Time-Dependent Particle-Antiparticle Asymmetries in the Neutral B-Meson System Michael D. Sokoloff University of Cincinnati The story of CP Violation has changed qualitatively in the past two years. Babar and BELLE have observed time-dependent CP violation in neutral B-mesons, in accord with the Standard Model. The ensemble of these and other results appear to validate the Kobayashi-Maskawa mechanism as the source of CP violation in the electroweak sector. New Physics may yet be manifest in CP violation measurements to come. fCP fCP

The Nature of Particle Physics Particle physicists study the fundamental constituents of matter and their interactions. Our understanding of these issues is built upon certain fundmental principles The laws of physics are the same everywhere The laws of physics are the same at all times The laws of physics are the same in all inertial reference systems (the special theory of relativity) The laws of physics should describe how the wave function of a system evolves in time (quantum mechanics) These principles do not tell us what types of fundamental particles exist, or how they interact, but they restrict the types of theories that are allowed by Nature. In the past 30 years we have developed a Standard Model of particle phyiscs to describe the electromagnetic, weak nuclear, and strong nuclear interactions of constituents in terms of quantum field theories.

Special Relativity From the reconstructed energy and momentum of the Energy and momentum form a four-vector (E,px,py,pz). The Lorentz invariant quantity defined by energy and momentum is mass: For the special case when an object is at rest so that its momentum is zero When a particle decays in the laboratory, we can measure the energy and momenta of it decay products (its daughter particles), albeit imperfectly. The energy of the parent is exactly the sum of the energies of its daughters. Similarly, each component of the parent’s momentum is the sum of the corresponding components of the daughters’ momenta. From the reconstructed energy and momentum of the candidate parent, we can calculate its invariant mass.

Classical Field Theory (E&M)

Fields and Quanta Electromagnetic fields transfer energy and momentum from one charged particle to another. Electromagnetic energy/momentum is quantized: E = hn ; p = hn/c These quanta are called photons: g In relativistic quantum field theory: Am g To calculate cross-sections and decay rates we use perturbation theory based on Feynman Diagrams:

Strong Nuclear Interactions of Quarks and Gluons Each quark carries one of three strong charges, and each antiquark carries an anticharge. For convenience, we call these colors: Just as photons are the quanta of EM fields, gluons are the quanta of strong nuclear fields; however, while photons are electrically neutral, gluons carry color-anticolor quantum numbers. The Nobel Prize in Physics 2004 Gross Politzer Wilczek

Baryons and Mesons Quarks are never observed as free particles. Baryons consist of three quarks, each with a different color (strong nuclear) charge proton = neutron = Mesons consist of quark-antiquark pairs with canceling color-anticolor charges Baryons and meson (collectively known as hadrons) have net color charge zero. A Van der Waals-types of strong interaction creates an attractive force which extends a short distance (~ 1 fm) to bind nucleii together.

Weak Charged Current Interactions neutrino scattering charm decay f ~ f As a first approximation, the weak charged current interaction couples fermions of the same generation. The Standard Model explain couplings between quark generations in terms of the Cabibbo-Kobayashi-Maskawa (CKM) matirx.

Weak Phases in the Standard Model b = f1; a = f2; g = f3

Particle-Antiparticle Mixing A second order weak charged current process, a box diagram amplitude, provides a mechanism by which particles oscillate into antiparticles. Particles decay exponentially with characteristic times Neutral B-mesons mix sinusoidally with characteristic times Experimentally which makes mixing observation relatively easy.

Time-Dependent CP Violation Both particles and antiparticles can decay to common final states which are CP eigenstates. As an example, The final state is invariant under charge and parity conjugation; that is, it remains . The Standard Model predicts that the CKM phase will produce a time dependent asymmetry in the decays of and to this final state, and that the asymmetry will vary sinusoidally. fCP fCP

Elements of Macroscopic CP Violation fCP

Some Relevant Feynman Diagrams

Elements of Macroscopic CP Violation fCP

The PEP-II Storage Ring at SLAC Total: 244 fb-1 (Jul 31st 04) PEP-II is SLAC’s e+e- B factory running at the (4S) c.m. energy The (4S) resonance decays to charged and neutral B-anti-B pairs

BaBar Detector All subsystems crucial for CP analysis Svt 5 layer double sided strips DCH 40 stereo layers DIRC: 144 quart bars, 11000 PMTS EMC 6580 crystals IFR: 19 layers SVT: 97% efficiency, 15 mm z hit resolution (inner layers, transverse tracks) SVT+DCH: (pT)/pT = 0.13 %  pT + 0.45 % DIRC: K- separation 4.2  @ 3.0 GeV/c  2.5  @ 4.0 GeV/c EMC: E/E = 2.3 %E-1/4  1.9 %

Belle Detector Aerogel Cherenkov cnt. n=1.015~1.030 SC solenoid 1.5T m / KL detection 14/15 lyr. RPC+Fe Tracking + dE/dx small cell + He/C2H5 CsI(Tl) 16X0 Aerogel Cherenkov cnt. n=1.015~1.030 Si vtx. det. 3 lyr. DSSD TOF counter SC solenoid 1.5T Belle Detector 8GeV e- 3.5GeV e+

Experimental Technique at the (4S) Resonance e+e-  (4S)  B B m- K- Flavor tag and vertex reconstruction Boost: bg = 0.55 Start the Clock Btag Brec (4S) m+ p+ p- KS m- Coherent L=1 state B0 Stop the Clock Exclusive B meson and vertex reconstruction

Identifying Fully Reconstructed B’s ( ) For fits, both Belle and Babar characterize signals and backgrounds with PDF’s which utilize Mbc, DE, tagging category, etc.

Tagging Errors and Finite Dt Resolution perfect tagging & time resolution typical mistagging & finite time resolution (f+) (f-) B0  D(*)-p+/ r+/ a1+ Ntagged=23618 Purity=84%

Effective Tagging Efficiency Q Q=e(1-2w)2 r = estimated tagging dilution Babar Tagging Performance Category e (%) w (%) Q (%) Lepton 9. 0. 3.3 0.6 7.9  0.3 Kaon I 16.7 0.2 9.9 0.7 10.7  0.4 Kaon II 19.8 0.3 20.9 0.8 6.7  0.4 Inclusive 20.0 0.3 31.6 0.9 2.7  0.3 Total 65.6 0.5 28.1 0.7 6 hep-ex/020825 v1 Summer 2002

sin2b Golden Sample: (cc)KS and (cc)KL 85 x 106 BB evts Here is the BaBar detector and you can notice the powerful Particle identification device, which is the DIRC 2938 events used to measure sin2f1 Summer 2002

sin(2b) Fit Results CP odd: sin 2f1 = 0.716  0.083 CP even: sin 2f1 = 0.78  0.17 |lf| = 0.948  0.051 (stat)  0.017 (sys) Scss = sin(2f1 ) = 0.759  0.074 (stat)  0.032 (sys) sin(2f1 ) = 0.719  0.074 (stat)  0.035 (sys) asumming |lf| = 1 (hep-ex/020825, v1) Summer 2002

} sin(2b) Fit Results hf =-1 hf =+1 sin2b = 0.755  0.074 sin2b = 0.741  0.067 (stat)  0.034 (sys) with |lf| = 1 |lf| = 0.948  0.051 (stat)  0.017 (syst) Sf = 0.759  0.074 (stat)  0.032 (syst) } hf =-1 Summer 2002

Golden modes with a lepton tag The best of the best! Ntagged = 220 Purity = 98% Mistag fraction 3.3% sDt 20% better than other tag categories background Consistent results across mode, data sample, tagging category sin2b = 0.79  0.11 Summer 2002

Standard Model Comparison One solution for b is in excellent agreement with measurements of unitarity triangle apex r = r (1-l2/2) h = h (1-l2/2) Method as in Höcker et al, Eur. Phys.J.C21:225-259,2001 2 sigma errors sin2b = 0.741  0.067 (stat)  0.034 (sys) sin2f1= 0.719  0.074 (stat)  0.035 (sys) sin2b = 0.722  0.040 (stat)  0.023 (sys) sin2f1= 0.728  0.056 (stat)  0.023 (sys) HFAG@ICHEP2004: Im(lyK) = 0.725  0.037 Nir@ICHEP2002: Im(lyK) = 0.734  0.054

sin2b from the Penguin Decay b  sss 2.4 from s-penguin to sin2 (cc) 2.7 from s-penguin to sin2 (cc)

B  pp to Measure sin2aeff With Penguins (P): No Penguins (Tree only): mixing decay

B  pp CP Asymmetry Results

B  pp CP Asymmetry Results PRL 93, 021601 (2004) 152M BB pairs

Time-Dependent CP Violation in B-Decays A January 2005 Summary Babar and BELLE have observed time-dependent CP violation in neutral B-mesons, in accord with the Standard Model. HFAG@ICHEP2004: Im(lyK) = 0.725  0.037 The ensemble of these and other results appear to validate the Kobayashi-Maskawa mechanism as the source of CP violation in the electroweak sector. New Physics may yet be manifest in CP violation measurements to come. Lots of experimental work is being done. Several “> 2.5s””” effects are stimulating theoretical work.