What’s the matter with anti-matter? A short history of CP violation Gabriella Sciolla M.I.T. Outline: The physics of CP violation What is CP and why is it interesting? CP in particle physics The “Standard Model”: a crush course Measurements of CP violation Tests of Standard Model and probe to New Physics Conclusion Summary & Prospects

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Symmetries and Physics Symmetries are a constant theme in Physics “For every continuous symmetry of the laws of physics, there must exist a conservation law” Noether’s theorem Continuous Symmetries Translational symmetry: All positions in space are physically indistinguishable Consequence: momentum p is conserved Rotational symmetry: All directions in space are physically indistinguishable Consequence: Angular Momentum L is conserved

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Discrete Symmetries Parity (P) Flips the space coordinates: Example: Time Reversal (T) Physics invariant when Charge Conjugation (C) Transforms matter into corresponding anti-matter

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Are C, P and T good symmetries of Nature? Strong and Electromagnetic Interactions Conserve separately P and C Weak Interaction Known to maximally violate both C and P Wu et al Only left-handed and right-handed anti- exist C,P,T: Symmetries of Nature?

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. CPT Theorem and CP conservation The CPT Theorem “In any relativistic quantum field theory the product CPT is always conserved” Consequence Since time reversal T was universally expected to be conserved  CP was expected to be conserved too What’s the big deal with CP? It has to do with our own existence…

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The CP symmetry What is CP? CP = C × P C: Charge Conjugation Particle  Anti-particle P: Parity Inverts space coordinates

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The importance of CP violation The Big Bang model predicts: matter and anti-matter produced in equal amounts matter and anti-matter annihilated into energy This obviously goes against experimental evidence… e-e- e+e+  

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Looking Out, Looking Back The Universe exists… Where did all the anti-matter go? …and it’s made of matter! 8

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The last echo of the Big Bang The Cosmic Microwave Background, a result of matter/anti- matter annihilation near the beginning of time Image taken by the Wilkinson Microwave Anisotropy Probe (WMAP)

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The matter dominated Universe Only 1/10 9 particles survived! What caused this tiny asymmetry?

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. 11 Courtesy of Alan Chou (SLAC) CP violation Remember CPT theorem: CP expected to be conserved!

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. CP violation in K decays In 1964 Fitch and Cronin discovered CP violation in the decays of K L mesons: K L   +  - K L             CP=-1 }         CP=+1 }

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The importance of CP violation discovery Revolutionary result: Fitch and Cronin awarded the Nobel Prize in NOBEL PRIZE J.Cronin V. Fitch symmetry between matter and anti-matter is broken How could this phenomenon be explained?

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Standard Model of Particle Physics 12 elementary particles 6 leptons 6 quarks 4 forces mediated by various bosons ForceCarrier(s)Mass (GeV/c 2 )Electric Charge Electromagneticphoton00 WeakW +, Z 0 80/90+1/0 Stronggluon00 GravitationalGraviton?0?

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Standard Model’s minor addition: minor addition: anti-matter Antiparticle vs. particle Same mass, but opposite quantum numbers Example: electrical charge flips Charge=-1 Charge=+1 Charge=+2/3 Charge=-2/3 Charge=+1/3 Charge=-1/3

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Photo courtesy of SLAC SLAC 40-inch bubble chamber, 1971

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. SLAC 40-inch bubble chamber, 1971 Photo courtesy of SLAC

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Standard Model’s recipes: how to make particles The 6 quarks are the building blocks of matter Baryons: 3 quarks Proton: (uud) Neutron: (udd) Lambda: (sud) Mesons: 1 quark (q) + 1 anti-quark (q) Charged pions:  +  - Neutral Pion  0 u ud Proton u d Charge=+2/3 Charge=-1/3 u ud Anti-Proton u d u u

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Standard Model’s recipes: how particles decay Most of the particles produced in the lab decay Usually in a tiny fraction of a second! Example of a weak decay:     -  Feynman Diagram Solid lines: quarks or leptons Dashed lines: carriers of forces Each vertex carries a coupling constant g W Its strength determines the probability of the decay time gWgW gWgW

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Weak Interactions: Quark-Lepton Symmetry? Experimental observation in weak interactions: Leptons always and only couple inside the same family Quarks instead violate this rule in     -  How to preserve lepton-quark symmetry? Introducing “Quark Mixing” mechanism… time

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Standard Model: Quark Mixing Mechanism “Weak eigenstates” are linear combinations of “Flavor eigenstates” Flavor eigenstates: quarks as we defined them so far Weak eigenstates: linear combinations of ordinary quarks The matrix that transforms flavor eigenstates (d,s) into weak eigenstates (d’, s’) is called mixing matrix Just a 2x2 rotation 1 parameter: Cabibbo angle  C

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. CP violation in the Standard Model What if extend this mechanism to 3 families of quarks? Kobayashi and Maskawa, 1973 Parameterization of the 3x3 rotation in complex space: 3 angles (Euler angles) and a complex phase This complex phase elegantly introduces CP violation in the Model explaining Fitch and Cronin’s results It also predicted the existence of third quark family

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Success of the CKM predictions The third families of quark and leptons were soon discovered L. Lederman Nobel Prize 88 Upsilon (bb) – Fermilab ‘77Tau lepton – SLAC ‘75 M. Perl Nobel Prize 95 Top quark – Fermilab ‘95

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. CKM and CP violation Why we love CKM Elegant and simple mechanism Good success record The CKM is predictive CKM Measure CP violation in channels theoretically very well understood and look for deviations w.r.t. Standard Model prediction

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. How to test CKM? Kaons known for 40 years but… Experimental results very hard to interpret theoretically: Loose constraints from  K measurement No constraints from  ’  yet… …or clear theory but very hard to reach experimentally: BF(K L    )~ ! Is there a way out? Yes, using B mesons…

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Unitarity of CKM implies: V † V = 1  6 unitarity conditions Of particular interest: All sides are ~ O(1)  possible to measure both sides and angles! Angles from CP asymmetries in B meson decays Sides from measurement of decay rates and mixing of B mesons The Unitarity Triangle     

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Testing the Standard Model Measuring directly and independently the angles tests the Standard Model in the CP violation sector B oscillations B decays CP violation in B decays

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Testing the Standard Model In practice: Measure sides first (easier) and identify allowed area for apex of the triangle Measure one angle and check for consistency  Confirmation of Standard Model

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Testing the Standard Model In practice: Measure sides first (easier) and identify allowed area for apex of the triangle Measure one angle and check for consistency  Discovery of New Physics!!!

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The Bs What are neutral B mesons? Bound states of b and d quarks: B characteristics: B 0 and B 0 look identical from outside Flavor can only be inferred by their decay products B 0 and B 0 decay after 1.6 ps in other lighter particles Some of these decays are especially interesting… ParticleQuarksMassChargeSpin B0B0 bd5.28 GeV/c 2 00 B0B0 bd5.28 GeV/c 2 00

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. CP violation in B 0 decays If CP is conserved, B 0 and B 0 will behave exactly the same Different types of CP violation: “Direct CP violation”: Decay rates for B 0 and B 0 to certain final states are not the same “Time-dependent CP violation”: The decay rate of B 0 and B 0 to some final states is not the same over time This kind of CP violation is especially interesting because the theory can make specific predictions…

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Time dependent CP asymmetry Consider the B 0 decays B 0  J/  K S Eigenstate of CP Clean experimental signature Time Dependent CP asymmetry It can be calculated that for this decay, the A CP (t) has a sinusoidal shape and its amplitude is related to angle       A CP (t) = sin2  sin  mt

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. How to measure CPV at B factories. Ingredient #1: Exclusive reconstruction Ingredient #2: Flavor tagging (coherent state) Ingredient #3:  t determination e-e-  4S B0B0 B0B0 e-e- ++ -- B reco B tag e+e+  z~  c  t ++ --

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The experimental challenge Rare events: Experimental accessible BF: ~  Millions of Bs needed! Time dependent analysis: Bs produced with a boost  Asymmetric B factory! Full B reconstruction and flavor tag State of the art detector with excellent tracking and particle identification:  BaBar Detector!

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The solution: asymmetric B factories Asymmetric e + e - B factories First proposed in 1987 by P. Oddone (LBL) Elegant and conceptually simple Challenging for accelerator builders! 2 beam pipes, 2 sets of magnets, difficult interaction region… Many proposals, only 2 survived: PEP-II at SLAC (California) KEK-B at KEK (Japan) Similar in design and achievements Will discuss PEP-II and BaBar as an example…

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The PEP-II accelerator Asymmetric B factory 9.0 GeV e - beam 3.1 GeV e + beam Very high luminosity 9 BB pairs/second > 500 M B mesons

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The SLAC accelerators BaBar Detector

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The B A B AR Detector ) DIRC (PID) 1.5 T solenoid CsI(Tl) EMC Drift Chamber Instrumented Flux Return Silicon Vertex Tracker e + (3.1GeV) e - (9GeV)

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The BaBar experiment at SLAC MIT people at work!

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Ingredient #1: Reconstruct the B 0 decay Accelerator and detector were completed in 1999 First goal: measure CP violation in the “golden channel” B 0  J/  K S Experimental challenge: Very rare decays BF (~10 -4 ) It took 2 years to accumulate enough data to measure CPV Today’s sample: >4,000 clean B decays

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Gold plated event at BaBar B 0  J/  K S B 0  K - X Zoom on interaction region

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Distinguish B 0 from B 0 We are measuring the asymmetry: B 0 and B 0 look identical from outside Flavor can only be inferred by their decay products Strategy: Combine the many sources of flavor tagging information using Artificial Neural Networks to optimize performance Very tricky business: the measurement is very sensitive to this ingredient!!! B0B0 D *- D0D0 l +l +   (soft) K +  B0B0 D *-   (hard) W+W+ Ingredient #2:

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Ingredient #3:  t measurement Time dependent analysis: The technique: e-e-  4S B0B0 B0B0 e+e+  z~  c  t ~ 250  m

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. The CP fit: sin2  from 88M B 0 B 0  sin(2  ) = ± stat ± syst

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. What did we learn? Compare measurement of angle  with measurement of sides: sin2  from BaBar vs. indirect constraints Excellent agreement with Standard Model expectation

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. CKM CKM and CPV: end of the story? Why we love CKM Elegant and simple mechanism The CMK is predictive Measurements in B and K sector confirm predictions Good News: new sources of CP violation must exist besides CKM (New Physics!)  Deviations from CKM expected in some channels Just one (major) problem: X It fails to explain the matter-antimatter asymmetry observed in the Universe by several orders of magnitude!

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. New Physics in penguin decays? Standard Model predicts A CP (t) New Physics can modify A CP (t): look for deviations >2.5  effect observed: more data needed… 0 S

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. sin2  charmonium vs penguins Fluctuation or first signs New Physics?  …more data will tell…

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Other sources of CP violations The explanation of the matter-antimatter asymmetry doesn’t necessarily reside in the quark sector Other possible sources of CP violation: CP violation in strong interactions Search for neutron EDM (electric dipole moment) CP violation in neutrinos Especially promising: Recent discovery of neutrino mixing: neutrinos have masses! 3x3 mixing matrix as in the quark sector CP violation term as in the CKM mechanism Interesting experiments planned in the near future Stay tuned!

November 13, 2003What can we learn from CPV? G. Sciolla – M.I.T. Conclusion The mysteries of CP violation are being uncovered thanks to new studies of B meson decays Standard Model is still holding well, but… First unambiguous evidence of CPV in B system First quantitative test of CP side of Standard Model New Physics must be hiding somewhere: Penguins? Neutrinos? The quest continues…