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Exploring Neutrino Magnetic Moments in Particle Physics and Astrophysics

Learn about the status, prospects, and recent results on neutrino magnetic moments, with insights on experimental measurements, astrophysical bounds, and implications for particle physics and astrophysics. Discover the intricacies of direct experiments, future projects, and key findings in the field.

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Exploring Neutrino Magnetic Moments in Particle Physics and Astrophysics

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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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