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f CP. f CP. 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.
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fCP fCP Time-Dependent Particle-Antiparticle Asymmetries in the Neutral B-Meson SystemMichael D. SokoloffUniversity 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. Michael D. Sokoloff
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. Michael D. Sokoloff
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 • 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. Michael D. Sokoloff
Classical Field Theory (E&M) Michael D. Sokoloff
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: Amg • To calculate cross-sections and decay rates we use perturbation theory based on Feynman Diagrams: Michael D. Sokoloff
The Nobel Prize in Physics 2004 Gross Politzer Wilczek 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. Michael D. Sokoloff
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. Michael D. Sokoloff
Weak Charged Current Interactions charm decay neutrino scattering 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. Michael D. Sokoloff
b = f1; a = f2; g = f3 Weak Phases in the Standard Model Michael D. Sokoloff
fCP Elements of Macroscopic CP Violation Michael D. Sokoloff
Some Relevant Feynman Diagrams Michael D. Sokoloff
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 Michael D. Sokoloff
BaBar Detector All subsystems crucial for CP analysis 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 3.5GeV e+ CsI(Tl) 16X0 TOF counter 8GeV e- Tracking + dE/dx small cell + He/C2H5 m / KL detection 14/15 lyr. RPC+Fe Si vtx. det. 3 lyr. DSSD
e+e- (4S) BB m- Flavor tag and vertex reconstruction K- Btag m- Brec m+ B0 KS B0 p+ Coherent L=1 state p- Start the Clock Stop the Clock Experimental Technique at the (4S) Resonance Boost: bg= 0.55 (4S) Exclusive B meson and vertex reconstruction Michael D. Sokoloff
( ) 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. Michael D. Sokoloff
typical mistagging & finite time resolution Tagging Errors and Finite Dt Resolution perfect tagging & time resolution (f-) (f+) B0D(*)-p+/ r+/ a1+ Ntagged=23618 Purity=84% Michael D. Sokoloff
r = estimated tagging dilution 6 hep-ex/020825 v1 Effective Tagging Efficiency QQ=e(1-2w)2 Michael D. Sokoloff
sin2b Golden Sample: (cc)KS and (cc)KL 85 x 106 BB evts 2938 events used tomeasure sin2f1 Michael D. Sokoloff
CP odd: sin 2f1 = 0.716 0.083 CP even: sin 2f1 = 0.78 0.17 sin(2b) Fit Results |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 Michael D. Sokoloff
|lf| = 0.948 0.051 (stat) 0.017 (syst) Sf = 0.759 0.074 (stat) 0.032 (syst) } hf =-1 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 Summer 2002 Michael D. Sokoloff
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 Michael D. Sokoloff
r = r (1-l2/2) h = h (1-l2/2) sin2b = 0.722 0.040 (stat) 0.023 (sys) sin2b = 0.741 0.067 (stat) 0.034 (sys) sin2f1= 0.728 0.056 (stat) 0.023 (sys) sin2f1= 0.719 0.074 (stat) 0.035 (sys) HFAG@ICHEP2004: Im(lyK) = 0.725 0.037 Standard Model Comparison One solution for b is in excellent agreement with measurements of unitarity triangle apex Method as in Höcker et al, Eur. Phys.J.C21:225-259,2001 Nir@ICHEP2002: Im(lyK) = 0.734 0.054 Michael D. Sokoloff
sin2b from the Penguin Decay bsss 2.4 from s-penguin to sin2 (cc) 2.7 from s-penguin to sin2 (cc) Michael D. Sokoloff
With Penguins (P): B pp to Measure sin2aeff No Penguins (Tree only): mixing decay Michael D. Sokoloff
B ppCP Asymmetry Results Michael D. Sokoloff
B ppCP Asymmetry Results PRL 93, 021601 (2004)152M BB pairs Michael D. Sokoloff
Time-Dependent CP Violation in B-DecaysA 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. Michael D. Sokoloff