157 1.1 1033 2.1 1.2 1032 0.24 0.55 1.9 1033 3.6 5 TeV 7 TeV

How to estimate physics time/integrated luminosity LEP1 statistics 1990 1991 1992 1993 1994 1995 scheduled for physics h 2504 2762 3439 2943 3175 3070 beam in coast 1048 1242 1742 1619 1871 1414 number of coasts 143 154 199 168 197 194 Coasts per day 1.37 1.34 1.39 1.49 1.52 average coast length 7.33 8.06 8.75 9.64 9.50 7.29 efficiency for physics (in coast/scheduled) % 41.85 44.97 50.65 55.01 58.93 46.06 Peak initial luminosity 1030 11.0 10.0 15.5 22.4 24.9 Integrated luminosity nb-1 12100 18900 28600 40000 64500 46100 Overall efficiency factor (integrated/scheduled*peak) 0.12 0.19 0.21 0.24 0.25 0.17 Expect to spend as much time out of physics as in Rampdown, injection, ramp, squeeze, prepare Faults, access, other problems If we average a 10h fill per day in 2009 we’ll be doing well (40% efficiency for physics) Overall efficiency factor Measure of how much physics we get from scheduled time with a given peak luminosity Includes all the time not in physics (as above) AND luminosity decay in coast If we get this up to 0.2 in 2009 we’ll be doing well