Potenzialit di Fisica dal Tevatron ad LHC e

Potenzialità di Fisica dal Tevatron ad LHC e a Super LHC Daniele del Re Universita’ di Roma “La Sapienza” and INFN Roma V 3

Outline • Brief intro on Tevatron and LHC • Discussion on luminosities, production cross sections and physics • Physics potentials per channel – Standard Model – Higgs – Beyond Standard Model • INFN Roma 1 activities – Are we on the right track for next years discoveries? 04/05/09 Daniele del Re (La Sapienza & INFN) 2

High Energy Physics High energy production of particles with large mass • Vector bosons, top, Higgs, new particles Needed for • Standard Model precision tests, discover Higgs, spot New Physics p p Lumi to date ~ 3. 6 1032 cm-2 s-1 04/05/09 Daniele del Re (La Sapienza & INFN) 3

Luminosity Matters Cross section depends on beam energy Large variation from Tevatron to LHC. Important consequences for discovery s Tevatron Lumi for 100 ev. Tev. s LHC Lumi for 100 ev. LHC Inclusive W ~20 nb 1 pb-1 ~`140 nb 1 pb-1 Inclusive Higgs 0. 011 pb 0. 1 -10 fb-1 1 -30 pb 3 -100 pb-1 ~1 fb ~100 fb-1 10 pb-1 - - 50 pb 2 pb-1 Z’ (1 Te. V) Model dep. Incl. Susy (mg, q~1 Te. V) 04/05/09 Daniele del Re (La Sapienza & INFN) 4

Expected Luminosities Tevatron LHC Now more than 6 fb-1 on tape. By year 2011 between 8 and 9. 5 fb-1. Run also in 2011? 2009 -2010: 10 Te. V run. O(100 pb-1) to be accumulated Later: 14 Te. V, instant lumi few 1033 cm-2 s-1 → 1034 cm-2 s-1, i. e. 0(10 -50 fb-1)/year SLHC after 2017? ? 04/05/09 Daniele del Re (La Sapienza & INFN) 5

SM Measurements: Still Cool Lots of physics goals: • Electroweak parameters: mtop, m. W, ΓW, sin 2θW and couplings SM precision test and consistency • Direct sensitivity to new physics (e. g. rare top decays. . ) • High precision cross sections to test QCD predictions • Constraints on parton density functions • Single top production • Measure background to many physics channels 04/05/09 Daniele del Re (La Sapienza & INFN) 6

SM at Tevatron: W Mass Analysis basics: • Leptons in central region • Use of p. Tlepton and T from missing energy • MW correlated with transverse mass New CDF measurement in preparation 04/05/09 Daniele del Re (La Sapienza & INFN) 7

SM at Tevatron: Top Decays (BR(t →Wb) ~ 100%) • Dilepton: two isolated, high PT leptons • l+jets: one lepton from one W (analyzed in tagged and untagged modes) • All-jets: must be b-tagged to control BG’s Event based additional constraints from kinematics Main systematics from Jet Energy Scale Combined fit to reduce uncertainty 04/05/09 Daniele del Re (La Sapienza & INFN) 8

Single Top Difficult analysis • Small cross section and large bkg Selection • High p. T isolated e or • MET from neutrino • 2 or 3 jets (at least 1 b-tagged jet) Intensive use of multivariate analysis 04/05/09 Daniele del Re (La Sapienza & INFN) 9

Rediscover SM at LHC SM process as benchmark to commission new experiments. Clean processes with well predicted s “standard candles” for: • MC tuning; • Lepton identification/trigger inefficiencies • Electron/Muon/Jets/Missing. ET energy scales and resolutions Cross sections • Z, W ~6 times larger than Tevatron • ttbar~100 times larger than Tevatron Start-up • Z and W inclusive cross sections and W/Z+jets measurements Masses • W and Z masses with techniques similar to Tevatron’s ones After 1 fb-1: sstat(MW)~40 Me. V, sstat(Mtop)~300 Me. V 04/05/09 Daniele del Re (La Sapienza & INFN) 10

An example: Z+jet/W+jet • Test of factorization, QCD, parton showering • Detailed check on background to most of the analyses. • To reduce systematics, measure ratios a de M in E M O R CMS and ratio of ratios # of calorimetric jets CMS • By-products 100 pb-1 – Use of Z as candle for jets+Z→ background # of calorimetric jets 04/05/09 Daniele del Re (La Sapienza & INFN) 11

Higgs Intro • In the SM electroweak symmetry broken via the Higgs mechanism • W and Z bosons acquire mass, photon remains massless • Higgs not yet seen • Limits for the Higgs bosons from direct searches and global EW fits 04/05/09 Daniele del Re (La Sapienza & INFN) 12

Higgs Branching Ratios BR BR Low mass: • b-bbar dominated. Select events with associated production to reject QCD bkg • other channels: tt and gg important in the intermediate mass region ~130 Ge. V High mass: • WW and ZZ mode only Leptons and vector boson reco provide largest discovery potential 04/05/09 Daniele del Re (La Sapienza & INFN) 13

Higgs: Tevatron vs LHC Different production modes (because of qq vs qqbar) • At Tevatron non-negligible W/Z associated production (Higgs + Z/W). Only mode used for low mass searches • At LHC large vector boson fusion mode (Higgs + 2 jets). Given larger backgrounds and large statistics LHC uses cleanest Higgs decay modes, i. e. no use of H→bb Tevatron LHC 04/05/09 Daniele del Re (La Sapienza & INFN) 14

Higgs at Tevatron: Analyses Low mass: • b-tagging • Multivariate analysis (neural networks) • Use topology constraints (in neural network NN) High mass: • Trigger on leptons • Perform analysis on different samples S/B~1/40 – Opposite-sign leptons Ø 0 jets for gg fusion Ø 1, 2 jets for other production modes – Same-sign leptons Ø H(WW)W → l+ l- X • Intensive use of multivariate analysis 04/05/09 Daniele del Re (La Sapienza & INFN) 15

Higgs at Tevatron: Exclusion all M Excluded Higgs in 160 Ge. V<m. H<170 Ge. V range 04/05/09 Daniele del Re (La Sapienza & INFN) 16

Exclusion Potential Impressive exclusion potential for the near future If ~10 fb-1 on tape all masses down to 115 Ge. V could be tested 04/05/09 Daniele del Re (La Sapienza & INFN) 17

Higgs Analysis Improvements: HF Tagger • Identification of heavy flavor jets on real data in CDF M • Statistical separation of fraction of b in Z+j events (2 fb-1) M e ad in RO E s(Z+b) = 0. 57 ± 0. 12 ± 0. 09 pb Work in progress: – To be used in ZH→ bb and WZ→l jj analyses 04/05/09 Frazioni(%) Misura Previsione MC b 1. 92 ± 0. 42 1. 15 c light 2/dof 0. 99 ± 0. 90 97. 09 ± 0. 58 87. 7 / 80 1. 88 96. 97 89. 1 / 80 Daniele del Re (La Sapienza & INFN) 18

Higgs at LHC At low mass (MH< 2 MZ) • Dominant bb; huge QCD background • H→tt accessible through VBF • H→WW(*) accessible through gluon-gluon fusion and VBF • H→gg: low BR (decays through top and W loops); thanks to excellent γ/jet separation and γ resolution very significant • H →ZZ*→ 4 l also accessible For higher masses • H→WW and H→ZZ→ 4 l final-states 04/05/09 Daniele del Re (La Sapienza & INFN) 19

Higgs at LHC: Some Examples H → WW → l l • 2 opposite-sign isolated and identified leptons • Kinematical and MET cuts • No central jets • Cut based & multivariate H → ZZ→ 4 l • Very clean signal (4 e, 4μ, 2 e 2μ) • high BR except at m. H ≈ 2 m. W • Excellent mass resolution (1. 5 – 2 Ge. V for MH= 130 Ge. V) 04/05/09 Daniele del Re (La Sapienza & INFN) E M M e ad in RO E e ad M in M RO 20

Higgs at LHC: Some Examples H → gg • Important for low mass searches • Reducible background – QCD, g+jet • Irreducible background – gg Selection • g isolation • Kinematics Fit to invariant mass Mgg • em calorimeter nice resolution s(M)/M~0. 7%(CMS) s(M)/M~1. 2%(ATLAS) 04/05/09 CMS Daniele del Re (La Sapienza & INFN) M e ad in RO E M 21

Higgs at LHC: Combined Results ATLAS and CMS have similar Higgs discovery potential • With 5 fb-1 5σ discovery for m. H in [~130, ~450] Ge. V • With 1 fb-1 possible observation in H→ WW (but in Tevatron excluded region) • Combining results further reduces lumi needed 04/05/09 Daniele del Re (La Sapienza & INFN) 22

CMS projection at 10 Te. V 04/05/09 Daniele del Re (La Sapienza & INFN) 23

Higgs: Considerations • Tevatron: large exclusion potential in next two years of data analysis for MH<200 Ge. V • Combinations and NN – OK for exclusions – Really questionable for discovery… • If Higgs not observed by Tevatron – LHC needed to push to larger masses • If hints of Higgs before end of 2010 – Hard to make a claim with NN-based analysis – LHC needed to have real confirmation LHC still crucial for Higgs discovery! After discovery SLHC can play an important role to determine Higgs properties (couplings and rare decays) 04/05/09 Daniele del Re (La Sapienza & INFN) 24

Beyond SM: Scenarios Limitations of the Standard Model • Hierarchy problem • Couplings don’t unify at one scale • Dark matter, Dark Energy • Neutrino masses Possible extensions of SM • Supersymmetry • Extra Dimensions • New Gauge groups Model inspired searches • Theory tells where to look • Model dependent optimization • Limits on theory parameters 04/05/09 Signature-based searches • Optimize selection to reduce backgrounds Daniele del Re (La Sapienza & INFN) 25

Super. Symmetry Adds to each SM fermion (boson) a bosonic (fermionic) partner. § R-parity can be conserved (RPC) or violated (RPV) § RPC implies: - SUSY particles produced in pairs - stable and neutral lightest SUSY particle (LSP) - no proton decay § LSP is a good candidate for cold Dark Matter MSSM Lagrangian depends on 105 parameters m. SUGRA requires only 5 parameters - Also other SUSY models exist: GMSB, … 04/05/09 Daniele del Re (La Sapienza & INFN) Par. Description m 0 Common scalar mass m 1/2 Common gaugino mass A 0 Common trilinear term tanb Ratio of Higgs vev sign(m) from Higgs sector 26

SUSY: topology Event topology • High-p. T jets from squark/gluino decays • Large ETmiss from LSP • High-p. T leptons from gaugino/slepton • High-p. T b-jets/t-jets (depending on model) p p q 04/05/09 ~ g ~ q ~ c 02 ~ q Daniele del Re (La Sapienza & INFN) ~0 c 1 In RPC models, chains end up with the LSP 27

Exotica and High Mass Gauge Bosons • New gauge bosons predicted by many extensions of the Standard Model with extended gauge symmetries: – Super-string inspired and GUT theories; – Left-Right Symmetric Models based on the gauge group SU(3)Cx. SU(2)Lx. SU(2)Rx. U(1)B-L predicting substructures of the known “elementary particles”; – Little Higgs Models. • Produced via Drell-Yan process • Stringent limits from precision EW experiments and direct searches • Signature: two high pt leptons. Peak in invariant mass 04/05/09 Daniele del Re (La Sapienza & INFN) 28

Beyond SM: Tevatron Results Searches in both SUSY and high mass resonances Real limit is the beam energy. Can’t explore large sparticle/new VB masses Two examples: SUSY in tri-leptons 04/05/09 Z’→ 2 leptons Daniele del Re (La Sapienza & INFN) 29

LHC SUSY ingredients: MET + high pt jets Different final states analyzed • Purely hadronic • 1 lepton • 2 leptons • 2 photons • . . . Different models/scenarios e. g. m. Sugra, GMSB, … CMS E M M e ad in RO Look for SUSY Higgs (charged and neutral) too M 04/05/09 a de in RO E M Daniele del Re (La Sapienza & INFN) 30

LHC Z’ • 2 opposite sign charged leptons with high p. T (hundreds of Ge. V) • low jet multiplicity, no real MET • Drell-Yan is the irreducible background Z’ → ee channel • good Mee resolution • saturation effects at high energy Z’ → μμ channel • Mμμ resolution ~10 times worse in signal region, resolution affected by misalignment at start-up Comparable sensitivity M 04/05/09 a de in RO E M Daniele del Re (La Sapienza & INFN) 31

Exotica Examples: Hidden Valley • Hidden Valley (HV) Scenarios predict long-lived neutral states with decay lengths comparable to LHC detector • Example with Higgs production • Implemented ad-hoc triggers based on HCAL, muon detector and inner tracker O(10%) efficient • Thousands of triggered events with lifetime > 1 m in 100 pb-1 04/05/09 Daniele del Re (La Sapienza & INFN) e ad M in E OM R ATLAS 32

Beyond the Beyond: SLHC • Increase mass reach – Production of new particles. Gluino e squark masses up to 3 Te. V – Z’ discoverable up to 5 -6 Te. V • SUSY properties – Masses of SUSY particles from kinematics (lepton-jet invariant masses) and spin • Higgs couplings – H → μμ • WW, WZ scattering • In general: – If discovery: a lot to understand, more stat needed – If no discovery: higher masses to check, more stat needed 04/05/09 Daniele del Re (La Sapienza & INFN) 33

LHC Readiness to Expected • At start-up uncertainties driven by knowledge of physics objects reconstruction • Plot: an example of Mtop-Jet Energy Scale correlation • LHC to be ready to first year physics calibrating jets, MET, leptons, photons – Energy scale – Resolutions – Efficiencies • SM processes needed • Invest time now to tune methods based on data control samples 04/05/09 Daniele del Re (La Sapienza & INFN) 34

Leptons, Photons, JETs and MET Physics object calibration examples Leptons Use of Z→ll and tag-and-probe approach • tight requirements on one lepton Z • other used as probe to measure ID Photons Energy scale calibration using p 0’s CMS JETS Di-jet, g/Z+jet events to calibrate Use of balance in transverse plane MET Find ad hoc control samples. Use of multijet events 04/05/09 Daniele del Re (La Sapienza & INFN) e ad M in E M O R 35

LHC Readiness to Unexpected The example of the multi-muon events at Tevatron. • Significant sample of events with at least one of the muon candidates is produced outside of the beam pipe New physics? Reconstruction effect not under control? Extra CDF event not simulated? …and Tevatron is running since ages, detector calibrations well known How many “multi-muon events” cases at LHC startup? Reduced by well-established calibration of physics object, relying very little on MC. 04/05/09 Daniele del Re (La Sapienza & INFN) 36

Conclusions Tevatron: Will dominate SM measurements for a while. Higgs can be excluded (m<200 Ge. V) in the next two years. Higgs discovery is hard. LHC: • Crucial for Higgs search. • Wide number of possible beyond-SM scenarios will also be explored. • Ready to (un)expected. Crucial role of calibrations SLHC (if any) • Deeper understanding of Higgs and New Physics discoveries • (or/and) Extend searches to larger energies INFN Roma 1 plays active role in physics analysis – Well balanced effort among Standard Model, Higgs, Beyond SM, exotica analyses and calibration (understanding) of physics objects See next slide 04/05/09 Daniele del Re (La Sapienza & INFN) 37

Summary of Activities in Dept. • Standard Model: Tevatron: Z+b-jet. ATLAS: Z → 2 CMS: Z/W+jets, Z incl. production. • Higgs: ATLAS: H→ZZ→ 4 l. CMS: H →WW→ 2 l 2. • SUSY: ATLAS: SUSY Higgs. CMS: GMSB in photons. • Exotica: ATLAS: Hidden Valley. CMS: Z’ → ee • Physics objects calibration: ATLAS: Z tag and probe for muons. 04/05/09 CMS: Z tag and probe fo electrons. JET calibration using g+jet. photon calibration with p 0. Daniele del Re (La Sapienza & INFN) 38

BACKUP 04/05/09 Daniele del Re (La Sapienza & INFN) 39

Tevatron Detectors 04/05/09 Daniele del Re (La Sapienza & INFN) 40

LHC Detectors 04/05/09 Daniele del Re (La Sapienza & INFN) 41

What Physics? Cross section depends on beam energy Large variation from Tevatron to LHC Important consequences for discovery Channel s @ 14 Te. V pp (inelastic) 80 mb Inclusive bbbar 500 b QCD (>50 Ge. V) 24 b Inclusive W 140 nb Inclusive Z 43 nb DY (>20 Ge. V) 53 nb Inclusive ttbar 830 pb NLO Inclusive Higgs 1 30 pb Inclusive SUSY @ 50 pb Z’ @ 1 Te. V 10 pb m g, q 1 Te. V Limit: 0. 5 pb * 4 103 pb-1 = 2 K events 04/05/09 Daniele del Re (La Sapienza & INFN) 42

Higgs at Tevatron: Exclusion at low M • Summary of exclusion limits at 115 Ge. V for different channels. • Final result as a combination of many different results 04/05/09 Daniele del Re (La Sapienza & INFN) 43

Strongest Discovery Modes undetected • New Physics predicts undetectable particles • MET: MET large missing E in transverse plane identifies new physics processes q q g g c 0 q q undetected Example of decay chain for low mass RPC SUSY . . . but MET very sensitive to detector inefficiencies and bad behaviors need to keep background very low • In addition to MET: presence of other particles to identify specific final states and suppress backgrounds – leptons – jets – photons 04/05/09 Daniele del Re (La Sapienza & INFN) 44

SUSY List of Experimental Priorities BSM Physics analysis Signature Min Luminosity Inclusive with MET + j + l Inclusive SS di-leptons Inclusive OS di-leptons Inclusive with di-t (had) e- (LFV) GMSB MET, e, MET, t MET, e+ gg 10 pb-1 100 pb-1 500 pb-1 1 fb-1 Z’, g 1/Z 1 , G → e e Z’, g 1/Z 1 , G → W’, W 1 → Z’/W’, g 1/Z 1 , G → q-q Background QCD, tt W+j, tt tt tt QCD tt g, W+jets Model / Parameters Low Mass (LM 1) “ “ “ NLSP = c 10 SSM Z’ ADD n=3 W’ Excited q, E 6 diquark e, HE 100 pb-1 2 Te. V DY HE jet HE 1 fb-1 3. 5 Te. V 100 pb-1 2 Te. V W QCD 200 pb-1 1 Te. V 1 fb-1 1. 7 Te. V 10 500 pb-1 200 pb-1 3 Te. V 1 fb-1 g. Z( ), g. W(l ) ADD n=2 -4 W→ , bb tt, ZZ QCD stau, g 4 MPl=5 Te. V g+G g HCSP UED, stable g 1 KK Black Holes low b trk 4 l Multi-part Will talk about these 04/05/09 Daniele del Re (La Sapienza & INFN) 45

Inclusive Analysis: To-do at Startup Credibility of inclusive analyses at start-up: • Tiny backgrounds (S/B > 10) after selection • Easy to disentangle signal vs bkg in inclusive distributions • Redundant measurements – Detector-wise and analysis-wise • Use of control samples for bkg shapes and resolutions – At the beginning forget about MC predictions • Keep it simple and robust – No complicated multivariate approaches 04/05/09 Daniele del Re (La Sapienza & INFN) 46

1) squark-gluino mass hierarchy, decay modes ~ Larg 2) SUSY production 3) cross section e BR ~ ( 2 0→ ~ BR( ~ ± l l) 2 →~ ln) Points and SUSY Phenomenology Cross section dependence ~ ~ ~1 fb ~ m(g)>m(qi) ~ m(g)>m(q) ~ m(g)<m(qj) ~ 0 0 Large BR( 2 →h ~ 10) BR( ~2±→W± ~1 0) ~100 fb 3) Intermediate SUSY ~20, c ~ 2±) particle BR (c ~1 pb ~ 0→Z 0~ Large BR( 10) 2 ~10 pb ~ ~ m(g)<m(q) BOTTOMLINE In red, phase space region for early discoveries: large cross sections, additional leptons in final state 04/05/09 Daniele del Re (La Sapienza & INFN) 47

Triggers for SUSY Trigger improvements are under development. So far • Jet. MET (fully hadronic analyses) – Based on Jet Pt reco, MET, HT – L 1 cuts: 1, 2, 3, 4 large p. T jets, HT, ET – HLT cuts: combinations of MET and jets with different thresholds (single Jet p. T>200 Ge. V, MET>65 Ge. V) • Single muon – For MET+Jet+muons analyses – L 1 cuts: p. T>7 Ge. V, info from DT, RPC, CSC – HLT cuts: p. T>3 Ge. V, isolation • Single electron – For MET+Jet+electrons analyses – L 1 cuts: p. T>12 Ge. V, some isolation – HLT cuts: p. T>15 Ge. V, detailed isolation 04/05/09 Daniele del Re (La Sapienza & INFN) 48

Fully Hadronic Mode: Results Signal and background in ETmiss Low mass (LM 1) S/B~20 • Main systematics on bkg from MET and Jet Energy Scale (~20%) 04/05/09 Daniele del Re (La Sapienza & INFN) 49

Mass Measurements c~02 ± • After discovery, particle properties measured and used as confirmation • Edge of dilepton invariant mass correlated with slepton and neutralino masses ~± l l l± ~ c 01 ~ ~ c 02 → l l → c~01 l+ l- • Combinatorial (SUSY+SM) background (two leptons from independent chains) removed by flavor subtraction (e pairs) • 1 fb-1 example: edge = (80. 4± 1. 4) Ge. V 04/05/09 Daniele del Re (La Sapienza & INFN) 50

MET + jets + leptons • • Spin is the defining property of SUSY - Crucial to distinguish from similar-looking models that can mimic SUSY (e. g. : Universal Extra Dimensions) It is difficult to measure @ LHC - No polarised beams - Indeterminate initial state from pp collision… • Example: second neutralino spin from angles in If neutralino spin is ½ , angular distribution of slepton is not spherical the lepton-quark invariant mass m(ql±) is charge asymmetric In SU 3 point, 5 10 fb-1 are already enough to exclude charge symmetry 04/05/09 ne ar far SU 3 Near + Far leptons L=30 fb-1 Daniele del Re (La Sapienza & INFN) Flavor subtracted [Bi] 51

SUSY spin measurements • • Spin is the defining property of SUSY - Crucial to distinguish from similar-looking models that can mimic SUSY (e. g. : Universal Extra Dimensions) It is difficult to measure @ LHC - No polarised beams - Indeterminate initial state from pp collision… • Example: second neutralino spin from angles in If neutralino spin is ½ , angular distribution of slepton is not spherical the lepton-quark invariant mass m(ql±) is charge asymmetric In SU 3 point, 5 10 fb-1 are already enough to exclude charge symmetry 04/05/09 ne ar far SU 3 Near + Far leptons L=30 fb-1 Daniele del Re (La Sapienza & INFN) Flavor subtracted [Bi] 52

GMSB: Selection Basics • If NLSP is neutralino 2 g in event g jet q • Selection – g, isolation, p. T > 80 Ge. V – High MET, Njets > 3 • Main backgrounds – – p jet g+jets W+jets … q q p jet … q g jet • If lifetime(c) ≠ 0 non-pointing g possible to extract lifetime • MET tails critical for early discoveries 04/05/09 Daniele del Re (La Sapienza & INFN) 53

Control Samples: Z/W bkg • • Data-driven estimation of Z bkg in ETmiss: shape and normalization using Z sample and replacing with Can be also used to get information about W background Measure in Z -> μμ m 04/05/09 Daniele del Re (La Sapienza & INFN) m Use in Z -> n n 54

ATLAS-CMS Comparison 04/05/09 Daniele del Re (La Sapienza & INFN) 55

Selection variables 1 st reco g with highest p. T • Photon isolation criteria – Track based isolation and H/E • p. T and h of the two photons with largest p. T – Hybrid superclusters • Cluster shape (asymmetry) MET – to distinguish between prompt signal g and background p 0→gg • Jets p. T and h – high energy quarks are produced in the SUSY chain from heavy sparticles decay 04/05/09 Daniele del Re (La Sapienza & INFN) 56

Exotica: Stable Particles • Heavy quasi-stable charged particles in “split supersymmetry” • Gluino hadronizes in so-called Rhadrons. • Gluinos can have large lifetimes • Long-lived particles stopped in the detector detected via calorimeter triggers when no beam in the LHC (e. g. interfill or beamgap) 04/05/09 Daniele del Re (La Sapienza & INFN) systematics 57

R-hadron Decay 04/05/09 Daniele del Re (La Sapienza & INFN) 58

Plan for early data taking • day 1: corrections from MC, including lessons from cosmics runs and testbeams • data<1 fb-1: use of high cross-section data driven methods. Tune MC • longer term: run full list of corrections described so far Integrated Minimum luminosity time Systematic uncertaintiy 10 pb-1 >1 month ~10% 100 pb-1 >6 months ~7% 1 fb-1 >1 year ~5% 10 fb-1 >3 years ~3% 04/05/09 numbers do not take into account 1) low p. T: low resolution, larger backgrounds larger uncertainties 2) large p. T: control samples have low cross section larger stat. needed Daniele del Re (La Sapienza & INFN) 59

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