1. Richard Kass The Ohio State University
|Vus| from Tau decay
Richard Kass
The Ohio State University
OUTLINE
Introduction
Recent measurements of branching fractions
Determination of |Vus|
Summary

2. How to determine |Vus| nt nt nt t- t- t-
e-, m-
ve, vm t- nt W- d u
Vud t- nt W- s u
Vus
strange hadronic decays:
K-, K-π0, K0π-, K0π-π0, etc.
leptonic decays
non-strange hadronic decays:
π-, π-π0, (3π)-, (3π)-π0, etc.
Measure the R’s
We can related the R’s to the CKM elements by:
|Vud|= ± PDG08
|Vud|= ± ,
T. Eronen, et al. PRL 100, (2008)
Pich, Tau06, hep-ph ,
Gamiz, et al.
PoS KAON 008/
δR is a SU(3) symmetry
breaking correction.
It is small, < 0.1●Rτ,ns/|Vud|2

3. Another way to determine |Vus|nt W- s u
Vus t- nt W- d u
Vud π- K-
Assume universality of couplings
EW corrections cancel
Take fK/fπ from Lattice QCD
|Vud| known
Measure B(t-®K-n)/B(t-®π-n)

4. The easiest way determine |Vus|
Unitarity of CKM matrix: |Vud|2+|Vus|2+|Vub|2=1
|Vub| is really small so forget about it.
|Vub|=(3.93±0.36)x10-3
|Vud| is measured really well.
|Vud|= ±

5. Some Experimental Details
Since the cross section for e+e-®Y(4S)®BB is about
the same as e+e-®t+t- a B factory is also a t factory.
Both experiments have a very large (~109) sample of tau events
Detectors are well matched to do tau physics:
k/p particle ID, g/p0 reconstruction, charged particle tracking, etc.
Can reduce most non-tau backgrounds to ≤ 1%:
bhabhas, m-pairs, e+e-®qq

6. A Bit of Recent History BFs dominated by CLEO & LEP
Fix ms & extract |Vus|
Simultaneous fit to extract |Vus| & ms

7. Recent Tau Results relevant to this talk
mode
BaBar
Belle
t-®π-v
ICHEP08 (S. Banerjee)
t-®K-v
t-®K0π-v
PL B654; 65, 2007
t-®K-π0v
PRD 76:051104, 2007
t-®p-p-p+v
PRL , 2008
t-®K-p-p+v
ICHEP08 (K. Inami)
t-®K-p-K+v
t-®K-K-K+v
ICHP08 (K. Inami)
t-®K-fv, PL B643 (2006) 5
t-®K-/K*-hv
arXiv:

8. t®K0π-n
Preliminary BaBar result presented at ICHEP 08 arXiv: v2
Reconstruct K0
using Ks®π+π- mode
BaBar
Preliminary
accept
tag side requires e or μ
Total efficiency = 1.1%
Backgrounds are primarily
due to other tau decays:
~20% background

9. t®K0π-n Data sample contains ~350x106 tau-pairs New World Average:
BaBar
Preliminary
Structure the data but not the
MC in the Kπ mass spectrum
BF(t®K0π-n)=(0.840±0.004±0.023)%
Consistent with recent Belle result:
BF(t®K0π-n)=(0.808±0.004±0.026)%
(PL B654; 65, 2007)
New World Average:
BF(t®K0π-n)=(0.835±0.022)% (S=1.4)

10. t®K-π0n High statistics ~211x106 t-pairs ®3x104 signal events
BF measurement limited by systematics
Again structure in the Kπ invariant mass spectrum not in MC
BaBar
backgrounds
Published: PRD 76:051104, 2007

11. t®(3h)-n t-®K-p-K+v t-®K-p-p+v t-®K-K-K+v BaBar: PRL 100 011801, 2008
Belle: presented at ICHEP 2008
Belle
t-®K-p-K+v
Belle
Belle
t-®K-p-p+v
t-®K-K-K+v

12. |Vus| from t branching fractions
mode
BWA2007 (%)
t-®K-v
0.691±0.023 (measured)
0.715±0.003 (Kμ2)
t-®K-π0v
0.426±0.016
t-®K0π-v
0.831±0.028 (S=1.3)
t-®K-π0π0v
0.058±0.024
t-®K0π-π0v
0.360±0.040
t-®K-p-p+v
0.280±0.016 (S=1.9)
t-®K-hv
0.0160±0.002
t-®(K03π)-v
0.074±0.030 estimated
t-®K1(1270)n®K-wv
0.067±0.021
t-®(K04π)-v
0.011±0.007 estimated
t-®K*-hv
0.12±0.004 (S=2)
t-®K-fv ±
TOTAL
2.830±0.074
2.854±0.071(Kμ2)
0.835±0.022
δRt= 0.240±0.032
Gamiz, et al. PoS KAON 008/arXiv:
2.834±0.074
2.858±0.071
|Vus|=0.2154±0.0031
|Vus|=0.2163± using Kμ2
|Vus| from BFs ~3σ lower
than unitarity calculation
|Vus|=0.2262± using unitarity

13. |Vus| from t spectral functions & branching fractions
K. Maltman et al., arXiv: S. Banerjee ICHEP08
(o,o) weight
non-spectral wts
Use various weight factors including
non-spectral weights based on
ALEPH data + updated t BFs.
|Vus|~3σ lower than
unitarity calculation.

14. |Vus| from t-®π-n & t-®K-n
New BaBar results from ICHEP08
measure B(t-®π-n), B(t-®K-n), B(t-®μ-nØ) relative to B(t-®e-nØ)
BaBar Preliminary
BaBar Preliminary
PDG06: (60.76±0.61)x10-2
PDG06: (3.84±0.13)x10-2

15. |Vus| from t-®π-n & t-®K-n
Assume universality of couplings
EW corrections cancel
Take fK/fπ from Lattice QCD
fK/fπ= 1.189±0.007, E. Follana, et al. PRL 100, (2008)
|Vud| known
|Vud| = ± ,
Use BaBar preliminary measurement of B(t®K-n)/B(t®π-n)
B(t®K-n)/B(t®π-n)= ± ±
|Vus|=0.2255±0.0023
Agrees with unitarity calculation!
|Vus|=0.2262±0.0011

16. Summary |Vus| using Rs is lower than other measurement (~3σ)
Theory/calculation issues?
Experiments still need to measure missing modes
Are correlations properly taken into account when averaging results?
New physics?
|Vus| using B(t-®K-n)/B(t-®π-n) agrees with unitarity
BUT both B(t-®K-n) & B(t-®π-n) are slightly lower than
expected from universality:
t-®mnØ: gμ/ge=1.0036±0.0020
t-®K-n: gμ/ge=0.9859±0.0057
t-®π-n: gμ/ge=0.9636±0.0087
New physics?
BaBar ICHEP08
More results expected from the B factories soon!
spectral functions from BaBar/Belle
expect measurements to be limited by systematics..

17. Extra Slides