From Belle to Belle II Peter Krian University of Ljubljana and J. - PowerPoint PPT Presentation

Seminar, Birmingham University, Dec 14, 2011 From Belle to Belle II Peter Križan University of Ljubljana and J. Stefan Institute “Jožef Stefan” University I nstitute of Ljubljana Peter Križan, Ljubljana

Contents  Highlights from B factories (+ a little bit of history)  Physics case for a super B factory  Accellerator and detector upgrade  SuperKEKB + Belle-II  Status and outlook Peter Križan, Ljubljana

A little bit of history... CP violation: difference in the properties of particles and their anti-particles – first observed in 1964 in the decays of neutral kaons. M. Kobayashi and T. Maskawa (1973): CP violation in the Standard model – related to the weak interaction quark transition matrix Their theory was formulated at a time when three quarks were known – and they requested the existence of three more! The last missing quark was found in 1994. ... and in 2001 two experiments – Belle and BaBar at two powerfull accelerators (B factories) - have further investigated CP violation and have indeed proven that it is tightly connected to the quark transition matrix Peter Križan, Ljubljana

CKM - Cabibbo-Kobayashi-Maskawa (quark transition) matrix: almost real and diagonal, but not completely! V ub Amplitude for the b  u transition V us V ud V cb Amplitude for the b  c V cd V cs transition V tb V td V ts CKM: unitary matrix Peter Križan, Ljubljana

CKM matrix: determines charged weak interaction of quarks Wolfenstein parametrisation: expand the CKM matrix in the parameter λ (= sin θ c = 0.22)   λ 2   − λ λ ρ − η 3 1 A ( i ) A, ρ and η : all of order one   2 λ   2 = − λ − λ + λ 2 4 V 1 A O ( )   2   λ − ρ − η − λ 3 2 A ( 1 i ) A 1       determines probability of b  u transitions Unitarity condition: + + = * * * V V V V V V 0 φ 2 ud ub cd cb td tb φ 1 φ 3 Goal: measure sides and angles determines CP violation in in several different ways, check B  J/ ψ K S decays  consistency Peter Križan, Ljubljana

Asymmetric B factories √s= 10. 58 10. 58 Ge V Ge V e + e - B ∆ z ~ z ~ c βγτ B Υ ( 4s ) ( 4s ) Υ ( 4s ) ( 4s ) ~ 200 µ m B ~ 20 ( e - ) = βγ =0. 56 ( e + ) = Ba Ba r Ba r p( e ) =9 9 Ge V e V p p( e ) =3. 1 3. 1 Ge V V 0. 56 ( e - ) = βγ =0. 42 ( e + ) = Be l l e l l e p( e ) =8 8 Ge V e V p p( e ) =3. 5 3. 5 Ge V V 0. 42 Peter Križan, Ljubljana

KM’s bold idea verified by experiment Relations between parameters as expected in the Standard  model Nobel prize 2008!  With essential experimental confirmations by BaBar and Belle! (explicitly noted in the Nobel Prize citation) Peter Križan, Ljubljana

The KM scheme is now part of the Standard Model of Particle Physics •However, the CP violation of the KM mechanism is too small to account for the asymmetry between matter and anti-matter in the Universe (falls short by 10 orders of magnitude !) •SM does not contain the fourth fundamental interaction, gravitation •Most of the Universe is made of stuff we do not understand... matter ~ no anti-matter dark energy dark matter Peter Križan, Ljubljana

Are we done ? (Didn’t the B factories accomplish their mission, recognized by the 2008 Nobel Prize in Physics ?) Matter - anti-matter asymmetry of the Universe: KM (Kobayashi-Maskawa) mechanism still short by 10 orders of magnitude !!! Peter Križan, Ljubljana

Two frontiers Two complementary approaches to study shortcomings of the Standard Model and to search for the so far unobserved processes and particles (so called New Physics, NP). These are the energy frontier and the intensity frontier . Energy frontier : direct search for production of unknown particles at the highest achievable energies. I ntensity frontier : search for rare processes, deviations between theory predictions and experiments with the ultimate precision.  for this kind of studies, one has to investigate a very large number of reactions events  need accelerators with ultimate intensity (= luminosity) Peter Križan, Ljubljana

Comparison of energy / intensity frontiers To observe a large ship far away one can either use strong binoculars or observe carefully the direction and the speed of waves produced by the vessel. Energy frontier (LHC) Luminosity frontier (Belle and Belle I I ) Peter Križan, Ljubljana

An example: Hunting the charged Higgs in the decay B -  τ − ν τ In addition to the Standard Model Higgs to be discovered at the LHC, in New Physics (e.g., in supersymmetric theories) there could also be a charged Higgs. b The rare decay B -  τ − ν τ is in SM mediated τ W ν τ by the W boson u In some supersymmetric extensions it can also b H ± τ proceed via a charged Higgs ν τ u The charged Higgs would influence the decay of a B meson to a tau lepton and its neutrino, and modify the probability for this decay. Peter Križan, Ljubljana

Missing Energy Decays: B -  τ − ν τ By measuring the decay probability (branching fraction) and comparing it to the SM expectation:  Properties of the charged Higgs (e.g. its mass) Peter Križan, Ljubljana

New Physics reach energy frontier vs. intensity frontier Belle II NP mass scale (TeV) Belle NP coupling Peter Križan, Ljubljana

Super B Factory Motivation 2 • Lessons from history: the top quark   V V V Physics of top quark   ud us ub First estimate of mass: BB mixing  ARGUS =   V V V V CKM cd cs cb Direct production, Mass, width etc.  CDF/D0     V V V  BaBar/Belle Off-diagonal couplings, phase td ts tb • Even before that: prediction of charm quark from the GIM mechanism, and its mass from K 0 mixing Peter Križan, Ljubljana

Unitarity triangle – 2011 vs 2001 CP violation in the B system: from the discovery (2001) to a precision measurement (2011). Peter Križan, Ljubljana

Unitarity triangle – new measurements Constraints from measurements of angles and sides of the unitarity triangle  Remarkable agreement, but still 10-20% NP allowed  search for New Physics! This summer: Unitarity triangle:  sin2 φ 1 (= sin2 β ) : final measurement from Belle  φ 3 (= γ ) new model-independent method  |V ub | from exclusive and inclusive semileptonic decays Peter Križan, Ljubljana

CP Violation in B decays to CP eigenstates f CP B 0 B 0 0 → − → Γ Γ 0 ( B ( t ) f ) ( B ( t ) f ) = = ∆ + ∆ CP CP ( ) sin cos A t S m t A m t B B 0 CP → + → Γ Γ 0 ( B ( t ) f ) ( B ( t ) f ) CP CP B 0 → J/ ψ K 0 in SM: S= sin2 φ 1 (= sin2 β ), A= 0 Peter Križan, Ljubljana

Final measurement of sin2 φ 1 (= sin2 β ) φ 1 from CP violation Belle, preliminary, 710 fb -1 measurements in B 0 → cc K 0 Improved tracking, more data (50% more statistics than last result with 480 fb -1 ); cc = J/ ψ , ψ (2S), χ c1  25k events cc K S detector effects: wrong tagging, finite ∆ t resolution, determined using control data samples cc K L Peter Križan, Ljubljana

Final measurement of sin2 φ 1 (= sin2 β ) Belle, preliminary, 710 fb -1 φ 1 from B 0 → cc K 0 Final result (preliminary) from Belle: S = 0.668 ± 0.023 ± 0.013 A = 0.007 ± 0.016 ± 0.013 (SM: S= sin2 φ 1 (= sin2 β ), A= 0 ) Still statistics limited, part of the syst. is statistics dominated! Tension between B ( B → τν ) and sin2 φ 1 (~2.5 σ ) remains Peter Križan, Ljubljana

CP violation in B  D + D - and D* + D* - SM: b  ccd, S= sin2 φ 1 (= sin2 β ), A= 0 B  D + D - 320 events  Large CP violation effects in many places in B decays! B  D* + D* - Vector-vector final state, need angular analysis for CPV measurement 1225 events, > 2x increase in yield vs the Peter Križan, Ljubljana 2009 paper

φ 3 (= γ ) with Dalitz analysis Dalitz method: The best way to Giri et al., PRD68, 054018 (2003) measure φ 3 Bondar et al. ( ) D 0 → K S π + π - m + = m(K S π + ) m - = m(K S π - ) 3-body D 0 → K S π + π - Dalitz amplitude 2 2 m - m - model dependent description of f D using continuum D* data ⇒ 2 2 m + m + systematic uncertainty φ 3 =(78 ± 12 ± 4 ± 9) o φ 3 =(68 ± 14 ± 4 ± 3) o Peter Križan, Ljubljana Belle, PRD81, 112002, (2010), 605 fb -1 BaBar, PRL 105, 121801, (2010)

φ 3 (= γ ) from model-independent/binned Dalitz method Dalitz method: How to avoid the model dependence?  Suitably subdivide the Dalitz space into bins M i : # B decays in bins of D Dalitz plane, K i : # D 0 (D 0 ) decays in bins of D Dalitz plane ( D* → D π ), c i , s i : strong ph. difference between symm. Dalitz points  Cleo, PRD82, 112006 (2010) Use only DK 4-dim fit for signal yield N sig = 1176 ± 43 ( ∆ E, M bc , cos θ thrust , F ); φ 3 =(77 ± 15 ± 4 ± 4) o Belle, 710 fb -1 arXiv:1106.4046 from c i , s i (statist.!) to be reduced with BESIII data Important method upgrade for large event samples at LHCb and super B factories Peter Križan, Ljubljana