1. Gabriella Sciolla (MIT)
Constraints on the Unitarity Triangle
from decays
Gabriella Sciolla (MIT)
CKM Nagoya, December 12-16, 2006
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

2. Constraints on the Unitarity Triangle from B
Outline
Introduction
Why we need another measurement of Vtd/Vts
Recent experimental results
Measurements of Vtd/Vts from Br vs. B K*g
Belle [370 fb-1]
Phys.Rev.Lett.96:221601,2006
BaBar [316 fb-1]
hep-ex/ submitted to PRL 2 days ago!
Conclusion and outlook
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

3. The measurement of Vtd/Vts
hep-ex/ (CDF)
The measurement of Vtd/Vts
Traditional approach: B0 vs Bs mixing
After a long quest, ms has been measured at the Tevatron
Why do we need any other measurement?
Theory error: calculation of parameter csi = fB_s/fB_d * sqrt(B_s/B_d) = quantifies Su(3) breaking corrections calculated in LQCD
Mention Lattice QCD
Box diagram
Precision ~4% dominated
by theory error
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

4. What do we learn from mixing?
One precise measurement of Rt improves our knowledge of the SM parameters ()
To go beyond the SM we need to be able to compare this measurement with independent constraints
Measurements of angle  not mature enough for meaningful comparison
The contribution from B mixing to the Rho/Eta plane is the measurement of this side of the UT. By measuring B_s mixing we were able to cut in half the error on the determination of this side, which vastly improved the measurement of the parameters of the SM rho and eta. But to go beyond the SM, we need to be able to compare this measurement with other constraints of similar precision. Ideally, we would like to compare this side against the measurement of the angle gamma. Unfortunately the measurement of gamma in not yet precise enough to make this comparison meaningful, therefore there is the need for an independent of measurement of Vtd/Vts that has different sensitivity to NP to physics compared to mixing.
Need for independent measurement of Vtd/Vts
with different sensitivity to New Physics
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

5. Vtd/Vts from Br  g and BK*gNP
s,d
Radiative penguin decays with bdg and bsg
In the SM, the ratio of BFs measures |Vtd/Vts|
Theory errors on |Vtd/Vts|~7.4%
New Physics Beyond the SM could take part in the loop and modify BFs… SM
Vtd,Vts
s,d
Light Cone Rum Rules
The BF of B->K*g is well measured (5%). The challenge here is to measure the numerator.
Old papers: Theory error between 8% (Rho gamma only) and 15% (average of charged and neutral modes).
New paper from Ball and Zwicki: error on average of modes: 8% theory error [ experimental error on 2006=12%]--> overall error: 14%
Zeta^2 = ratio of form factors; DeltaR = correction from weak annihilation effects
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

6. Brg  : analysis overview
Two body decay
pCMg~mB/2
Exclusive meson reconstruction
r0 p+p-
r+ p+p0
 p+p- p0
Exclusively reconstruct B meson
Beam energy constrained mass mES
Impose energy conservation: DE~0
Brg MC
mES (GeV)/c2
Brg MC
DE (GeV)/c2
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

7. Constraints on the Unitarity Triangle from B
Brg  : challenges
Very small Branching Fractions
B0r0g ~ 0.5 x 10-6
B+r+g ~ 1 x 10-6
Combinatorics from random pions
 ~ 150 MeV
Background from BK*
Stringent pion identification (BaBar)
Pion identification + K* veto (Belle)
Huge continuum background due from p0  
Multivariate techniques to suppress qq
Veto photons from p0 decays  p+ p- 
Here is a sketch that illustrates why this background is so insidious: …
BF(K*gamma) ~ 50*BF(RhoGamma)
PID performance: around 1 GeV Efficiency ~80-85%; pion MisID ~1%
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

8. Continuum suppression @ Belle
(spherical)
(jet-structure)
Combination of two variables:
Output of B flavor tagging algorithm
Likelihood ratio constructed with:
Fisher discriminant using shape variables
cos*B
Dz when available
Performance of 2-D cut in the variables above for B0r0g channel:
The two experiments have different approaches to continuum suppression
angle between the B and the beam in B RefFrame
separation in z coordinate between the two B candidates in the event
92% background rejection
45% signal efficiency
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

9. Continuum suppression @ BaBar
Combine 30+ discriminating variables in NN
Shape variables (e.g. R2)
Decay products of other B (e.g )
Properties of B decays (e.g. Dz)
Rejects >98% bgd.
keeping ~50% sig.
Black: background
Red: signal MC
NN output
Background Rejection Efficiency
Using appropriate control samples we are able to understand our NN to the 1% level.
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B
Signal Efficiency

10. Constraints on the Unitarity Triangle from B
 and  veto
Explicitly rejects photon coming from p0  
Suppress both continuum and B backgrounds
Method
Combine g candidate with all other
photons (gi) in the event
Obtain pdf(mass(ggi),Egi)’s for
signal and p0/h in continuum MC
Cut on likelihood ratio  p+ p- 
While this veto is useful, what gets rid of most of the combinatorial background is a generic continuum suppression technique. The two experiments address this need in different ways.
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

11. Signal extraction - Belle
Phys.Rev.Lett.96:221601,2006
Signal extraction - Belle
mES(GeV/c2)
Drastic reduction of background before fit
Tight cuts on continuum
Cut on |coshel| to reject peaking backgrounds
e.g.: Br
2-D maximum likelihood fit to mES and E
Observed B05.2
We are now ready for the last step: signal extraction. This is performed differently in the two experiments.
Helicity angle of rho is the angle between the direction of the pi+ in rho RF and the direction of the B flight (confirm)
-- Signal
-- K*g
-- Continuum
-- Other
E(GeV)
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

12. Constraints on the Unitarity Triangle from B
Phys.Rev.Lett.96:221601,2006
Belle’s results (370 fb-1)
First observation of B0
Isospin test
Important because isospin conservation is assumed in combined fit
Probability of a larger isospin violation <4.9%
In addition they perform a combined fit to all 3 modes enforcing isospin
25%
SM expectation
B+ ~ 1.0 x 10-6
B0 ~ 0.5 x 10-6
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

13. Signal extraction - BaBar
hep-ex/
Signal extraction - BaBar
Maximum likelihood fit to signal + background (continuum + B)
B: 4D fit to mES, E, NN, helicity
B: 5D fit includes Dalitz angle
B
-- Signal
-- Background
— S+B
B
B
B
Helicity angle of rho is the angle between the direction of the pi+ in rho RF and the direction of the B flight (confirm)
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

14. BaBar new results (316 fb-1)
hep-ex/
BaBar new results (316 fb-1)
4 d max likelihood fit: K. Koeneke
B+ 
3.8
B0 
4.9
B0 
2.2
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

15. BaBar new results (316 fb-1)
hep-ex/
BaBar new results (316 fb-1)
First evidence of B+
Best measurement of all of these BFs
Isospin test:
19%
Consistent with 0: isospin symmetry
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

16. What do we learn? B
Use BF from isospin-constrained combined fits for B
Note:
BaBar+Belle average
Ball, Jones, Zwicky (hep-ph )
B
8.2%
7.4%
Experimental error on BF: 16%
Rho Gamma: 8.5% experimental error, 8% theory error --> overall error ~ 14%
Mixing: overall 4% dominated by theory
If exp error decreases by sqrt(2) in 1-2 years, both exp and theory error ~8% --> overall error ~11%
In excellent agreement with mixing
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

17. What do we learn? Use only B
To simplify theory interpretation, use only  and in isospin average (not a member of iso-triplet!)
Note:
BaBar’s BF(B) from combined fit
Belle’s BF(B) from isospin average
Ball, Jones, Zwicky (hep-ph )
B
7.5%
9.4%
Experimental error on BF: 16%
Rho Gamma: 8.5% experimental error, 8% theory error --> overall error ~ 14%
Mixing: overall 4% dominated by theory
If exp error decreases by sqrt(2) in 1-2 years, both exp and theory error ~8% --> overall error ~11%
Problem with omega: rho is an isospin-triplet involving uu and dd only; omega involves ss too. Like pions vs eta: eta does have ss component in it!
OMEGA IS NOT PART OF ISOSPIN TRIPLET!
In excellent agreement with mixing
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

18. Constraints on the Unitarity Triangle from B
Conclusion
Recent improvement in extraction of Vtd/Vts from B
New BF for B from BaBar
Improvement in theory (hep-ph )
Average of BaBar and Belle
A new test of New Physics
Comparing Vtd/Vts from B vs. B mixing
8.2%
7.5%
Good agreement with B mixing
Good agreement with UT apex excluding B mixing
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

19. Constraints on the Unitarity Triangle from B
The future of B
How well can we do by 2008?
Experimental error on Vtd/Vts: 8.2% 4.7%
Just assuming 1 ab-1/B factory
Improvements in analysis technique will help further
Theory error on Vtd/Vts
Light Cone Sum Rules: 7.4% (now), 5% in 2008?
Anything from Lattice QCD?
CFR: Error from mixing ~ 4%, theory dominated
BF(B) or BF(B?
Is it time to trade a slightly larger experimental error for a slightly better theory error?
This is clearly just the beginning of this measurement: plenty of room for improvements in the future.
7.4% using 700 fb-1 --> 2 fb 4.7%
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

20. ---------------------------------------
Backup
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

21. Summary of results: BaBar vs Belle
Experimental error on BF: 16%
Rho Gamma: 8.5% experimental error, 8% theory error --> overall error ~ 14%
Mixing: overall 4% dominated by theory
If exp error decreases by sqrt(2) in 1-2 years, both exp and theory error ~8% --> overall error ~11%
Isospin-constrained combined fits:
Combine 3 modes to reduce stat. error
Combine only  modes to reduce theory error
not a member of iso-triplet!
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

22. Constraints on the Unitarity Triangle from B
BaBar Results - all
Systematics
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

23. After correcting for Data-MC agreement: 1% systematics
NN BaBar R2
Background shape validation:
Black: continuum MC
Red: off-peak DATA
Signal NN shape validation.
BD control sample: NNnsig/NNBack
After correcting for Data-MC
agreement: 1% systematics
DATA/MC efficiency ratio vs cut on NN
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B

24. Constraints on the Unitarity Triangle from B
Belle all …
Gabriella Sciolla – MIT
Constraints on the Unitarity Triangle from B