-decaying nuclei as a tool to measure relic neutrinos

G. Mangano The Path to Neutrino Mass Workshop

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-decaying nuclei as a tool to -decaying nuclei as a tool to measure Relic Neutrinosmeasure Relic Neutrinos

Gianpiero Mangano Gianpiero Mangano INFN, Sezione di Napoli, ItalyINFN, Sezione di Napoli, Italy

Workshop 3-6 September 2007 University of Aarhus

The Path to Neutrino Mass


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The issue: Cosmic Neutrino Background (CvB)


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Summary:

•CvB as we suppose to know it

•A ’62 paper by S. Weinberg and v chemical potential

•Massive neutrinos and neutrino capture on beta decaying nuclei

•Clustering and v local density

•The case of 3H

•Outlooks

Based on a work in collaboration with A. Cocco and M. Messina, JCAP

0706, 015 (2007), hep-ph/0703075


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CvB as we suppose to know it

As photons but much earlier, neutrinos decouple from the comoving thermal bath during the expansion

neutrino decoupling: weak interactions become too weak at T ~ MeV

eVTKTT 4B

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vi Tpe

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detailed neutrino decoupling:

small entropy release to v’s from e+-e- annihilation

• momentum dependent distortion in v distribution

• smaller photon temperature

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CEm

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p

MHpi

W

Fpt

0 2 4 6 8 10

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0.025

0.05

0.075

0.1

0.125

0.15

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T-3 f(p)

p/T


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z=T a e x Nveff

1.4 0.73% 0.52% 3.05

v

effxvR N

3/4

11

4

8

71

G. M. et al 2005


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Extra neutrinos from out of equilibrium decay of scalars after neutrino decoupling

Neutrinos decays into scalar particles (neutrinoless Universe)

22* 2/)(

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yy

ya eA

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ExoticsEffects seen in CMB and LSS


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Bounds from BBN particles (decoupled) should not contribute too much to the expansion rate H

Cuoco, Lesgourgues, G.M. and Pastor 2005

Beacom, Bell and Dodelson 2004

Bell, Pierpaoli and Sigurdson 2005

Hannestad 2005

Neutrino decay: bounds from LSS…


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CvB: very low energy, difficult to measure directly by v-scattering

1. Large De Broglie wavelength ~0.1 cm

Coherent scattering over macroscopic domain

Wind force on a test body, acceleration ~ 10-28 cm2 s-1

Today: Cavendish torsion balances can test acceleration as small as 10-13 cm2 s-1 !!

2. Accelerators:

Too small even at LHC or beyond !

2442 )/)(/(10/)( cmTeVEeVmsGvp vF


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A ’62 paper by S. Weinberg and v chemical potential


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Neutrino-antineutrino asymmetry (=/Tv, EF()) strongly constrained by Big Bang Nucleosynthesis

1) chemical potentials contribute to neutrino energy density

2) a positive electron neutrino chemical potential (more neutrinos than antineutrinos) favour n p processes with respect to p n processes.

Change the 4He abundance!

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4

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22

....7

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120

7v

i

ii T


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Though different neutrino flavor may have different chemical potentials, they however mix under oscillations

A. Dolgov et al 2002A. Cuoco et al 2004

Likelihood contours 68 & 95 c.l.

very small!

2hB


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Massive neutrinos and neutrino capture on beta decaying nuclei (NC)

eNNv

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(NC) (A, Z) (A, Z 1)

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dn/dEe

NCNC

W0

m

Ee-me

m 0

m= 0

2m

2 mv gap in electron spectrum around Q

Weinberg: if neutrinos are degenerate we could observe structures around the beta decaying nuclei endpoint Q

v’s are NOT degenerate but are massive!


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Neutrino masses

Terrestrial bounds

ve <2 eV (3H decay)

v <0.19 MeV (pion decays)

v <18.2 MeV ( decays)

Cosmology Bounds on i mi

A.Marrone, IFAE 2007

G. Fogli et al. 2007


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Issues:

1. Rates

Nuclear form factors (shape factors) uncertainties: use beta observables


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Super-allowed transitions

This is a very good approximation also for allowed

transitions since

i-th unique forbidden


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Cross sections times vv as high as 10-41 cm2 c

A. Cocco, G.M. and M. Messina 2007


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allowed 1st unique forbidden 2nd unique forbidden 3rd unique forbidden

allowed 1st unique forbidden 2nd unique forbidden 3rd unique forbidden

(bottom)

(top) Q = 1 keVQ = 100 keVQ = 10 MeV


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3H

1272 nuclei

799 nuclei

Beta decaying nuclei having BR() > 5 selected from 14543 decays listed in the ENSDF database


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2. Background

Observing the last energy bins of width

signal/background >1

It works for <mv

dn/dTe

mTe

2m


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•Clustering and v local density

Massive neutrinos cluster on CDM and baryonic structures. The local density at Earth (8 kpc away from the galactic center) is expected to be larger than 56 cm-3

Neutrinos accrete when their velocity becomes comparable with protocluster velocity dispersion (z<2)

Usual assumption: Halo profile governed by CDM only

NFW universal profile


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A. Ringwald and Y. Wong 2004

N-1-body simulations


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A. Ringwald and Y. Wong 2004

N-1-body simulations

Milky Way

Top curve: NFW Bottom curve: static present MW matter profile


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The case of 3H

8 events yr-1 per 100g of 3H (no clustering)

up to 102 events yr-1 per 100 g of 3H due to clustering effect

signal/background = 3 for =0.2 eV if mv=0.7 eV

=0.1 eV if mv=0.3 eV


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Outlooks

Relic neutrinos and NC

•neutrino mass scale?

•NC: high rates, but detection only for quasi degenerate mass scale (mv> 0.1 - 0.2 eV);

•other background rejection methods? More careful analysis of kinematics (daughter nucleus recoil, polarized nuclei which de-excite via gamma emission,…);

•look for the best nucleus; other processes?

•other low energy neutrino fluxes: thermal v’s from the Sun, diffused flux, old stars (POP III),…

-decaying nuclei as a tool to measure relic neutrinos

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