Measurements of sin2  from B-Factories Masahiro Morii Harvard University The BABAR Collaboration BEACH 2002, Vancouver, June 25-29, 2002

BEACH 2002, May 25-29, 2002M. Morii, Harvard University2 Introduction CP violation in B 0 decays gives access to the angles of the Unitarity Triangle sin2  measured to ±0.08 dominated by B 0  J/  K S Where does this leave us? See D. Marlow’s talk

BEACH 2002, May 25-29, 2002M. Morii, Harvard University3 Unitarity Triangle and sin2  Measured sin2  agrees with indirect constraints Shrinking  (sin2  ) alone may not reveal new physics Must measure the sides and the other angles Next possibility at the B Factories?

BEACH 2002, May 25-29, 2002M. Morii, Harvard University4 Measuring sin2  Time-dependent CP asymmetry in B 0  f CP is CKM phase appears here Easy!

BEACH 2002, May 25-29, 2002M. Morii, Harvard University5 Penguin Pollution Unlike J/  K S,     mode suffers from significant pollution from the penguin diagrams with a different weak phase To estimate  eff – , we need: P/T ratio – about 1/3 from BR(B  K  )/BR(B   )  = strong phase difference between P and T T = TreeP = Penguin

BEACH 2002, May 25-29, 2002M. Morii, Harvard University6 Mode B A B AR BR  10 6 Belle BR  10 6 Taming Penguins Take advantage of the isospin symmetry All preliminary

BEACH 2002, May 25-29, 2002M. Morii, Harvard University7 B 0   0  0 Branching Ratio B A B AR : Preliminary 54 fb -1 BR(  0  0 ) < 3.3×10 –6 (90% CL) Belle: Preliminary 31.7 M BB 2.2  “bump” in the signal Fitted BR= (2.9 ± 1.5 ± 0.6)×10 –6 BR(  0  0 ) < 5.6×10 –6 (90% CL) CLEO: 9.13 fb -1 BR(  0  0 ) < 5.7×10 –6 (90% CL) BELLE Expect first observation in the near future

BEACH 2002, May 25-29, 2002M. Morii, Harvard University8 CP Asymmetry in B 0      Same method as sin2  measurements Difference: the direct CP term cannot be neglected 9 GeV 3.1 GeV  4S B tag B CP Tag using l ±, K ± Moving with  = 0.55 CP final state # of events with

BEACH 2002, May 25-29, 2002M. Morii, Harvard University9 Challenges Specific to B 0    +   Topology B 0  h  h  simple to reconstruct Particle ID must separate   ± from K ± DIRC (B A B AR ) and Aerogel (Belle) Significant background from continuum Event-shape variables  Fisher discriminant Common with other CP measurements Flavor tagging Vertex reconstruction And, of course, as much as possible

BEACH 2002, May 25-29, 2002M. Morii, Harvard University10 B 0 Reconstruction m bc (or m ES ) and  E peak cleanly for the two-body signal K  and KK peaks shifted in  E  Additional discrimination     MC off-resonance data     MC     MC BELLE

BEACH 2002, May 25-29, 2002M. Morii, Harvard University11 Whole event is jettyThe other B decays spherically Continuum Background Most of the background come from continuum Use event shape variables that represent “jettiness” to suppress them Signal udsc background Examples

BEACH 2002, May 25-29, 2002M. Morii, Harvard University12 Sphericity Angle Angle  S between the sphericity axes of the B candidate and the rest of the event Cut at 0.8 removes 83% of the continuum background B A B AR     MC background reject

BEACH 2002, May 25-29, 2002M. Morii, Harvard University13 Fisher Discriminant B A B AR uses the “ CLEO ” Fisher Momentum flow in 9 cones around the candidate axis Output of Fisher goes into the likelihood fit     MC D 0    data Bkg MC m ES sideband data

BEACH 2002, May 25-29, 2002M. Morii, Harvard University14 Bkg MC off-res. data Fisher Discriminant Belle’s Fisher discriminant uses: Modified Fox-Wolfram moments B flight direction Output is turned into a likelihood ratio R Cut at removes 95% of continuum background     MC D 0    data reject

BEACH 2002, May 25-29, 2002M. Morii, Harvard University15 Event Sample – BABAR B A B AR 55.6 fb -1 preliminary     enhanced for these plots with a cut on Fisher K  continuum

BEACH 2002, May 25-29, 2002M. Morii, Harvard University16 Event Sample – Belle Belle 41.8 fb -1 KK Continuum

BEACH 2002, May 25-29, 2002M. Morii, Harvard University17 Maximum Likelihood Fit Start from the physics function: Fold in  t resolution and mis-tag probabilities Multiply by PDFs for m ES,  E B A B AR uses particle ID and Fisher in the fit Belle uses these variables in event selection Add PDFs for background (K , KK, continuum) Feed the candidates and turn the crank…

BEACH 2002, May 25-29, 2002M. Morii, Harvard University18 B A B AR B ELLE CP Fit Results BABAR and Belle disagree by >2  Belle 1.2  outside the physical boundary Is there any problem? Crosscheck systematics B A B AR (preliminary) Belle (hep-ex/ ) S  –0.01 ± 0.37 ± 0.07 C  –0.02 ± 0.29 ± 0.07 Belle uses

BEACH 2002, May 25-29, 2002M. Morii, Harvard University19 CP Asymmetries – BABAR     enhanced for these plots with a cut on Fisher No significant asymmetry

BEACH 2002, May 25-29, 2002M. Morii, Harvard University20 CP Asymmetries – Belle Rate difference (= C  )  t-dependent asymmetry (= S  and C  ) Subtract bkg

BEACH 2002, May 25-29, 2002M. Morii, Harvard University21 Crosschecks Both experiment made extensive crosschecks, e.g. Asymmetry in background? Look for asymmetries in K  or mass sideband Vertex resolution of the 2-body decays? Measure B lifetime with , K  Measure mixing with K  Likelihood values and errors? Toy Monte Carlo studies BELLE

BEACH 2002, May 25-29, 2002M. Morii, Harvard University22 Monte Carlo Fit Test Generate ~1000 “toy” experiments Belle used (  0.7,  0.7) for the central values Fit and compare: Likelihood values Pull distributions Errors Lowest probability: 5.4% B A B AR  (S  )  (C  ) MC Measured B A B AR BELLE Measured Everything looks reasonable

BEACH 2002, May 25-29, 2002M. Morii, Harvard University23 B A B AR B ELLE Interpretation How well do we know  ? (*Gronau and Rosner, PRD65, ) Average B A B AR and Belle Assume  = 26°, P/T = 0.28 B A B AR (preliminary) Belle (hep-ex/ ) Average* S  –0.01 ± 0.37 ± 0.07–0.66 ± 0.26 C  –0.02 ± 0.29 ± 0.07–0.49 ± 0.21 NB: Large uncertainty

BEACH 2002, May 25-29, 2002M. Morii, Harvard University24 Measured S  ±1  corresponds to Interpretation Gronau and Rosner PRD65, Indirect: B A B AR + Belle Accuracy comparable to the indirect constraints We are starting to measure 

BEACH 2002, May 25-29, 2002M. Morii, Harvard University25 Summary B A B AR and Belle measured sin2  eff using B 0    +   Direct constraint on  is reaching useful accuracy Things to watch out for: sin2  eff with higher statistics  Resolve “discrepancy” BR(B 0    0   )  Better bound on  eff –  B A B AR (preliminary) Belle (hep-ex/ ) S  –0.01 ± 0.37 ± 0.07 C  –0.02 ± 0.29 ± 0.07

BEACH 2002, May 25-29, 2002M. Morii, Harvard University26 Bound on  eff –  Full isospin analysis (Gronau & London, 1990) requires and separately Too hard for B A B AR /Belle  Upper limits on average BR Use BR(  0  0 ) to put upper bound on  eff –  Grossman and Quinn, 1998; Charles, 1998 Gronau, London, Sinha, Sinha PLB 514: , 2001 Allowed was assumed

BEACH 2002, May 25-29, 2002M. Morii, Harvard University27 GLSS Bound on  eff –  If I use and GLSS bound weaker for smaller BR(     ) Better measurements of BR(     ) and BR(     ) will give us a better handle on the penguins in the near future B A B AR 90% CL Small     Large    

BEACH 2002, May 25-29, 2002M. Morii, Harvard University28 B Flight Direction Angle  B of the B candidate momentum relative to the beam axis Signal Background ~flat BELLE

BEACH 2002, May 25-29, 2002M. Morii, Harvard University29 Systematic Errors BABAR: Dominated by the shape of the particle ID variable Belle: Uncertainties of the background fractions Fit bias near the physical boundary for S  Wrong tag fraction for C  All measurements are statistically limited

BEACH 2002, May 25-29, 2002M. Morii, Harvard University30 Interpretation Measurements favor maximally negative C  Corresponds to  =  90° Maybe a good news No discrete ambiguity! Time will tell Gronau and Rosner PRD65,  = 26°, P/T = 0.28