Part 4 ! Thomas Blake Warwick Week 2015

An introduction to Flavour Physics

! Part 4 ! Thomas Blake Warwick Week 2015

1 An introduction to Flavour Physics

• What’s covered in these lectures: 1. An introduction to ﬂavour in the SM.! 2.Neutral meson mixing and sources of CP violation. 3.CP violation in the SM. 4.Flavour changing neutral current processes.! ➡Neutral meson mixing, rare decays, lepton ﬂavour violation and constraints on new particles.

2 The ﬂavour problem

• If there is TeV-scale new physics (and we hope there is), why doesn’t it manifest itself in ﬂavour changing neutral currents (FCNCs)?

3 No FCNC at tree level in SM

qi qi qi qi qi qj qi qi

Vij Z0 W g

• Charged current interaction is the only ﬂavour changing process in the SM.

• Flavour changing neutral current processes are therefore forbidden at tree level (require a loop process involving a virtual W exchange).

4 Effective theories

• In mesons/baryons there is a clear separation of scale. E

! m m > ⇤ H W b QCD ⇤ • We want to study the physics of the mixing/decay at or below a scale Λ, in a theory in which contributions L from particles at a scale below and above Λ are present. Replace the full theory with an effective theory valid at Λ,

( , ) ( )+ = ( )+ C ( ) L L H ! L L Le↵ L L iOi L i X

operator product expansion

5 Fermi’s theory

• Example: ➡ In the Fermi model of the weak interaction, the full electroweak lagrangian (which was unknown at the time) is replaced by the low-energy theory (QED) plus a single operator with an effective coupling constant.

d u d u

GF W EW QED + (ud)(e⌫¯) L ! L p2 ⌫ e ⌫ e

6 FCNC processes

• Two types of FCNC process: 0 0 B Bs ➡ ∆F = 2, meson anti-meson mixing. s

➡ ∆F = 1, e.g. Bs → �+�- . Commonly µ described as rare decays. µ+ ! 0 0 • In the SM these processes are B K⇤ suppressed:

➡ Loop processes which are CKM µ+ suppressed and can be highly GIM 0 suppressed. Bs µ

7 FCNC processes

• Two types of FCNC process: 0 0 B Bs ➡ ∆F = 2, meson anti-meson mixing. s

➡ ∆F = 1, e.g. Bs → �+�- . Commonly µ described as rare decays. µ+ ! 0 0 • In the SM these processes are B K⇤ suppressed:

➡ Loop processes which are CKM µ+ suppressed and can be highly GIM 0 suppressed. Bs µ

8 Mixing

9 Reminder: GIM mechanism

• Take mixing diagram as an V q = s, d example, have an amplitude b Vtb tq⇤ t(c, u)

Bq W W Bq 0 0 ¯ (B B )= (V ⇤ V )(V ⇤ V )A t qb qd q0b qd qq0 A ! q¯ V ⇤ ¯ q,q0 tq Vtb b summing over X the internal up- type quarks Can then plug-in V ⇤ V + V ⇤ V + V V =0 ub ud cb cd tb ⇤ td

0 0 (B B )= (V ⇤ V )[V ⇤V (A A )+V ⇤ V (A A )] A ! qb qd tb td tq uq cb cd cq uq q X for the B system the top dominates m m /m2 / q q0 W 10 New physics in B mixing?

• Introduce a multiplicative factor M = M 12 12,SM · s,d

consistent with SM (Re ∆ =1, Im ∆ = 0) 11 New physics in B mixing?

• Introducing new physics with at some higher energy scale ΛNP with coupling �NP  = + NP (d) Le↵ LSM d 4 Oi i ⇤NP X 4 2 2 g mt NP (Vtb⇤Vtd) 2 4 c.f. 2 16⇡ mW ⇤NP

SM contribution NP contribution from box diagram (at dimension 6), can include tree level FCNC

12 Mixing constraints

• Everything is consistent with the SM, so instead can set constraints on NP scale from mixing.

Operator Re(⇤)Im(⇤)Re(c)Im(c) Constraint µ 2 4 7 9 (sL dL)(sLµdL) 9.8 10 1.6 10 9.0 10 3.4 10 mK , "K ⇥ 4 ⇥ 5 ⇥ 9 ⇥ 11 (sRdL)(sLdR) 1.8 10 3.2 10 6.9 10 2.6 10 mK , "K µ ⇥ 3 ⇥ 3 ⇥ 7 ⇥ 7 (cL uL)(cLµuL) 1.2 10 2.9 10 5.6 10 1.0 10 mD, q/p , D ⇥ 3 ⇥ 4 ⇥ 8 ⇥ 8 | | (cRuL)(cLuR) 6.2 10 1.5 10 5.7 10 1.1 10 mD, q/p , D µ ⇥ 2 ⇥ 2 ⇥ 6 ⇥ 6 | | (bL dL)(bLµdL) 5.1 10 9.3 10 3.3 10 1.0 10 md, S 0 J/ KS ⇥ 3 ⇥ 3 ⇥ 7 ⇥ 7 (bRdL)(bLdR) 1.9 10 3.6 10 5.6 10 1.7 10 md, S 0 J/ KS µ ⇥ 2 ⇥ 2 ⇥ 6 ⇥ 6 (bL sL)(bLµsL) 1.1 10 1.3 10 7.6 10 7.6 10 ms ⇥ 2 ⇥ 2 ⇥ 5 ⇥ 5 (b s )(b s ) 3.7 10 3.7 10 1.3 10 1.3 10 m R L L R ⇥ ⇥ ⇥ ⇥ s

ΛNP in TeV when coupling =1 coupling (c = �) when ΛNP = 1TeV

13 Small couplings?

• New ﬂavour violating sources (if there are any) are highly tuned, i.e. must come with a small coupling constant or must have a very large mass. generic tree-level NP 4 1 ⇤NP > 2 10 TeV ⇠ ⇠ ⇥ generic loop-order 1 > 3 2 ⇤NP 2 10 TeV ⇠ (4⇡) ⇠ ⇥ tree-level with “alignment” 2 (ytVti⇤Vtj) ⇤NP > 5TeV ⇠ ⇠ loop-order with “alignment” (y V V )2 t ti⇤ tj⇤ > 2 ⇤NP 0.5TeV ⇠ (4⇡) ⇠ 14 Minimal Flavour Violation

• One good way to achieve small couplings is to build models that have a ﬂavour structure that is aligned to the CKM. ➡ Require that the Yukawa couplings are also the unique source of ﬂavour breaking beyond the SM.

• This is referred to as minimal ﬂavour violation.

• The couplings to new particles are naturally suppressed by the Hierarchy of the CKM elements.

15 Rare decays

16 Rare b → s decays

• Can write a Hamiltonian for the effective theory as

4 GF ↵e = V V ⇤ C (µ) (µ) , He↵ p tb ts 4⇡ i Oi 2 i X

Wilson coefﬁcient Local operator with (integrating out different Lorentz structure scales above μ) (vector, axial vector current etc)

17 Rare b → s decays

• Can write a Hamiltonian for the effective theory as

! 4 GF ↵e = V V ⇤ C (µ) (µ) , He↵ p tb ts 4⇡ i Oi 2 i ! X

! Weak decay Loop suppression (1/mW)2 CKM suppression (1/4π)2 !

• Conventional to pull SM loop contributions out the front as constants.

18 Beyond the SM

• In the same way can introduce new particles that give rise to corrections NP e↵ = 2 NP ! H ⇤NP O

! NP scale local operator

• Once again, the constant, �, can share some, all or none of the suppression of the SM process.

19 Operators

right handed currents photon penguin (suppressed in SM)

mb µ⌫ mb µ⌫ = s¯ P bF , 0 = s¯ P bF , O7 e R µ⌫ O7 e L µ⌫ mb µ⌫ a a mb µ⌫ a a = g s¯ P T bG , 0 = g s¯ P T bG , O8 s e2 R µ⌫ O8 s e2 L µ⌫ µ µ =¯s P b `¯ ` , 0 =¯s P b `¯ ` , O9 µ L O9 µ R µ µ =¯s P b `¯ ` , 0 =¯s P b `¯ ` . O10 µ L 5 O10 µ R 5

vector and axial-vector current

20 Operators (beyond SM)

• Scalar and pseudo-scalar operators (e.g. from Higgs penguins)

! =¯sP b ``¯ , 0 =¯sP b ``¯ , OS R OS L ! ¯ ¯ P =¯sPRb `5` , P0 =¯sPLb `5` ! O O

• Tensor operators

! ¯ µ⌫ ¯ µ⌫ T =¯sµ⌫ b ` ` , T5 =¯sµ⌫ b ` 5` , ! O O

• All of these are vanishingly small in SM.

• In principle could also introduce LFV versions of every operator.

21 Generic ∆F = 1 process

• In the effective theory, we then have

! (B f)=V ⇤Vtq Ci(MW )U(µ, MW ) f i(µ) B ! A ! tb h |O | i i X ! Hadronic matrix element !

• For inclusive processes can relate sum over exclusive states to calculable quark level decays, 2 2 ! (B Xs)= (b s)+ (⇤ /m ) B ! B ! O QCD B • For exclusive processes, need to compute form-factors / decay constants etc.

22 Generic ∆F = 1 process

• Inclusive processes are theoretically clean, but experimentally challenging.

• Exclusive processes are theoretically challenging. ➡ Involve non-perturbative quantities.

• Estimate form-factors using, light-cone-sum-rules and Lattice QCD.

23 Form factors

• Unfortunately, we don’t just have free quarks and we need to compute hadronic matrix elements (form-factors and decay constants). ➡ Non-pertubative QCD, i.e. difﬁcult to estimate. e.g how to deal with this:

Fortunately we have tools B f to help us in different kinematic regimes.

24 Theoretical tools (crib sheet)

• Lattice QCD ➡ Non-perturbative approach to QCD using discretised system of points in space and time. As the lattice becomes inﬁnitely large and the points inﬁnitely close together the continuum of QCD is reached.

• Light-Cone-Sum-Rules ➡ Exploit parton-hadron duality to compute form-factors and decay constants.

• Operator product expansions. ➡ Used to match physics to relevant scales.

25 Theoretical tools (crib sheet)

• Heavy quark expansion. ➡ Exploit the heaviness of the b-quark, m ⇤ b QCD • QCD factorisation. ➡ Light quark has large energy in the meson decay frame, e.g. quarks in π have large energy in B → π decays in the B rest frame.

• Soft Collinear Effective Theory. ➡ Model system as highly energetic quarks interacting with soft and collinear gluons.

• Chiral perturbation theory.

26 Which processes?

• Will mainly focus on recent measurements of B decay processes, b → s transitions are some of the least well tested.

• You can also study FCNC decays of charm and strange mesons.

• The GIM mechanism is more effective in both charm and strange meson decays:

➡ For charm mesons the masses and mass differences, e.g. (mb - ms), are small. ➡ For strange mesons top contribution is suppressed relative to B meson decays because Vts ≪ Vtb.

27 + - Bs → � �

• Golden channel to study FCNC decays.

• Highly suppressed in SM. 1.Loop suppressed. neutral current 2.CKM suppressed (axial-vector) (at least one off diagonal element) 3.Helicity suppressed (pseudo-scalar B to b µ two spin-1/2 muons) t 0 Bs W Z0 + s¯ µ also receives contributions from W box diagrams 28 + - Bs → � �

• Golden channel to study FCNC decays. Interesting probe of • Highly suppressed in SM. models with new or enhanced scalar operators 1.Loop suppressed. (no helicity suppression), 2.CKM suppressed e.g. SUSY at high tan β. (at least one off diagonal element) 3.Helicity suppressed (pseudo-scalar B to b µ two spin-½ muons) 0 0 h Bs b + s¯ µ

29 + - Bs → � � in the SM

• Only one operator contributes in SM:

=(s b )(¯µµ µ) ! O10 L µ L 5

• Branching fraction in SM: Single hadronic matrix element (decay constant) CKM factors 0 sµ b B = if pµ h | 5 | i B

2 2 2 2 2 2 0 + Vtb⇤Vtq GF ↵e MBMµfB 4Mµ 2 (Bd,s µ µ) 3 1 2 C10(mb) B ! ⇡ 16⇡ H s MB | | 2 Mµ 2 helicity suppression ⇥ MB ! 30 + - Bs → � � • Very rare decay with branching fraction of 10-9:

31 + - Bs → combination � � CMS and LHCb (LHC run I) ) 2 c 60 Data • Signal and background Combining results from CMS 0 + − 50 Bs→ µ µ B0→ µ+µ− ] Combinatorial bkg. and LHCb experiments from 40 Semileptonic bkg. Peaking bkg. LHC run 1. 30

20 ➡ Observe Bs signal and 10 evidence for B0. S/(S+B) weighted cand. / (40 MeV/ 0 5000 5200 5400 5600 5800 2 m − [MeV/c ] CMS and LHCb (LHC run I) µ+µ ] 9 0.9 L 40 1 ln SM ⇤ [10 0.8 2 2 30 ) ◊

1 10 µ 9 + 0.7 5.7 20 µ 1 ◊

⇥ 6.3 10 99.73% 10 0 0.6 7 b LHCb + CMS, [arXiv:1411.4413 B ◊ 95.45% 10

B( 0 68.27% 0.5 5 0 2 4 6 8 0 + 9 B(Bs ⇥ µ µ ) [10 ] 0.4

L 10 ln

0.3 ⇤ 8 SM 2 0.2 6 SM 4 0.1 a 2 c 0 0 0 1 2 3 4 5 6 7 8 9 0 0.2 0.4 0.6 0.8 0 + 9 0 + 9 B(Bs ⇥ µ µ ) [10 ] B(B ⇥ µ µ ) [10 ] 32 the end of a long road …

10−8 10−4

10−9 10−5

10−10 10−6 2012 2013 2014

10−7

−8 10 CLEO Belle ARGUS BaBar 0 + − UA1 LHCb SM: Bs → µ µ −9 10 CDF CMS L3 ATLAS Limit (90% CL) or BF measurement 0 + D0 CMS+LHCb SM: B → µ µ − 10−10 1985 1990 1995 2000 2005 2010 2015 Year 33 Testing MFV

• Ratio of the rates of the CMS and LHCb (LHC run I) ] L ln

∆ 10

two decays is a test of 2 − MFV which predicts: 8 SM and MFV

2 2 0 0 Vtd fB0 6 (B /Bs ) | |2 2 R / Vts f 0 | | Bs 4

2 ~1/25 0 LHCb + CMS, [arXiv:1411.4413 0 0.1 0.2 0.3 0.4 0.5 R from Lattice Data are consistent with SM/MFV

34 Photon polarisation

• In radiative B decays, angular momentum conservation allows b W − s ! b s R(L) Vtb Vts L(R) L ! R R ! bR sLL ! t • However, the charged current interaction γL(R) only couples to left handed quarks. Need to helicity ﬂip the b- or s-quark.

• The right-handed contribution is therefore suppressed by (b s ) m A L ! R R s (b s ) ⇠ m A R ! L L b

35 Inclusive b → s �

• Can perform either a semi-inclusive measurement, summing a large number of Xs ﬁnal states (e.g. K+, K*, …) or a fully inclusive measurement where Xs is not reconstructed.

➡ Cuts on M(Xs) or E� complicate theory calculations.

6 Result (B X ) = (343 21 7) 10 B ! s E >1.6GeV ± ± ⇥ background subtracted data

BF consistent with SM shapes in MC 10 3 ×10 expectation (a) 12 (b) 106 10 Continuum MC (impressive5 prediction 8 10 BB MC Signal MC Events / 100 MeV Events / 100 MeV 6 of the104 SM) 4

103 2

0 1.6 1.8 2 2.2 2.4 2.6 2.8 3 1.6 1.8 2 2.2 2.4 2.6 2.8 3 Eγ* (GeV) Eγ* (GeV)

FIG. 2: Estimated signal and background yields vs. photon energy in the CM frame based on MC simulation, at two stages of the event selection: (a) after requiring an unvetoed high-energy photon (logarithmic scale); (b) after all selection requirements BaBar, Phys. Rev. D. 86. 1120082 (2012) (linear scale). The three contributions are shown cumulatively. The signal distribution is for a KN model with mb =4.65 GeV/c , 36 while the continuum distribution has been scaled as described in Sec. III.

1200 (a) 1800 (b) 1600 1000 Signal MC 1400 800 BB MC 1200 Continuum MC 1000 600 800 400 600 400 200 200 0 0 0 0.5 1 1.5 2 2.5 3 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 CM Electron Momentum (GeV/c) cos θ* (e,γ)

400 1000

300 800 600 200 400 100 200

0 0 0 0.5 1 1.5 2 2.5 3 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 CM Muon Momentum (GeV/c) cos θ* (µ,γ)

FIG. 3: Lepton distributions from MC simulation, after the photon selection requirements but before applying lepton tagand NN criteria. Plots (a) and (b) are for electron tags, plots (c)and(d)formuontags.Plots(a)and(c)showtheCM-frame momentum distributions, with vertical lines indicating theminimumselectionrequirements.Plots(b)and(d)showthecosine of the CM angle between the lepton and the high-energy photon,afterapplyingthemomentumcriteria;theverticallinesshow 2 the minimum requirement on this quantity. The signal (black dots) is from a KN model with mb =4.65 GeV/c .TheBB background (solid blue histogram) and continuum background(dashedred)arefromtheMCsimulations.Eachdistributionis separately normalized to best illustrate its behavior. b → s � constraints

• Constraints on right-handed currents in b → s � decays:

inclusive time dependent CP angular 0 0 branching fraction. violation in B [KS⇡ ] distribution of + ! B K⇤e e ! Results are consistent with LH polarisation expected in SM 37 + b s ` ` decays ! J/(1S) b ccs¯ photon tree! level penguin

( ) (2S) C7 d dq2

( ) ( ) ( ) ( ) 7 C9 C9 )"*( C10 !"#$%&$%$"'$(C +,"-(*!.#)"'$( ',"#%!/01,".(&%,2(cc¯ )/,3$(,4$"('5)%2( #5%$.5,6*((

2 4[m(µ)] q2 38 + b s ` ` decay rates ! Theory Binned LCSR Lattice Data LHCb CMS ] ] 1.5 2 -2 5 + + + − 0 0 + B → K µ µ B K⇤ µ µ GeV 4 ! c /GeV 4 LHCb

4 1 × c

-7

× 3

[10 -8 2 2 q 0.5 /d [10 B 2 d

q 1 /d

B 0 0 5 10 15 20 d 0 0 5 10 15 20 q2 [GeV2/c4] q2 [GeV2/c4] • 3 form-factors • 7 form-factors

• No enhancement at low q2 • Enhancement at low q2 from from virtual photon (angular virtual photon momentum conservation).

Large theory uncertainties (from QCD) 39 B →K*0 µ+µ-

• Four-body ﬁnal state. µ+

✓` B0 ➡ Angular distribution provides K+ µ 0 ✓K K⇤ many observables that are ⇡ 0 sensitive to NP. (a) ✓K and ✓` deﬁnitions for the B decay

K+ 2 nˆK⇡ nˆµ+µ e.g. at low q the angle ⇡ 0 µ B µ 0 between the decay planes is K⇤ + K ⇡

pˆ sensitive to the photon + K⇡ µ polarisation. µ+ (b) deﬁnition for the B0 decay • System described by three µ nˆK⇡ nˆ + 2 µµ angles and q . µ 0 + B K ⇡

K 0 ⇡+ µ+ ⇤ K + pˆK⇡ µ (c) deﬁnition for the B0 decay

40 B →K*0 µ+µ-

Angular distribution:

1 d3( + ¯) 9 = 3 (1 F )sin2 ✓ + F cos2 ✓ + d( + ¯)/dq2 ~ 32⇡ 4 L K L K d⌦ P h + 1 (1 F )sin2 ✓ cos 2✓ 4 L K l fraction of longitudinal F cos2 ✓ cos 2✓ + S sin2 ✓ sin2 ✓ cos 2 polarisation of the K* L K l 3 K l

+S4 sin 2✓K sin 2✓l cos + S5 sin 2✓K sin ✓l cos forward-backward 4 2 asymmetry of the + 3 AFB sin ✓K cos ✓l + S7 sin 2✓K sin ✓l sin

dilepton system 2 2 +S8 sin 2✓K sin 2✓l sin + S9 sin ✓K sin ✓l sin 2 i The observables depend on form-factors for the B → K* transition plus the Wilson coefﬁcients. 41 Latest LHCb result, shown at Moriond 2015, LHCb-CONF-2015-002

42 Form-factor “free” observables • Can construct ratios of observables which in QCD factorisation/SCET are independent of form-factors.

P 0 = S / F (1 F ) 5 5 L L p

local tension with SM predictions (vector like NP contribution or unexpected large QCD effect?) Latest LHCb result, shown at Moriond 2015, LHCb-CONF-2015-002 Latest LHCb result,

43 global ﬁts to b → s data

• Global ﬁts to the b → s data favour a new vector like contribution.

➡ Could be sign of new physics (heavier partner of the Z) or a sign that we don’t understand something about QCD, c c loop contributions will also look vector-like.

branching fractions angular observables combination

44 Interpretation of global ﬁts

Optimist’s view point Pessimist’s view point

Vector-like contribution could Vector-like contribution could come from new tree level point to a problem with our contribution from a Z’ with understanding of QCD, e.g. mass of few TeV (the Z’ will are we correctly estimating also contribute to mixing, a the contribution for charm challenge for model builders) loops that produce dimuon pairs via a virtual photon.

More work needed from experiment/theory to disentangle the two 45 (charged) lepton ﬂavour violation

46 Charged LFV

• Essentially forbidden in SM by µ smallness of the neutrino mass. e ⌫ Powerful null test of the SM. x • Any visible signal would be an indication of NP.

4 m⌫ (µ e) 4 B ! / mW 54 10 ⇠

47 SINDRUM II µ LFV 1989–1993 @PSI R(μAu→eAu) • Three different signatures <7.0×10-13 1. µ e at rest (MEG at PSI). ! 2. µ 3 e (SINDRUM at PSI). ! 3. µ conversion in ﬁeld of nucleus.

SINDRUM 1983–1986 @SIN(PSI) B(μ→eee) MEG <1.0×10-12 2008–2013 @PSI B(μ→eγ) <5.7×10-13

25 year’s ago 48 LFV large number of experimental� signatures

• Expect improvement from Belle 2 and for � → 3µ from LHCb.

49 A look into the future

50 New Physics?

• As we saw in the last lecture, measurements of the CKM matrix and the properties (closure) of the Unitarity triangle are consistent with the Standard Model picture of ﬂavour physics. ➡ Nobel prize for Kobayahsi and Maskawa in 2008.

• However, there are some interesting “hints” of new physics:

➡ Tension in Vub (and Vcb).

➡ Enhancement of D(*)�ν. all at ~3� ➡ P5’ anomaly in B →K*0 µ+µ-. ➡ Muon g-2.

• There’s still plenty of room for discoveries …

51 LHCb running conditions

• LHCb is currently running at a luminosity of 4x1032 cm-2s-1 .

• Displacing LHC beams to run at a lower luminosity that ATLAS and CMS.

! running at a levelled luminosity !

• How do we interpret this number?

! (pp bb)=(75.3 5.4 13.0)µb in LHCb acceptance ! ± ± ! 30 k bb pairs per second ⇠ • Higher luminosity means more B mesons produced per year and in turn better statistical precision.

52 LHCb upgrade current trigger scheme

• Aim to run at 2x1033.

• Main limitation with the current detector is the 1 MHz readout rate.

• Need to cut much harder maintain the 1MHz rate with higher luminosity (end up removing as much signal and background).

• Ambitious plan to read out the full detector at 40 MHz to a software farm.

• Also plans to replace vertex and tracking detectors to cope with higher luminosity.

• Upgrade planned for LS2 (2018).

53 KEKB to SuperKEKB

Belle II Colliding bunches

New IR e- 2.6 A

New superconducting New beam pipe /permanent final focusing & bellows e+ 3.6 A quads near the IP

Replace short dipoles with longer ones (LER)

Add / modify RF systems for higher beam current

Low emittance positrons to inject Positron source Damping ring Redesign the lattices of HER & New positron target / LER to squeeze the emittance capture section

TiN-coated beam pipe Low emittance gun with antechambers Low emittance electrons to inject

To obtain x40 higher luminosity Peter Križan, Ljubljana 54 Rare kaon decays

also CP • Two rare kaon decay experiments are just starting: ➡ KOTO at J-PARC, searching for K0 ⇡0⌫⌫¯ L ! ➡ NA62 at CERN, searching for K+ ⇡+⌫⌫¯ ! • The main advantage of ﬁnal states with neutrinos is that there is no contribution from quark loops involving light quarks (which can annihilate to produce charged leptons).

KOTO NA62

55 Charged LFV

• Upgrade to MEG underway, aiming for O(10-14). Expected to start data taking soon.

• New µ →3e experiment (Mu3e) at PSI.

• Two new conversion experiments, one at PSI (Mu2e) and one at J-PARC (COMET).

• Expect improvements for LFV 50 μm thick silicon wafer decays from Belle 2. � Interesting challenges, e.g. very thin detectors for µ→3e. 56 Recap

• In today’s lecture we discussed: ➡ Flavour changing neutral current processes and constraints on new particles. ➡ Minimal flavour violation. ➡ Charged lepton flavour violation. ➡ Future flavour experiments.

57 Further reading

• There are a number of good sets of lecture notes on ﬂavour physics available on arXiv that give a more detailed overview of this ﬁeld.

➡ A. J. Buras, “Weak Hamiltonian, CP violation and rare decays,” [arXiv:hep-ph/9806471].

➡ A. J. Buras, “Flavor physics and CP violation,” [arXiv:hep-ph/0505175].

➡ G. Isidori, “Flavor physics and CP violation,” [arXiv:1302.0661].

➡ Y. Grossman, “Introduction to ﬂavor physics,” [arXiv:1006.3534].

➡ Y. Nir, “Flavour physics and CP violation,” [arXiv:1010.2666].

➡ M. Neubert, “Effective ﬁeld theory and heavy quark physics,” [arXiv:hep-ph/0512222].

58 Further reading

• Most introductory particle physics text books include a basic introduction to ﬂavour physics.

• There are also more specialist books available, e.g. ➡ I. I. Bigi and A. I. Sanda. “CP violation” ➡ CP violation, G.C.Branco, L.Lavoura & J.P.Silva

59 Fin