theoretical motivation analysis procedure systematics results
DESCRIPTION
Theoretical Motivation Analysis Procedure Systematics Results. David Doll , on behalf of the BaBar Collaboration. APS 04/12/08. arXiv:0708.4089v2 [ hep -ex ], PRL 99, 221802 (2007). *535 M pairs at Belle. Highly suppressed Flavor Changing Neutral Current - PowerPoint PPT PresentationTRANSCRIPT
Theoretical MotivationAnalysis ProcedureSystematicsResults
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APS 04/12/08
David Doll, on behalf of the
BaBar Collaboration
ννKB
ννKB
Theoretical Motivation
• Highly suppressed Flavor Changing Neutral Current• Not well constrained experimentally• Several models enhance BF(Unparticle Model, MSSM at large tan β,…)
Standard Model BF Experimental Limit on BF (90% CL)*
62.16.0 108.3
5104.1
2
*535 M pairs at Belle
arXiv:0708.4089v2 [hep-ex],PRL 99, 221802 (2007)
BaBar’s previous best upper limit is 7.8x10-5 for semileptonic tags with 81.9 fb-1
Current analysis at 319 fb-1
BB
APS 04/12/08 ννKB
Analysis Procedure, TaggingPerform a ‘semileptonic’ tagged analysis
◦Fully reconstruct the ‘tag B’ in the decay◦Look at the rest of the event for our signal
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νlDB 0
}πππ,ππ,{πKD 00
B+
0D
l
B-
KTag B Signal B
APS 04/12/08 ννKB
Random Forest (RF) Use a multivariate analysis tool from
StatPatternRecognition (arXiv:physics/0507143v1) 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
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BNS
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APS B->Knunu 04/12/08
Final Predictions, Continuum Use sideband region in
Estimate the continuum data in the signal region from amount of data in sideband
RF continuum est.
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APS B->Knunu 04/12/08
0Dm
πKfor m -D0
sideband
Final Predictions, Peaking 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
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APS B->Knunu 04/12/08
trendline0Dm signal
region
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.
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Statistical Uncertainty
Systematic uncertainty
APS B->Knunu 04/12/08
MC Background prediction
Control Sample• Both Bs decay semileptonicly requiring:
• no remaining charged tracks in the event• momentum of each lepton>1.24 GeV/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.
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APS B->Knunu 04/12/08
B-
0D
l
B+
0D
l
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
) tagsingl tagdouble(
) tagsingle tagdouble(
MC
Data
R
R
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APS B->Knunu 04/12/08
πKD0
Signal Systematics Correlations btwn.
Variables: ◦ 1-D distributions already
resolved◦ Need to account for correlations
in order use the control sample to evaluate signal box efficiency in signal MC
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APS B->Knunu 04/12/08
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
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APS B->Knunu 04/12/08
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:
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C.L. 90% @104.2)ννKBF(B 5
APS B->Knunu 04/12/08