Christoph Schwanda1 The Belle B Factory Past, present and future Christoph Schwanda, Innsbruck, Oct-18, 2006

Christoph Schwanda2 Goal of the B factory experiments “Study CP violation in the B meson system and probe the Cabibbo-Kobayashi-Maskawa mechanism of flavor mixing” (or something like that)

Christoph Schwanda3 B mesons Bound state of a light d- or u- with a heavy b-quark M(B 0 ) = ( /- 0.5 ) MeV/c 2 M(B + ) = ( /- 0.5 ) MeV/c 2  (B 0 ) = ( / ) ps  (B + ) = ( / ) ps d b u b B0B0 B+B+

Christoph Schwanda4 CP transformation Under C, particles and anti-particles are interchanged by conjugating all internal quantum number (e.g., Q  -Q) Under P, the handedness of space is reversed, (x,y,z)  (-x,-y,-z) Under CP, a left-handed electron e - L is transformed into a right-handed positron e + R

Christoph Schwanda5 Why is CP violation interesting? In the SM, CP violation is described by a single phase CP violation is necessary to understand the baryon density in the universe [Sakharov, Sov. Phys. JETP Lett. 5, 24 (1967)] In general, New Physics models introduce new CP violating phases

Christoph Schwanda6 Common misunderstandings Did the B factories discover CP violation? –No! CP violation was first observed in 1964 in neutral K   decays [PRL 13, 138 (1964)]. This type of CP violation is related to K 0 - anti-K 0 mixing ( “indirect” CP violation ) and described by the parameter   = (2.28 +/ ) x 10 -3

Christoph Schwanda7 Common misunderstandings Then, did the B factories discover direct CP violation (CP violation arising solely from decay amplitudes)? –No! Direct CP violation was established by the NA48 and KTeV experiments also in K   decays  '  = (1.72 +/ ) x 10 -3

Christoph Schwanda8 Take away message “The B factories did not discover CP violation(*) but they confirmed the Kobayashi-Maskawa mechanism of CP violation” (*) They first observed CP violation in B meson decays and new CP-violating observables though.

Christoph Schwanda9 Charged current interaction in the SM V CKM is a unitary 3x3 matrix; it contains three real parameters and one complex phase This phase is responsible for all CP violating phenomena observed so far! The KM mechanism [Kobayashi, Maskawa, Prog. Theor. Phys. 49, 652 (1973)]

Christoph Schwanda10 Wolfenstein parametrization = |V us | = 0.22

Christoph Schwanda11 The unitarity triangle   =  1  =  2  =  3   (1,0)(0,0) ( 

Christoph Schwanda12 The B factories can Measure the sides (mainly |V cb |, |V ub |) and the angles  1,  2 and  3 in the unitarity triangle Thus overconstraining the UT, we can test the Kobayashi-Maskawa mechanism

Christoph Schwanda13 KEKB and Belle ~1 km in diameter Mt. Tsukuba KEKB Belle 8 GeV e - x 3.5 GeV e + E cm = GeV ( Y(4S) resonance ) L peak = x cm -2 s -1 (I will not discuss BaBar and PEP-II)

Christoph Schwanda14 Luminosity history Now, about 600 million B anti-B events recorded!

Christoph Schwanda15 The Belle detector  / K L detection 14/15 lyr. RPC+Fe CsI(Tl) 16X 0 Si vtx. det. 3(4) lyr. DSSD SC solenoid 1.5T 8 GeV e  3.5 GeV e  Aerogel Cherenkov cnt. n=1.015~1.030 C entral D rift C hamber small cell +He/C 2 H 5 TOF counter

Christoph Schwanda16 The Belle collaboration 13 countries, 55 institutes, ~400 collaborators IHEP, Vienna ITEP Kanagawa U. KEK Korea U. Krakow Inst. of Nucl. Phys. Kyoto U. Kyungpook Nat’l U. EPF Lausanne Jozef Stefan Inst. / U. of Ljubljana / U. of Maribor U. of Melbourne Aomori U. BINP Chiba U. Chonnam Nat’l U. U. of Cincinnati Ewha Womans U. Frankfurt U. Gyeongsang Nat’l U. U. of Hawaii Hiroshima Tech. IHEP, Beijing IHEP, Moscow Nagoya U. Nara Women’s U. National Central U. National Taiwan U. National United U. Nihon Dental College Niigata U. Osaka U. Osaka City U. Panjab U. Peking U. U. of Pittsburgh Princeton U. Riken Saga U. USTC

Christoph Schwanda17 Extracting a B signal Methods to extract B signal yield: 1) Cut on M B and fit to  E 2) Cut on  E and fit to M B 3) Double dimensional fit to M B and  E distribution 4) If B->P 1 P 2 P 3 : cut  E and M B box and look at resonant structures in M(P 1 P 2 ) mass distribution. Using special Y(4S) kinematics, two nearly independent variables M B and  E can be used to select B meson signal: M B = (E beam ) 2 – (  P i ) 2  E =  E i - E beam * *

Christoph Schwanda18 Continuum suppression e+e+ e-e- e+e+ e-e- qq Signal B Other B Dominant Background for rare Decays: Continuum Jet-like e + e   qq “continuum” (~4x BB) To suppress: use event shape variables   continuum Y (4S) Fox-Wolfram moments Angle between B meson and beam axis direction B events Spherical

Christoph Schwanda19 The decay B 0  J/  K s 0 CP violation in this decay arises from the quantum interference of these two diagrams b c d c s d J/  KSKS b d c KSKS b c s ddt t + tree diagram box diagram + tree diagram Vtd “golden mode”

Christoph Schwanda20 Time-dependent CP asymmetry  B0 (  t) = rate of B’s decaying to J/  K s (at t 2 ) when the B flavor has been B 0 (at t 1 )  anti-B0 (  t) = rate of B’s decaying to J/  Ks (at t 2 ) when the B flavor has been anti-B 0 (at t 1 )  t = t 2 -t 1 time difference between flavor measurement and decay for J/  K s : S =  CP sin2  1 = +sin2  1 A = 0 (  CP : CP eigenvalue) Mixing-induced CPVDirect CPV

Christoph Schwanda21 Principle of the measurement  t =  z/  c,  = at KEKB e+e+ e-e- l+l+ J/  KsKs z z1z1 z2z2 B0B0 anti-B 0 tag-side CP-side zz

Christoph Schwanda22 B 0  J/  K s with 535M BB pairs Nsig = 7482 Purity 97 % CP odd Nsig = 6512 Purity 59 % CP even 00 B 0  J/  K S B 0  J/  K L _ 535M BB

Christoph Schwanda23 B 0  J/  K S 0 B 0  J/  K L B 0 tag _ 0 Asym. = -  CP sin2  1 sin  m  t sin2  1 = ±0.038 A = ±0.028 sin2  1 = ±0.057 A = ±0.033 stat error background subtracted B 0 tag _

Christoph Schwanda24 sin 2  1 from b  c anti-c s trees 5.5% rel. err.

Christoph Schwanda25 sin2  history ( )

Christoph Schwanda26 The decay B 0   K s This decay proceeds through a penguin loop diagram In the SM: S(J/  K s )=S(  K s ) New physics in loops (new CP violating phases) would lead to: S(J/  K s )  S(  K s )

Christoph Schwanda  21  K S signal 307  21  K S signal unbinned fit SM “sin2  1 ” =  0.50  0.21(stat)  0.06(syst) A =  0.07  0.15(stat)  0.05(syst) “sin2  1 ” =  0.50  0.21(stat)  0.06(syst) A =  0.07  0.15(stat)  0.05(syst) _ 535M BB

Christoph Schwanda28 Theory tends to predict positive shifts (originating from phase in Vts) sin 2  1 from b  q anti-q s penguins Smaller than b  ccs in all of 9 modes Smaller than b  ccs in all of 9 modes Naïve average of all b  s modes sin2  eff = 0.52 ±  deviation between penguin and tree (b  s) (b  c) Naïve average of all b  s modes sin2  eff = 0.52 ±  deviation between penguin and tree (b  s) (b  c)

Christoph Schwanda29 The decay B 0   +  - B0B0 d b – d – bt – t B0B0 – V * tb V td V * tb V td Mixing diagramDecay diagram (tree) B0B0 b – d d u – d – u // // V ud V * ub With the tree diagram only S     = +sin2  2 A     = 0 S     = +sin2  2 A     = 0 11 33 22 V ud V * ub V td V * tb V cd V * cb

Christoph Schwanda30 first error: stat., second: syst. background subtracted  +  − yields  +  − asymmetry _ 535M BB 1464±65 signal events Large Direct CP violation (5.5  ) in disagreement with BaBar Large mixing-induced CP violation (5.6  )

Christoph Schwanda31 2()2() BaBar(  /  /  ) + Belle(  /  )  Global Fit = [ 98 ] º  /  2 = [93 ]  +11  9 consistent with a global fit w/o  /  2

Christoph Schwanda32 r 3()3() Time-dependent analyses get sin(2  1 +  3 ) Best contraint on  3 comes from Dalitz analysis of B -  D(*)K(*) - with D  K s  +  - r = |A 2 | |A 1 | B+:B+: r B-:B-:  /  3 = [53 ]  +15  18

Christoph Schwanda33 |V ub | M.Morii diagram

Christoph Schwanda34 Summary Many, many results… Belle published ~200 journal papers All these measurements beautifully consistent with KM mechanism

Christoph Schwanda35 A look into future Now, have we learned everything about CP violation? –No! There must be more sources of CP violation –The CP violation in the SM model cannot explain the baryon density of the universe by orders of magnitude –New physics (if found at the LHC) comes with new sources of CP violation

Christoph Schwanda36 New sources of CP violation Strong interaction violates CP (electric dipole moment of the neutron) CP violation in the lepton sector (neutrino oscillations) New physics (new heavy particles)  Belle can look for this source by measuring CP violation in loop diagrams (precision measurements)

Christoph Schwanda37 SuperKEKB Asymmetric energy e  e  collider at E CM =m(  (4S)) to be realized by upgrading the existing KEKB collider. Super-high luminosity  8  /cm 2 /sec  1  BB per yr.  9  10 9     per yr. Higher beam current, more RF, smaller  y * and crab crossing  L = 4  /cm 2 /sec Belle with improved rate immunity

Christoph Schwanda38 Physics case of SuperB Not the first time CP violation would tell us something about physics at higher energies LHC will measure masses, SuperB could measure phases  complementarity which allows to constrain new physics scenarios

Christoph Schwanda39 Thank you very much for your invitation!