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

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/0612017 - submitted to PRL 2 days ago! Conclusion and outlook Gabriella Sciolla – MIT Constraints on the Unitarity Triangle from B

The measurement of Vtd/Vts hep-ex/0609040 (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

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

Vtd/Vts from Br  g and BK*g NP 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

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

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

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

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

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

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

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

Signal extraction - BaBar hep-ex/0612017 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

BaBar new results (316 fb-1) hep-ex/0612017 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

BaBar new results (316 fb-1) hep-ex/0612017 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

What do we learn? B Use BF from isospin-constrained combined fits for B Note: BaBar+Belle average Ball, Jones, Zwicky (hep-ph 0612081) 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

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 0612081) 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

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 0612081) 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

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

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

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

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

After correcting for Data-MC agreement: 1% systematics NN systematics @ 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

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