b tn and b d ( * ) tn decays at babar
DESCRIPTION
B tn and B D ( * ) tn decays at BaBar. Guglielmo De Nardo University of Napoli “Federico II” and INFN Representing the BaBar collaboration 36 th International Conference on High Energy Physics July 2012, Melbourne, Australia. Tagging method. Tag this B. Then look for signal. - PowerPoint PPT PresentationTRANSCRIPT
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B tn and B D(*) tn decays at BaBar
Guglielmo De NardoUniversity of Napoli “Federico II” and INFN
Representing the BaBar collaboration
36th International Conference on High Energy PhysicsJuly 2012, Melbourne, Australia
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Tagging method
• Weak signal signature Decay with missing momentum
(many neutrinos in the final state) Lack of kinematics constraints in
final state
• background rejection improved reconstructing the companion B
• Look for signal in the rest of the event Expect to find nothing more than
visible signal decay products No additional track and little
activity in the calorimeter
e+,μ+
Tag this B Then look for signal
νμ, νe
ντ
D0
e+,μ+
ντ
τ+
B+
ϒ(4S)
νμ, νe
ντ
ντ
τ+
X-
B+
ϒ(4S)
B-
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Leptonic B decays
• B l➝ n very clean theoretically. SM uncertainty in the B decay constant fB .and |Vub| value.
+ W+b
u
l+
nℓ
B+
• Interesting probe of physics beyond the SM, since also a charged Higgs can mediate the decay
H+b
u
l+
nℓ
B+
• B ➝ tn used in global UT fits. B ➝ mn out of reach of current B-factories
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B tn with hadronic tags at BaBar
• Fit to residual energy in calorimenter simultaneously in 4 reconstructed modes (t enn, t , mnn t , pn t rn)
• Floating parameters: BF and 4 background yields• Combinatorial B tag background estimated from data.
B+ background shape from MC• Excess of events over background of 3.8 s
MC modelling ofsignal Eextra PDF checked withdouble tags
arXiv:1207.0698[hep-ex]Submitted to Phys.Rev.D (R)
te tm
tr tp
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Comparison with the 2HDM type II
• Uncertainty in Standard Model prediction mostly due to |Vub||Vub|incl = (4.33 ± 0.28)×10-3
|Vub|excl = (3.13 ± 0.30)×10-3
fB = (189 ± 4) MeV (HPQCD arXiv:1202.4914)
B tn measurement
BaBar|Vub| measurement (exclusive decays)BaBar|Vub| measurement (inclusive decays)
SM
BABAR
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Constraints on the tan b vs mH+ plane in 2HDM type II
Most of the parameter space of 2HDM is excluded at 90% C.L., if we assume exclusive |Vub| determination
90% C.L. exclusion for mH+ up to 1 TeV at very high tan b (>70) using inclusive|Vub|
Excl. at 2s Excl. at 3s
Excl. at 2s Excl. at 3s
Exclusive |Vub| Inclusive|Vub|
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Ratio of B D(*) tn to B D(*) tn
• Semileptonic decays with a t
• We test the SM measuring the ratios
• SM predictions are R(D) = 0.297 ± 0.017 and R(D*) = 0.252 ± 0.003
D* only
H+ contr. here
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8M2miss p*l
Analysis strategy
• Full reconstruction of a tag B in hadronic decays. • Identify e or m and reconstruct a D meson (D*+, D*0, D+, D0)• Kinematic requirement: q2 > 4 GeV2
• 2D likelihood fit to M2miss=(Pee-ptag-pD-pl)2 and p*l
Yields floating Fixed parameters B D l n normalization BB combinatorial and continuum bkgsB D tn signal cross-feeds among modesB D** l n background (from a D(*) p0 l n CS)
arXiv:1205.5442[hep-ex]Submitted to Phys.Rev.Lett.
PDF taken from Monte Carlo
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B D* t n results
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B D t n results
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Systematic Uncertainties
• Main systematics uncertainties D** background yield from a
D(*) p0 l n Data control sample Signal MC statistic
o For PDF extraction BB and continuum background
D(*) p0 l n Control sample
M2miss
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Comparison with Standard Model
Combinination yields c2 / n.d.o.f. = 14.6/2(probability: 6.9 × 10-4)3.4s away from SM
Z. Phys C46, 93 (1990)PRD 82, 0340276 (2010)PRD 85, 094025 (2012)and recent updates
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2HDM type II cannot explain the excess
• A Charged Higgs within 2HDM type II contribution:
Taking into account the effect of tan b/mH on efficiency
R(D) tan b/mH = 0.44 ± 0.02R(D*) tan b/mH = 0.75 ± 0.04
Mutually exclusive with CL >99.8%
PRD 78, 015006 (2008)PRD 85, 094025 (2012)
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Conclusions
• Updated result on B t n with hadronic tagging
BF(B t n ) = (1.8 ± 0.5± 0.2) × 10-4.arXiv:1207.0698 [hep-ex], submitted to Phys.Rev.D (R)
Agreement with the SM in tension using exclusive |Vub| measurements (2.4s)Better agreement using inclusive |Vub| (1.6s)
• Improved measurement of R(D(*)) = BF(B D(*) t n) / BF(B D(*) l n)
R(D*) = 0.332 ± 0.024 ± 0.018 R(D) = 0.440 ± 0.058 ± 0.042
exceeding the SM predicted values by 3.4 s.
arXiv:1205.5442[hep-ex], submitted to Phys.Rev.Lett.
• 2HDM type II (alone) cannot accomodate the results and theorists already at work building models