1. Search for Bsμμ and Bdμμ with 2 fb-1 of data
CDF 8925
Slava Krutelyov
UCSB
with
D.Glenzinski, H.Held (KIT), C.-J.Lin (FNAL)
T.Kamon, M.Weinberger (TAMU)
M.Herndon (UWisconsin)
SUSY-Group Meeting
08/29/2007
blessed on Aug 09
Motivation and history
Analysis
Setup
Event selection: signal discriminants
muon ID with LH
Neural Net
(optimized) Expectations and results
Effects on SUSY

2. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

3. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Motivations: Models n
l’i23
l i22 ~ m b s
MSSM
With RPV: can proceed at tree level
couplings not constrained much otherwise
In general case has a diagram ~ tan6b/MH4
tan4b/MH4 come from MSSM is a 2HDM
remaining tan2b is from SUSY (stop L-R mixing)
Just need large tanb, not too-high MH, some stop mixing
SO(10) with Yukawa unification tanb~50 !
mSUGRA with large tanb
Other BSM: with no extra flavor structure the enhancement < ~ a factor of 2
With improving limits start asking any theorist “Is it allowed by Bsμμ?”
More in the end of the talk
EXCLUDED
Bsmm appears to get into the “model exclusion hall of fame”
Near 200 citations (combined for CDF/DØ RunII) in the past ~3 years
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S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

4. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Bits of history
Search for Bsmm is as old as hadron colliders
First looked at by UA1
Recent limits are all from Tevatron
DØ is often close to CDF
Prior
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S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

5. Bs(d)m+m- Ingredients
Normalize to B+J/y K+ decays
Construct discriminant to select Bs and suppress bgd
MC sim for signal
Data mass sidebands for bgd estimate
Minimize expected 90% C.L. upper limit
Normalization mode
Signal sample (baseline)
Bd Bs
N(UU+UX) ~ 3×104
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S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

6. Improving sensitivity: muon ID
Dx c2 cut  use muon LH (LH>0.1)
Combined dX, dPhi, dZ, EM, HAD
add dE/dX cut
Z>-0.2
Suppress combinatorics
~x2 less events (after preselection)
Bring Bhh below the horizon
Bhh fakes are ~0.05 for Bs and ~0.5 for Bd windows
cf. ~ 0.3 (Bs) and ~2 (Bd) with Dx c2 cut
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S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

7. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Normalization mode
B+J/ψK+ + c.c.
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

8. Discriminating variables
Used as inputs to Neural Net
R=1 a l μ
pmm Bs
l/s
pTmm
pTm
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

9. Preselections: signal+sidebands
Vertex Requirements:
c2(vtx) < 15
s(L3D) < 150 mm
L3D < 1 cm
0 < l < 3 mm
(l = proper decay length)
l/s(l) > 2
pT(B)>4 GeV && |y(B)|<1
4669 < M(mm) < 5969 MeV
In addition:
Isolation>0.5
Pointing angle Da<0.7
Bsmm Search Sample:
N(CMU-CMU) = 15594
N(CMU-CMX) = 15072
(completely Bgd dominated)
Note: without muon LH & dE/dX
~x2 more backgrounds here
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S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

10. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Signal MC
Use Pythia
BGen for systematics
Reweigh to follow pT distribution from data
Compare using B+ data and MC
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

11. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
NN: inputs
After applying pre-selections use sidebands (bgd) and signal MC to train NN
6 inputs to NN training
λ – lifetime
λ/σ – lifetime significance
Δα – 3D poining (vtx vs momentum)
Iso
pT(B)
pT(μ) min – lower of the pair
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S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

12. NN inputs: x-check w data B+ plots
Input variables are well-modeled
including pT(μ) high used in the trial NN
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S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

13. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
NN: output
Compared to LH (used previously) get a better (~2 times) rejection at the same efficiency
LH had 3 vars: Iso, P(λ), Δα
5 var NN: add λ/σ and pT(B)
7 var NN includes both pT(μ)
introduces mass biasnot used
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

14. NN output: x-check for biases
The correlation is negligible
No evidence of a bias here or in other x-checks
checked w/ control samples, trained on part of sidebands, bootstrap
use of sidebands is justifiable
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

15. NN outputs: x-check w data B+
Good agreement
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

16. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Control Samples
Independent bkg control samples to cross check bkg estimate procedure
OS - : Opposite-sign dimuon sample with ct<0
SS+ : Same-sign dimuon sample with ct>0
SS- : Same-sign dimuon sample with ct<0
FM : Fake muon sample ct>0
(require at least one muon leg to fail our muon likelihood and dE/dX requirement)
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

17. Control Samples: NN x-checks
NN performance: observation is consistent with expectations
Using a wider ± 150 MeV signal window for cross-check
For obsv<pred, prob= probability for making an observation ≤ obsv
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

18. Applying NN: getting expected bgd
CMU-CMU
CMU-CMX
Shape in sidebands give contribution of combinatorial bgd to signal bins
Separate fit in each NN bin: pol1 in bins 1, 2; pol0 in bin 3
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

19. Inputs to the (exp./obs.) limit
Inputs to be used in the “main” formula
The biggest uncertainty is from fu/fs (after bgd stat)
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

20. Optimization: choice of NN bins
Relative (unnormalized) numbers are shown
The choice (of 3 bins) is
[0.8, 0.95]U(0.95, 0.995]U(0.995, 1]
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

21. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Bhh contributions
Contribution to Bdμμ
Contribution to Bsμμ
The contribution to Bs is small, considerable for Bd
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

22. Expectations and observations: Bs
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

23. Expectations and observations: Bd
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

24. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Results: limits
New world-best result
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

25. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Results: 2D plots
P-value with bgd-only hypothesis, 10K pseudoexperiments
CMU-CMU CMU-CMX
Bsmm % %
Bdmm % %
Observed events are consistent with expectation
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

26. Results: 2D plot combined
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S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

27. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Results: 1D plots Bs
2 events in CMU-CMU channel
1 event in CMU-CMX channel
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

28. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Limits history
Getting better and better
faster than 1/sqrt(Lumi), slower than 1/Lumi
Unofficial Tevatron combination: Br(Bsμμ) < 95%
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

29. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

30. SUSY contemplations (1)
The importance of Bsμμ grows with tanβ
SUSY with large tanβ becomes more popular
driven by a more significant aμ now at ~3.4 σ away from SM
The SO(10) scenario by Raby et al. is practically excluded now
R. Dermisek et al.,
hep-ph/ (2005)
[easy model to exclude]
SO(10)
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S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

31. SUSY contemplations (2)
Light MSSM Higgs scenario is next in line for significant exclusion.
Belyaev et al.
SUSY07
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

32. SUSY contemplations (3)
CDF Limit
5.8x10-8
2 fb-1
The limit eats further into the mSUGRA space now
not as significant with bsγ constraint considered
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

33. SUSY contemplations (4)
Start getting beyond bsγ at high tanβ
Still a way to go  2x10-8 will be way more noticeable
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

34. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
Summary
We have updated the Bmm analysis with 2 fb-1
The limits improved significantly:
95%CL
95%CL
Both limits are the best in the world!!!!
Plan to prepare/publish in PRL
draft in progress ( to GPs this week?)
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

35. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1
backup
08/29/2007
S. Krutelyov Search for Bs,d-->mumu with 2 fb-1