CERN

Antimatter really ?

Thanks to A. Höcker for material from his Summer Studen Lectures 2005

Richard Jacobsson 1 Paul Dirac (1933) CERN

e+

ixtmxtγψμ∂−() ψ,,0 () = μ

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 is exppganding with finite size and a ge…. Î Mind boggling “existential” questions arise

Richard Jacobsson 2 Particle/ dynamicsCERN

What happens if particles and are brought together?

z A particle can annihilate with its antiparticle to form gamma rays

z An example whereby is converted into ppgyyure energy by Einstein’s formula E = mc2

z Conversely, gamma rays with sufficiently higggyh energy can turn into a particle- 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. /= 0 • Very unnatural…. • Even if it had been the case it would have been driven to zero duringgg the initial stages

2. = 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 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 symmet tbkiftt/tittry breaking of matter/antimatter symmet ry Δn nn− η = baryonbaryon baryon 10 − ¾ Baryon asymmetry parameter = ~ 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 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 protons, 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−

• 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: ε AK( → ππ+−) = L → +− AK()S ππ =±×(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 ( )→≠ ππππ +++ − )Pb(()) Prob( Kt ( ) →+ − )

z CP Violation in the decay (direct CP violation)

¾ Due to th e small ness o f th e eff ect , it t ook several experi ment s and over 30 years o f e ffor t t o 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

−−λλρ23() ⎛⎞VVudVus ub ⎛⎞1/2 Ai ⎜⎟ VVVV= ⎜⎟ ⇒ −− 122 / 2 A + O( 4) ⎜⎟cd cs cb ⎜⎟λλλλ λ ⎜⎟VVV⎜⎟ Aλρη32()11−− i − A λ ⎝⎠td ts tb ⎝⎠ η

Im ∗∗∗++= 0 VVud us VV cd cs VV td ts 0 K system ∗ + ∗ +=∗ VVud ub VV cd cb VVtd tb 0 VV∗∗+= VV∗ + VV 0 OOλλ()λ + λ ()()+=O 5 0 us ub cs cb ts tb λ OOO()33++= (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 (BR for Bd ~ 2 10 ) ()s − R% (()BR for B09 ~ 4 10× ) R% t s 0 → u → BDKss bccs +− γ ′ BKK0 → δγ ~1° s BJ0 → /ψφφ,... BJK00→ /ψ ()00, ()1,0 s sS Re 0 bsss→ +− B → φφ 0 → s , ... BDDsss, ...

Richard Jacobsson 17 What have we achieved? CERN

z Experiments up to now has established the KM mechanism as the dominant source of CP violation at the electroweak scale

¾ Remarkable agreement

z SM CP violation is always a rare phenomenon: • either the CP asymmetry is small • or/and the decay rate is suppressed

10 z In terms of cosmology, this CP violation is OFF by O(10 ) !!

¾ The Universe would have contained ONE galaxy…..

z Proof of New Physics!

¾ But where and what?

¾ Tippg of the iceberg Æ Rock the iceberg to see what is below!

Richard Jacobsson 18 LHCb Experiment at LHC CERN

σ μ z Cross section for bb production at 14 TeV: bb ~ 500 b 12 ¾ Enormous production rate at LHCb: ~ 10 bb pairs per year! → much higher statistics than the current B factories

0 → ψ z Expect ~ 2 00,000 reco ns truc t ed B J/ KS ev ent s/yeas/year cf current B-factory samples of ~ 4000 events → precision on sin 2β ~ 0.02 in one year for LHCb (similar to current world average pp)recision)

0 + Λ z But in addition, all b-hadron species are produced: B , B , Bs, Bc , b … In particular can study the Bs (bs) system, inaccessible at the B factories

z ATLAS and CMS are also planning to do B physics but will only have a lepton trigger, and poor hadron identification

Richard Jacobsson 19 bb events CERN

pp interaction π+ (primary vertex) b and b quarks are produced in pairs π− (mostly in the forward direction) 0 B L Κ− b-hadron π+ b + − π b l

b

z Need to measure ppproper time of B deca y: b = doesn't occur t mB L / pc hence decay length L (~ 1 cm in LHCb) and momentum p from decay products (which have ~ 1–100 GeV)

3 z Also need to tag production state of B: θ b [rad] 2 3 whether it was B or B 1 2 1 θ [rad] Use charge of lepton or kaon from decay 0 b b of the other b hadron in the event

θ b b

Richard Jacobsson 20 LHCb in its cavern CERN

Offset interaction point (to make Shielding wall best use of existing cavern) (against radiation)

Electronics + CPU farm

Detectors can be moved away from beam-line for access

Richard Jacobsson 21 LHCb detector CERN

Richard Jacobsson 22 Low energy antimatter studiesCERN

Antihydrogen

z 1996:

¾ First production of 9 antihydrogen at LEAR (CERN), moving with 90% of the speed of light

z 2002:

¾ Production of 1,000,000 antihydrogen atoms at the AD (CERN), moving with 1/1 000 000 of the speed of light

Richard Jacobsson 23 Deccelerator CERN

z 188 m long z Antiproton Production, z Storage and Deceleration z 3 - 0.005 GeV energy

Richard Jacobsson 24 Antimatter traps CERN

z Trap for antiparticle storage

z E.g. spectroscopy =?

Richard Jacobsson 25 Summary CERN It is ‘(not un-)likely’ that precision measurements on CPiltiCP violation w illdiill discover New Physics indirectly before the direct observations come!

Richard Jacobsson 26