probing the origins of neutrino masses and baryon asymmetry of the universe
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Probing the origins of neutrino masses and baryon asymmetry of the universe. Takehiko Asaka (Niigata Univ.). @ Maskawa Institute for Science and Culture (2014/01/27). Contents. Overview – n MSM – RH neutrinos and Dark Matter RH neutrinos and Baryon Asymmetry Search for RH neutrinos - PowerPoint PPT PresentationTRANSCRIPT
Probing the origins of neutrino masses and baryon asymmetry of the universe
@Maskawa Institute for Science and Culture (2014/01/27)
Takehiko Asaka (Niigata Univ.)
Contents
27/01/2014Takehiko Asaka (Niigata Univ.)
2
Overview – nMSM –
RH neutrinos and Dark Matter
RH neutrinos and Baryon Asymmetry
Search for RH neutrinos
Summary
TA, Blanchet, Shaposhnikov ’05TA, Shaposhnikov ‘05
TA, Ishida ‘10TA, Eijima, Ishida ‘11, ‘12
TA, Eijima, Watanabe ‘13TA, Eijima ‘13
Introduction
27/01/2014Takehiko Asaka (Niigata Univ.)
3
Higgs had been discovered !!
All elementary particles in the Standard Model had been confirmed by experiments !!
2012/07/04
27/01/2014Takehiko Asaka (Niigata Univ.)
4
What’s next after Higgs discovery?
Prologue: Physics beyond the SM About 20 years ago …,
There was no “convincing” evidence for physics beyond the standard model (SM)
People looked for physics beyond the SM “mainly” based on theoretical arguments and curiosities:
Hierarchy problemNaturalness problemGravity, String, …Strong CP problemWhy 3 generations?Why anomalies cancel?…
27/01/2014Takehiko Asaka (Niigata Univ.)
5
News from the skyNeutrino Oscillations
Cosmic MicrowaveBackground (CMB)
[SuperK]
[WMAP]27/01/2014Takehiko Asaka (Niigata Univ.)
6
Physics beyond the SM In the last decade(s), we have collected
quite “convincing” evidences for physics beyond the SM Neutrino oscillations
Baryon asymmetry
Dark matter
Dark energy
Primordial density perturbations
27/01/2014Takehiko Asaka (Niigata Univ.)
7
Physics beyond the SM In the last decade(s), we have collected
quite “convincing” evidences for physics beyond the SM Neutrino oscillations
Baryon asymmetry
Dark matter
Dark energy
Primordial density perturbations
Today, I would like to explain nMSM, which can solve first three problems!
??
??
27/01/2014Takehiko Asaka (Niigata Univ.)
8
Origin of neutrino masses Neutrino mass scales
Atmospheric: Solar :
⇒ Need for physics beyond the SM ! Important questions:
“What is the origin of neutrino masses?”
“How do we test it experimentally?”
Takehiko Asaka (Niigata Univ.) 27/01/2014
9
10Standard Model
R
(left-handed) (right-handed)
R
R
ud
R
R
cs
R
R
tb
L
ud
e L
en L
n L
n
L
cs
Re R
L
tb
HiggsBosons
Quarks and Leptons Gauge Bosons
h 𝑔𝑍 0
𝑊 ±
𝛾
27/01/2014Takehiko Asaka (Niigata Univ.)
11Standard Model
R
(left-handed) (right-handed)
R
R
ud
R
R
cs
R
R
tb
L
ud
e L
en L
n L
n
L
cs
Re R
L
tb
HiggsBosons
Quarks and Leptons Gauge Bosons
h 𝑔𝑍 0
𝑊 ±
𝛾
27/01/2014Takehiko Asaka (Niigata Univ.)
12Neutrino Minimal SM (nMSM)
R
(left-handed) (right-handed)
R
R
ud
R
R
cs
R
R
tb
L
ud
e L
en L
n L
n
L
cs
Re R
L
tb
HiggsBosons
Quarks and Leptons Gauge Bosons
h 𝑔𝑍 0
𝑊 ±
𝛾
TA, Blanchet, Shappshnikov (‘05),TA, Shaposhnikov (‘05)
𝜈𝑅1𝜈𝑅2𝜈𝑅3
27/01/2014Takehiko Asaka (Niigata Univ.)
Extension by RH neutrinos
Seesaw mechanism ()
Light active neutrinos → explain neutrino oscillations
Heavy neutral leptons Mass Mixing
+ h.c.2
cMR R R R R
ML i F L n n n n n
0 01 1( , ) . ( , ) . .02 2
c cDc L
L R TD R
c
M M
M ML h c h c
M NMN
Mnn
n nn
nn
𝜈𝐿=𝑈𝜈+Θ𝑁
1TD D
M
M M MMn
1 2 3( , , )TU M U diag m m mn
(𝑁≃𝜈¿¿𝑅)¿
mixing in CC current
Where is the
scale of mass?
Minkowski ’77Yanagida ’79Gell-Mann, Ramond, Slansky ‘79Glashow ‘79
Takehiko Asaka (Niigata Univ.) 27/01/2014
13
Scale of Majorana mass The simplest case: one pair of and
221 /TD D M
M
M M M F M MMn n
2atmM mn
Majorana Mass
Neut
rino
Yuka
wa C
oupl
ing tF F
eF F
Takehiko Asaka (Niigata Univ.) 27/01/2014
14
Convenstional seesaw scenario:
Neutrino Yukawa couplings are comparable to those of quarks and charged leptons
Explain smallness of neutrino masses via seesaw
Decays of RH neutrino(s) can account for baryon asymmetry through leptogenesis
Physics of RH neutrino cannot be tested directly by experiments
[Fukugita, Yanagida]
[Yanagida; Gell-Mann, Ramond, Slansky]
27/01/2014Takehiko Asaka (Niigata Univ.)
15
Scale of Majorana mass The simplest case: one pair of and
221 /TD D M
M
M M M F M MMn n
Majorana Mass
Neut
rino
Yuka
wa C
oupl
ing tF F
eF F
Baryogenesis via leptogenesis
Fukugita, Yanagida ‘86
Takehiko Asaka (Niigata Univ.) 27/01/2014
16
The nMSM: No new mass scale is introduced
Oscillation of RH neutrinos can account for baryon asymmetry of the universe
Lightest RH neutrino (~keV) can be DM
Physics of RH neutrinos can be tested directly by experiments
[TA, Blanchet, Shaposhnikov; TA, Shposhnikov]
[Dodelson, Widrow,…]
[Akhmedov, Rubakov, Smirnov/ TA, Shaposhnikov]
27/01/2014Takehiko Asaka (Niigata Univ.)
17
Scale of Majorana mass The simplest case: one pair of and
221 /TD D M
M
M M M F M MMn n
Majorana Mass
Neut
rino
Yuka
wa C
oupl
ing tF F
eF F
Baryogenesis via leptogenesis
Fukugita, Yanagida ‘86
Baryogenesis via neutrino osc.Akhmedov, Rubakov,
Smirnov ‘98TA, Shaposhnikov ‘05
Takehiko Asaka (Niigata Univ.) 27/01/2014
18
19
Dark Matter Candidate
Neutrino Oscillation dataMasses and mixings
Baryon Asymmetry of the Universe (BAU)Mechanism via neutrino oscillation
Roles of three HNL
27/01/2014Takehiko Asaka (Niigata Univ.)
LINK
1N
2 3 and N N
Unique Candidate:lightest heavy neutral lepton N1 with keV mass
Dark matter in the nMSM
27/01/2014
20
Takehiko Asaka (Niigata Univ.)
Dodelson, Widrow / Shi, Fuller / Dolgov, Hansen / Abazajian, Fuller, Patel /…(Incomplete list)
§2
Decays of DM N1 is not completely stable particle !
Dominant decay: for keV Lifetime can be very long
N1 is not completely dark ! Subdominant decay: Branching ratio is small
But, severely restricted from X-ray observations
+ …
+ …
𝜏 N1=5×1026 sec ( keV𝑀 1 )
5( 10−8
Θ 2 )
𝐵𝑟=27𝛼𝑒𝑚 /8𝜋
27/01/2014Takehiko Asaka (Niigata Univ.)
21
Due to smallness of Yukawa couplings,N1 is not thermalized in the early universe
Production scenarios: Dodelson-Widrow scenario
Production via active-sterile neutrino mixing
Dominant production at
Shi-Fuller scenarioProduction is boosted in the presence of lepton asymmetry due to
the MSW effect
Production of DM
W,Z na N1𝜽❑
27/01/2014Takehiko Asaka (Niigata Univ.)
22
Cosmological Constraints Radiative decays of DM
No signal Upper bound on mixing angle !
Light heavy neutral lepton = WDM
Lower bound on mass (Ly-a forest observations) (DW scenario)
Phase-space analysis (Tremaine-Gunn bound)
𝜆𝐹𝑆 Mpc( keV𝑀 1 )⟨|𝑞𝑁|⟩⟨|𝑞𝜈|⟩
Erase structures on smaller scales!
Boyarsky, Lesgourgues, Ruchayskiy, Viel ’09,…..
27/01/2014Takehiko Asaka (Niigata Univ.)
23
Tremaine, Gunn ‘79Boyarsky, Ruchayskiy, Iakubovskyi ‘08Gorbunov, Khmelnitsky, Ruvakov ‘08
Dark Matter
27/01/2014Takehiko Asaka (Niigata Univ.)
24
Laine, Shaposhnikov ‘08
Dark Matter
27/01/2014Takehiko Asaka (Niigata Univ.)
25
Dodelson-Widrow mechanism does not work due to stringent constraints from X-ray and Ly-a Shi-Fuller mechanism ?? Entropy production ?? U(1)_B-L extension ?? (see Ishida, Jeong, Takahashi ‘13) …
Yukawa couplings of N1 are very suppressed N1 decouples from the seesaw mechanism
-> Lightest active neutrino N1 contribution is negligible for baryogenesis
N2 and N3 are responsible for Seesaw mass matrix for neutrino masses Baryon asymmetry of the universe
Entropy Production in the nuMSM
27/01/2014Takehiko Asaka (Niigata Univ.)
26
TA, Takeda ‘14
Entropy production by heavier neutral lepton N2 and N3 can cool down DM’s velocity dispersion !
Active neutrino masses
exclude the degenerate masses of active neutrinos
27/01/2014Takehiko Asaka (Niigata Univ.)
27
Baryogenesis via neutrino oscillation
BAU in the nMSM
27/01/2014
28
Takehiko Asaka (Niigata Univ.)
Akhmedov, Rubakov, Smirnov (’98) TA, Shaposhnikov (‘05)
§2
Takehiko Asaka (Niigata Univ.)
29
We find baryons mostly, not antibaryons ! Existence of antiproton
In cosmic rays, At TEVATRON, X
Asymmetry between baryons and antibaryons
2011/05/25(Wed)
Baryon v.s. antibaryon
How large ???
Baryon proton ( )
neutron ( )
Antibaryonantiproton ( )antineutron ( )
Takehiko Asaka (Niigata Univ.)
30Baryon asymmetry of the universe (BAU)
2011/05/25(Wed)
[Strumia 06]
Planck 2013 resultsarXiv:1303.5076
Baryon number densityEntropy density
Baryon Number = (# of baryons) (# of antibaryons)
:Bn:s
𝒏𝑩
𝒔 =(𝟖 .𝟓𝟕𝟗±𝟎 .𝟏𝟎𝟗 )×𝟏𝟎−𝟏𝟏
Takehiko Asaka (Niigata Univ.)
31
Primordial abundances of 4He, D, 3He, Li
BAU from BBN
2011/05/25(Wed)
[PDG][Strumia 06]
Takehiko Asaka (Niigata Univ.)
32Brief history of the universe
2011/05/25(Wed)
Inflation
BBN
Recombination
Today
generateBAU ! Baryogenesi
s
CMB 4He, D,…
Takehiko Asaka (Niigata Univ.)
33Conditions for baryogenesis
2011/05/25(Wed)
Sakharov (1967)
“According to our hypothesis, the occurrence of C asymmetry is the consequence of violation of CP invariance in the nonstationary expansion of the hot Universe during the superdense stage, as manifest in the difference between the partial probabilities of the charge-conjugate reactions.”
Takehiko Asaka (Niigata Univ.)
34Conditions for baryogenesis
2011/05/25(Wed)
Sakharov (1967)(1) Baryon number B is violated
(2) C and CP symmetries are violated
(3) Out of thermal equilibrium
Let us see whether the SM satisfies these conditions
Takehiko Asaka (Niigata Univ.)
35B violation in the SM
2011/05/25(Wed)
At classical level, B and L are conserved At quantum level, B and L are violated by non-perturbative anomaly effect
BL is conserved, but B+L is violated !
𝜕𝜇( 𝑗𝐵𝜇 − 𝑗𝐿𝜇 )=0
𝜕𝜇( 𝑗𝐵𝜇+ 𝑗𝐿𝜇 )≠0
Takehiko Asaka (Niigata Univ.)
36B and L
2011/05/25(Wed)
Energy
• Chern-Simons number (integer)
Takehiko Asaka (Niigata Univ.)
37
2011/05/25(Wed)
B and L At T = 0 Energy
Instanton
B+L breaking effect is negligible
[‘t Hooft ’76]
Takehiko Asaka (Niigata Univ.)
38
2011/05/25(Wed)
B and L For high temperatures
Energy Sphaleron
[Moore ‘00]
Sphaleron process is in equilibrium
[Buchmuller]
[Kuzumin, Rubakov, Shaposhnikov ’85]
Takehiko Asaka (Niigata Univ.)
39Sphaleron conversion
2011/05/25(Wed)
Initial (B-L) asymmetry is converted into B
(B-L)=0 initially leads to B=0 universe asymmetries are wahshed out!
[Khlebnikov, Shaposhnikov ‘88, Harvey, Turner ‘90]
We have to generate(B-L)>0 initially to explain B>0 universe !
Takehiko Asaka (Niigata Univ.)
40Baryogenesis conditions in the SM
2011/05/25(Wed)
B+L violations Sphaleron for T>100GeV
CP violation 1 CP phase in the quark-mixing (CKM) matrix
too small Out of equilibrium
Strong 1st order phase transition if but not satisfied
2 2 2 2 2 2 2 2 2 2 2 2 12 19CPV ( )( )( )( )( )( ) / 10CP t c t u c u b s b d s d EWJ m m m m m m m m m m m m T
[Kajantie, Laine, Rummukainen, Shaposhnikov]
<72GeVHM114.4GeV (exp.)HM
We have to go beyond the SM !!
Takehiko Asaka (Niigata Univ.)
41
2011/05/25(Wed)
Neutrino Masses
Baryon Asymmetry of the Universe
Leptogenesis
Baryogenesis via neutrino osc.
Overview
RH neutrinos
Seesaw
Seesaw
Takehiko Asaka (Niigata Univ.)
42
2011/05/25(Wed)
Leptogenesis Majorana masses break
RH neutrino decay can produce
Produced L is partially converted into B by sphaleron
[Fukugita, Yanagida ’86]
lepton number
( ) ( ) if CPVN L N L
CP violation
2011/05/25(Wed)Takehiko Asaka (Niigata Univ.)
43
CP violation in neutrino Yukawa couplings
Takehiko Asaka (Niigata Univ.)
44Out of equilibrium decay
2011/05/25(Wed)
For , is in thermal equilibrium
For EQ
Out of equilibrium decay of
Takehiko Asaka (Niigata Univ.)
45BAU via Leptogenesis
2011/05/25(Wed)
CP asymmetry
Sphaleron conv.
Efficiency factor
Number of
[Giudice et al 03]
Takehiko Asaka (Niigata Univ.)
46
2011/05/25(Wed)
Lower bound on mass M1
[Giudice et al ‘03]
Lower bound on mass
Takehiko Asaka (Niigata Univ.)
47Conventional seesaw scenario
2011/05/25(Wed)
Neutrino masses
BAU
RH neutrinos
Leptogenesis
Smallness of mn & BAU
SUSY GUTGauge coupling unification Naturalness problemLSP dark matterREWSB
Seesaw
Exp. test of RH is impossible!
Question
2011/05/25(Wed)Takehiko Asaka (Niigata Univ.)
48
Can we have a realistic scenario of baryogenesis, even if RH neutrinos have Majorana masses smaller than ~ 100GeV ?
Answer:
Yes!
Baryogenesis via neutrino oscillation
2011/05/25(Wed)
49
Takehiko Asaka (Niigata Univ.)
[Akhmedov, Rubakov, Smirnov ‘98][TA, Shaposhnikov ’05]
Scale of Majorana mass The simplest case: one pair of and
221 /TD D M
M
M M M F M MMn n
Majorana Mass
Neut
rino
Yuka
wa C
oupl
ing tF F
eF F
Baryogenesis via leptogenesis
Fukugita, Yanagida ‘86
Baryogenesis via neutrino osc.Akhmedov, Rubakov,
Smirnov ‘98TA, Shaposhnikov ‘05
Takehiko Asaka (Niigata Univ.) 27/01/2014
50
Takehiko Asaka (Niigata Univ.)
51Baryogenesis conditions
2011/05/25(Wed)
B and L violations (B+L) violation due to sphaleron L violation due to Majorana masses
Majorana masses < 100 GeV negligible for T>100 GeV
C and CP violations 1 CP phase in quark sector 6 CP phases in lepton sector
Takehiko Asaka (Niigata Univ.)
52Baryogenesis conditions
2011/05/25(Wed)
Out of equilibrium No 1st order EW phase transition as in the MSM Heavy neutral leptons can be out of equilibrium, if Yukawa couplings are small enough
To ensure this condition up to T ~ 100GeV7
1,2,3 2 10f La
tR QL
N2,3
Conclusion: The nMSM can potentially realize all three conditions for baryogenesis
53Baryogenesis via neutrino oscillations
RH neutrinos are created and oscillate with CPV The total lepton number is zero but is distributed
between LH and RH leptons The asymmetry of left-handed leptons is transferred
into baryon asymmetry by sphaleron effects
[Akhmedov, Rubakov, Smirnov ’98/ TA, Shaposhnikov ’05]
Idea: Oscillation of RH neutrinos is a source of BAU
2011/05/25(Wed)Takehiko Asaka (Niigata Univ.)
Shaposhnikov (’08), Canetti, Shaposhnikov (‘10)TA, Ishida (‘10), Canetti, Drewes, Shaposhnikov (’12), TA, Eijima, Ishida (‘12)Canetti, Drewes, Shaposhnikov (‘12), Canetti, Drewes, Frossard, Shaposhnikov (‘12)
Takehiko Asaka (Niigata Univ.)
54Key points
27/01/2014
Baryogenesis via leptogenesis
Baryogenesis via neutrino osc.
BB
LL
sphaleron
sphaleron
B L B L
Takehiko Asaka (Niigata Univ.)
55First step: at F2 order
2011/05/25(Wed)
N2 and N3 are produced via scatterings
N2 and N3 oscillate
La
tR QL
N2,3
N2
N3
N NLF †F
2†
8NTV F Fk
Medium effects𝑇 osc (𝑀 0 𝑀𝑁 𝛥𝑀 )1 /3
Takehiko Asaka (Niigata Univ.)
56Second step: at F4 order
2011/05/25(Wed)
Active flavor asymmetries are generated
N2,3
L LN†F F
[TA, Shaposhnikov]
Evolution rates of and are different due to CPV in
Evolution of each asymmetries
2011/05/25(Wed)Takehiko Asaka (Niigata Univ.)
57
Active sector Sterile sector
Evolution of asymmetries
2011/05/25(Wed)Takehiko Asaka (Niigata Univ.)
58
[Kuzmin, Rubakov, Shaposhnikov]
Shaleron converts L partially into baryon asymmetry
28 079 totB L
42.5 10 ( )Btot W
n L Ts
𝒏𝑩
𝒔 =(𝟖 .𝟓𝟕𝟗±𝟎 .𝟏𝟎𝟗 )×𝟏𝟎−𝟏𝟏
[Planck 2013]
Baryogenesis via neutrino osc.Oscillation of heavy neutrinos can be a source of BAU
CPV in oscillation and production generates asymmetries Asymmetries are separated into LH and RH leptons Asymmetry in LH leptons is converted into BAU
Akhmedov, Rubakov, Smirnov (’98) / TA, Shaposhnikov (‘05)
Yield of BAU depends on Yukawa couplings and masses
Shaposhnikov (’08), Canetti, Shaposhnikov (‘10)TA, Ishida (‘10), Canetti, Drewes, Shaposhnikov (’12), TA, Eijima, Ishida (‘12)Canetti, Drewes, Shaposhnikov (‘12), Canetti, Drewes, Frossard, Shaposhnikov (‘12)
Especially, CP violating parametersand mass difference
𝑇 osc (𝑀 0 𝑀𝑁 𝛥𝑀 )1 /3
Takehiko Asaka (Niigata Univ.) 27/01/2014
59
Baryogenesis via neutrino osc.Region accounting for
Canetti, Shaposhnikov ‘10
IH
NH
8.55-9.00)
Takehiko Asaka (Niigata Univ.) 27/01/2014
60
Baryogenesis via neutrino osc.Region accounting for
(1) quasi-degenerate(2) masses are
TA, Eijima ‘13Two RH neutrino case
NHIH MeV (NH)
MeV (IH)
8.55-9.00)
Takehiko Asaka (Niigata Univ.) 27/01/2014
61
Baryogenesis via neutrino osc.Region accounting for
(1) quasi-degenerate(2) masses are
TA, Eijima ‘13Two RH neutrino case
NHIH MeV (NH)
MeV (IH)
8.55-9.00)
Such light RH neutrinos can be directly tested by experiments!
Takehiko Asaka (Niigata Univ.) 27/01/2014
62
Direct search experiment PS191
Beam dump experiment performed at CERN in 1984
Production Detection
Upper bounds mixing elements → Lower bound on lifetime of
[Bernardi et al ‘86, ’88]
𝜋+¿ ,𝐾 +¿→𝑒 +¿𝑁 ¿¿ ¿
𝑁⟶ ℓ+¿ ℓ−𝜈 , ℓ−𝜋+¿¿ ¿
Takehiko Asaka (Niigata Univ.) 27/01/2014
63
BBN constraint on lifetime Long-lived may spoil the success of BBN
Speed up the expansion of the universe p-n conv. decouples earlier overproduction of
Distortion of spectrum of active neutrinos
Additional neutrinos may not be thermalized Upper bound on lifetime
Dolgov, Hansen, Rafflet, Semikoz (’00) One family case:
𝑛+𝜈⟷𝑝+𝑒− ,…
sec for Takehiko Asaka (Niigata Univ.) 27/01/2014
64
Constraints on light RH neutrinos
Cosmology
Direct search
Normal hierarchy Inverted hierarchy
MeV MeVMeV
TA, Eijima ‘13
Takehiko Asaka (Niigata Univ.) 27/01/2014
65
Implication to 02 decay
§
Takehiko Asaka (Niigata Univ.) 27/01/2014
66
Constraints on light RH neutrinos
Cosmology
Direct search
Normal hierarchy Inverted hierarchy
MeV MeVMeV
TA, Eijima ‘13
Takehiko Asaka (Niigata Univ.) 27/01/2014
67
Mixing elements in IH caseMixing elements of heavy neutrinos
Mixing elements strongly depend on “”
We find allowed range of Majorana phase !
Θ𝛼 𝐼=⟨Φ ⟩ 𝐹 𝛼𝐼
𝑀 𝐼
𝑊𝑁 𝐼
𝑔Θ𝛼 𝐼ℓ𝛼+¿ ¿
Takehiko Asaka (Niigata Univ.) 27/01/2014
68
Majorana phase in IH casesin𝜂 1 sin𝜂 0.3 all is allowed
𝐾 +¿→𝑒+¿𝑁 ¿¿
+cc 𝐾 +¿→𝜇+¿𝑁 ¿ ¿
+cc
Majorana phase is restricted for MeV!
Excluded by BBN +PS191
Excluded by BBN +PS191
Takehiko Asaka (Niigata Univ.) 27/01/2014
69
decays in IHEffective neutrino mass from light and heavy neutrinos 𝑚eff=𝑚𝑖𝑈 𝑒𝑖
2 + 𝑓 𝛽 (𝑀 𝐼 )𝑀 𝐼Θ𝑒𝐼2 =[1− 𝑓 𝛽 (𝑀 𝑁 ) ]𝑚eff
𝜈 TA, Eijima, Ishida (‘11)
𝑚eff𝜈𝜂=
0𝜋
Heavy neutrinos give negative contribution to
Constraint on restricts the predicted range of
Takehiko Asaka (Niigata Univ.) 27/01/2014
70
Search for heavy neutrinos at T2K
§
TA, Eijima, Watanabe [JHEP1303 (2013) 125]
Takehiko Asaka (Niigata Univ.) 27/01/2014
71
Search for light sterile neutrinos Production by meson decays
Peak searchMeasure in
Decays inside the detector𝑁⟶ ℓ+¿ ℓ
−𝜈+𝑐 .𝑐 . ¿
𝐸𝑒=𝑚𝐾
2 −𝑚𝑒2−𝑀𝑁
2
2𝑚𝐾
even
ts
𝐾 +¿→𝑒+¿𝑁 ¿¿
𝐾 +¿→𝑒+¿ν ¿ ¿𝐾 +¿→𝑒+¿𝑁 ,𝐾 +¿→𝜇+ ¿𝑁 ¿ ¿¿ ¿
[Shrock ’80]
𝐾 +¿→𝑒+¿𝑁 ¿¿
𝐸𝑒
CERNPS191
Takehiko Asaka (Niigata Univ.) 27/01/2014
72
Search for heavy neutrinos at T2K
𝑁
Production of Detection of
𝐾 +¿→ℓ +¿+𝑁 ¿ ¿ 𝑁→ℓ−+𝜋+¿ ¿
Estimate flux of at ND280 Count # of signal decay inside ND280 Derive upper bounds on mixing angles
SK
(ℓ−=𝑒− ,𝜇−)
Takehiko Asaka (Niigata Univ.) 27/01/2014
73
Sensitivity: PS191 vs T2K
T2K at POT has a better sensitivity than PS191 ( POT) !
PS191
T2K
TA, Eijima, Watanabe ‘13
Takehiko Asaka (Niigata Univ.) 27/01/2014
74
Signal vs Background Signal events: BG events:
To reduce BG, Use the invariant mass distribution of and
since it has a peak at for signal decay Use the low density part of detector filled with argon gas
(9m^3) out of 61.25m^3
See also the recent proposal to search for heavy neutrinos at the CERN SPS.
𝑁→ℓ−+𝜋+¿ ¿
(CC-) (CC-coherent)
arXiv:1310.1762
Takehiko Asaka (Niigata Univ.) 27/01/2014
75
Summary The SM + three right-handed neutrinos
(nMSM) Lightest right-handed neutrino with mass
~10keV can be dark matterThe simplest Dodelson-Widrow scenario conflicts
with X-ray and Ly-alpha constraintsSome other production mechanism is needed
Heavier two right-handed neutrinos can be responsible to baryon asymmetry of the universeBaryogenesis via neutrino oscillationsGood target for future search experiments
27/01/2014Takehiko Asaka (Niigata Univ.)
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Three sterile neutrinos We may call N2, N3 and N1 as “bright”, “clear” and
“dark”
Clear and Bright, NC and NB: Heavier onesNeutrino oscillationsBaryon asymmetryM~10GeV, F~10-7,
Dark, ND: Lightest oneDark matter (production?)M~keV, F<10-12, q<10-4
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Backup
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Comparison
T2K2013/4/12: 6.39x10^20 POT2013/5/8: 6.63x10^20 POT
GOAL: 7.8x10^21 POT
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Neutrino Yukawa couplings for 1/2 1/2
PMNS /NF U D Dn
2 31/2 diag( , )ND M M
1 2 31/2 diag( , , )0D m m mn
0 0
cos sin
sin cos
12 13 12 13 13
PMNS 23 12 23 12 13 23 12 23 12 13 23 13
23 12 23 12 13 23 12 23 12 13 23 13
1
1
i
i i i
i i
c c s c s e
U c s s c s e c c s s s e s c e
s s c c s e s c c s s e c c
[Casas, Ibarra ’01]
Parameters of active neutrinos
Parameters of sterile neutrinos
: active n masses
: sterile n masses
1
Dirac phase
Im
(in NH)
Majorana phase
complex number
Takehiko Asaka (Niigata Univ.) 27/01/2014
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Effective neutrino mass 𝑚eff= ∑
𝑖=1,2,3𝑚𝑖𝑈 𝑒𝑖
2 + ∑𝐼=1,2,3
𝑓 𝛽 (𝑀 𝐼 )𝑀 𝐼Θ𝑒𝐼2
active neutrinos sterile neutrinos
[Blennow, Frenandez-Martinez, Pavon, Mnendez ’10]
𝑓 𝛽 (𝑀 )=𝑀0𝜈𝛽𝛽 (𝑀 )/𝑀 0𝜈𝛽𝛽(0)
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in the MSM
in the nMSM is smaller than active ’s one
No significant constraint on in the nMSM !
NH case IH case
[TA, Eijima, Ishida ’11]
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