-decaying nuclei as a tool to measure relic neutrinos
Post on 05-Jan-2016
18 Views
Preview:
DESCRIPTION
TRANSCRIPT
G. Mangano The Path to Neutrino Mass Workshop
1
-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
G. Mangano The Path to Neutrino Mass Workshop
2
The issue: Cosmic Neutrino Background (CvB)
G. Mangano The Path to Neutrino Mass Workshop
3
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
G. Mangano The Path to Neutrino Mass Workshop
4
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
o3/1
1068.1k 945.111
4
33,
32
1121827.0)3(
4
3 cmTnTgnkkfff
eV
mh
eV
m
h
mnk
kk
c
kk
kk
2.932.93
1 22
,
12
1)( /
2
2
vi Tpe
ppf
G. Mangano The Path to Neutrino Mass Workshop
5
detailed neutrino decoupling:
small entropy release to v’s from e+-e- annihilation
• momentum dependent distortion in v distribution
• smaller photon temperature
)(,28
2
2
CEm
G
p
MHpi
W
Fpt
0 2 4 6 8 10
0
0.025
0.05
0.075
0.1
0.125
0.15
0.175
T-3 f(p)
p/T
G. Mangano The Path to Neutrino Mass Workshop
6
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
G. Mangano The Path to Neutrino Mass Workshop
7
Extra neutrinos from out of equilibrium decay of scalars after neutrino decoupling
Neutrinos decays into scalar particles (neutrinoless Universe)
22* 2/)(
2
22
21
1)(
yy
ya eA
eyyf
ExoticsEffects seen in CMB and LSS
G. Mangano The Path to Neutrino Mass Workshop
8
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…
G. Mangano The Path to Neutrino Mass Workshop
9
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
G. Mangano The Path to Neutrino Mass Workshop
10
A ’62 paper by S. Weinberg and v chemical potential
G. Mangano The Path to Neutrino Mass Workshop
11
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!
44
4
2
22
....7
15
7
303
120
7v
i
ii T
G. Mangano The Path to Neutrino Mass Workshop
12
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
G. Mangano The Path to Neutrino Mass Workshop
13
Massive neutrinos and neutrino capture on beta decaying nuclei (NC)
eNNv
veNN
ZAZAe
eZAZA
'
'
)1,(),(
)1,(),(
e
e
()
(A, Z) (A, Z 1)
Beta decay
e
e
()Neutrino Capture on aBeta Decaying Nucleus
(NC) (A, Z) (A, Z 1)
)(
)(
G. Mangano The Path to Neutrino Mass Workshop
14
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!
G. Mangano The Path to Neutrino Mass Workshop
15
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
G. Mangano The Path to Neutrino Mass Workshop
16
Issues:
1. Rates
Nuclear form factors (shape factors) uncertainties: use beta observables
G. Mangano The Path to Neutrino Mass Workshop
17
Super-allowed transitions
This is a very good approximation also for allowed
transitions since
i-th unique forbidden
G. Mangano The Path to Neutrino Mass Workshop
18
Cross sections times vv as high as 10-41 cm2 c
A. Cocco, G.M. and M. Messina 2007
G. Mangano The Path to Neutrino Mass Workshop
19
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
G. Mangano The Path to Neutrino Mass Workshop
20
3H
1272 nuclei
799 nuclei
Beta decaying nuclei having BR() > 5 selected from 14543 decays listed in the ENSDF database
G. Mangano The Path to Neutrino Mass Workshop
21
2. Background
Observing the last energy bins of width
signal/background >1
It works for <mv
dn/dTe
mTe
2m
G. Mangano The Path to Neutrino Mass Workshop
22
•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
G. Mangano The Path to Neutrino Mass Workshop
23
A. Ringwald and Y. Wong 2004
N-1-body simulations
G. Mangano The Path to Neutrino Mass Workshop
24
A. Ringwald and Y. Wong 2004
N-1-body simulations
Milky Way
Top curve: NFW Bottom curve: static present MW matter profile
G. Mangano The Path to Neutrino Mass Workshop
25
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
G. Mangano The Path to Neutrino Mass Workshop
26
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),…
top related