Martin zur Nedden, HU Berlin 1 B-Physics at ATLAS Precise B-Decays Measurement sensitive to BSM Physics at ATLAS Martin zur Nedden Humboldt-Universität zu Berlin For the ATLAS Collaboration Europhysics Conference on High Energy Physics 2007 July 2007, Manchester, England

Martin zur Nedden, HU Berlin 2 B-Physics at ATLAS Outline ATLAS B-physics strategy, detector and trigger CP violation effects and sensitivity to physics beyond the standard model Rare B-decays It is a pleasure to give this talk in the United Kingdom, which provides both of B-Physics conveners in ATLAS and is deeply involved in many of the studies presented here.

Martin zur Nedden, HU Berlin 3 B-Physics at ATLAS B Physics at LHC LHC at CERN: proton-proton collisions at √s = 14 TeV, bunch crossing rate 40 kHz, circumference 27 km 4 experiments at LHC –ATLAS/CMS: general purpose detectors –LHCb: for dedicated B-Physics –ALICE: for heavy ion physics High bb production cross section: ~ 500 µb (~ 1 bb pair in 100 p-p collisions). Those of interest must be selected by efficient B-trigger. Luminosity operation plans: –about 100 pb -1 in 2008, –more than 1 fb -1 in 2009 reaching then luminosity of cm -2 s -1 (~10 fb -1 per year) –Design: high-luminosity: cm -2 s -1 (~100 fb -1 per year)

Martin zur Nedden, HU Berlin 4 B-Physics at ATLAS General Strategy for B-Physics at ATLAS ATLAS is a general-purpose experiment: main emphasis on high-pT physics beyond the Standard Model ATLAS has also capabilities for a rich B-physics programme: precise vertexing and tracking, good muon identification, high-resolution calorimetry, dedicated and flexible B-physics trigger scheme. ATLAS has a well-defined B-physics programme for all stages of the LHC operation: Huge b-hadron production statistics allow precise measurements of their properties Theoretical descriptions of heavy flavoured hadrons need input from LHC Precision measurements already achievable after one year of data taking Measurements extending the discovery potential for physics beyond SM measurements of CP violation parameters that are predicted to be small in the SM (e.g in B s  J/  (  ) ) measurements of rare B-decays (B d  K* , B d  K* , B s  , B s  , B s  , B   ) Focus on physics topics that will not be accessible for the B-factories mainly B s, baryon and double heavy flavour hadrons (B s  D s , B s  J/  (  ),  b  J/  0, …)

Martin zur Nedden, HU Berlin 5 B-Physics at ATLAS 46 m long, 22 m diameter, 7'000 t total weight ATLAS Experiment

Martin zur Nedden, HU Berlin 6 B-Physics at ATLAS ATLAS Multi Level Trigger <2.5  s ~10 ms ~1 s HLT ~1-2 kHz out ~100 Hz out LEVEL 1 TRIGGER Hardware based (FPGAs ASICs) Uses coarse granularity calorimeter and muon information Identifies Regions of Interest for further processing LEVEL 2 TRIGGER Full granularity within RoI Confirm LVL1 trigger Combine info from different detectors in RoIs around LVL1 EVENT FILTER Refines LVL2 selection using “offline-like” algorithms Better alignment and calibration data available HLT: software based B physics will be using ~10% of total trigger resources: fast, efficient and selective trigger strategies needed.

Martin zur Nedden, HU Berlin 7 B-Physics at ATLAS Trigger Strategies for B-Physics limited bandwidth for B-triggers: highly efficient and selective trigger needed. c- and b-events contain mostly low p T particles: challenge to trigger on those events many b-decays contain J/ψ : useful for calibration, optimization and understanding of detector, trigger as well as B-physics B-trigger is based on single- and di-muons in final state BR ~ 10 %, but clean signature at early level in trigger and give flavour tag lower lumi (< 2*10 33 cm -2 s -1 ) LVL1 single  -trigger with additional LVL1 signature or a jet in calorimeter at LVL2 use LVL1 Regions of Interest (RoI) to seed LVL2 reconstruction: Jet RoI: for hadronic final states (e.g. B s → D s (  π)π) EM RoI: for e/  final states (e.g. J/ψ → ee, K*γ,  γ) Muon RoI: to recover di-muon final-states in which second muon was missed at LVL1 LVL1 di-muon trigger high lumi (>2x10 33 cm -2 s -1 ) LVL1 di-μ trigger B → J/ψ(  ), rare decays (B → , B  K 0* μμ), double semi leptonic decays Developments and studies by Rutherford, Technion (Haifa) and Tokio all single-  all di-  h (hadron) b (beauty) c (charm) J/  ATLAS  rates for 14 TeV and cm -2 s -1

Martin zur Nedden, HU Berlin 8 B-Physics at ATLAS CP violation in B s  J/  Φ s = -2λ 2 η = -2  : tiny in SM (  from CKM fitter) σ(Φ s ) ~ (for m s =20 ps -1) σ(ΔΓ s )/ΔΓ s = 13% σ(Γ s )/Γ s = 1% σ(A || )/ A || = 0.9% σ(A T )/ A T = 3% New Physics could lead to enhanced and measurable CP violation. 7 parameters extracted in maximum likelihood fit to angular distribution of the decay : A || (t=0), A T (t=0), δ 1, δ 2 (2 ind. magnitudes and phases) ΔΓ s, Γ s, Φ s (weak decay parameter) - despite enormous LHC statistics and well-controlled background – several parameters get highly correlated - to avoid failing a fit due to high  m s -Φ s correlation,  m s was fixed Results for 30 fb -1 luminosity: signal events: B s mass resolution: 16.5 MeV Background from J/Ψ K 0* and bb  J/ΨX: 15 % ε(tag) / wrong tag fraction jet charge 63.0 % / 38 % electron 1.2 % / 27 % muon 2.5 % / 24 % Results from Lancaster University

Martin zur Nedden, HU Berlin 9 B-Physics at ATLAS Δm s Measurement Luminosity (fb -1 ) 5σ limit (ps -1 ) 95% CL sensitivity (ps -1 ) ATLAS sensitivity: Given the low value measured by CDF, ATLAS will be able to measure  m s with ~10 fb -1 (one year). CDF Mixing due to weak interaction: in B 0 s  D s π, B 0 s  D s a 1 decays: Probability that initially (t=0) pure Bs0 is measured As B s 0 (p + ) or as B s 0 -bar (p - ): Δm s derived from: B 0 s  D s π : Univ. Innsbruck B 0 s  D s a 1 : Univ. Siegen

Martin zur Nedden, HU Berlin 10 B-Physics at ATLAS b → d, s transitions (FCNC) are forbidden at the tree level in SM and occur at the lowest order through one-loop-diagrams “penguin” and “box” Main points to study: good test of SM and its possible extensions information of the long-distance QCD effects determination of the |V td | and |V ts | some of the rare decays as background to other rare decays (for example B d  0  +  - as bkg for B d,s  +  - ) Rare B-Decays Bsμ+μ-Bsμ+μ-

Martin zur Nedden, HU Berlin 11 B-Physics at ATLAS ATLAS offline analysis : B s   Cuts B 0 s signal BG (bb   X) p T >6 GeV, ΔR  <0.950 events 6.0×10 6 events M  cut ( M μμ = M Bs MeV) ×10 -2 Isolation cut: no charged tracks with p T > 0.8 GeV in cone  < 15 degrees ×10 -2 L xy /  (L xy )>11,  2 <15 (transverse decay length) vertex fit with pointing to primary vertex constraint 0.4 < 0.7×10 -4 All cuts720±12 Expected signal v.s. inclusive bb  μμX background Background:

Martin zur Nedden, HU Berlin 12 B-Physics at ATLAS Projected upper limits : B s   extraction of upper limit on Br(B s  μμ) (from 7 signal and (20±12) background events) ATLAS experiment expects to reach the sensitivity of SM prediction Still factor of 10 above ATLAS has proven that the measurement of B s  μμ is still feasible at nominal LHC luminosity cm -2 s -1. This would mean 100 fb -1 just in one year. Tevatron projection Analysis by Univ. of Moscow, Bergen and Lancaster

Martin zur Nedden, HU Berlin 13 B-Physics at ATLAS Semi-muonic exclusive rare B-decays in ATLAS ATLAS statistics errors SM model theory MSSM with C 7eff > 0 expected statistics of reconstructed events at L = 30 fb -1 A FB shape and BR provides strong indirect tests of BSM physics shape of distribution sensitive to trigger and offline selection cuts, especially at low q 2 region small μμ opening angle is trigger challenging Λ b example: detector acceptance and trigger muon: p T cuts prefers higher q 2 and causes A FB reduction by factor of 0.6 at q 2 /M b 2 < 0.1 ATLAS statistical errors 6% in this area Λ b  Λμμ: 800 events with 30 fb -1 Analysis by Univ. Prague, Cosenza and Moscow

Martin zur Nedden, HU Berlin 14 B-Physics at ATLAS Conclusions ● well-defined B-Physics programme ● different Trigger Strategies for low and high luminosity phases well-prepared ● CP violation studies for B s ● rare B-decays measurable with ATLAS sensitive to BSM. ● precision B-physics measurements provide an additional method for searches for new physics at LHC