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CP Violation in Neutrino Factories: Mass Hierarchy Searches

Explore CP violation in neutrinos, mass hierarchy searches, and beta beams. Discover the experiments, optimization, and precision measurements involved in CPV phenomenology. Learn about the connection to measurement and the importance of leptogenesis. Dive into the challenges and strategies for measuring CPV and discover the latest developments in neutrino research.

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CP Violation in Neutrino Factories: Mass Hierarchy Searches

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  1. CP violation and mass hierarchy searches with Neutrino Factories and Beta Beams NuGoa – Aspects of Neutrinos Goa, India April 10, 2009Walter Winter Universität Würzburg TexPoint fonts used in EMF: AAAAAAAA

  2. Contents • Motivation from theory: CPV • CPV Phenomenology • The experiments • Optimization for CPV • CP precision measurement • CPV from non-standard physics • Mass hierarchy measurement • Summary

  3. Motivation from theory

  4. Where does CPV enter? • Example: Type I seesaw (heavy SM singlets Nc) Could also be type-II, III seesaw,radiative generation of neutrino mass, etc. Block-diag. Primary source of CPV(depends BSM theory) Charged leptonmass terms Eff. neutrinomass terms Effective source of CPV(only sectorial origin relevant) Observable CPV(completely model-indep.) CC

  5. Connection to measurement • From the measurement point of view:It makes sense to discuss only observable CPV(because anything else is model-dependent!) • At high E (type I-seesaw): 9 (MR)+18 (MD)+18 (Ml) = 45 parameters • At low E: 6 (masses) + 3 (mixing angles) + 3 (phases) = 12 parameters LBL accessible CPV: dIf  UPMNS real CP conserved CPV in 0nbb decay Extremely difficult! (Pascoli, Petcov, Rodejohann, hep-ph/0209059) There is no specific connectionbetween low- and high-E CPV! But: that‘s not true for special (restrictive) assumptions!

  6. Why is CPV interesting? • Leptogenesis:CPV from Ncdecays • If special assumptions(such as hier. MR,NH light neutrinos, …)it is possible that dCPis the only source ofCPV for leptogensis! (Nc)i (Nc)i ~ MD(in basis where Ml and MR diagonal) Different curves:different assumptions for q13, … (Pascoli, Petcov, Riotto, hep-ph/0611338)

  7. How well do we need to measure? • We need generic argumentsExample: Parameter space scan for eff. 3x3 case (QLC-type assumptions, arbitrary phases, arbitrary Ml)The QLC-type assumptions lead to deviations O(qC) ~ 13 • Can also be seen in sum rules for certain assumptions, such as(F: model parameter) • This talk: Want Cabibbo-angle order precision for dCP! (arXiv:0709.2163) (Niehage, Winter, arXiv:0804.1546)

  8. CPV phenomenology

  9. Terminology • Any value of dCP(except for 0 and p)violates CP • Sensitivity to CPV:Exclude CP-conservingsolutions 0 and pfor any choiceof the other oscillationparameters in their allowed ranges

  10. Measurement of CPV • Antineutrinos: • Magic baseline: • Silver: • Platinum, Superb.: (Cervera et al. 2000; Freund, Huber, Lindner, 2000; Huber, Winter, 2003; Akhmedov et al, 2004)

  11. Degeneracies Iso-probability curves • CP asymmetry(vacuum) suggests the use of neutrinos and antineutrinos • One discrete deg.remains in (q13,d)-plane(Burguet-Castell et al, 2001) • Additional degeneracies: (Barger, Marfatia, Whisnant, 2001) • Sign-degeneracy (Minakata, Nunokawa, 2001) • Octant degeneracy (Fogli, Lisi, 1996) Neutrinos Antineutrinos Best-fit

  12. Intrinsic vs. extrinsic CPV • The dilemma: Strong matter effects (high E, long L), but Earth matter violates CP • Intrinsic CPV (dCP) has to be disentangled from extrinsicCPV (from matter effects) • Example: p-transitFake sign-solutioncrosses CP conservingsolution • Typical ways out: • T-inverted channel?(e.g. beta beam+superbeam,platinum channel at NF, NF+SB) • Second (magic) baseline Critical range True dCP (violates CP maximally) NuFact, L=3000 km Degeneracy above 2s(excluded) Fit True (Huber, Lindner, Winter, hep-ph/0204352)

  13. The magic baseline

  14. CPV discovery reach … in (true) sin22q13 and dCP Best performanceclose to max. CPV (dCP = p/2 or 3p/2) Sensitive region as a function of trueq13 anddCP dCP values now stacked for each q13 No CPV discovery ifdCP too close to 0 or p No CPV discovery forall values of dCP 3s ~ Cabibbo-angleprecision at 2sBENCHMARK! Read: If sin22q13=10-3, we expect a discovery for 80% of all values of dCP

  15. The experiments

  16. Beta beam concept… originally proposed for CERN (CERN layout; Bouchez, Lindroos, Mezzetto, 2003; Lindroos, 2003; Mezzetto, 2003; Autin et al, 2003) (Zucchelli, 2002) • Key figures (any beta beam): g, useful ion decays/year? • Often used “standard values”:3 10186He decays/year1 101818Ne decays/year • Typical g ~ 100 – 150 (for CERN SPS) g More recent modifications: • Higher g(Burguet-Castell et al, hep-ph/0312068) • Different isotope pairs leading to higher neutrino energies (same g) (http://ie.lbl.gov/toi) (C. Rubbia, et al, 2006)

  17. Current status: A variety of ideas “Classical” beta beams: • “Medium” gamma options (150 < g < ~350) • Alternative to superbeam! Possible at SPS (+ upgrades) • Usually: Water Cherenkov detector (for Ne/He) (Burguet-Castell et al, 2003+2005; Huber et al, 2005; Donini, Fernandez-Martinez, 2006; Coloma et al, 2007; Winter, 2008) • “High” gamma options (g >> 350) • Require large accelerator (Tevatron or LHC-size) • Water Cherenkov detector or TASD or MID? (dep. on g, isotopes) (Burguet-Castell et al, 2003; Huber et al, 2005; Agarwalla et al, 2005, 2006, 2007, 2008, 2008; Donini et al, 2006; Meloni et al, 2008) • Hybrids: • Beta beam + superbeam(CERN-Frejus; Fermilab: see Jansson et al, 2007) • “Isotope cocktail” beta beams (alternating ions)(Donini, Fernandez-Martinez, 2006) • Classical beta beam + Electron capture beam(Bernabeu et al, 2009) • … • The CPV performance depends very much on the choice from this list! Often: baseline Europe-India

  18. Neutrino factory:International design study (Geer, 1997; de Rujula, Gavela, Hernandez, 1998; Cervera et al, 2000) IDS-NF: • Initiative from ~ 2007-2012 to present a design report, schedule, cost estimate, risk assessment for a neutrino factory • In Europe: Close connection to „Euronus“ proposal within the FP 07 • In the US: „Muon collider task force“ Signal prop. sin22q13 Contamination Muons decay in straight sections of a storage ring ISS

  19. IDS-NF baseline setup 1.0 • Two decay rings • Em=25 GeV • 5x1020 useful muon decays per baseline(both polarities!) • Two baselines:~4000 + 7500 km • Two MIND, 50kt each • Currently: MECC at shorter baseline (https://www.ids-nf.org/)

  20. NF physics potential • Excellent q13, MH, CPV discovery reaches (IDS-NF, 2007) • Robust optimum for ~ 4000 + 7500 km • Optimization even robust under non-standard physics(dashed curves) (Kopp, Ota, Winter, arXiv:0804.2261; see also: Gandhi, Winter, 2007)

  21. Optimization for CPV

  22. Optimization for CPV • Small q13:Optimize discovery reach in q13 direction • Large q13:Optimize discovery reach in (true) dCPdirection~ Precision! • What defines “small” vs “large q13”? A Double Chooz, Day Bay, T2K, … discovery? Optimization for large q13 Optimization for small q13

  23. Large q13 strategy • Assume e.g. that Double Chooz discovers q13 • Minimum wish listeasy to define: • 5s independent confirmation of q13 > 0 • 3s mass hierarchy determination for any (true) dCP • 3s CP violation determination for 80% (true) dCP(~ 2s sensitvity to a Cabibbo angle-size CP violation) For any (true) q13 in 90% CL D-Chooz allowed range! • What is the minimal effort for that? • NB: Such a minimum wish list is non-trivial for small q13 (arXiv:0804.4000; Sim. from hep-ph/0601266; 1.5 yr far det. + 1.5 yr both det.)

  24. Example: Minimal beta beam (arXiv:0804.4000) • Minimal effort = • One baseline only • Minimal g • Minimal luminosity • Any L (green-field!) • Example: Optimize L-g for fixed Lumi: • CPV constrains minimal g • g as large as 350 may not even be necessary!(see hep-ph/0503021) • CERN-SPS good enough? Sensitivity for entire Double Chooz allowed range! 5yr x 1.1 1018 Ne and 5yr x 2.9 1018 He useful decays

  25. Small q13 strategyExample: Beta beams • Assume that Double Chooz … do not find q13 • Example: Beta beam in q13-direction (for max. CPV) • „Minimal effort“ is a matter of cost! LSF ~ 2 50 kt MIDL=400 km (LSF) (Huber et al, hep-ph/0506237) (Agarwalla et al, arXiv:0802.3621)

  26. Experiment comparison • The sensitivities are expected to lie somewhere between the limiting curves • Example: IDS-NF baseline(~ dashed curve) (ISS physics WG report, arXiv:0810.4947, Fig. 105)

  27. CP precision measurement

  28. Why is that interesting? • Theoretical exampleLarge mixingsfrom CL and n sectors?Example: q23l = q12n = p/4, perturbations from CL sector(can be connected with textures)(Niehage, Winter, arXiv:0804.1546; see also Masina, 2005; Antusch, King 2005 for similar sum rules) • The value of dCP is interesting (even if there is no CPV) • Phenomenological exampleStaging scenarios: Build one baseline first, and then decide depending on the outcome • Is dCP in the „good“ (0 < dCP < p) or „evil“ (p < dCP < 2p) range?(signal for neutrinos ~ +sin dCP) dCPandoctantdiscriminatethese examples!

  29. Performance indicator: CP coverage • Problem: dCP is a phase (cyclic) • Define CP coverage (CPC):Allowed range for dCP which fits a chosen true value • Depends on true q13 and true dCP • Range:0 < CPC <= 360 • Small CPC limit:Precision of dCP • Large CPC limit:360 - CPCis excluded range

  30. CP pattern • Performance as a function of dCP (true) • Example: Staging.If 3000-4000 km baseline operates first, one can use this information to determine if a second baseline is needed Precision limit Exclusion limit (Huber, Lindner, Winter, hep-ph/0412199)

  31. CPV from non-standard physics?

  32. CPV from non-standard interactions • Example: non-standard interactions (NSI) in matter from effective four-fermion interactions: • Discovery potential for NSI-CPV in neutrino propagation at the NFEven if there is no CPV instandard oscillations, we mayfind CPV!But what are the requirements for a model to predict such large NSI? ~ current bound IDS-NF baseline 1.0 (arXiv:0808.3583) 3s

  33. CPV discovery for large NSI • If both q13 and |eetm| large, the change to discover any CPV will be even larger: For > 95% of arbitrary choices of the phases • NB: NSI-CPV can also affect the production/detection of neutrinos, e.g. in MUV(Gonzalez-Garcia et al, hep-ph/0105159; Fernandez-Martinez et al, hep-ph/0703098; Altarelli, Meloni, 0809.1041; Antusch et al, 0903.3986) IDS-NF baseline 1.0 (arXiv:0808.3583)

  34. Models for large NSI? • Effective operator picture:Describes additions to the SM in a gauge-inv. way! • Example: NSI for TeV-scale new physicsd=6: ~ (100 GeV/1 TeV)2 ~ 10-2 compared to the SMd=8: ~ (100 GeV/1 TeV)4 ~ 10-4 compared to the SM • Current bounds, such as from CLFV: difficult to construct large (= observable) leptonic matter NSI with d=6 operators (except for ettm, maybe)(Bergmann, Grossman, Pierce, hep-ph/9909390; Antusch, Baumann, Fernandez-Martinez, arXiv:0807.1003; Gavela, Hernandez, Ota, Winter,arXiv:0809.3451) • Need d=8 effective operators! • Finding a model with large NSI is not trivial! n mass d=6, 8, 10, ...: NSI

  35. Systematic analysis for d=8 Feynman diagrams Basis (Berezhiani, Rossi, 2001) • Decompose all d=8 leptonic operators systematically • The bounds on individual operators from non-unitarity, EWPD, lepton universality are very strong! (Antusch, Baumann, Fernandez-Martinez, arXiv:0807.1003) • Need at least two mediator fields plus a number of cancellation conditions(Gavela, Hernandez, Ota, Winter, arXiv:0809.3451) Avoid CLFVat d=8:C1LEH=C3LEH Combinedifferentbasis elements C1LEH, C3LEH Canceld=8CLFV But these mediators cause d=6 effects Additional cancellation condition(Buchmüller/Wyler – basis)

  36. Mass hierarchy (MH)

  37. Motivation • Specific models typically come together with specific MH prediction (e.g. textures are very different) • Good model discriminator (Albright, Chen, hep-h/0608137) 8 8 Normal Inverted

  38. Matter effects • Magic baseline: • Removes all degeneracy issues (and is long!) • Resonance: 1-A  0 (NH: n, IH: anti-n)Damping: sign(A)=-1 (NH: anti-n, IH: n) • Energy close to resonance energy helps (~ 8 GeV) • To first approximation: Pem ~ L2 (e.g. at resonance) • Baseline length helps (compensates 1/L2 flux drop) (Cervera et al. 2000; Freund, Huber, Lindner, 2000; Huber, Winter, 2003; Akhmedov et al, 2004)

  39. Baseline dependence Event rates (A.U.) • Comparison matter (solid) and vacuum (dashed) • Matter effects (hierarchy dependent) increasewith L • Event rate (n, NH) hardly drops with L • Go to long L! (Dm212  0) NH matter effect Vacuum, NH or IH NH matter effect (Freund, Lindner, Petcov, Romanino, 1999)

  40. Mass hierarchy sensitivity • For a given set of true q13 and dCP: Find the sgn-deg.solution • Repeat that for all true true q13 and dCP (for this plot)

  41. Small q13 optimization: NF Em-L (single baseline) L1-L2 (two baselines) • Magic baseline good choice for MH • Em ~ 15 GeV sufficient (peaks at 8 GeV) (Kopp, Ota, Winter, 2008) (Huber, Lindner, Rolinec, Winter, 2006)

  42. Small q13 optimization: BB (Agarwalla, Choubey, Raychaudhuri, Winter, 2008) • Only B-Li offers high enough energies for „moderately high“ g • Magic baseline global optimum if g>=350 (B-Li) • Recently two-baseline setups discussed(Coloma, Donini, Fernandez-Martinez, Lopez-Pavon, 2007; Agarwalla, Choubey, Raychaudhuri, 2008)

  43. Optimization for large q13 (arXiv:0804.4000) • Performance as defined before (incl. 3s MH) • L > 500 km necessary • Large enough luminosity needed • High enough g necessary • Ne-He: limited to g > 120 • B-Li: in principle, smaller g possible • High g = high E = stronger matter effects!

  44. Physics case for CERN-India?(neutrino factory) • MH measurement if q13 small (see before; also de Gouvea, Winter, 2006) • Degeneracy resolution for 10-4≤ sin22q13≤ 10-2(Huber, Winter, 2003) • Risk minimization (e.g., q13 precision measurement) (Gandhi, Winter, 2007) • Compementary measurement(e.g. in presence of NSI)(Ribeiro et al, 2007) • MSW effect verification (even for q13=0) (Winter, 2005) • Fancy stuff (e.g. matter density measurement) (Gandhi, Winter, 2007)

  45. Summary • The Dirac phase dCP is probably the only realistically observable CP phase in the lepton sector • Maybe the only observable CPV evidence for leptogenesis • This and f1, f2: the only completely model-inpendent parameterization of CPV • What precision do we want for it? Cabibbo-angle precision?  Relates to fraction of „dCP“ ~ 80-85% • For a BB or NF, the experiment optimization/choice depends on q13 large or small • Other interesting aspects in connection with CPV: CP precision measurement, NSI-CPV • MH for small q13 requires magic baseline

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