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

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

Particle Physics ※ (ni)L – (nj )R – g vertices described in general by: eij and 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

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 …………

Astrophysics Bounds/Indications From: Big Bang Nucleosynthesis degree of freedom Stellar Cooling via Cooling of SN1987a via nactive  nsterile Absence of solar (KamLAND-03 < 2.8x10-4) ranges of mn(astro) < 10-10 – 10-12 mB 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 ……)

Magnetic Moments & Solar Neutrinos 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 – 10-12 mB

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 for nD/nM & diag./tran. moments -- no modeling involved interpretation of results : need to take into account difference in |n>initial

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

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 10-7 mB (90% CL)

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

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 10-10 mB (90% CL) Visual scan T > 900 keV mn(ne) < 1.0 X 10-10 mB (90% CL) Auto scan T > 300 keV mn(ne) < 1.7 X 10-10 mB (90% CL) studies of hidden n-sources and/or low energy background necessary

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

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 10-10 mB (90% CL) more data/improvement to get to sensitivity range mn(ne) 1.0 X 10-10 mB

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:

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. Nn increase X~3 from 10 keV to 10 eV in Ge (1/T  atomic energy level threshold) BIG statistical boost in mn comes from enhancement in fn by, e.g. artificial n-sources, b-beams etc. BUT: for systematics control, coupled with low threshold to keep mn >> SM rates maintain low background level

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 10-11 mB

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 amplification by 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

Reactor Neutrino Interaction Cross-Sections 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

“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 10-11 mB for a 1 kg detector at ~1 cpd background level Threshold ~ 100 eV

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 practical consequences remain to be seen ; NO indications yet experimental studies push on new neutrino sources & detection techniques/ranges/channels potential importance in other areas