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Neutrino Magnetic Moments: Status and Prospects

Neutrino Magnetic Moments: Status and Prospects. Physics Overview Astrophysics Bounds Recent Results on Direct Expe riments Future Projects Summary. Henry T. Wong Academia Sinica, Taiwan @ Neutrino 2004, Paris. Motivations. e.g.

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Neutrino Magnetic Moments: Status and Prospects

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  1. Neutrino Magnetic Moments: Status and Prospects • Physics Overview • Astrophysics Bounds • Recent Results on Direct Experiments • Future Projects • Summary Henry T. Wong Academia Sinica, Taiwan @Neutrino 2004, Paris

  2. Motivations e.g. • fundamental neutrino properties & interactions ; a channel to differentiate Dirac/Majorana neutrinos (nD/nM) • look for surprises and/or constrain parameter space with future precision oscillation data • explore new neutrino sources ; understand known ones • explore new detection channels & techniques, esp. @ low energy • explore roles of neutrinos in astrophysics

  3. Particle Physics ※(ni)L – (nj )R – g vertices described in general by: • eijand bij are the electric & magnetic dipole moments coupling ni & nj • constrained by symmetry principles, nD/nM, diagonal/transition moments (ni =/ nj ?) [ e.g. nM & i=jb=e=0 ] ※Experimental measureable “neutrino magnetic moment” depends on |nl > after oscillation distance L • Subtleties/Complications: • measureable is an effective/convoluted parameter (c.f. 0nbb) • physics information depends on exact |n> compositions at the detector

  4. Experimental Manifestations • Minimally-Extended Standard Model with nD : mn VERY small many ways to significantly enhance it (nM, WR …..) • study consequences from the change of neutrino spin states in a (astrophysical) medium • 1/T spectral shape in n-e scattering, T is electron recoil energy • Neutrino radiative decays • …………

  5. Astrophysics Bounds/Indications From: • Big Bang Nucleosynthesis degree of freedom • Stellar Cooling via • Cooling of SN1987a vianactive nsterile • Absence of solar (KamLAND-03 < 2.8x10-4) ranges of mn(astro) < 10-10 – 10-12mB Complications/Assumptions : • astrophysics modeling (e.g. Solar B-field) • Neutrino properties (e.g nD / nM ; no other anomalous interactions) • Global treatment (e.g. effects from matter, oscillations ; interference/competitions among channels ……)

  6. For completeness/historical footnote …… Magnetic Moments & Solar Neutrinos • ne produced in the Sun interact with B to become nx(xe), via spin-flavor precession(SFP), with or without resonance effects in solar medium. • used to explain anti-correlation of Cl-ndata with Sun-spot cycles in late 80’s • scenario compatible with all solar neutrino data • KamLAND data fixes LMA as the solution for solar neutrino problem  SFP cannot be the dominant contribution • [ndata + LMA allowed region + no ]  constrain mn B dr : [Akhmedov et al., Miranda et al. …] ranges of mn(solar) < 10-10 – 10-12mB

  7. Direct Experiments • using sources understood by independent means : reactor n , accelerator n , n at detector , n-sources (future) • look for 1/T excess due to n-e scattering via mn channel over background and Standard Model processes • reactor n :reactor ON/OFF comparison to filter out background uncertainties • n : account for background spectra by assumptions/other constraints • limits independent of |n>final : valid fornD/nM & diag./tran. moments--no modeling involved • interpretation of results : need totake into account difference in |n>initial

  8. Solar n : SK & Borexino ※ SK spectral distortion over oscillation “bkg”[hep-ex/0402015] • 8B n • SK alone :mn(n) < 3.6 X 10-10mB (90% CL) • + all n data :mn(n-LMA) < 1.3 X 10-10mB (90% CL) • + KamLAND :mn(n-LMA) < 1.1 X 10-10mB (90% CL) • ※ Borexino/CTF spectral analysis[PLB 563,2003] • mainly 7Be n • bkg=0 :mn(n) < 1.2 X 10-9mB (90% CL) • Assume linear bkg + best fit : mn(n) < 5.5 X 10-10mB (90% CL)

  9. Accelerator n : LSND & DONUT ※LSND[PRD 63, 2001]: • select “single electron” events • taking SM s(nm-e), measured s(ne-e) agrees with SM set limit ※ DONUT[PLB 513, 2001]: • observed nt from Ds decays at expected level • look for “single electron” events at level >> SM s(n-e) • observed 1 event with 2.3 expected background @ e=9% • limit: mn(nt) < 3.9 X 10-7mB (90% CL)

  10. Reactor n @ Bugey : MUNU • CF4 TPC (total mass 11.4 kg; containment e~0.5 at 1 MeV) • excellent “single electron” event selection via 4p liquid scintillator & tracking • distinguish start/end of track & measure scattering angle w.r.t. reactor direction measure neutrino energy • Reactor ON/OFF comparison forward/background events comparison

  11. MUNU data (66.6 d ON/16.7 d OFF)[PLB 564, 2003] • excess of counts < 900 keV ; NO explanations yet [fn(reactor) below 2 MeV not well-known] • limits depends on energy range taken : • Visual scan T > 700 keV mn(ne) < 1.4 X 10-10mB (90% CL) • Visual scan T > 900 keV mn(ne) < 1.0 X 10-10mB (90% CL) • Auto scan T > 300 keV mn(ne) < 1.7 X 10-10mB (90% CL) • studies of hidden n-sourcesand/or low energy background necessary

  12. Reactor n @ Kuo-Sheng : TEXONO • simple compact all-solid design : HPGe (mass 1 kg) enclosed by active NaI/CsI anti-Compton, further by passive shieldings & cosmic veto • focus on 10-100 keV range for high signal rate & robustness: • mn >> SM [decouple irreducible bkg unknown sources make searches more conservative] • T<<Ends/dT depends on total fn flux but NOT spectral shape [well known : ~6 fission-n ~1.2 238U capture-n per fission ] • selection: single-event after veto, anti-Comp., PSD Inner Target Volume

  13. TEXONO data (4712/1250 hours ON/OFF)[PRL 90, 2003] • comparable bkg level to underground CDM experiment at 10-20 keV : ~ 1 day-1keV-1kg-1 (cpd) • analysis threshold 12 keV • No excess of counts ON/OFF comparison • Limit: mn(ne) < 1.3 X 10-10mB (90% CL) • more data/improvement to get to sensitivity range mn(ne) 1.0 X 10-10mB

  14. Combined Analysis [Grimus et al., …. ] • use all available information, incl. LMA global fit & error contour • take nM only transition moments ni nj & m†=m • adopt mn direct limits from SK spectral shape & reactor expts “Total” Magnetic Moment : Reactor n: n at SK:

  15. Sensitivity Improvement Scales as: Nn: signal events B : background level m : target mass t : measurement time • Nn fn (neutrino flux) & related to T-threshold • T-threshold : e.g. Nnincrease X~3 from 10 keV to 10 eV in Ge (1/T  atomic energy level threshold) • BIG statisticalboost in mncomes from enhancement in fn by, e.g. artificial n-sources, b-beams etc. • BUT: for systematics control, coupled with • low threshold to keepmn >> SM rates • maintain low background level

  16. GEMMA Project : Reactor n(Russia) • at Kalininskaya Power Plant • Improvement over TEXONO-HPGe parameters : • f~2X1013 cm-2s-1 at 15 m • 2 kg HPGe target size • 2 keV threshold • Sensitivity : • mn(ne)  3 X 10-11mB

  17. MAMONT Project : 3H-source(Russia, USA, Germany) • TRITIUM SOURCE of 40 MCi activity (4 kg 3H) with flux of 61014 cm-2s-1(!) • ULTRA-LOW-THRESHOLD DETECTORS Eth~10 eV (!): SILICON CRYODETECTOR 15100cc M=3kg, ionization-into-heat conversion effect (CWRU-Stanford-JINR) • HIGH-PURITY-GERMANIUM DETECTOR 6150cc, M=4.8kg, internal amplificationby avalanche multiplication(ITEP) • SENSITIVITY (95% C.L.):2.5 10-12B 50 cm Conceptual layout of the -e scattering experiment with 40 MCi tritium source

  18. TEXONO - ULEGe Reactor Neutrino Interaction Cross-Sections On-Going Data Taking (200 kg CsI) : • SM s(ne) • T > 2 MeV • R&D (ULEGe Prototype): • Coh. (nN) • T < 1 keV Results & More Data (HPGe) : • mn(ne) • T ~ 10-100 keV

  19. “Ultra-Low-Energy” HPGe Prototype • modular mass 5 g  can be constructed in multi-array form • threshold <100 eV after modest PSD • R&D on sub-keV background/calibration/threshold • applications in nN coherent scattering & Dark Matter searches • T>500 eV can be used for mn(ne)  3 X 10-11mB for a 1 kg detector at ~1 cpd background level Threshold ~ 100 eV

  20. Summary & Outlook Surprises Need Not be Surprising in Neutrino Physics …. • a conceptually rich subject ; much neutrino physics & astrophysics can be explored n-osc. : Dmn , Uij 0nbb : mn, Uij , nD/nM mn: mn, Uij , nD/nM , n  g • practicalconsequences remain to be seen ; NO indications yet • experimental studies push on new neutrino sources & detection techniques/ranges/channels potentialimportance in other areas

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