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First Evidence for the Decay R. Aaij et al. * ( LHCb Collaboration) PowerPoint Presentation
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First Evidence for the Decay R. Aaij et al. * ( LHCb Collaboration)

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  1. First Evidence for the Decay R. Aaijet al.*(LHCb Collaboration) Physics Review Letter (PRL) 110, 021801 (2013) David Amdahl Physics 542, Fall 2013 27 Sep 13

  2. Opening Statement • Search for rare decays and is performed with data collected in 2011 & 2012 • Data samples comprise of 1.1 fb-1 of proton-proton collisions at = 8 TeV and 1.0 fb-1 at = 7 TeV at the Large Hadron Collider • Standard Model “precisely predicts” branching fractions, • Question: Will the decays deviate from the Standard Model?

  3. Outline • Review of Branching Fraction • Motivation • Design of Experiment • Mass Distribution • Results

  4. Review of Branching Fraction • Define Γas decay rate or the probability per unit time that any given particle will disintegrate • Mean lifetime: τ= 1/Γ • Most particles decay by several different routes • Branching fraction, , of the ith decay mode = • Reference: Griffiths, Introduction to Elementary Particles, Second Revised Edition.

  5. Motivation Theory Reference from Subject Paper: Buras, Girrbach, Guadagnoli, & Isidori, “On the Standard Model Prediction for ”, Eur. Phys. J. C., 2012, 72:2172. SM Prediction Experiment Experiment Ref. Table Reference: Buchalla, Buras, & Lautenbacher, “Weak Decays beyond Leading Logarithms”, Rev. Mod. Phys., Vol 68, No 4., Oct 1996.

  6. Design of Experiment • Paper addresses 3 disciplines: 1) Selective Criteria for desired decay • Impact Geometry • Angles & distances of primary & secondary interaction vertices • Particle properties • Momentum, mass, decay times • Number of tracks 2) Identifying & Separating background components 3) Uncertainty Quantification • All disciplines supported by theory & simulation

  7. Calculation of Branching Fraction Start with: Simplifies to: Where: : Number of observed signal events : Normalization factors Actual Values: = (2.52 ± 0.23) X 10-10 = (6.45 ± 0.30) X 10-11

  8. Invariant Mass Distribution of Selected Candidates (Black Dots) • Overall Fit (Blue) • Components • (Red Dashed) • (Green Dashed) • Other Decays (Pink)(Cyan)(Black Short Dashed) • Background (Dashed Blue)

  9. Results • Experimental results stated as Branching Fraction, • at 95% confidence • Paper states results agree with Standard Model predictions