CERN Antimatter really matters? Thanks to A. Höcker for material from his Summer Studen Lectures 2005 Richard Jacobsson 1 Paul Dirac (1933) CERN e+ μ ixtmxtγψ∂−μ (),,0 ψ () = Carl Anderson in 1932 “If we accept the view of complete symmetry between positive and negative electric charge so far as concerns the fundamental laws of Nature, we must regard it rather as an accident that the Earth (and presumably the whole solar system), contains a preponderance of negative electrons and positive protons. It is quite possible that for some of the stars it is the other way about, these stars being built up mainly of positrons and negative protons. In fact, there may be half the stars of each kind. The two kind of stars would both show exactly the same spectra, and there would be no way of distinguishing them by present astronomical methods.” Also in the 30s: ¾ Universe is exppganding with finite size and a ge…. Î Mind boggling “existential” questions arise Richard Jacobsson 2 Particle/antiparticle dynamicsCERN What happens if particles and antiparticles are brought together? z A particle can annihilate with its antiparticle to form gamma rays z An example whereby matter is converted into ppgyyure energy by Einstein’s formula E = mc2 z Conversely, gamma rays with sufficiently higggyh energy can turn into a p article- antiparticle pair Particle-antiparticle tracks in a bubble chamber Richard Jacobsson 3 5, 4, 3, 2, 1, Big Bang! CERN z Initial state of the Universe p + p ÅÆ γ + γ ¾ Soup of energy, and particle and antiparticles ¾ “Quasithermal” equilibrium z Two starting possibilities for the baryon number (Bp =1= 1, Bp = -1) 1. <B(t=0)> /= 0 • Very unnatural…. • Even if it had been the case it would have been driven to zero duringgg the initial stages 2. <B(t=0)> = 0 - Two possibilities 1. All annihilates leaving behind a Universe void of matter but filled with photons at 2.7K today ¾ Anthropic principle rules this out…. 2. Annihilation rate falls below expansion rate before all is annihilated • RiRegions o f an tittithUitimatter in the Universe • Î Antimatter search! 3. …unless….. Richard Jacobsson 4 Naturally existing antimatter?CERN No evidence of large antimatter regions at less that 20 Mpc (600 Mly) z Indirect search ¾ No peaks in gamma-ray diffuse background from nucleon-antinucleon annihilation ¾ No distorsions compatible with matter and antimatter annihilations in Cosmic Microwave Background z Direct search for antimatter ¾ Single anti-helium, anti-carbon nucleon Æ anti-stars! ¾ BESS experiment, Balloon-borne Experiment with Superconducting Spectrometer • Antihelium / helium < 10-6 ¾ AMS – Alpha Magnetic Spectrometer Richard Jacobsson 5 …unless… Baryogenesis! CERN ? B(t=0)=0 Æ B(t > 10-11s) /= 0 z StSpontaneous symme tbkiftt/titttry breaking of matter/antimatter symmet ry Δ − nbaryonnnbaryon baryon −10 ¾ Baryon asymmetry parameter η = = ~ O()10 nnγγ as required by nucleosynthesis to generate abundance of light elements in the Universe (if B(t=0) = 0 would have been preserved, after freeze-out η = Ο (10−18)) 1 baryon out of 1010 pairs did not annihilate and survived z Where did the photons go? Naïve estimate of η by comparing the estimated atom density in the universe (~ 1. 6/m3) with the photon gas density at 2.73 K cosmic background radiation temperature (~4.2×108/m3) Richard Jacobsson 6 Universe in the making CERN The Universe begun as an extremely hot and dense soup of energy and particles The rapidly expanding Universe is already endowed with an excess of matter over antimatter by one in a billion and small density variations The souppq of quarks condenses into p rotons, neutrons,.. The first light nuclei are formed Atoms are formed This marks the limit between the use of telescopes and accelerators! Recent research shows that we only know what 4% of the Universe is and that its expansion is accelerating Richard Jacobsson 7 What’s behind baryogenesis?CERN z Andrei Sakharov’s criteria for baryogenesis (1967): 1) Baryon number violation η(t=0) = 0 Æ η(today) /= 0 2) C and CP violation otherwise the process generating excess of baryons will be exactly equal to process generating excess of antibaryons 3) Departure from thermal equilibrium Richard Jacobsson 8 Discrete symmetries CERN z Invariance under the discrete parity, charge conjugation, time reversal transformations requires: P : fxt(r′′ , ) Hixt (rrr ,)=− f ( xt ′′ , ) Hi ( − xt ,) C :()()()(): fxt( r′′, )( Hixtrrr, )(= f xt ′′, )( Hixt, ) T :(,)(,)(,)(, fxtrrr′′ Hix tfxtHixt=− ′ ′ r −) z Fundamental consequences of CPT theorem ¾ Relation between spin and statistics: fields with integer spin (“bosons ” ) commute and fields with half-numbered spin (“fermions”) anticommute Æ Pauli exclusion principle ¾ Particles and antiparticles have equal mass and lifetime, equal magnetic moments with opposite sign, and opposite quantum numbers ()mmm−</ 10−18 • Best test KKK000 • Electromagnetic and strong interactions are C, P and T invariant Richard Jacobsson 9 C and P in weak interaction CERN z Weak interaction violates both C and P symmetries μνν−−→++ z Consider the decay of a polarized muon: polarized e μ e P The preferred emission handedness of the electron: P transformation (i.e. direction of an electron reversing all three is opposite to the muon directions in space) polarization. suppressed yields constellation that is suppressed in nature. CC Similar situation for C Applying CP, the resulting transformation (i.e. reaction—in which an replace all particles with antimuon preferentially their antiparticles). suppressed emits a positron in the same direction as the polarization—is observed. handedness of the positron: B. Cahn, LBL Richard Jacobsson 10 CP violation in neutral K CERN Γ→()if ≠Γ→ () i f ∗+−====00 z Stranggpe particles: (KK , ,K )I=1/ 2 : K usK, usK, dsK, ds 0 0 ¾ Experimentally one does not observe the neutral “flavor eigenstates” K and K but rather long- and short-lived neutral states: KL and KS z The observed pionic decays were thought to be cleanly ππ)0 ¾ KS(CP=+1)Æ ( (CP=+1) πππ)0 ¾ KL(CP=-1) Æ ( (CP = -1) z Cronin, Fitch et al. discovered in 1964 CP-violating decay π0π0 ¾ KL(CP=-1) Æ (CP = +1) →π+π– KL Today’s most precise measurement for amplitude ratio: AK( → ππ+−) ε = L → ππ+− AK()S =±×(2. 282 0. 017) 10−3 Richard Jacobsson 11 Three types of CP violation CERN z CP Violation in mixing (indirect CP violation) s d + =+00 0 W 0 Oscillations! Kt() gt () K ht () K K tc, tc, K d W − s Prob()()()KK00→≠Prob() KK 00 → 0 = 0 = 0 = 0 = ¾ Oscillating systems Ksd Dcu Bbdd Bbss z CP Violation in interference between decays with and without mixing (indirect CP violation) Pb(()Prob(Kt00 ( )→≠ππ+++ − )Pb(()) Prob( Kt ( ) → ππ+ − ) z CP Violation in the decay (direct CP violation) ¾ Due to the sma llness o f the e ffect , it t ook several experi ment s and over 30 years o f e ffor t to observe this phenomenon Prob(Kf→≠ ) Prob( Kf → ) Richard Jacobsson 12 CP violation in B CERN z A much richer repertoire of CP phenomena available in b-hadrons ¾ Start of “B-factories” at the end of 90s (BaBar (SLAC), BELLE (KEK)) BaBar 2005 B0 Æ J/ψ K0 ((Gold‘Gold-plated channel ’ ) ¾ ¾ Three ingredients b c W+ c s s d b d db cd ∝ ∗g VVcb cs c d b u c t s = d s d d B0 mixing B0 decay K0 mixing Richard Jacobsson 13 VP violation in SM CERN z How can we incorporate this phenomena in the SM? z Weak decay through transitions between families of quarks mediated by W Æ Flavor quarks (‘weak eigenstates’) are not the same as the physical quarks (‘mass eigenstates’) Æ Only if quarks are massive! (SM CP violation after appearance of Higgs field) + ′ W ⎛⎞⎛dVVVdud us ub ⎞⎛⎞ ⎜⎟⎜′ = ⎟⎜⎟ U sVVVscd cs cb o Li, V ⎜⎟⎜ ⎟⎜⎟ ij D ⎜⎟⎜′ ⎟⎜⎟ Lj, ⎝⎠⎝bVVVbtd ts tb ⎠⎝⎠ d’ d d -1/2 γμ + s’ = V s Lcc = 2 g (u, c, t)L V s W μ + h.c. b’ b b Quark mixing matrix - Cabibbo-Kobayashi-Maskawa (CKM) matrix, 1973 (KM) Æ KM introduced third family which gave a complexe phase to generate CP violation Richard Jacobsson 14 Quark mixing CERN 2 z The |Vij | are transition probabilities and hence the matrix has to be unitary z For example, a t quark can decay into a d, s, or b quark and nothing else; thus, the sum of the decay probabilities into these quarks must be one: ¾ Unitarity constraints! 222++= VVVtd ts tb 1 uct t b c s u d s b Richard Jacobsson 15 Unitarity triangles CERN z Wolfstein parametrization of CKM matrix −−λλρ23λ ()η ⎛⎞VVudVus ub ⎛⎞1/2 Ai ⎜⎟ VVVV= ⎜⎟ ⇒ −−λλλ122 / 2 A + O( λ 4) ⎜⎟cd cs cb ⎜⎟ ⎜⎟VVV⎜⎟ Aλρηλ32()11−− i − A ⎝⎠td ts tb ⎝⎠ Im ∗∗∗++= 0 VVud us VV cd cs VV td ts 0 K system ∗ + ∗ +=∗ VVud ub VV cd cb VVtd tb 0 ∗∗+=∗ + OO()λ + (λ )()+=O λ 5 0 VVus ub VV cs cb VV ts tb 0 OOO()λλ33++= (λ )0( 3 ) 0 ∗∗∗ B system + + = 4 22 d VVud cd VVus cs V ubVcb 0 O ()λλλ++=O ()O ()0 ∗ + ∗∗+ = VVud td VV us ts VV ub tb 0 0 Bs system ∗∗+ ∗ + = VcdVVVVV td cs tscbtb 0 relative size of CP-violating effect Richard Jacobsson 16 ‘Flavour’ of what we do…. CERN z Measuring all parameters in as many processes as possible and confront them with SM and with different measurements of the same parameters Im 00↔ΔΔ ()ρ,η BBmmsssd:/ +− 0 →μμ 010× − B()s (BR for Bd ~ 2 10 ) R% (()BR for B09~ 4× 10− ) R% t s 0 → u BDKss bccs→ 0 +− γ′ BKK→ δγ ~1° s 0 → ψφφ 00→ ψ BJs / ,..