1 Performance Studies for the LHCb Experiment Performance Studies for the LHCb Experiment Marcel Merk NIKHEF Representing the LHCb collaboration 19 th International Workshop on Weak Interactions and Neutrinos Oct 6-11, Geneva, Wisconsin, USA

2  Direct Measurement of angles:  (sin(2  )) ≈ 0.03 from J/  Ks in B factories Other angles not precisely known  Knowledge of the sides of unitary triangle: (Dominated by theoretical uncertainties)  (|V cb |) ≈ few % error  (|V ub |) ≈ 5-10 % error  (|V td |/|V ts |) ≈ 5-10% error (assuming  m s < 40 ps -1 )  In case new physics is present in mixing, independent measurement of  can reveal it… B Physics in 2007

3 Large bottom production cross section: bb/year at 2x10 32 cm -2 s -1  Triggering is an issue All b hadrons are produced: B u (40%), B d (40%), B s (10%), B c and b-baryons (10%) Many tracks available for primary vertex  Many particles not associated to b hadrons  b hadrons are not coherent: mixing dilutes tagging B LHC √s14 TeV L (cm -2 s -2 )2x10 32 cm -2 s -1  bb 500  b  inel /  bb 160 bb production: (forward) LHCb: Forward Spectrometer with: Efficient trigger and selection of many B decay final states Good tracking and Particle ID performance Excellent momentum and vertex resolution Adequate flavour tagging BsBs KK KK  ,K   DsDs B Decay eg.: B s ->D s h bb bb

4 Simulation and Reconstruction All trigger, reconstruction and selection studies are based on full Pythia+GEANT simulations including LHC “pile-up” events and full pattern recognition (tracking, RICH, etc…) Sensitivity studies are based on fast simulations using efficiencies and resolutions and from the full simulation No true MC info used anywhere ! VELO RICH1 TT T1 T2 T3

5 Evolution since Technical Proposal Reduced Reduced material material Improved Improved level-1 trigger level-1 trigger

6 Track finding strategy VELO seeds Long track (forward) Long track (matched) T seeds Upstream track Downstream track T track VELO track T tracks  useful for RICH2 pattern recognition Long tracks  highest quality for physics (good IP & p resolution) Downstream tracks  needed for efficient K S finding (good p resolution) Upstream tracks  lower p, worse p resolution, but useful for RICH1 pattern recognition VELO tracks  useful for primary vertex reconstruction (good IP resolution)

7 Result of track finding Typical event display: Red = measurements (hits) Blue = all reconstructed tracks Efficiency vs p :Ghost rate vs p T : Eff = 94% (p > 10 GeV) Ghost rate = 3% (for p T > 0.5 GeV) VELO TT T1 T2 T3 On average: 26 long tracks 11 upstream tracks 4 downstream tracks 5 T tracks 26 VELO tracks 20  50 hits assigned to a long track: 98.7% correctly assigned Ghosts: Negligible effect on b decay reconstruction

8 Experimental Resolution  p/p = 0.35% – 0.55% p spectrum B tracks  IP = 14  + 35  /p T 1/p T spectrum B tracks Momentum resolution parameter resolution Impact parameter resolution

9 Particle ID B->hh decays: RICH 1 RICH 2  (K->K) = 88%  (p->K) = 3% Example:

10 Trigger 40 MHz pile-up 1 MHz 40 kHz 200 Hz output Level-1: Impact parameter Rough p T ~ 20% HLT: Final state reconstruction Calorimeter Muon system Pile-up system Vertex Locator Trigger Tracker Level 0 objects Full detector information L0 Level-0: p T of , e, h,   ln p T  ln IP/  IP L1 Signal Min. Bias B->  Bs->DsK

11 Flavour tag l B0B0 B0B0 D   K-K- b b s u s u Bs0Bs0 K+K+ tagging strategy:  opposite side lepton tag ( b → l )  opposite side kaon tag ( b → c → s ) (RICH, hadron trigger)  same side kaon tag (for B s )  opposite B vertex charge tagging  eff [%] Wtag [%]  tag [%] B d   B s  K K Combining tags effective efficiency :  eff =  tag (1-2w tag ) 2 sources for wrong tags: B d -B d mixing (opposite side) b → c → l (lepton tag) conversions… Knowledge of flavour at birth is essential for the majority of CP measurements

12 Efficiencies, event yields and B bb /S ratios Nominal year = bb pairs produced (10 7 s at L=2  cm  2 s  1 with  bb =500  b) Yields include factor 2 from CP-conjugated decays Branching ratios from PDG or SM predictions

13 CP Sensitivity studies CP asymmetries due to interference of Tree, Mixing, Penguin, New Physics amplitudes: 1. Time dependent asymmetries in Bs->DsK decays. Interference between b->u and b->c tree diagrams due to Bs mixing  Sensitive to  +  s (Aleksan et al) 2. Time dependent asymmetries in B->  and Bs->KK decays. Interference between b->u tree and b->d(s) penguin diagrams  Sensitive to ,  d,  s (Fleischer) 3. Time Integrated asymmetries in B-> DK* decays. Interference between b->u and b->c tree diagrams due to D-D mixing  Sensitive to   (Gronau-Wyler-Dunietz)  Time dependent asymmetry in B d ->J/  K s decays  Sensitive to  d  Time dependent asymmetry in B s ->J/   decays  Sensitive to  s Mixing phases: Measurements of Angle   tree  mix  pe n  new + ++

14 B s oscillation frequency:  m s Needed for the observation of CP asymmetries with B s decays Use B s  D s    If  m s = 20 ps  1 Can observe >5  oscillation signal if well beyond SM prediction  (  m s ) = ps  1  m s < 68 ps  1 Proper-time resolution plays a crucial role Full MC Expected unmixed B s  D s    sample in one year of data taking.

15 Mixing Phases  Bd mixing phase using B->J/  K s  Bs mixing phase using B s ->J/    s /  s ) = Background-subtracted B   J/  (  )K S CP asymmetry after one year If  m s = 20 ps  1 :  (sin(  s )) = NB: In the SM,  s =  2  ~  0.04  (sin(  d )) = Angular analysis to separate CP even and CP odd Time resolution is important: Proper time resolution (ps)   = 38 fs

16 1. Angle  from B s  D s K (after 5 years of data)  (  ) = 14  15 deg After one year, if  m s = 20 ps  1,  s /  s = 0.1, 55 <  < 105 deg,  20 <  T1/T2 < 20 deg: No theoretical uncertainty; insensitive to new physics in B mixing Simultaneous fit of B s ->D s  and B s ->D s K:  Determination of mistag fraction  Time dependence of background Time dependent asymmetries: B s (B s ) ->D s - K + : →  T1/T2 + (  +  s ) B s (B s ) ->D s + K - : →  T1/T2 – (  +  s ) A Ds-K+ A Ds+K- (2 Tree diagrams due to Bs mixing)

17 Measure time-dependent CP asymmetries in B      and B s  K  K  decays: A CP (t)=A dir cos(  m t) + A mix sin(  m t) Method proposed by R. Fleischer: SM predictions: A dir (B 0      ) = f 1 (d,,  ) A mix (B 0      ) = f 2 (d,, ,  d ) A dir (B s  K  K  ) = f 3 (d’, ’,  ) A mix (B s  K  K  ) = f 4 (d’, ’, ,  s ) Assuming U-spin flavour symmetry (interchange of d and s quarks): d = d’ and = ’ 4 measurements (CP asymmetries) and 3 unknown ( , d and )  can solve for  2. Angle  from B      and B s  K  K  d exp(i )= function of tree and penguin amplitudes in B 0      d’ exp(i ’)= function of tree and penguin amplitudes in B s  K  K  (b->u processes, with large b->d(s) penguin contributions)

18 2. Angle  from B      and B s  K  K  (cont.) Extract mistags from B   K    and B s   K  Use expected LHCb precision on  d and  s pdf for  pdf for d blue bands from B s  K  K  (95%CL) red bands from B      (95%CL) ellipses are 68% and 95% CL regions (for  input = 65 deg) “fake” solution d vs   (  ) = 4  6 deg If  m s = 20 ps  1,  s /  s =0.1, d =0.3, = 160 deg, 55 <  < 105 deg: U-spin symmetry assumed; sensitive to new physics in penguins

19 Application of Gronau-Wyler method to D  K *  (Dunietz): Measure six rates (following three + CP-conjugates): 1) B   D  (K    )K * , 2) B   D CP (K  K  )K * , 3) B   D  (K    ) K *  No proper time measurement or tagging required Rates = 3.4k, 0.6k, 0.5k respectively (CP-conj. included), with B/S = 0.3, 1.4, 1.8, for  =65 degrees and  =0 3. Angle  from B   D  K *  and B   D  K *  A 1 = A 1 √2 A 2 A3A3 A3A3 22  55 <  < 105 deg  20 <  < 20 deg  (  ) = 7  8 deg No theoretical uncertainty; sensitive to new physics in D mixing (Interference between 2 tree diagrams due to D0 mixing)

20 Measurement of angle  : New Physics? 1. Bs->DsK 2. B-> , Bs->KK 3. B->DK*  not affected by new physics in loop diagrams  affected by possible new physics in penguin new physics in penguin  affected by possible new physics in D-D mixing  Determine the CKM parameters A, ,  independent of new physics  Extract the contribution of new physics to the oscillations and penguins

21 Possible sources of systematic uncertainty in CP measurement:  Asymmetry in b-b production rate  Charge dependent detector efficiencies… can bias tagging efficiencies can fake CP asymmetries  CP asymmetries in background process Experimental handles:  Use of control samples: Calibrate b-b production rate Determine tagging dilution from the data: e.g. B s ->D s  for B s ->D s K, B->K  for B-> , B->J/  K* for B->J/  K s, etc  Reversible B field in alternate runs  Charge dependent efficiencies cancel in most B/B asymmetries  Study CP asymmetry of backgrounds in B mass “sidebands”  Perform simultaneous fits for specific background signals: e.g. B s ->D s  in  B s ->D s K, B s ->K  & B s ->KK, … Systematic Effects

22 Conclusions  LHC offers great potential for B physics from “day 1” LHC luminosity  LHCb experiment has been reoptimized: Less material in tracking volume Improved Level1 trigger  Realistic trigger simulation and full pattern recognition in place  Promising potential for studying new physics