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Flavour-specific asymmetry: searching for new physics at LHCb

Flavour-specific asymmetry: searching for new physics at LHCb. Robert W. Lambert, CERN. Outline. Introduction What is flavour specific asymmetry? (… some maths) The experimental challenge for LHCb Sensitivities and Outlook Highlights:

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Flavour-specific asymmetry: searching for new physics at LHCb

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  1. Flavour-specific asymmetry:searching for new physics at LHCb Robert W. Lambert, CERN Nikhef, 17th February 2011

  2. Outline • Introduction • What is flavour specific asymmetry? (… some maths) • The experimental challenge for LHCb • Sensitivities and Outlook • Highlights: • Proof of principle of method for the first time with real data • Update of sensitivities including systematics • Many real-data plots presented here for the first time Nikhef, 17th February 2011

  3. Surprise! … DØ May 2010 Nikhef, 17th February 2011

  4. Translate • pp-interactions within a symmetric experiment • Correct all experimental biases (magnets, mis-id …) • Observe • In the SM, the favored way to make charge asymmetry is if: • Which comes from B0-mixing: • In the standard model it is almost negligible ≠ ≠ ≠ Nikhef, 17th February 2011

  5. Not unexpected Nikhef, 17th February 2011

  6. Not unexpected • CPV must be very much higher than the standard model Nikhef, 17th February 2011

  7. Not unexpected • CPV must be very much higher than the standard model REALITY SM (maximal) You Are Here Where did you go?Guys…? Guys…?? Nikhef, 17th February 2011

  8. Not unexpected • CPV must be very much higher than the standard model REALITY SM (maximal) Mass of entire solar system: 2x1030 kg Mass of largest asteroid, Ceres: 1021 kg Area ~ Kazakhstan: Population~one small dog Nikhef, 17th February 2011

  9. Flavour-specific asymmetry … a smoking gun for new physics?? Nikhef, 17th February 2011

  10. Flavour-specific asym. • Flavour-specific decays • Favoured/Allowed • Not allowed at tree • Through mixing • Flavour specific asymmetry, afs, parameterises CPV in mixing Nikhef, 17th February 2011

  11. B0 Mixing • Simplify to one hamiltonian • Mass-decay-eigenstates are not flavoureigenstates • Four observables on the real part of this equation: • Average width • Average mass • Width Difference • Mass Difference Nikhef, 17th February 2011

  12. B0 Mixing • Simplify to one hamiltonian • Flavoureigenstates are not CP-eigenstates • Imaginary part, a phase, where all CPV lives: • afs is very small in the standard model: Nikhef, 17th February 2011

  13. Discovery Potential • afs is sensitive to new physics (NP): • Sensitive to loop contributions • Sensitive to new CPV phases • If we allow a single NP phase in the mixing  ? Nikhef, 17th February 2011

  14. Discovery Potential • afs is sensitive to new physics (NP): • Sensitive to loop contributions • Sensitive to new CPV phases • If we allow a single NP phase in the mixing  ? Nikhef, 17th February 2011

  15. Discovery Potential • afs is sensitive to new physics (NP): • Sensitive to loop contributions • Sensitive to new CPV phases • If we allow a single NP phase in the mixing  • Put in the numbers… ? Nikhef, 17th February 2011

  16. Discovery Potential • afs is sensitive to new physics (NP): • Sensitive to loop contributions • Sensitive to new CPV phases • If we allow a single NP phase in the mixing  • Up to 200-times the SM ... but ... (4x10-3)< D measurement ? Nikhef, 17th February 2011

  17. Hot Topic SM-like new physics lives here Nikhef, 17th February 2011

  18. What can we expect from LHCb? Nikhef, 17th February 2011

  19. LHCbis Fantastic • LHCb is a dedicated, precision, b-physics experiment • More statistics: we’re in the forward region, and at LHC Nikhef, 17th February 2011

  20. Being Exclusive • Our forte: exclusive, reconstructed, b-decays • In particular, time-dependent measurements ~100k Ds in 5 fb-1 ~100k Ds in 0.2 fb-1 Nikhef, 17th February 2011

  21. Experimental Challenge Nikhef, 17th February 2011

  22. The simple formula 10-3 -> 10 -5 Nikhef, 17th February 2011

  23. The simple formula Very Complicated • Polluting asymmetries are much larger than afs • Detector asymmetrydc ~(10-2) • Production asymmetrydp~(10-2) • Background asymmetrydb~(10-3) 10-3 -> 10 -5 10 -2 10 -2 10 -3 Nikhef, 17th February 2011

  24. Pollutants Where do they come from? What can we do about them? Nikhef, 17th February 2011

  25. LHC • An amazing machine • Unfortunately also not CP symmetric Nikhef, 17th February 2011

  26. Production Asymmetry,dp • LHC is a proton-proton collider: not CP-symmetric • LHCb is at high rapidity where production asym. are largest • There is never a simple control channel to measure dp Explicitly asymmetric at LHC dp(B0 and B0) Pythia Valence Quark Scattering Nikhef, 17th February 2011

  27. Simplify • We measure time-dependent decay rates: • Ac, Ap and Afs are correlated and cannot be separately fitted • First, reparameterise Nikhef, 17th February 2011

  28. Reparameterise • Just to make it easier to see what we’re doing… • production asymmetryis an initial state asymmetry • Changes the mixing amplitude, does not change the physics • Fit for x1 independently, which now only has detector asym • … unfortunately that’s the largest pollutant … Nikhef, 17th February 2011

  29. LHCb Nikhef, 17th February 2011

  30. Detector Asymmetry, dc Asymmetry in Muons of offline selected signal (LHCb unofficial) • Magnet divides +/- charge, allowing +/- asymmetry • by reversing magnet in D0: dc reduced from 3% -> ~0.1% Left Right Left Right After 4Tm Magnet Before 4Tm Magnet +ve -ve -ve +ve Nikhef, 17th February 2011

  31. Detector Asymmetry, dc Asymmetry in Muons of offline selected signal (LHCb unofficial) • With both magnet polarities dcvastly reduced • But that’s not the whole story … Left Right Left Right After 4Tm Magnet Before 4Tm Magnet +ve -ve -ve +ve Nikhef, 17th February 2011

  32. Detector Asymmetry, dc 120 K-, p . 100 K+, p 80 hadronic cross-section / mb 60 40 20 0 0.1 1 10 100 1000 momentum in lab frame P / GeV c lab Kaon interaction cross-section Resultant charge asymmetry (MC) • Matter detector hadronic interactions are asymmetric • Dominant systematic at order 1% … need a control channel PDG K- p K+ p Kaon PDG cross-section -1 Nikhef, 17th February 2011

  33. Real Data Bs ~800 mb-1 PV Bs SV m- Ds+ TV LHCb Preliminary p+,K+,K- EVT: 49700980 RUN: 70684 mm Nikhef, 17th February 2011

  34. Real Data Bd LHCb Preliminary K-,K+,p+ ~800 mb-1 TV D+ SV PV m- Bd EVT: 141526660 RUN: 70666 mm Nikhef, 17th February 2011

  35. Momentum Spectra • Must match for the detector asymmetryto cancel Yields in tight D-mass windows Ratio Bd / Bs LHCb Unofficial Resample within theBs distribution to correctthe differences Nikhef, 17th February 2011

  36. Momentum Spectra • Can re-sample in P(p) without changing afs Yields in tight D-mass windows Ratio Bd / Bs LHCb Unofficial Pions, cancellation excellent Reduce systematic to order 0.05% 7% of Bs events thrown away Still #Bs >> 2*#Bd Nikhef, 17th February 2011

  37. The subtraction method • Take Bs/Bd with the same final states ( =KKp m) • All production asymmetry is in x2/x3, just throw it away • Measure the difference between Bs and Bd Nikhef, 17th February 2011

  38. One more to go.. • Background asymmetry… every one is different Can fit most of thisin the sidebands Nikhef, 17th February 2011

  39. Peaking background • Peaking background will also be asymmetric … • Need to find a variable to separate the peaking background MC09 Signal Peaking BG Nikhef, 17th February 2011

  40. Log(IP) • Peaking background is clearly identified, good separation LHCb Unofficial KKp Mass – Ds Mass / MeV Log(IPD / mm) Nikhef, 17th February 2011

  41. Log(IP) • Peaking background is clearly identified, good separation LHCb Unofficial Signal Peaking BG KKp Mass – Ds Mass / MeV Log(IPD / mm) B-like background Nikhef, 17th February 2011

  42. Double-charged • Cross-check where there should be no signal D+ m- D- m+ 50% Signal D+ m+ D- m- 100% background Nikhef, 17th February 2011

  43. Log(IP) • There should be no signal peak in the wrong-sign plot • Good. A hint of a cascade process, add a small systematic. LHCb Unofficial B-like background Log(IPD / mm) Peaking BG KKp Mass – Ds Mass / MeV Nikhef, 17th February 2011

  44. Sensitivities and Outlook Nikhef, 17th February 2011

  45. After 1fb-1 of LHCb • LHCb measurement cuts at right-angles to D SM-like new physics lives here Remaining systematicsasymmetric and dependon central value from fit. Measurement statisticallylimited up to ~50 fb-1 Nikhef, 17th February 2011

  46. Conclusion • D have made an astounding measurement (3.2 s!) • At LHCb we will measure: • Detector,background and production asymmetries fitted in data • s~0.5%, First result expected after 100 pb-1 • s~0.2%, 5 s possible after 1 fb-1 • s~0.05%… keep going until 50 fb-1, 20 s, or rule out most NP from Nikhef, 17th February 2011

  47. Cereal loops New Physics inspecial boxes! Now in bitesize-chunks! Two exciting flavours! Act now and getyour first 105 decays free! AfsDG and Dms in every box! Nikhef, 17th February 2011

  48. End • Backups are often required Nikhef, 17th February 2011

  49. References • Nierste, hep-ph/0406300, 2006 • Georgi, hep-ph/0703260 • V. M. Abazov et al., D0, PRL 98 (2007) pp. 151801 • N. Brook et al., LHCb-note CERN-LHCb-2007-054 • Y.-M. Yao et al., the Particle Data Group, Review 2006, http://pdg.lbl.gov/ • M. Botlo et. al, SLAC-PUB-5795 SSCL-538 (1992) pp. 1-56 • E. Norrbin and T. Sjostrand, Eur. Phys. J. C. 17 (2000) pp. 137-161 Nikhef, 17th February 2011

  50. Literature • Reading material: • LHCb • CERN-LHCb-2007-054 Public note from old Monte Carlo • CERN-THESIS-2008-045 Paul’s Thesis • CERN-THESIS-2009-001 Rob’s Thesis • CERN-THESIS-2010-076 Ken’s Thesis • Theory • hep-ph 0406300 U. Nierste • hep-ph 0612167[JHEP] A. Lenz, U. Nierste • hep-ph 0605028[PRL] Y. Grossman et al. • hep-ph 0604112[PRL] Z. Ligetiet al. • Other measurements • hep-ex 0505017[PRD] Belle • hep-ex 0202041[PRL] Babar • hep-ex 0101006[PRL] Cleo • Note 9015 CDF inclusive Nikhef, 17th February 2011

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