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Understanding Neutrino Physics: Insights and Challenges Beyond the Standard Model

Neutrinos, the least understood particles, are critical for advancing our understanding of the universe and the fundamental theory of particles and forces. This talk by Peter Dornan at MUTAC 2006 explores the implications of neutrino physics, the significance of neutrino oscillations, and their role in expanding beyond the Standard Model. Neutrinos are not massless, support the existence of lepton flavor violation, and interact weakly, prompting questions about their nature—Dirac or Majorana? The discussion emphasizes the necessity for complex experimentation and measurement to uncover the mysteries hidden within the neutrino sector.

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Understanding Neutrino Physics: Insights and Challenges Beyond the Standard Model

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  1. Neutrino Physics & the ISS Peter Dornan Imperial College London

  2. Least understood particle Beyond the Standard Model A trivial Addition? The Window on the Fundamental Theory? Ultimate theory must relate quarks & leptons Cannot do this without a full understanding of the neutrino sector Cannot do this with LHC or ILC Why do Neutrino Physics? P Dornan - MUTAC 2006

  3. Neutrinos are BSM • In the SM • Neutrinos are massless • Lepton Flavour is Conserved • Neutrino & antineutrino distinguished on the basis of helicity • Neutrino Oscillation shows • Neutrinos have mass • Lepton Flavour is not Conserved • Helicity cannot distinguish neutrinos from antineutrinos P Dornan - MUTAC 2006

  4. A Minor Extension of the SM? • Neutrinos are Dirac Particles • Right handed Neutrinos exist • With no known interactions • Or very very weak ones • Lepton Flavour is not respected • But overall lepton number is conserved • So Distinguish Neutrino and Antineutrino on the basis of Lepton Number • - whatever it is • Masses, Mixing Parameters - and CP Violation • - just yet more parameters to feed into the theory P Dornan - MUTAC 2006

  5. A Window on a Higher Theory? • now we can speculate • Neutrinos are Majorana States • Neutrino and anti neutrino are not distinct • Right handed neutrinos exist at very high masses - ~ unification scale • Mixing angles - and probably masses – could be related to those in the quark sector • More forms of CP violation in the lepton area than the MNS phase • And this will solve the matter-antimatter mystery P Dornan - MUTAC 2006

  6. Why Neutrino Physics? • These are the “Elevator” Answers • For the Ultimate Theory of Particles and Forces • For our Understanding of the Universe • But • Improving our Knowledge demands Complex & Challenging Experimentation. • The basic tool is neutrino oscillation From Hitoshi Murayama When you meet your favourite senator And want a $1B But also to explain to immigration at O’Hare why you are coming to Fermilab P Dornan - MUTAC 2006

  7. Neutrino Oscillation • Neutrinos are produced - and detected - as lepton flavour - electron, muon, tau - eigenstates • Oscillations – neutrinos produced with one flavour change to another as they pass through space • In the SM lepton flavour is conserved • - no oscillations • For oscillation must have two sets of eigenstates – flavour e-states and mass e-states P Dornan - MUTAC 2006

  8. Oscillation Parametrisation `atmospheric’ `cross/reactor’ `solar’ Oscillation defined by 3 mixing angles, q12, q13, q23 1 phase, d P Dornan - MUTAC 2006

  9. For just two state system Oscillation Probability Depends upon Mixing Angle, Mass Squared Difference, L/E More Complex for a three state system and additional complications if neutrinos pass through matter P Dornan - MUTAC 2006

  10. SSM Prediction Gallium Chlorine Oscillation Signals - n Disappearance • The early evidence Super-K Atmospheric results nm disappearance having travelled through the earth Deficits in Solar Neutrino Flux P Dornan - MUTAC 2006

  11. Super-K - L/E Analysis K2K First Long Baseline SK-I + SK+II Preliminary Data/prediction L/E (km/GeV) Appearance Signals - Atmospheric 1R-m spectrum No oscillation Number of events Oscillation 1 2 3 4 Enrec (GeV) P Dornan - MUTAC 2006

  12. SSM Prediction Appearance Signals - Solar • The SNO Result • Total Neutrino Flux as Expected • Verifies Standard Solar Model • ne Detected Flux Low • Electron Neutrinos have oscillated to mu or tau neutrinos Neutral Currents - Detects all Neutrinos Charged Current - Detects Electron Neutrinos P Dornan - MUTAC 2006

  13. Appearance Signals - Solar • Kamland Reactor Experiment P Dornan - MUTAC 2006

  14. Small - only an upper limit from the Chooz Reactor Experiment Determining just how small q13 is the next pressing problem for neutrino oscillation physics The Third Angle, q13 P Dornan - MUTAC 2006

  15. Where are we? from: Maltoni, Schwetz, Tortola, Valle (’04) Also know m2 > m1from matter effects in the sun P Dornan - MUTAC 2006

  16. How to Proceed? • What Questions remain to be answered • Many! • What must we measure? • Everything we can • What can we measure? • Quite a lot • With the right ingenuity - and investment P Dornan - MUTAC 2006

  17. Unanswered – Non Oscillation Expts • Are Neutrinos Dirac or Majorana? • Neutrinoless double-beta decay • What is the Absolute Mass? • Tritium Decay Spectrum • Neutrinoless double-beta decay • Cosmological data P Dornan - MUTAC 2006

  18. Unanswered – Oscillation Expts • Is q23 maximal? • How small is q13? • CP Violation in the lepton sector? • Mass hierarchy? • m3 < or > m2 • Is the MNS approach correct? • CPT violation? • The ultimate accuracy on the mixing angles and the mass differences • What accuracy is needed? • (LSND? Sterile neutrino(s)? ) P Dornan - MUTAC 2006

  19. Mass Hierarchy? Require matter interactions to distinguish. Long Baseline Nona > T2K Inverted Normal Leads to degeneracies in superbeam expts. Critical for Neutrinoless double beta decay P Dornan - MUTAC 2006

  20. CP Violation • Vitally important for our understanding of nature and the universe • Arises from phases which flip sign on the change particle  antiparticle • In SM Non-zero phase in the CKM quark mixing matrix • Describes observed CP violating effects • Does not explain the matter antimatter asymmetry • Standard MNS matrix has one phase, d, (like CKM) • BUT, if neutrinos are Majorana additional phases and potential for substantial CP violation P Dornan - MUTAC 2006

  21. ne Appearance in a nm Beam - SuperBeam ne Disappearance in a ne Beam - Reactor q13 and d - Leptonic CP Violation d leads to CP Violation No d term P Dornan - MUTAC 2006

  22. The Imminent Future • Two long base line experiments using a nm beam • MINOS • Numi Beam from FNAL to Soudan 735 km • Two Detectors – near and far – magnetized Fe-scintillator • Look for nm disappearance  q23, Dm223 • ne Appearance  q13 (~factor 2 better than Chooz) • OPERA • CNGS Beam from CERN to Gran Sasso 732 km • One Far Detector – Emulsion • Look for nt Appearance P Dornan - MUTAC 2006

  23. In 3 – 10 Years - q13 • Main aim is q13 - but will also improve other parameters • Two off-axis Superbeam Experiments • T2K • Nona • One or more Reactor Experiments • Double Chooz • and maybe • Braidwood, Daya Bay, Angra dos Deis …… P Dornan - MUTAC 2006

  24. Possible Reactor Experiments P Dornan - MUTAC 2006

  25. “far detector “near detector” Reactor Measurements of q13 No Dependence on d, No matter effects P Dornan - MUTAC 2006

  26. Long baseline neutrino oscillation experiment from Tokai toKamioka　（T2K） (~100xK2K) • J-PARC (50 GeV PS) • Construction: 2001~2007 • Operation: 2008~ • T2K (Approved in Dec-03) • Construction: 2004~2008 • Experiment: 2009 ~ JAERI@Tokai-mura (60km N.E. of KEK) Super-K 50kton Neutrino Beam Line Phase 1 (0.75MW + SK) • nmnx disappearance • Precise Dm2, sin22q • nmne appearance • Finite q13 ? 3GeV PS 600MeV Linac 50GeV PS (0.75MW) FD Phase 2  4MW, Mton, CPV To SK P Dornan - MUTAC 2006

  27. For 5yr running d(Dm223) < 1×10-4 eV2 d(sin22q23) ~ 0.01 90%C.L. sensitivities CHOOZ excluded Dm2(eV2) x 20 Off axis 2.5deg, 40GeV 5yr sin22q13 T2K prediction P Dornan - MUTAC 2006

  28. Nona • Upgrade of FNAL NuMi program. • Off-axis configuration, and larger proton intensity (6.5x1020 proton/year). • Very Long Baseline (810km) and sizeable matter effects • Complementary to T2K program (mass hierarchy). • <En> ~ 2.22GeV • 30Kton “fully” active detector. • Liquid scintillator. P Dornan - MUTAC 2006

  29. Nona Sensitivity similar to T2K. – improve with antineutrino run. ● Sensitivity to mass hierarchy. ● Synergies with T2K & reactor experiments: different matter effects and different degeneracies. P Dornan - MUTAC 2006

  30. The Precision Era - after T2K and Nova • Around 2012 - 2015 • We shall have good measurements of • q12, q23, Dm212, Dm223 • Probably have a measurement of q13 • Possibly know the mass hierarchy • So can now plan for the ultimate neutrino measurements • Refine all parameters • Check consistency • Measure CP Violation • This is the aim of the ISS P Dornan - MUTAC 2006

  31. CP Violation P Dornan - MUTAC 2006

  32. Neutrino source – options: • Second generation super-beam • CERN, FNAL, BNL, J-PARC II • Beta-beam • Neutrino Factory P Dornan - MUTAC 2006

  33. The International Scoping Study • International scoping study of a future Neutrino Factory and super-beam facility • Motivation • Organisation • Status • Physics Group • Accelerator Group • Detector Group • ISS: next steps P Dornan - MUTAC 2006

  34. ISS: motivation • Neutrino Factory – prior to launch of ISS • Several studies at the turn of the century • US Studies I, II, IIa • ECFA/CERN Study • NuFact-J Study established feasibility & R&D programme • MUCOOL, MICE, MERIT…. • But there have been advances since then • Also appreciation of the need for an integrated accelerator-detector-physics approach • and an international approach P Dornan - MUTAC 2006

  35. ISS: motivation • Goal: timely completion of conceptual design • Significant international effort taking several years • Requires successful bids to provide the resources • Preparation for design study • Review physics case • Critical comparison of options • Review options for accelerator complex: • Prepare concept-development and hardware-R&D roadmaps for design-study phase • Review options for neutrino-detection systems • Emphasis: identify concept-development and hardware-R&D roadmaps for design-study phase • Establish the Cost Drivers & Optimize • Physics/$ - where there are alternatives • Absolute scientific value - where only one method P Dornan - MUTAC 2006

  36. ISS: organisation P Dornan - MUTAC 2006

  37. Meetings • Plenary meetings to date: • CERN: 22 – 24 September 2005 • Attendance: 92 • Americas: 15 Asia: 12 Europe 65 • KEK: 23 – 26 January 2006 • Attendance: 67 • Americas: 11 Asia: 28 Europe 28 • Working groups: • Physics: • Workshops: Imperial: 14 – 21 November 2005 • Boston 6 – 10 March 2006 • Phone meetings • Accelerator: • Workshops: BNL: 07 – 12 December 2005 • Phone meetings • Detector: • Phone meetings • Detector/Physics parallel at Physics workshops P Dornan - MUTAC 2006

  38. Acknowledgments • This will be a very brief review of the activity in the ISS • From the meetings - very many people have contributed so - it is hard to acknowledge everyone - so I apologise for failing to mention many of the contributors • All plots and contributors can be found on the web P Dornan - MUTAC 2006

  39. Physics Group • Theory subgroup : • What is the new physics • Need to distinguish between alternative theories • Establish the case for high-precision, high-sensitivity neutrino-oscillation programme • Phenomenological subgroup • Review models of neutrino oscillations • Identify measurables that distinguish them and assess the precision required • Experimental subgroup: • Use realistic assumptions on the performance of accelerator and detector to: • Evaluate performance of the super-beam, beta-beam and Neutrino Factory alone or in combination • Make meaningful comparisons • Muon physics subgroup: • Lepton-flavour violating processes – clear synergy with neutrino oscillations – possibly the next major discovery P Dornan - MUTAC 2006

  40. Some Theoretical Ideas • Flavour symmetry: • Quarks and charged leptons do not carry the same hidden quantum numbers • All neutrinos carry the same hidden quantum numbers • Allows differences in mass hierarchies and mixing matrices to be explained through symmetry breaking • Random sampling of many such models indicates that large θ13 is favoured P Dornan - MUTAC 2006

  41. Some Theoretical Ideas • Quark-lepton complementarity • Intriguing Relations • Coincidence • fundamental • GUTs motivate relationships between the quark and lepton mixing matrices • Measurable relations • Need Precision P Dornan - MUTAC 2006

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  44. A Possible Neutrino Sum Rule P Dornan - MUTAC 2006

  45. Towards a performance comparison • A Major Goal of the ISS • Now many options • Must be reduced if there is to be a realistic design for a ‘precision era’ neutrino facility • Requires justifiable assumptions: • Accelerator: flux, energy spectrum • Detector: Ethresh, ERes (background, x-sect. uncertainty…) and optimised facility (accelerator, baseline, & detectors) Already a very substantial amount of work P Dornan - MUTAC 2006

  46. Cases under Consideration • Off axis super-beam: • T2HK taken as example • Plan to explore different options (essentially vary E and L) • Beta beam: • Low :  = 100 and L = 130 km • High flux (~1018 decays per year) and high flux (1019 dpy) • High :  = 350 and L = 700 km • High flux (~1018 decays per year) and high flux (1019 dpy) • Also Beta beam abd superbeam combination • Neutrino Factory • Performance studied as a function of: • E and L • Ethresh and ERes P Dornan - MUTAC 2006

  47. Sample - CP sensitivity v. sin22q13 Huber, Lindner, Rolinec, Winter Work in progress But highlights the importance of q13 in defining a strategy P Dornan - MUTAC 2006

  48. CPT & the MNS Theory Murayama • In the Quark sector the CP violation parameters are determined in many ways • Can we do the same in the neutrino sector? • With 3 flavours and CPT • CP violation related in • ne -> nm • nm -> nt • ne -> nt Needs tau modes P Dornan - MUTAC 2006

  49. Beta beam, super beam comparison Preliminary! Need to include better treatment of background and sys. err. Couce • High θ13: • Beta beam & super beam alone: •  sensitivity good • Poor sign(m232) sensitivity P Dornan - MUTAC 2006

  50. Neutrino Factory: optimisation • Study performance as a function of muon energy and baseline • Detector: • 100 kton, magnetised iron • Importance of threshold sensitivity • Can trade muon energy against detector threshold and resolution P Dornan - MUTAC 2006

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