Flavor Physics: the Next Decade(S) Zoltan Ligeti ([email protected])

Flavor Physics: the Next Decade(S) Zoltan Ligeti (Ligeti@Berkeley.Edu)

Flavor Physics: the next decade(s) Zoltan Ligeti ([email protected])

Aug 10–21 2020, Online & World-wide Disclaimers

• If available, I prefer giving summer school lectures on the blackboard

– More fun for you, and also for me

– Sketching a plot on the blackboard, we automatically focus on what matters

– Time spent updating many of the plots was not useful, but I still tried

• Do interrupt any time with any questions or comments! I really mean it! (Let’s try to make this as interactive as possible, but I may not notice raised hands in zoom)

Z L – p.1/1 What is particle physics?

• Central question: What are the elementary degrees of freedom and interactions? L = ?

• Most experimentally observed phenomena consistent with the “standard model” (Michelson 1894: “... it seems probable that most of the grand underlying principles have been ﬁrmly established ...”)

• Standard Model of Standard Model particle physics: of cosmology:

• Inconsistent: Two very successful theories, but this cannot be the full story

Z L – p.1/2 What is particle physics?

• Central question: What are the elementary degrees of freedom and interactions? L = ?

• Clearest empirical evidence that SM is incomplete: – Dark matter – Baryon asymmetry of the Universe – Neutrino mass – Inﬂation in the early universe [have a plausible theoretical picture] – Dark energy [cosmological constant? need to know more to understand?]

Z L – p.1/2 The Universe: matter vs. antimatter

• Gravity, electromagnetism, strong interaction are same for matter and antimatter • As the early Universe cooled, quarks and antiquarks annihilated

N(baryon) N − N ∼ 10−9 ⇒ q q ∼ 10−9 N(photon) Nq + Nq t < 10−6 s (T > 1013 K ∼ 1 GeV)

• The SM prediction is ∼1010 times smaller

[Nonzero! Sakharov conditions: (i) baryon number violation; (ii) charge (C) and charge-parity (CP ) violation; (iii) deviation from thermal equilibrium]

• All present in SM; additional CP violation is required What is the microscopic theory of CP violation? How precisely can we probe it?

Z L – p.1/3 Outline

• Physics beyond the standard model must exist • Introduction: Hitchhiker’s guide to flavor physics ... Sensitivity to high scales, Lepton flavor, Quark flavor

• Testing the SM ... Kaons, CP violation in B decays, new physics in B mixing

• Hints of lepton universality violation ... In B → K(∗)`+`−, in B → D(∗)τν¯

• Other future directions ... Higgs, top, new physics ﬂavor ... Maybe other topics... depends on today...

Z L – p.1/4 Intro to ﬂavor The standard model + neutrino mass

• Gauge symmetry: SU(3)c × SU(2)L × U(1)Y parameters ± 0 Gauge symmetry: 8 gluons W , Z , γ 3 (+θQCD)

• Particle content: 3 generations of quarks and leptons

Particle content: QL(3, 2)1/6, uR(3, 1)2/3, dR(3, 1)−1/3 10 ∗ Particle content: LL(1, 2)−1/2, `R(1, 1)−1 12 or 10

u c t ν1 ν2 ν3 Particle content: quarks: leptons: d s b e µ τ

• Symmetry breaking: SU(2)L × U(1)Y → U(1)EM 0 symmetry breaking: φ(1, 2) Higgs, with vev: hφi = √ 2 1/2 v/ 2

 ij Yν I I ∗ ij I I  Λ LLiLLj φ φ violates lepton number Not known: LY = −Ye LLi φ eRj − ij I ˜ I Yν LLi φ νRj requires νR ﬁelds • We don’t even know what is the Lagrangian that describes the particles observed!

Z L – p.1/5 Quark and lepton mixing

• Fermions with same quantum numbers mix, Yukawas deﬁne mass eigenstates:

    −iδ   Ma1 Ma2 Ma3 1 c13 s13e c12 s12 M =  M M M  =  c s  1  −s c   b1 b2 b3   23 23   12 12  iδ Mc1 Mc2 Mc3 −s23 c23 −s13e c13 1

• If neutrinos are Majorana, multiply by: diag (eiα1/2, eiα2/2, 1)

The additional phases α1,2 don’t affect oscillation experiments, only lepton # viol.

Always think about mass eigenstates: if neutrino masses were larger, we would

have gotten used to thinking of π → µν2 and π → µν3, instead of π → µνµ

◦ ◦ ◦ • Leptons (PMNS): θ12 ≈ 33 (solar), θ23 ≈ 49 (atm), θ13 ≈ 9 , δ unknown

◦ ◦ ◦ ◦ • Quarks (CKM): θ12 ≈ 13 , θ23 ≈ 2 , θ13 ≈ 0.2 , δ ≈ 68

Z L – p.1/6 What is ﬂavor physics?

• Flavor physics: interactions that distinguish between the generations Neither strong nor electromagnetic interactions In SM: only weak interaction with W ± (from diagonalizing Higgs couplings)

• Flavor parameters: quark & lepton masses, mi (12)

Flavor parameters: quark & lepton mixing, Vij,Uij (10, or 8?)

Majority of the parameters of the SM (extended for mνi 6= 0) (only 6 more)

• Quark mixing: Cabibbo-Kobayashi-Maskawa (CKM) matrix, Vij (3 × 3 unitary) The only source of ﬂavor change in the SM, depends on 4 param’s: {λ, A, ρ, η} η = the KM phase — the only source of CP violation in the SM

• Many testable relations, sensitive to possible deviations from the standard model

• Any new particle that couples to quarks or leptons ⇒ new ﬂavor parameters (Understanding these param’s can be crucial — “new physics ﬂavor problem”)

Z L – p.1/7 Flavor changing processes

• Flavor change: Initial flavor number 6= final flavor number ¥

(Flavor number)i = (# particlesi) − (# antiparticlesi) ¥

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Only W interactions change ﬂavor (type of fermions)

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Strength: CKM matrix, Vij

E.g.: B− → ψK− (b → ccs¯ ), B− → D0µ−ν¯ (b → cµ−ν¯), etc.

Flavor changing neutral currents (FCNC): ﬂavor change involving ¥

• ¥

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up or down quarks, but not both, and/or ` or ν, but not both

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E.g.: K0 – K0 mixing (sd¯ → sd¯ ), µ → eγ, B → Kµ+µ− (b → s)

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¥ ¥ ¦¨§ © § 2 2 2 ¦¨§ © §

• FCNC only at loop level; suppressed by (mi − mj )/mW

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£ £ [Glashow – Iliopoulos – Maiani (GIM) mechanism] £

• FCNCs are highly suppressed in the SM, probe differences between generations

Z L – p.1/8

Neutral meson mixing (a special FCNC)

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• Why is ∆mK/mK ∼ 7 × 10 ?

¥ ¥ ¦¨§ © § 2 ¦¨§ © §

∆mK 2 2 mc 2

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In the SM: w cs cd 4 K

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• If exchange of a heavy particle X was responsible for a fraction of ∆mK

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§ QCD

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¢ ¢ £ ∆mK MX ∆mK TeV-scale particles with loop-suppressed coupling can still be visible [g ∼ O(10−3)]

0 0 ¯ 0 ¯ 0 • Four neutral mesons: K (¯sd), Bd (bd), Bs (bs), D (cu¯) [top decays before forming hadrons] Quantum mechanical two-level systems

Oscillation between a particle and its antiparticle

0 ¯0 E.g., Bs – Bs oscillation measured by LHCb =⇒

Z L – p.1/9 Spectacular track record

• Uncertainty principle ⇒ heavy particles, which cannot be produced, affect lower energy processes, E2/M 2 suppressed if interference ⇒ probe very high scales

• High mass-scale sensitivity due to suppressed SM predictions

– Absence of KL → µµ ⇒ charm quark (Glashow, Iliopoulos, Maiani, 1970)

– K ⇒ 3rd generation (t, b quarks) (Kobayashi & Maskawa, 1973)

– ∆mK ⇒ mc ∼ 1.5 GeV (Gaillard & Lee; Vainshtein & Khriplovich, 1974) > – ∆mB ⇒ mt ∼ 100 GeV (bound in 1987: 23 GeV) ⇒ large CP violation & FCNC

• Critical in developing SM — it is only unambiguous since 1998 that mν 6= 0 What can future data tell us about BSM physics?

Z L – p.1/10 Anticipated increases in sensitivity

• Scales of dim-6 operators probed — various mechanisms devised to let TeV-scale NP obey these bounds (Pattern and orders of magnitudes matter more than precise values)

mesons leptons EDM higgs top

[hatched: MFV]

[European Strategy Update 2020, arXiv:1910.11775]

• µN → eN may be the largest increase in mass-scale sensitivity in next 10–15 yrs

Z L – p.1/11 Some ﬂavor-related questions

• Will LHC see new physics, beyond the Higgs?

• Will NP be seen in the quark sector? Current data: several hints of lepton universality violation (see later)

• Will NP be seen in charged lepton sector? µ → eγ, µ → eee, τ → µγ, τ → µµµ ?

• Neutrinos: Is 3 ﬂavor oscillation paradigm OK? What is the nature of ν mass?

• No one knows — an exploratory era! (n.b.: 2 generations + superweak is “more minimal” to accommodate CPV, than 3 generations...)

• Near future: “anomalies”, both in quark & lepton sector, might ﬁrst be established Long term: large increase in discovery potential in many modes

Z L – p.1/12 Lepton ﬂavor Neutrino oscillation measurements

• Three mixing angles have been measured

2 2 2 • Oscillation between two ﬂavors (δm = m1 −m2) 2 2 2 δm L GeV Posc = sin (2θ) sin 1.27 eV2 km E • Atmospheric neutrinos: 1 ∼ (10−3)×(101...4) / (100±1)

half of up-going νµ get lost

• Solar neutrinos: δm2 L/E 1 • Two mass-squared differences are measured, but not the absolute mass scale

(Short baseline anomalies not easy to ﬁt, e.g., w/ 4 ﬂavors)

Z L – p.1/13 Neutrinos — a history of surprises

• Most theorists’ expectations around late 80’s – early 90’s:

– Solar neutrino problem will go away, we do not understand the Sun Wrong

– If it does not, solution must be small angle MSW, since it’s cute Wrong

2 2 – Expect ∆m23 ∼ 10 − 100eV , since it’s cosmologically interesting (DM) Wrong

– Expect θ23 ∼ Vcb ' 0.04, motivated by simple GUT models Wrong

– Atmospheric neutrino anomaly will go away, because it requires large Wrong mixing angle — the ﬁrst that became compelling( ⇒ Nobel, 2002)

– Tribimaximal mixing ansatz, predicted θ13 near zero Wrong ◦ θ13 ∼ 9 , not too small — helps CP violation searches [inspired by H. Murayama] • Experiments crucial, independent of prevailing theoretical “guidance” • Keep open mind about lepton partner (slepton) properties — may be unexpected!

Z L – p.1/14 Lepton vs. quark mixing

• Are the origin of quark and lepton masses & mixings related?

• Some lepton processes are especially clean; quark sector observables more rich

• Cannot directly measure neutrino mass eigenstates (possible for e, µ, τ and quarks)

• Neutrino FCNCs seem impossible to search for; e.g., νi → νj γ, X → νiν¯j(Y )

• Magnitudes of mixing matrix elements, assuming 3-generation unitarity:

UPMNS : sin θ12 = 0.5514 ± 0.0011 , sin θ13 = 0.1490 ± 0.0022 , +51 ◦ sin θ23 = 0.755 ± 0.015 , δ = (195−25) . [νﬁt 2020, converted]

VCKM : sin θ12 = 0.22650 ± 0.00048 , sin θ13 = 0.00361 ± 0.00010 ,

sin θ23 = 0.04053 ± 0.00072 , δ = 1.196 ± 0.044 . [PDG 2020]

• SM ﬂavor puzzle extended: why lepton & quark masses and mixings so different?

Z L – p.1/15 Neutrinos — many unknowns

• Are neutrinos = their own antiparticles? (Different than all other known particles? Theoretically favored, most leptogenesis models)

• What is the absolute mass scale? We know two mass-squared differences > At least one state has mνi ∼ 50 meV P Cosmology: mi <0.12 − 0.3 eV [Planck 2018]

(depends on assumptions; can relax, e.g., [1901.04352])

• Value of CP violating phase δ ? • Is the mass hierarchy “normal” or “inverted”? If inverted hierarchy: planned 0νββ experiments will be If inverted hierarchy: able to determine if ν = ν or ν 6= ν Normal hierarchy: may or may not see 0νββ, even in Majorana case

Z L – p.1/16 Charged lepton ﬂavor violation (CLFV)

• Expect 104 better sensitivity (Mu2e, COMET) ⇒ 10× higher mass scales probed!

• mν 6= 0 ⇒ lepton ﬂavor is violated, no reason to impose it as a symmetry on NP If there are new TeV-scale particles that carry lepton number (e.g., sleptons), then they have their own mixing matrices ⇒ charged lepton ﬂavor violation (CLFV)

• In many SUSY models (& other scenarios), NP in the quark and lepton sectors may originate from the same underlying physics

• Experimental sensitivity is complementarity to high-pT LHC searches

• Flavor vs. naturalness: heavier NP ⇒ less constraints on its ﬂavor structure Flavor vs. naturalness: “naturalness’ loss — ﬂavor’s gain”

• CLFV measurements can discover NP signals due to TeV-scale NP with SM-like ﬂavor structure, or 10–1000 TeV NP with generic ﬂavor ⇒ cast a wide net

Z L – p.1/17 CLFV: many processes, big improvements

• SM predictions incredibly small TeV-scale loop-level NP may be observable

m4 ∝ ν < 10−50 rates 4 mW [diagrams: hep-ph/9501334] • Many interesting processes; NP-dependent which is most sensitive: µ → eγ, µ → eee, µ + N → e + N (0), µ−pp → e+nn, τ → µγ, τ → eγ, τ → µµµ,

τ → eee, τ → µµe, τ → µee, τ → µπ, τ → eπ, τ → µKS, eN → τN

• τ decays: µ → eγ, eee vs. τ → µγ, µµµ 0 0 0 lγ lP lS lV lll lhh Λh 10-5 decays

Either can “win”, huge NP model depen- τ 10-6 dence: B(τ → µγ)/B(µ → eγ) ∼ 104±3 10-7

-8 CLEO • Belle II: improve 2 orders of magnitude 10 BaBar Belle LHCb 10-9 Belle II • Any discovery ⇒ broad program to map -10 ' ' ------

0 0 0 0 0 0 0 0 0 0

10 S S S S γ γ φ φ η η η η ω ω Λ Λ Λ Λ π π π π π π µ µ µ ρ ρ π π - - f f - - - - K* K* e e e

------K K K K K K K K - - 90% C.L. upper limits for LFV - - K* K* - - + + + + + + K K + + + + + K K + - - + + + + + e - - e + + + µ e - - µ µ e e e π π µ µ µ 0 0 S S e K K e µ π π µ µ µ µ µ e e π π µ µ µ µ e µ e e e e

K K e e ------K K ------K K e e - - π µ e µ π e µ µ e e π µ µ π e K out the detailed structure µ K e µ

Z L – p.1/18 The long quest to discover CLFV

• Pursued for almost a century!

1 10 -1

10 -3

10 -5

10 -7

10 -9

10 -11

10 -13

10 -15

10 -17

10 -19 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030

• Next 10–20 years: 102–104 improvement; any signal would trigger broad program

Z L – p.1/19 Electric dipole moments

• SM + mν: CPV can occur in: (i) quark mixing; (ii) lepton mixing; and (iii) θQCD

Only observed δKM 6= 0, baryogenesis implies there must be more

−10 • Neutron EDM bound: “the strong CP problem”, θQCD < 10 — axion?

θQCD is negligible for CPV in ﬂavor-changing processes

• EDMs from CKM: vanish at one- and two-loop EDMs from CKM: large suppression at three-loop level

• E.g., SUSY: quark and lepton EDMs can be generated at one-loop Generic prediction (TeV-scale, no small param’s) above cur-

rent bounds; if mSUSY ∼ O(10 TeV), may still discover EDMs • Expected 102–103 improvements: complementary to LHC Discovery would give (rough) upper bound on NP scale

Z L – p.1/20 Testing quark ﬂavor

(Expect huge increases in relevant data sets) LHCb — at CERN

• Major LHCb upgrade in LS2 (raise instantaneous luminosity to 2 × 1033/cm2/s) Major ATLAS and CMS upgrades in LS3, for HL-LHC

• LHCb, 2017, Expression of Interest for an upgrade in LS4 to 2 × 1034/cm2/s Not yet approved — an integral part of the full exploitation of the LHC

Z L – p.1/21 The LHCb detector at CERN Belle II — SuperKEKB in Japan

• First collisions 2018 (unﬁnished detector), with full detector starting spring 2019 Goal: 50 × the Belle and nearly 100 × the BABAR data set

• Discussions started about physics case and feasibility of a factor ∼ 5 upgrade, similar to LHCb Phase-II upgrade aiming 50/fb → 300/fb, after LHC LS4

Z L – p.1/22 New accelerator, novel concepts & techniques to achieve 1036 luminosity (2/13/2017) Recent surprise: CMS “B – parking” in 2018

10 B-Parking • Collected 10 B-s; hope to compete w/ LHCb on RK(∗) anomaly [CMS @ LHCC, Nov 2018]

Effort in 2018 paid off, 12B triggered events on tape Up to 5.5 kHz in the second part of the fill where events are smaller

Now studying processing 7.6 PB on tape strategy Avg event size is 0.64 MB 1.1B events were already fully (1MB for standard events) processed in order to help development of trigger/

reconstruction !16 [email protected]

Z L – p.1/23 Testing quark ﬂavor

• The (u, c, t) W ± (d, s, b) couplings:    1 2 3  Vud Vus Vub 1 − 2λ λAλ (ρ − iη) V =  V V V  =  −λ 1 − 1λ2 Aλ2  + ... CKM  cd cs cb   2  3 2 Vtd Vts Vtb Aλ (1 − ρ − iη) −Aλ 1 | {z } CKM matrix Only 4 parameters: λ (“Cabibbo angle”, from K → π`ν), A (from b → c`ν) Only 4 parameters: used to be less precise: ρ¯ and η¯ (only source of CP violation) CKM measurements: magnitudes ∼ decay rates, phases ∼ CP violation CKM measurements: 9 complex observables ⇒ many testable relations

• Many observables are f(ρ, η) — need to compare: 2 2 2 – b → u`ν¯ ⇒ |Vub/Vcb| ∝ ρ + η – ∆m /∆m ⇒ |V /V |2 ∝ (1 − ρ)2 + η2 Bd Bs td ts “unitarity triangle” – CP violation in K, B, Bs decay

Z L – p.1/24 Precision SM tests with kaons

• CPV in K system is at the right level (K accommodated with O(1) KM phase)

0 • Hadronic uncertainties preclude precision tests (K notoriously hard to calculate) 0 Cannot yet rule out a large BSM contribution to the measured value of K

(N.B.: bad luck in part — heavy mt enhanced hadronic uncertainties, but helps for B physics)

−10 ± −11

• K → πνν : precise theory, but tiny rates 10 (K ), 10 (KL)

A ∝ (λ mc) + i(λ mc) c : GIM suppressed

 (λ Λ2 ) u : GIM suppressed

QCD

+ + 0 Experimentally, O(1) uncertainty in K → π νν¯, and much larger in KL → π νν¯

• CERN NA62: aim ∼100 K+ → π+νν¯ events at SM level 0 0 Far from theory limits J-PARC KOTO: aim to observe KL → π νν¯ at SM level

Z L – p.1/25 The quest for K+ → π+νν¯

• 50 years of searches (more than for Higgs), sensitive to O(100 TeV)

+ + +4.0 −11 • NA62 @ ICHEP: B(K → π νν¯) = (11.0−3.5) × 10 — at the SM level 0 • KOTO, 2019: 4 events in KL → π νν¯ search; @ ICHEP: 4 → 3 w/ 1.05 ± 0.28 BG

Z L – p.1/26 B mesons: what’s special about them?

• Many interesting processes with clean theoretical interpretations: – Top quark loops not too strongly suppressed – Large CP violating effects possible, some with clean interpretation

– Some of the hadronic physics understood model independently( mb ΛQCD)

• Experimentally feasible to study: – Υ(4S) resonance is clean source of B mesons – Long B meson lifetime

(If |Vcb| were as large as |Vus|, no B factories built, these lectures would not take place, etc.) – Timescale of oscillation and decay comparable: ∆m/Γ ' 0.77 (and ∆Γ Γ)

Z L – p.1/27  a   a   CP violation    a a CPV in interference between decay and mixing

• Can get theoretically clean information in some 0 A B fCP cases when B0 and B0 decay to same ﬁnal state q/p 0 0 0 A Mass eigenstates: |BH,Li = p|B i ∓ q|B i B

• Time-dependent CP asymmetry: 0 0 Γ[B (t) → fCP ] − Γ[B (t) → fCP ] afCP = 0 0 Γ[B (t) → fCP ] + Γ[B (t) → fCP ]

• If amplitudes with one weak phase dominate, hadronic physics drops out:

afCP = (±1) sin(phase difference between decay paths) sin(∆m t) arg[(q/p)(A/A)]

• Measure phases in the Lagrangian with small theoretical uncertainties

Z L – p.1/28 Quantum entanglement — use EPR

• B0B0 pair created in a p-wave (L = 1) evolve coherently and undergo oscillations

Two identical bosons must be in a symmetric state — if one decays as a B0 (B0), then at the same time the other B must be B0 (B0)

• EPR effect used for precision physics:

Measure B decays and ∆z

• First decay ends quantum correlation and determines ﬂavor of other B at t = t1

Z L – p.1/29 Hadron colliders — no quantum correlation

0 • Bs with sufﬁcient boost to study CPV at Tevatron & LHC (+ Belle data on rates)

¯ 0 • gg, qq¯ → bb: measure ﬂavor of a b hadron, and ﬂavor of Bs as a function of time 0 Need excellent time resolution, and fully reconstructed Bs to know its boost

Z L – p.1/30 CP violation in B → ψKS by the naked eye

• CP violation is an O(1) effect: sin 2β = 0.698 ± 0.017

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Γ[B0(t) → ψK] − Γ[B0(t) → ψK] af = = sin2 β sin(∆m t) CP Γ[B0(t) → ψK] + Γ[B0(t) → ψK] • CP violation in K decays is small because of small CKM elements, not because CP violation is generically small — it is O(1) in some B decays

Z L – p.1/31 a   a   CP violation    a  a The B-factories money plot

1.5 excluded at CL > 0.95 • Spectacular progress in last 20 years excluded area has CL > 0.95 γ The CKM mechanism dominates CP 1.0 • ∆md & ∆ms violation & ﬂavor changing processes sin 2β 0.5 ∆md • The implications of the consistency of εK α γ β

η 0.0 measurements are often overstated α

Vub α • Larger allowed region if there is NP •0.5

•1.0 γ εK CKM f i t t e r sol. w/ cos 2β < 0 Summer 19 (excl. at CL > 0.95) •1.5 •1.0 •0.5 0.0 0.5 1.0 1.5 2.0 ρ

Z L – p.1/32 The B-factories money plot

0.7 ∆m & ∆m CKM • Spectacular progress in last 20 years γ d s f i t t e r 0.6 ε ∆md K Summer 19

0.5 sin 2β sol. w/ cos 2β < 0 • The CKM mechanism dominates CP (excl. at CL > 0.95) 0.4 excluded area has CL > 0.95 > areaexcludedhas CL η violation & ﬂavor changing processes 0.3 α α 0.2 V • The implications of the consistency of ub 0.1 γ β α measurements are often overstated 0.0 0.7•0.4 •0.2 0.0 0.2 0.4 0.6 0.8 1.0 ρ CKM f i t t e r 0.6 γ(α) • Larger allowed region if there is NP Summer 19 0.5 Compare tree-level (lower plot) and 0.4 excluded area has CL > 0.95 > areaexcludedhas CL

• η 0.3 loop-dominated measurements α 0.2

Vub 0.1 • LHCb: constraints in the Bs sector γ β 0.0 •0.4 •0.2 0.0 0.2 0.4 0.6 0.8 1.0 (2nd–3rd gen.) caught up with Bd ρ • O(20%) NP contributions to most loop-level processes (FCNC) are still allowed

Z L – p.1/32

Testing quark ﬂavor — take II

• Assume that NP is negligible in tree-level processes, arbitrary in FCNCs (loops)

• Consider tree-level + meson mixing:

General parametrization of many models by two real parameters (in addition to SM):

CSM CNP 2iσ 0 0 0 0 SM: NP: he =ANP(B →B )/ASM(B →B ) 2 2 mW Λ

What is the scale Λ? How different is the CNP coupling from CSM?

• Is h = O(1) allowed? If not, the CKM mechanism dominates

To answer, redo CKM ﬁt: tree-dominated unchanged, loop-mediated modiﬁed

(Importance of these constraints known since the 70s, conservative picture of future progress)

Z L – p.1/33 NP in B mixing: improvements this decade

• At 95% CL: NP ∼< (0.25 × SM) ⇒ NP ∼< (0.08 × SM)

Nowp•value LHCb 50/fb + Belle II 50/p•valueab 0.20 0.30 excluded area has CL > 0.95 CKM excluded area has CL > 0.95 CKM f i t t e r f i t t e r Summer 19 Prospects NP 2 2 0.25 |Cij| 4.5 TeV 0.15 Scale: h ' • ∗ 2 0.20 |Vti Vtj| Λ s 0.10 s 0.15 h h ( 3 2.3 × 10 TeV 0.10 ⇒ Λ ∼ 20 TeV (tree + CKM) 0.05 0.05 2 TeV (loop + CKM) 0.00 0.00 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.00 0.05 0.10 0.15 0.20 0.25 0.30

hd hd Similar to LHC mg˜ reach (q) SM 2iσq [color: 2σ, dotted: 3σ] M12 = M12 (1+hqe ) [2006.04824] • BSM sensitivity would continue to increase until much larger data sets (LHCb will collect 300/fb after second upgrade in LS4, initial plans for a possible Belle II upgrade)

• Complementary to high-pT searches

Z L – p.1/34 Summary (1)

• FCNC and CP violation measurements probe scales 1 TeV

• CP violation beyond SM must exist; KM phase is the dominant contribution so far

• New physics in most FCNC processes can still be ∼> 20% of the SM • CP violation is O(1), just screened by small mixing angles in K and D decays

• Data sets and sensitivities will improve by orders of magnitude

• Interesting theory and experimental challenges

Z L – p.1/35