* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Overview of Neutrino Physics Issues and Opportunities Andr´ e de Gouvˆ
Peter Kalmus wikipedia , lookup
Search for the Higgs boson wikipedia , lookup
Large Hadron Collider wikipedia , lookup
Compact Muon Solenoid wikipedia , lookup
Symmetry in quantum mechanics wikipedia , lookup
ATLAS experiment wikipedia , lookup
Renormalization wikipedia , lookup
Theory of everything wikipedia , lookup
History of quantum field theory wikipedia , lookup
Supersymmetry wikipedia , lookup
Quantum chromodynamics wikipedia , lookup
Higgs mechanism wikipedia , lookup
Scalar field theory wikipedia , lookup
Renormalization group wikipedia , lookup
An Exceptionally Simple Theory of Everything wikipedia , lookup
Elementary particle wikipedia , lookup
Future Circular Collider wikipedia , lookup
Minimal Supersymmetric Standard Model wikipedia , lookup
Bruno Pontecorvo wikipedia , lookup
Weakly-interacting massive particles wikipedia , lookup
Technicolor (physics) wikipedia , lookup
Standard Model wikipedia , lookup
Super-Kamiokande wikipedia , lookup
Grand Unified Theory wikipedia , lookup
Faster-than-light neutrino anomaly wikipedia , lookup
Mathematical formulation of the Standard Model wikipedia , lookup
André de Gouvêa Northwestern Overview of Neutrino Physics Issues and Opportunities André de Gouvêa Northwestern University The 9th ICFA Seminar SLAC National Accelerator Laboratory, October 28–31, 2008 October 28, 2008 ν Overview André de Gouvêa Northwestern Outline 1. What We Have Learned About Neutrinos; 2. What We Know We Don’t Know; 3. What We Are Trying to Understand; 4. Where Do We Go From Here? Conclusions. October 28, 2008 ν Overview André de Gouvêa Northwestern (By Now Old) News from ν Flavor Oscillations Neutrino oscillation experiments have revealed that neutrinos change flavor after propagating a finite distance. The rate of change depends on the neutrino energy Eν and the baseline L. • νµ → ντ and ν̄µ → ν̄τ — atmospheric experiments [“indisputable”]; • νe → νµ,τ — solar experiments [“indisputable”]; • ν̄e → ν̄other — reactor neutrinos [“indisputable”]; • νµ → νother from accelerator experiments [“indisputable”]. The simplest and only satisfactory explanation of all this data is that neutrinos have distinct masses, and mix. October 28, 2008 ν Overview André de Gouvêa Northwestern [Gonzalez-Garcia, PASI 2006] October 28, 2008 ν Overview André de Gouvêa Northwestern October 28, 2008 ν Overview André de Gouvêa Northwestern [Gonzalez-Garcia, PASI 2006] October 28, 2008 ν Overview André de Gouvêa Northwestern Previous fits shown assuming two-flavor mixing. Of course, there are three neutrinos. . . Phenomenological Understanding of Neutrino Masses & Mixing νe Ue1 νµ = Uµ1 ντ Uτ 1 Ue2 Ue3 Uµ2 Uµ3 Ueτ 2 Uτ 3 ν1 ν2 ν3 Definition of neutrino mass eigenstates (who are ν1 , ν2 , ν3 ?): ∆m213 < 0 – Inverted Mass Hierarchy • m21 < m22 ∆m213 > 0 – Normal Mass Hierarchy • m22 − m21 |m23 − m21,2 | tan θ12 ≡ 2 October 28, 2008 |Ue2 |2 |Ue1 |2 ; tan θ23 ≡ 2 |Uµ3 |2 |Uτ 3 |2 ; Ue3 ≡ sin θ13 e−iδ ν Overview André de Gouvêa Putting It All Together: Northwestern [absent: new MINOS results] [Gonzalez-Garcia, PASI 2006] October 28, 2008 ν Overview André de Gouvêa Northwestern (including new MINOS result – better ∆m213 measurement) [from Gonzalez-Garcia, Maltoni] October 28, 2008 ν Overview André de Gouvêa Northwestern What We Know We Don’t Know (1): Missing Oscillation Parameters 2 2 (m3) (m2) (m1)2 (∆m2)sol • Is CP-invariance violated in neutrino oscillations? (δ 6= 0, π?) νe 2 (∆m )atm νµ (∆m2)atm 2 normal hierarchy (m2)2 (m1)2 • Is ν3 mostly νµ or ντ ? (θ23 > π/4, θ23 < π/4, or θ23 = π/4?) • What is the neutrino mass hierarchy? (∆m213 > 0?) ντ (∆m )sol • What is the νe component of ν3 ? (θ13 6= 0?) ⇒ All of the above can “only” be (m3)2 addressed with neutrino oscillation inverted hierarchy experiments. Ultimate goal not just to measure parameters → test formalism (over-constrain parameters?) October 28, 2008 ν Overview André de Gouvêa Northwestern The “Holy Graill” of Neutrino Oscillations – CP Violation In the old Standard Model, there is only onea source of CP-invariance violation: ⇒ The complex phase in VCKM , the quark mixing matrix. Indeed, as far as we have been able to test, all CP-invariance violating phenomena agree with the CKM paradigm: • K ; • 0K ; • sin 2β; • etc. Neutrino masses and lepton mixing provide strong reason to believe that other sources of CP-invariance violation exist. a modulo October 28, 2008 the QCD θ-parameter, which will be “willed away” as usual. ν Overview André de Gouvêa Northwestern CP-invariance Violation in Neutrino Oscillations The most promising approach to studying CP-violation in the leptonic sector seems to be to compare P (νµ → νe ) versus P (ν̄µ → ν̄e ). where ∆1i = Aµe = ∗ Ue2 Uµ2 e ∆m21i L 2E , i = 2, 3. i∆12 ∗ i∆13 − 1 + Ue3 Uµ3 e −1 The amplitude for the CP-conjugate process is Āµe = ∗ Ue2 Uµ2 e i∆12 ∗ i∆13 − 1 + Ue3 Uµ3 e −1 . ∗ ∗ ∗ [remember: according to unitarty, Ue1 Uµ1 = −Ue2 Uµ2 − Ue3 Uµ3 ] October 28, 2008 ν Overview André de Gouvêa Northwestern In general, |A|2 6= |Ā|2 (CP-invariance violated) as long as: ∗ • Nontrivial “Weak” Phases: arg(Uei Uµi ) → δ 6= 0, π; • Nontrivial “Strong” Phases: ∆12 , ∆13 → L 6= 0; • Because of Unitarity, we need all |Uαi | = 6 0 → three generations. All of these can be satisfied, with a little luck: given that two of the three mixing angles are known to be large, we need |Ue3 | = 6 0. The goal of next-generation neutrino experiments is to determine the magnitude of |Ue3 |. We need to know this in order to understand how to study CP-invariance violation in neutrino oscillations! [talks by Y. Wang, M. Messier, E. Kearns] October 28, 2008 ν Overview André de Gouvêa Northwestern In the real world, life is much more complicated. The lack of knowledge concerning the mass hierarchy, θ13 , and θ23 , for example, leads to several degeneracies and ambiguities. Note that, in order to see CP-invariance violation, we need the “subleading” terms (and need to make sure that the leading atmospheric terms do not average out)! In order to ultimately measure a new source of CP-invariance violation, we will need to combine different measurements: – oscillation of muon neutrinos and antineutrinos, – oscillations at accelerator and reactor experiments, – experiments with different baselines (or broad energy spectrum), – etc. [talk by Y. Wang, M. Messier, E. Kearns] October 28, 2008 ν Overview André de Gouvêa Northwestern What We Know We Don’t Know (2): How Light is the Lightest Neutrino? (m3)2 (m2)2 2 So far, we’ve only been able to measure 2 (∆m )sol (m1) The lightest neutrino mass is only poorly νe (∆m2)atm neutrino mass-squared differences. νµ (∆m2)atm ντ constrained: m2lightest < 1 eV2 qualitatively different scenarios allowed: • m2lightest ≡ 0; (m2)2 —————— ↑ (∆m2)sol (m1)2 (m3)2 normal hierarchy • m2lightest ∆m212,13 . inverted hierarchy m2lightest = ? m2 = 0 • m2lightest ∆m212,13 ; ↓ —————— October 28, 2008 Need information outside of neutrino oscillations: β-decay, cosmology, neutrinoless double β-decay ν Overview André de Gouvêa Northwestern What We Know We Don’t Know (3) – Are Neutrinos Majorana Fermions? A massive charged fermion (s=1/2) is described by 4 degrees of freedom: + (e− L ← CPT → eR ) νL l Lorentz + (e− R ← CPT → eL ) you A massive neutral fermion (s=1/2) is described by 4 or 2 degrees of freedom: (νL ← CPT → ν̄R ) __ νR? νL? l Lorentz “DIRAC” (νR ← CPT → ν̄L ) you (νL ← CPT → ν̄R ) How many degrees of freedom are required to describe massive neutrinos? October 28, 2008 “MAJORANA” l Lorentz (ν̄R ← CPT → νL ) ν Overview André de Gouvêa Northwestern Why Don’t We Know the Answer? If neutrino masses were indeed zero, this is a nonquestion: there is no distinction between a massless Dirac and Majorana fermion. Processes that are proportional to the Majorana nature of the neutrino vanish in the limit mν → 0. Since neutrinos masses are very small, the probability for these to happen is very, very small: A ∝ mν /E. The “smoking gun” signature is the observation of LEPTON NUMBER violation. This is easy to understand: Majorana neutrinos are their own antiparticles and, therefore, cannot carry “any” quantum numbers — including lepton number. October 28, 2008 ν Overview André de Gouvêa Northwestern Search for the Violation of Lepton Number (or B − L) Best Bet: search for Neutrinoless Double-Beta × Decay: Z → (Z + 2)e− e− 1 disfavoured by 0ν2β ←(next) Helicity Suppressed Amplitude ∝ ∆m223 < 0 10− 2 ←(next-next) ∆m223 > 0 10− 3 90% CL (1 dof) −4 10 10− 4 10− 3 10− 2 10− 1 lightest neutrino mass in eV October 28, 2008 disfavoured by cosmology | mee | in eV 10− 1 Observable: mee ≡ P i mee E 2 Uei mi Are other probes competitive? 1 [see talk by G. Gratta] ν Overview mass (eV) André de Gouvêa 10 12 10 11 10 10 Northwestern TeV t τ b 10 9 10 8 µ s 10 7 10 6 10 5 10 4 10 3 10 2 c d What We Are Trying To Understand: GeV ⇐ NEUTRINOS HAVE TINY MASSES u MeV e keV ⇓ LEPTON MIXING IS “WEIRD” ⇓ 10 10 -1 -2 ν2 10 -3 10 10 eV 1 ν3 meV ν1 -4 VM N S ∼ 0.8 0.5 0.2 0.4 0.6 0.7 0.4 0.6 0.7 VCKM 1 ∼ 0.2 0.001 0.2 1 0.01 0.01 0.001 1 -5 10 0 1 October 28, 2008 2 3 4 generation What Does It Mean? ν Overview André de Gouvêa Northwestern Who Cares About Neutrino Masses: Only∗ “Palpable” Evidence of Physics Beyond the Standard Model The SM we all learned in school predicts that neutrinos are strictly massless. Massive neutrinos imply that the the SM is incomplete and needs to be replaced/modified. Furthermore, the SM has to be replaced by something qualitatively different. —————— ∗ There is only a handful of questions our model for fundamental physics cannot explain properly. These are, in order of “palpability” (my opinion): • What is the physics behind electroweak symmetry breaking? (Higgs or not in SM). • What is the dark matter? (not in SM). • Why does the Universe appear to be accelerating? Why does it appear that the Universe underwent rapid acceleration in the past? (not in SM – is this “particle physics?”). October 28, 2008 ν Overview André de Gouvêa Northwestern What is the New Standard Model? [νSM] The short answer is – WE DON’T KNOW. Not enough available info! m Equivalently, there are several completely different ways of addressing neutrino masses. The key issue is to understand what else the νSM candidates can do. [are they falsifiable?, are they “simple”?, do they address other outstanding problems in physics?, etc] We need more experimental input, and it looks like it may be coming in the near/intermediate future! October 28, 2008 ν Overview André de Gouvêa Northwestern Options include: • modify SM Higgs sector (e.g. Higgs triplet) and/or • modify SM particle content (e.g. SU (2)L Triplet or Singlet) and/or • modify SM gauge structure and/or • supersymmetrize the SM and add R-parity violation and/or • augment the number of space-time dimensions and/or • etc Important: different options → different phenomenological consequences October 28, 2008 ν Overview André de Gouvêa Northwestern [Albright and Chen, hep-ph/0608137] Flavor Theories Bottom Line– “We can’t compute what |Ue3 | is – must measure it!” (same goes for the mass hierarchy, δ) October 28, 2008 ν Overview André de Gouvêa Northwestern Comments On Current Flavor Model-Building Scene: • VERY active research area. Opportunity to make bona fide prediction regarding parameters that haven’t been measured yet but will be measured for sure in the near future → θ13 , δ, mass hierarchy, etc; • For flavor symmetries, more important than determining the values of the parameters is the prospect of establishing non-trivial relationships among several interesting unkowns; e.g., sin2 θ13 ∼ ∆m212 /|∆m213 | if hierarchy is normal, sin2 θ13 ∼ (∆m212 /|∆m213 |)2 if hierachy is inverted is common “prediction” of many flavor models (often also related to cos 2θ23 ). October 28, 2008 ν Overview André de Gouvêa Northwestern How Do We Learn More? In order to learn more, we need more information. Any new data and/or idea is welcome, including • searches for lepton number violation (neutrinoless double beta decay, etc); • precision measurements of the neutrino oscillation parameters; • searches for charged lepton flavor violation (µ → eγ, etc); • searches for fermion electric/magnetic dipole moments (electron edm, muon g − 2, etc); • searches for new physics at the TeV scale – we need to understand the physics at the TeV scale before we can really understand the physics behind neutrino masses (is there low-energy SUSY?, etc). October 28, 2008 ν Overview André de Gouvêa Northwestern mass (eV) Only Palpable Evidence of Physics Beyond the Standard Model! 10 12 10 11 10 10 TeV NEUTRINOS HAVE MASS t τ b 10 9 10 8 µ s 10 7 10 6 10 5 10 4 10 3 10 2 c d GeV – are neutrinos their own antiparticles? u MeV e keV – we may run into more surprises! Discovery → intriguing theoretical questions: eV 1 -1 -2 -3 10 meV ν1 -4 0 – lepton mixing 6= quark mixing: why? – how do neutrinos acquire mass? Too many choices! -5 10 – neutrino masses charged fermion masses: why? ν3 ν2 10 10 – how light is the lightest neutrino? – is the three neutrino + mixing paradigm complete? 10 10 Discovery → well-defined experimental questions: 1 October 28, 2008 2 3 4 fermion – how do we learn more about this new physics? ν Overview André de Gouvêa Northwestern Backup Slides . . . October 28, 2008 ν Overview André de Gouvêa Northwestern What I Mean By the Standard Model The SM is a quantum field theory with the following defining characteristics: • Gauge Group (SU (3)c × SU (2)L × U (1)Y ); • Particle Content (fermions: Q, u, d, L, e, scalars: H). Once this is specified, the SM is unambiguously determined: • Most General Renormalizable Lagrangian; • Measure All Free Parameters, and You Are Done! (after several decades of hard experimental work. . . ) If you follow these rules, neutrinos have no mass. Something has to give. October 28, 2008 ν Overview André de Gouvêa Northwestern Candidate νSM SM as an effective field theory – non-renormalizable operators 1 Li HLj H LνSM ⊃ −λij 2Λ + O Λ2 + H.c. There is only one dimension five operator [Weinberg, 1979]. If Λ 1 TeV, it leads to only one observable consequence... after EWSB LνSM ⊃ mij i j 2 ν ν ; mij = v2 λij Λ . • Neutrino masses are small: Λ v → mν mf (f = e, µ, u, d, etc) • Neutrinos are Majorana fermions – Lepton number is violated! • νSM effective theory – not valid for energies above at most Λ/λ. • What is Λ? First naive guess is that M is the Planck scale – does not work. Data require Λ < 1015 GeV (anything to do with the GUT scale?). What else is this “good for”? Depends on the ultraviolet completion! October 28, 2008 ν Overview André de Gouvêa Northwestern Another νSM Why don’t we just enhance the fermion sector of the theory? One may argue that it is trivial and simpler to just add LYukawa = −yiα Li HN α + H.c., and neutrinos get a mass like all other fermions: miα = yiα v • Data requires y < 10−12 . Why so small? • Neutrinos are Dirac fermions. B − L exactly conserved. • νSM is a renormalizable theory. This proposal, however, violates the rules of the SM (as I defined them)! The operator M2N N N , allowed by all gauge symmetries, is absent. In order to explain this, we are forced to add a symmetry to the νSM. The simplest candidate is a global U (1)B−L . U (1)B−L is upgraded from accidental to fundamental (global) symmetry. October 28, 2008 ν Overview André de Gouvêa Northwestern Old Standard Model, Encore The SM is a quantum field theory with the following defining characteristics: • Gauge Group (SU (3)c × SU (2)L × U (1)Y ); • Particle Content (fermions: Q, u, d, L, e, scalars: H). Once this is specified, the SM is unambiguously determined: • Most General Renormalizable Lagrangian; • Measure All Free Parameters, and You Are Done. This model has accidental global symmetries. In particular, the anomaly free global symmetry is preserved: U (1)B−L . October 28, 2008 ν Overview André de Gouvêa Northwestern New Standard Model, Dirac Neutrinos The SM is a quantum field theory with the following defining characteristics: • Gauge Group (SU (3)c × SU (2)L × U (1)Y ); • Particle Content (fermions: Q, u, d, L, e, N , scalars: H); • Global Symmetry U (1)B−L . Once this is specified, the SM is unambiguously determined: • Most General Renormalizable Lagrangian; • Measure All Free Parameters, and You Are Done. Naively not too different, but nonetheless qualitatively different → enhanced symmetry sector! October 28, 2008 ν Overview André de Gouvêa Northwestern Hint for Non-Zero θ13 in the Current Data? G.L. Fogli et al, arXiv:0806.2649 [hep-ph] October 28, 2008 ν Overview André de Gouvêa Northwestern | | | [C. Galbiati, Nu2008] October 28, 2008 ν Overview