Search for New Physics Search for New Physics with B-Mesons with B-Mesons Stefan Spanier University of Tennessee 1 Stefan Spanier
• Energy budget of Universe Dark Energy: ~70% Dark Matter: ~25% ~25% Antimatter: 0% ~70% 2 Stefan Spanier
• Understanding the Small = Understanding the Big ? matter In Big-Bang Cosmology Universe initially contained equal amounts anti-matter of matter, anti-matter and photons photons Most particles & anti-particles annihilated each other while the Universe was still very dense to form photons. Today’s (visible) Universe has a lot of cosmic micro- wave photons and a tiny bit of matter: One baryon per 10 9 microwave photons. Only one anti-particle per 10 9 particles. T< 3K Sometime a process distinguishing particles from anti-particles was at work… 3 Stefan Spanier
• Baryogenesis 3 fundamental conditions to construct a baryon asymmerty A. Sakharov Toy Model of Baryogenesis _ Rate r _ q q,l Condition II : r r CP Violation _ _ Condition I q q,l _ Rate r _ B anti-symmetric q q q _ _ q q q _ freeze out q q _ q q q _ q q q Condition III B symmetric Non-equilibrium Standard Model provides the ingredients ! 4 Disclaimer: There are many realizations, but all need CP violation. Stefan Spanier
• Standard Model - CP Symmetry C : charge conjugation (particle – antiparticle) -x P : parity P x = -x , P( x v ) = ( x v ) x For decay of particle X into final state f: _ _ CP ( X f ) = X f • A difference between decay rates of a particle and its Anti-particle implies CP violation. CP violation can be ingredient to explain ratio of matter to anti-matter. - C and P maximally violated in the Standard Model - 1964 CP violation observed in neutral kaon decays ! 5 Stefan Spanier
10 -35 s 10 28 K Grand Unification Transition It may have happened 10 -10 s 10 15 K Electroweak Era (100 GeV) 10 -6 s 10 13 K Quark-Hadron transition here ! But … (1 GeV) 10 9 K Nucleosynthesis 1 min light elements created SM Higgs is heavy (125 GeV [LHC]) 1 Byr 20 K Galaxies form no departure from thermal equilibrium 14 Byr 3 K Today CP violation in the Standard Model is 10 orders of magnitude too small ! Something else has happened ! B-factory can reach > 10 16 K … ~ 6 Stefan Spanier
• Standard Model of Particle Physics particles anti-particles _ _ _ Charge Charge u c t d s b + 2/3 + 1/3 Quarks _ _ _ - 1/3 - 2/3 d s b u c t B=1/3 B=-1/3 C Baryon number e - _ _ _ e -1 0 Leptons e + e 0 +1 L=1 L=-1 Lepton number Standard Model mass _ C: Charge conjugation symmetry p : anti-proton _ u _ _ C p = p d _ u In today’s accelerators (cosmic rays) particles and anti-particles are created and annihilate in pairs ! 7 Stefan Spanier
• CP Violation in the Standard Model W b c,u u c t CKM matrix - parametrize transitions with d 3 strengths and one complex phase s b ~ 1 , ( ) the phase is accessible arg( ) with B mesons ! t d _ b d arg( ) u b DK, K … J/ K 0 , K 0 , D*D* … (0,0) (1,0) CP magnitude ~ triangle area) Branching Fractions < 10 -4 / 8 Stefan Spanier
• CP Violation Phenomenology Quantum Mechanics 101 To observe CP-violation (phase) a particle decay needs to depend on at least two complex amplitudes A 1 and A 2 decay rate amplitude 2 • Only one amplitude: |A 1 | 2 = |a 1 e i 1 | 2 = |a 1 | 2 rate not sensitive to phase • Two amplitudes: |A 1 + A 2 | 2 = |a 1 e i 1 + a 2 e i 2 | 2 2 + a 2 2 + 2 a 1 a 2 cos( 1 – 2 ) = a 1 rate depends on phase 9 Stefan Spanier
• Relevant Amplitudes in B-Meson Decays Tree amplitude Penguin Amplitude e.g. B 0 J/ K 0 e.g. B 0 K 0 S S _ W _ _ _ _ b c t J/ b s c s B 0 W gluon B 0 _ _ _ s s K 0 K 0 d d S d d S weak coupling * * ~V cb V cs ~V tb V ts • Penguins allow for Physics Beyond ~ _ _ g s s b b s the Standard Model ! b d ( δ 23 RR ) ~ + η ’ b • Different Penguins in different ways R s s ~ g s 0 s B _ R e.g. additional Phase from s s s Supersymmetry ? Ks K 0 d d d S d d d Study Penguins !!! new coupling 10 Stefan Spanier
• Direct CP Violation _ _ Rate(B 0 f ) Rate(B 0 f ) •CP violation hadronic time i i A a e e i i i i : weak phases : strong phases i i Rate difference: R R - 2 a i a sin( ) sin( ) j i j i j i , j Short range, long range (rescattering) hadronic interactions need to be understood ! New Physics can change the expected rates. 11 Stefan Spanier
_ • Direct CP Violation in B 0 K + - (B 0 K - + ) From 454 million neutral B decays reconstruct 1606 signals. Challenge: distinguish K + - from + - and K + K - which are also present. - 0 N K- + N K+ - B K B A B AR 0 Asymmetry B K N K- + N K+ - + = -0.133 0.030 stat 0.009 syst 4.2 [ Phys.Rev.Lett. 93 (2004) 131801] Significant asymmetry (13%) is 100,000 stronger than the one measured in neutral kaon decays. Bang on Standard Model expectation 12 Stefan Spanier
_ • B 0 B 0 Oscillation Measurement _ B 0 , B 0 can oscillate (mix) into each other one more amplitude e W - e - t c b d _ D - W W 0 0 B d B d Box amplitude: - - - - t c d b * ~ V tb V td W + e + Characteristic decay products tag the B 0 flavor: e unmix – mix A mix ( t) = unmix + mix N(e + e - ) – N(e - e - /e + e + ) = N(e + e - ) + N(e - e - /e + e + ) D D cos ( m d t) ( t) 6.3 ps 12.6 ps m d = 0.493 0.012 stat 0.009 sys ps -1 13 Stefan Spanier
• CP Violation in Interference between Mixing and Decay Observe as an asymmetry between transitions of particle % anti-particle. The cleanest way is via a decay of B 0 into a CP eigenstate: flavor tag _ Quantum B 0 entangled S / K 0 J/ K 0 B 0 S e + e - Y(4S) (golden modes) _ B 0 time mixing contains CP phase) sin2 = 0 : no CP violation S and K 0 sin2 0.7 : expected in Standard Model for J/ K 0 S with 4% theoretical uncertainty in SM, only. 14 Stefan Spanier
• CP Violation in Interference between Mixing and Decay Observe as an asymmetry between transitions of particle % anti-particle. The cleanest way is via a decay of B 0 into a CP eigenstate: flavor tag _ Quantum B 0 entangled B 0 e + e - Y(4S) K 0 _ S B 0 time mixing + direct CP violation 15 Stefan Spanier
• B Meson Production Use Electron-Positron collider _ – Y(4S) resonance decays nearly 100% into B-meson pairs (B + B - ,B 0 B 0 ) – Accelerator can be tuned in; production just above threshold – Clean environment _ – Coherent B 0 B 0 production b e + d L = 1 e - [CLEO] - d e + hadrons b e - Y(4s) uu,dd,ss ~ 2.1 nb d ~ 30 m cc ~ 1.3 nb bb ~ 1.05 nb PEP-II B A B AR Off On (energy) mass(B) = 5.28 GeV/c 2 E M ( MeV ) CM ( 4 S ) 16 Stefan Spanier
• Asymmetry Measurement with BaBar , e , K LEP/CDF Flavor tag Partial reconstruction perfect B time e + 3 GeV resolution e - : 9 GeV K S B resolution function J/ e z L B Decay Time (ps) Full reconstruction B Factories e perfect time resolution Lorentz Boost =0.56 z> = < t> c ~ 250 m .. instead of ~ 30 m in CM B Decay Time Difference (ps) 17 Stefan Spanier
330 M BB pairs Run5 BaBar integral luminosity fb -1 Run4 1650 mA e - 2500 mA e + 4 ns bunch spacing Run3 ~ 8 BB pairs / s Run2 Run1 Y(4s) - 40 MeV 18 2000 2006 Stefan Spanier
• BaBar Collaboration • 10 countries • 63 institutions • ~550 physicists 19 Stefan Spanier
• BaBar Detector Silicon Vertex Tracker 5 layers of double sided Si strips DIRC 144 synthetic fused silica bars 11000 PMTs e + Drift Chamber 40 axial stereo layers e - 1.5T Solenoid Electromagnetic Calorimeter Instrumented Flux Return 6580 CsI(Tl) crystals 19 layers of RPCs Limited Streamer tubes in upper/lower barrel sextant 20 Stefan Spanier
• The Cherenkov Detector , e , K B (~80%) cos C ( ) = v/c n( ) identify particle also by measuring the identify particle by measuring C , number of photons N with momentum p is known from tracking: N L sin 2 C L = pathlength in medium Number of photons Cherenkov angle [rad] in quartz for certain d track momentum [GeV/c] track momentum [GeV/c] 21 Stefan Spanier
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