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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 timedependent CP violation in neutral B-mesons, in accord with the Standard Model. B B 0 The ensemble of these and other results appear to validate the Kobayashi-Maskawa mechanism as the source of CP violation in the electroweak sector. Michael D. Sokoloff fCP B 0 B New Physics may yet be manifest in CP violation measurements to come. Seminar at NKU, 26 October 2004 0 1 0 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. Seminar at NKU, 26 October 2004 Michael D. Sokoloff 2 Special Relativity • Energy and Momentum – Energy and momentum form a four-vector (t,x,y,z). 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 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. • • 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. Seminar at NKU, 26 October 2004 Michael D. Sokoloff 3 Classical Field Theory (E&M) Seminar at NKU, 26 October 2004 Michael D. Sokoloff 4 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 m In relativistic quantum field theory: A g To calculate cross-sections and decay rates we use perturbation theory based on Feynman Diagrams: Seminar at NKU, 26 October 2004 Michael D. Sokoloff 5 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 Seminar at NKU, 26 October 2004 Michael D. Sokoloff 6 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. • Seminar at NKU, 26 October 2004 Michael D. Sokoloff 7 Weak Charged Current Interactions neutrino scattering charm decay l ~ l 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. Seminar at NKU, 26 October 2004 Michael D. Sokoloff 8 Weak Phases in the Standard Model b = f1; a = f2; g = f3 Seminar at NKU, 26 October 2004 Michael D. Sokoloff 9 Elements of Macroscopic CP Violation B 0 Seminar at NKU, 26 October 2004 Michael D. Sokoloff B 10 0 fCP Some Relevant Feynman Diagrams Seminar at NKU, 26 October 2004 Michael D. Sokoloff 11 The PEP-II Storage Ring at SLAC Total: 244 fb-1 (Jul 31st 04) • PEP-II is SLAC’s e+eB factory running at the (4S) c.m. energy • The (4S) resonance decays to charged and neutral B-anti-B pairs Seminar at NKU, 26 October 2004 Michael D. Sokoloff 12 BaBar Detector All subsystems crucial for CP analysis 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 % SVT: 13 Belle Detector Aerogel Cherenkov cnt. n=1.015~1.030 SC solenoid 1.5T 3.5GeV e+ CsI(Tl) 16X0 TOF counter 8GeV eTracking + dE/dx small cell + He/C2H5 Si vtx. det. 3 lyr. DSSD m / KL detection 14/15 lyr. RPC+Fe 14 Experimental Technique at the (4S) Resonance e+e- (4S) B B m- Boost: bg = 0.55 e- - K Btag (4S) Flavor tag and vertex reconstruction e+ B0 B KS 0 Coherent L=1 state t z bg c m- Brec z Start the Clock - + m + Exclusive B meson and vertex reconstruction Stop the Clock Seminar at NKU, 26 October 2004 Michael D. Sokoloff 15 Identifying Fully Reconstructed B’s ( ) For fits, both Belle and Babar characterize signals and backgrounds with PDF’s which utilize Mbc, E, tagging category, etc. Seminar at NKU, 26 October 2004 Michael D. Sokoloff 16 Tagging Errors and Finite t Resolution perfect tagging & time resolution Btag= B Btag= B 0 0 (f+) B0 D(*)-+/ r+/ a + Ntagged=23618 Purity=84% typical mistagging & finite time resolution (f-) 1 - t / B e fUnmixed (t) = 1 (1- 2w) cos(md t) R Mixed 4 B October 2004 Seminar at NKU, 26 Michael D. Sokoloff 17 Effective Tagging Efficiency Q Q=e(1-2w)2 Babar Tagging Performance Category r = estimated tagging dilution Q (%) e (%) w (%) 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 Seminar at NKU, 26 October 2004 Michael D. Sokoloff 18 sin2b Golden Sample: (cc)KS and (cc)KL 85 x 106 BB evts 2938 events used to measure sin2f1 Seminar at NKU, 26 October 2004 Michael D. Sokoloff 19 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 Seminar at NKU, 26 October 2004 Michael D. Sokoloff 20 sin(2b) Fit Results hf =+1 hf =-1 sin2b = 0.755 0.074 sin2b = 0.723 0.158 sin2b = 0.741 0.067 (stat) 0.034 (sys) with |lf| = 1 |lf| = 0.948 0.051 (stat) 0.017 (syst) hf =-1 Sf = 0.759 0.074 (stat) 0.032 (syst) } Summer 2002 Seminar at NKU, 26 October 2004 Michael D. Sokoloff 21 Golden modes with a lepton tag The best of the best! Ntagged = 220 Purity = 98% Mistag fraction 3.3% t 20% better than background other tag categories Consistent results across mode, data sample, tagging category sin2b = 0.79 0.11 Seminar at NKU, 26 October 2004 Michael D. Sokoloff 22 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 sin2bb == 0.741 0.722 0.067 0.040 (stat) (stat) 0.034 0.023 (sys) (sys) sin2 sin2 sin2ff11== 0.719 0.728 0.074 0.056 (stat) (stat) 0.035 0.023 (sys) (sys) Nir@ICHEP2002: Im(lyK) = 0.725 0.734 0.037 0.054 HFAG@ICHEP2004: Seminar at NKU, 26 October 2004 Michael D. Sokoloff 23 sin2b from the Penguin Decay b sss 2.4 from s-penguin to sin2b (cc) 2.7 from s-penguin to sin2b (cc) Seminar at NKU, 26 October 2004 Michael D. Sokoloff 24 B to Measure sin2aeff With Penguins (P): No Penguins (Tree only): l Vtb*Vtd Vud* Vub = VtbVtd* V V * ud ub mixing decay l = e Seminar at NKU, 26 October 2004 1+ P /T ei e - ig C sin( ) 2 ia l = e C = 0 S = sin(2a ) i ig 2 ia 1+ P /T e e 2 S = 1 - C sin(2aeff ) Michael D. Sokoloff 25 B CP Asymmetry Results Seminar at NKU, 26 October 2004 Michael D. Sokoloff 26 B CP Asymmetry Results PRL 93, 021601 (2004) 152M BB pairs Seminar at NKU, 26 October 2004 Michael D. Sokoloff 27 Time-Dependent CP Violation in B-Decays A Summary Babar and BELLE have observed timedependent 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 “> 2.5” effects are stimulating theoretical work. Seminar at NKU, 26 October 2004 Michael D. Sokoloff 28