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

First Evidence for the Decay R. Aaij et al. * ( LHCb Collaboration) Physics Review Letter (PRL) 110, 021801 (2013). David Amdahl Physics 542, Fall 2013 27 Sep 13. Opening Statement. Search for rare decays and is performed with data collected in 2011 & 2012

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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

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