Ionization cross sections of neutrino electronagnetic interactions with electrons Chih-Pan Wu Dept. of Physics, National Taiwan University P. 1
Constrain ν EM Properties by Ge Reference : Phys. Lett. B 731 , 159, arXiv:1311.5294 (2014). Phys. Rev. D 90 , 011301(R), arXiv:1405.7168 (2014). Phys. Rev. D 91 , 013005, arXiv:1411.0574 (2015). P. 2
ν -e Non-standard Interactions (NSI) E E E T ( ) ( T ) , q , q ( T ) , q Weak = − g 1 / 2 Magnetic moment A = + Interaction g 2 sin 1 / 2 v w 2 2 1 1 + − 2 m e T E An Example for enhanced signals at low T! P. 3
Solar ν Background in LXe Detectors 99.98% ER rejection J. Aalbers et. al. (DARWIN collaboration), JCAP 11 , 017, arXiv:1606.07001 (2016). P. 4 J.-W. Chen et. al ., Phys. Lett. B 774 , 656, arXiv:1610.04177 (2017).
Outline • Atomic ionization cross sections of neutrino- electron scattering – Why & when atomic effects become relevant? – MCRRPA: a framework of ab initio method • Discovery potential of ton-scale LXe detectors in neutrino electromagnetic properties – arXiv: 1903.06085 – solar nu v.s. reactor nu + Ge detector P. 5
Why Atomic Responses Become Important? The space uncertainty is inversely proportional to its incident momentum: λ ~ 1/p • 2 important factors: Atomic Size is inversely proportional to its – neutrino momentum orbital momentum: Zm e α ~ Z *3.7 keV – Energy transfer T Z: effective charge P. 6
Atomic Ionization Process for ν | 𝑁 | 2 The weak scattering amplitude: The EM scattering amplitude: P. 7
Electroweak Currents Lepton current: Atomic (axial-)vector current: , 1 , 0 Sys. Error: ~ 𝛽 ≈ 1% P. 8
The Form Factors & Related Physical Quantities neutrino millicharge : : charge form factor charge radius squared : : anomalous magnetic neutrino magnetic moment : : anapol e ( P -violating) electric dipole moment : : electric dipole anapole moment : ( P , T -violating) P. 9
“effective” Magnetic Moment µ ν and d ν interactions are not distinguishable where f and i are the mass eigenstate indices for the outgoing and incoming neutrinos, A ie ( E ν , L ) describes how a solar neutrino oscillates to a mass eigenstate ν i with distance L from the Sun to the Earth. P. 10
Bound Electron Wave Function |w > |u > ⅇ 𝛿 𝜈 ⅇ 𝑔 | 𝛿 𝜈 |Ψ 𝑗 > ത < Ψ < 𝑥| 𝛿 𝜈 |𝑣 > EM interaction Weak interaction Non-standard interactions 𝛿 𝜈 → 𝑊 𝛿 𝜈 + 𝐵 𝛿 𝜈 𝛿 5 → NSI Opⅇrators P. 11
One-Electron Dirac Spinors Then the radial Dirac equations can be reduced to P. 12
Atomic Response Functions Do multipole expansion with J Initial states could be Final continuous wave functions approximated by could be obtained by MCRRPA bound electron orbital and expanded in the ( J , L ) basis wave functions given of orbital wave functions by MCDF P. 13
Ab initio Theory for Atomic Ionization MCDF: multiconfiguration Dirac-Fock method u a ( r , t ) ( t ) Dirac-Fock method: is a Slater determinant of one-electron orbitals 𝜔(𝑢) 𝑗 𝜖 𝜀 ሜ 𝜖𝑢 − 𝐼 − 𝑊 𝐽 (𝑢) 𝜔(𝑢) = 0 and invoke variational principle 𝑣 𝑏 (റ 𝑠, 𝑢) . to obtain eigenequations for ( t ) multiconfiguration: Approximate the many-body wave function ( t ) by a superposition of configuration functions For Ge: ቐ𝜔 1 = Zn 4𝑞 1/2 2 = ( t ) C ( t ) ( t ) 𝜔 2 = Z𝑜 4𝑞 3/2 2 MCRRPA: multiconfiguration relativistic random phase approximation u a ( r , t ) RPA: Expand into time-indep. orbitals in power of external potential − = + + + i t i t i t u ( r , t ) e u ( r ) w ( r ) e w ( r ) e ... a + − a a a a = + − + + i t i t C ( t ) C [ C ] e [ C ] e ... + − a a a a P. 14
Here use square brackets with subscripts to designate the coefficients in powers of e ± i ω t in the expansion of various matrix elements: 𝛿 𝛽𝛾 : Lagrange multipliers MCDF Equations: † : functional derivatives 𝜀 𝛽 0 + = EC C H 0 † with respect to 𝑣 𝛽 a b ab b 0 − = † δ * C C H u 0 a b ab ab The zero-order equations are MCDF equations for unperturbed orbitals u a and unperturbed weight coefficients C a . MCRRPA Equations: ( ) ( ) − + = E C H C H C V C a ab b ab b ab b 0 b b ( ) ( ) † − − + † δ δ * * * C C i H C C C C H a b ab ab a m b a b ab 0 ab ab ( ) − + = † * δ w u C C V a b ab ab The first-order equations are the MCRRPA equations describing the linear response of atom to the external perturbation v ± . P. 15
Atomic Structure of Ge Multiconfiguration of Ge Ground State (Coupled to total J =0) : Selection Rules for J =1, λ =1: Angular Momentum Selection Rule: Parity Selection Rule: P. 16
Multipole Expansion Transition matrix elements of atomic ionization by nu-EM interactions: P. 17
Benchmark: Ge & Xe Photoionization Exp. data: Ge solid Theory: Ge atom (gas) Above 100 eV error under 5%. B. L. Henke, E. M. Gullikson, and J. C. Davis, Atomic Data and Nuclear Data Tables 54 , 181-342 (1993). J. Samson and W. Stolte, J. Electron Spectrosc. Relat. Phenom. 123 , 265 (2002). I. H. Suzuki and N. Saito, J. Electron Spectrosc. Relat. Phenom. 129 , 71 (2003). P. 18 L. Zheng et al ., J. Electron Spectrosc. Relat. Phenom. 152 , 143 (2006).
Approximation Schemes Longitudinal Photon Approx. (LPA) : V T = 0 V L = 0, q 2 = 0 Equivalent Photon Approx. (EPA) : Strong q 2 -dependence in the denominator : long-range interact ion Real photon limit q 2 ~ 0 : relativistic beam or soft photons q μ ~ 0 Free Electron Approx. (FEA) : q 2 = -2 m e T Main contribution comes from the phase space region similar with 2-body scattering Atomic effects can be negligible : E ν >> Z m e α T ≠ B i (binding energy) P. 19
Numerical Results: Weak Interaction = = E 10 k eV E 1 M eV v v e e (1) short range interaction 2 2 E = v cutoff : T 0 . 38 k eV e (2) neutrino mass is tiny + Max 2 E m v e e (3) E ν >> Z m e α Kinematic forbidden by the inequality: − FEA works well away from p 2 m T q 2 E T r e Max e → the ionization thresholds. (backward scattering , m 0 ) ν e P. 20
Numerical Results: NMM = E 1 M eV v e = E 10 k eV v e Similar with WI cases. FEA still faces a cutoff with lower E ν . For right plot, EPA becomes better when T approaches to E ν ( q 2 -> 0). Consistent with analytic Hydrogen results. P. 21
Numerical Results: Millicharge = = E 1 M eV E 10 k eV v v e e EPA worked well due to q 2 dependence in the denominator of scattering formulas of F 1 form factor (a strong weight at small scattering angles). P. 22
Double Check on Our Simulation • We perform ab initio many-body calculations for atomic initial & final states WF in ionization processes, and test by – Comparing with photo-absorption experimental data, for typical E1 transition, the difference is <5%. – In general, we have confidence to report a 5~10% theoretical errors. – It agrees with some common approximations under the crucial condition as we know in physical picture P. 23
Solar ν As Signals in LXe Detectors P. 24 J.-W. Chen et. al ., arXiv:1903.06085 (2019).
Expected Experimental Limits Assuming an energy resolution from the XENON100 experiment P. 25 J.-W. Chen et. al ., arXiv:1903.06085 (2019).
What Else? Portals to the Dark Sector: 1. Remain a large region for the possibility of LDM (Ex: Dark Sectors) 2. Other interactions, or interacted with electrons K. Olive et al . (Particle Data Group), Chin. Phys. C 38 , 090001 (2014). P. 26 R. Essig, J. A. Jaros, W. Wester, P. H. Adrian, S. Andreas et al ., arXiv:1311.0029.
Spin-Indep. DM-e Scattering in Ge & Xe P. 27 J.-W. Chen et. al ., arXiv:1812.11759 (2018).
Sterile Neutrino Direct Constraint q 2 < 0 q 2 > 0 • Non-relativistic massive sterile neutrinos decay into SM neutrino. At m s = 7.1 keV, the upper limit of μ ν sa < 2.5*10 -14 μ B at 90% C.L. • • The recent X-ray observations of a 7.1 keV sterile neutrino with decay lifetime 1.74*10 -28 s -1 can be converted to μ ν sa = 2.9*10 -21 μ B , much tighter because its much larger collecting volume. P. 28 J.-W. Chen et al ., Phys. Rev. D 93 , 093012, arXiv:1601.07257 (2016).
Constraints on millicharged DM P. 29 L. Singh et. al . (TEXONO Collaboration), arXiv:1808.02719 (2018).
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