Theoretical Motivation Analysis Procedure Systematics Results David Doll

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 Theoretical Motivation Analysis Procedure Systematics Results David Doll, on behalf of the Ba.

Theoretical Motivation Analysis Procedure Systematics Results David Doll, on behalf of the Ba. Bar Collaboration 1 APS 04/12/08

Theoretical Motivation Standard Model BF *535 M Experimental Limit on BF (90% CL)* ar.

Theoretical Motivation Standard Model BF *535 M Experimental Limit on BF (90% CL)* ar. Xiv: 0708. 4089 v 2 [hep-ex], PRL 99, 221802 (2007) pairs at Belle • Highly suppressed Flavor Changing Neutral Current • Not well constrained experimentally • Several models enhance BF(Unparticle Model, MSSM at large tan β, …) Ba. Bar’s previous best upper limit is 7. 8 x 10 -5 for semileptonic tags with 81. 9 fb-1 Current analysis at 319 fb-1 2 APS 04/12/08

Analysis Procedure, Tagging Perform a ‘semileptonic’ tagged analysis ◦ Fully reconstruct the ‘tag B’

Analysis Procedure, Tagging Perform a ‘semileptonic’ tagged analysis ◦ Fully reconstruct the ‘tag B’ in the decay ◦ Look at the rest of the event for our signal Tag B B+ Signal B B- 3 APS 04/12/08

Random Forest (RF) Use a multivariate analysis tool from Stat. Pattern. Recognition (ar. Xiv:

Random Forest (RF) Use a multivariate analysis tool from Stat. Pattern. Recognition (ar. Xiv: physics/0507143 v 1) Sampling with replacement of both the training data and the input variables (bagging) Optimize the ‘Punzi’ Figure of Merit The important input variables: number of charged tracks in the signal B (opposite the ‘tag B’) the missing energy in the event the signal Kaon candidate’s momentum the unmatched neutral energy in the event 4 APS B->Knunu 04/12/08

Final Predictions, Continuum Use sideband region in the continuum data in the signal region

Final Predictions, Continuum Use sideband region in the continuum data in the signal region from amount of data in sideband RF continuum est. Estimate sideband 5 APS B->Knunu 04/12/08

Final Predictions, Peaking estimate from RF output, separated into sideband/signal regions Subtract sideband from

Final Predictions, Peaking estimate from RF output, separated into sideband/signal regions Subtract sideband from signal region in both Data and MC and take the ratio MC: Data Extrapolate a line into the signal region trendline signal region 6 APS B->Knunu 04/12/08

Background Systematics Continuum systematic from difference between MC and data Peaking background systematic from

Background Systematics Continuum systematic from difference between MC and data Peaking background systematic from difference between the a trendline fit to all the MC: Data, vs. a trendline fit to just the peaking component (above) We also take a systematic based on our MC weighting procedure. MC Background prediction Statistical Uncertainty Systematic uncertainty 7 APS B->Knunu 04/12/08

Control Sample • Both Bs decay semileptonicly requiring: • no remaining charged tracks in

Control Sample • Both Bs decay semileptonicly requiring: • no remaining charged tracks in the event • momentum of each lepton>1. 24 Ge. V/c • Resolved differences between signal MC and double tag data: • particle substitutions • kinematic corrections • brute force variable redistribution. • Serves as control sample for evaluating systematics for the multivariate analysis. B+ B 8 APS B->Knunu 04/12/08

Signal Systematics Tagging Efficiency: Taken from ratio below in which both tags are Kaon

Signal Systematics Tagging Efficiency: Taken from ratio below in which both tags are Kaon Momentum: Evaluated by comparing phase space theory with SM-predicted theory 9 APS B->Knunu 04/12/08

Signal Systematics Correlations Variables: btwn. ◦ 1 -D distributions already resolved ◦ Need to

Signal Systematics Correlations Variables: btwn. ◦ 1 -D distributions already resolved ◦ Need to account for correlations in order use the control sample to evaluate signal box efficiency in signal MC 10 APS B->Knunu 04/12/08

Signal Systematics Signal Box Eff. : ◦ Retrain RF with double tag MC control

Signal Systematics Signal Box Eff. : ◦ Retrain RF with double tag MC control sample substituted for signal MC ◦ Evaluate systematic by comparing efficiency of the RF cut on double tag MC to double tag data Ntrkleft=1: ◦ The control sample identified with this cut, not present in signal MC ◦ Evaluate systematic from separate rectangular cut based investigation 11 APS B->Knunu 04/12/08

Results Upper limit at the 90% confidence level Expect 30. 7 +/- 10. 7

Results Upper limit at the 90% confidence level Expect 30. 7 +/- 10. 7 events, corresponding to an upper limit of 2. 9 x 10 -5 Inside the RF box, we saw 38 events, which gives an upper limit: 12 APS B->Knunu 04/12/08