Neutrinos at the High Energy Frontier
Alain Blondel Nuphys2013 2013-12-19
MOTIVATION
The only known BSM physics at the particle physics level is the existence of
neutrino masses
-- There is no unique solution for mass terms: Dirac only? Majorana only? Both?
-- if Both, existence of (2 or 3) families of massive right-handed (~sterile) i ,i
neutrinos is predicted («see-saw» models)
masses are unknown (<eV to >1010GeV)
-- Arguably, right handed neutrinos are the most likely ‘new physics’ there is
-- can high energy particle physics experiments participate to the search?
Alain Blondel Nuphys2013 2013-12-19
Adding masses to the Standard model neutrino 'simply' by adding a Dirac mass
term
implies adding a right-handed neutrino (new particle)
No SM symmetry prevents adding then a term like
and this simply means that a neutrino turns into a antineutrino
(the charge conjugate of a right handed antineutrino is a left handed neutrino!)
It is perfectly conceivable that both terms are present  ‘see-saw’
Alain Blondel Nuphys2013 2013-12-19
Neutrino physics -- Alain
Blondel
See-saw in the most general way :
MR  0
mD  0
Dirac + Majorana
mass terms
MR = 0
mD  0
Dirac only, (like e- vs e+):
m
L R
R L
Iweak= ½ 0
½ 0
4 states of equal masses
MR  0
mD = 0
Majorana only
m
L
R
Iweak= ½
½
2 states of equal masses
Some have I=1/2 (active)
All have I=1/2 (active)
Some have I=0Alain
(sterile)
Blondel TLEP design study r-ECFA 2013-07-20
MR  0
mD  0
Dirac + Majorana
m
Iweak=
L NR
R NL
½ 0
½ 0
4 states , 2 mass levels
m1 have I=1/2 (~active)
m2 have I=0 (~sterile)
Neutrinos : the New Physics there is… and a lot of it!
SM
L
I= ½
Dirac mass term
only
R
½
L R
½ 0
R L
½ 0
Majorana
mass term only
L
½
R
½
Dirac AND Majorana
Mass terms
NR
0
L
½
X 3 Families
6 massless states
NL
0
R
½
X 3 Families
X 3 Families
X 3 Families
3 masses
12 states
3 active neutrinos
3 active antinu’s
6 sterile neutrinos…
3 mixing angles
1 CP violating phase
3 masses
6 active states
No steriles
3 mixing angles
3 CP violating phases
0v
6 masses
12 states
6 active states
6 sterile neutrinos…
More mixing angles
and CPV phases
0v
 Leptogenesis and
Dark matter
Mass hierarchies are all unknown except m1 < m2
Preferred scenario has both Dirac and Majorana terms …
… a bonanza of
extreme
experimental
challenges
Alain
Blondel TLEP
design study r-ECFA
2013-07-20
Note that this is not necessary
as we have no idea of mD and MR !
Alain Blondel Nuphys2013 2013-12-19
𝒎𝒗 =
𝒎𝑫𝟐
𝑴
has been invoked to explain the smallness
of active neutrino masses
(maybe)
𝒎
𝒎𝒕𝒐𝒑
𝒎𝒕𝒐𝒑
𝑴
𝑮𝑼𝑻
is a pretty large hierarchy problem is’nt it?
... but we dont really know that this implies M  MGUT
nor that the see-saw mixing is small
nor what is the family dependence of this reasoning.
Alain Blondel Nuphys2013 2013-12-19
Manifestations of right handed neutrinos
𝒗 = 𝒗𝑳 cos - 𝑵𝒄𝑹 𝐬𝐢𝐧
for one family
see-saw   (mD/M)
𝑵 = 𝑵𝑹 cos + 𝒗𝑳 c sin
𝒗 = light mass eigenstate
N = heavy mass eigenstate
 𝒗𝑳 which couples to
weak interaction
-- mixing with active neutrinos leads to various observable consequences
-- if very light (eV) , possible effect on neutrino oscillations
-- if mixing in % or permil level, possibly measurable effects on
 PMNS matrix unitarity violation and deficit in Z invisible width
 occurrence of Higgs invisible decays H ii
 violation of unitarity and lepton universality in W or  decays
-- etc etc..
-- Couplings are small (mD/M) (but who knows?) and generally out of reach of
hadron colliders
-- how about high statistics e+e- ?
Alain Blondel Nuphys2013 2013-12-19
Back to the future
30 years later and with experience gained on LEP, LEP2 and the B factories
we can propose a Z,W,H,t factory of 1000 times the luminosity of LEP2
CERN is launching a 5 years international design study of Circular Colliders
100 TeV pp collider (VHE-LHC) and high luminosity e+e- collider (TLEP)
-- kick-off meeting 12-15 February 2014 in Geneva --
Alain Blondel Nuphys2013 2013-12-19
IPAC’13 Shanghai
http://arxiv.org/abs/1305.6498.
TLEP Facility Luminosity
1E+37
Luminosity
/cm2/s
Z
1E+36
WW
ZH
1E+35
tt
1E+34
0
100
200
300
400
Ecm (GeV)
CONSISTENT SET OF PARAMETERS FOR TLEP
TAKING INTO ACCOUNT BEAMSTRAHLUNG
Will consider also : x10 upgrade with e.g. charge compensation?
(suppresses beamstrahlung and beam-beam blow up)
Alain Blondel Nuphys2013 2013-12-19
Goal performance of e+ e- colliders
complementarity
•
Luminosity : Crossing point between circular and linear colliders ~ 4-500 GeV
As pointed out by H. Shopper in ‘The Lord of the Rings’ (Thanks to Superconducting RF…)
Combined know-how {LEP, LEP2 and b-factories} applied for large e+e- ring collider
High Luminosity +Alain
Energy
resolution
Calibration  precision on Z, W, H,11t
Blondel
Nuphys2013and
2013-12-19
STATISTICS
(e+e-  ZH, e+e- →W+W-, e+e- → ZH,[e+e-→ t𝑡] )
circumference
max beam energy
no. of IPs
Luminosity/IP at 350 GeV c.m.
Luminosity/IP at 240 GeV c.m.
Luminosity/IP at 160 GeV c.m.
Luminosity/IP at 90 GeV c.m.
TLEP-4 IP, per IP
80 km
175 GeV
4
1.3x1034 cm-2s-1
4.8x1034 cm-2s-1
1.6x1035 cm-2s-1
5.6 1035 cm-2s-1
statistics
106tt pairs
2 106 ZH evts
108 WW pairs
1012 Z decays
at the Z pole Alain
repeat
the
LEP physics
programme in a few minutes…
Blondel
Nuphys2013
2013-12-19
to appear in JHEP
Alain Blondel Nuphys2013 2013-12-19
best-of FCC/TLEP #2: Precision EW measts
Asset: -- high luminosity (1012 Z decays + 108 Wpairs + 106 top pairs )
-- exquiste energy calibration up and above WW threshold
target precisions
Also -- sin2 W 10-6
-- S= 0.0001 from W and Z hadronic widths
-- orders of magnitude on FCNCs and rare decays e.g. Z , e, e in 1011 Z
ll
events etc. etc.
Design study to establish possibility of theoretical calculations of corresponding precision.
Alain Blondel Nuphys2013 2013-12-19
NB without TLEP the SM line would have a 2.2 MeV width
-6 +several tests of same precision
in other wordsAlain
....Blondel
()=

610
Nuphys2013 2013-12-19
Neutrino counting
In October 1989 LEP determined that the number of neutrino families was 3.110.15
In Feb 1990 Cecilia Jarlskog commented that this number could smaller than 3
if the left handed neutrino(s) has a component of (a) heavy sterile neutrino(s)
which is kinematically suppressed or forbidden
Alain Blondel Nuphys2013 2013-12-19
Alain Blondel Nuphys2013 2013-12-19
At the end of LEP:
Phys.Rept.427:257-454,2006
N = 2.984 0.008
- 2  :^) !!
Test of the unitarity of the PMNS matrix
This is determined from the Z line shape scan
and dominated by the measurement of the
hadronic cross-section at the Z peak maximum 
The dominant systematic error is the theoretical
uncertainty on the Bhabha cross-section (0.06%)
which represents an error of 0.0046 on N
Improving on N by more than a factor 2 would require a large effort
to improve on the Bhabha cross-section calculation!
Alain Blondel Nuphys2013 2013-12-19
Another solution:
determine the number of neutrinos from the radiative returns
e+e-   Z ( vv )
in its original form (Karlen) the method only counts the ‘single photon’ events
and is actually less sensitive than claimed. It has poorer statistics and requires running
~10 GeV above the Z pole. Systematics on photon selection are not small.
present result: Nv= 2.920.05
Alain Blondel Nuphys2013 2013-12-19
Neutrino counting at TLEP
given the very high luminosity, the following measurement can be performed
𝜸𝒁(𝒊𝒏𝒗)
𝜸𝒁 → 𝒆𝒆, 𝝁𝝁
𝑵𝒗 =

𝑺𝑴
𝒆, 
The common  tag allows cancellation of systematics due to photon selection, luminosity
etc. The others are extremely well known due to the availanbility of O(1012 ) Z decays.
The full sensitivity to the number of neutrinos is restored , and the theory uncertainty

on 𝒆 𝑺𝑴 is very very small.
A good measurement can be made from the data accumulated at the WW threshold
where  ( Z(inv) ) ~4 pb for |cos| <0.95
161 GeV (107 s) running at 1.6x1035/cm2/s x 4 exp  3x107  Z(inv) evts,  =0.0011
adding 5 yrs data at 240 and 350 GeV ............................................................  =0.0008
Optimal (but dedicated ) point at 105 GeV (20pb and higher luminosity)   =0.0004?
under study.
Alain Blondel Nuphys2013 2013-12-19
ILC
Z – tagging
by missing mass
total rate  gHZZ2
ZZZ final state  gHZZ4/ H
 measure total width H
empty recoil = invisible width
‘funny recoil’ = exotic Higgs decay
easy control below theshold
e-
H
Z*
e+
Z
HF2012 summary Physics-- Alain Blondel 16-11-2012 Fermilab
best-of FCC/TLEP #1: Higgs factory
(constrained fit
including ‘exotic’)
4 IPs
(2 IPs)
2 106 ZH events in 5 years
Best across the board
«A tagged Higgs beam».
sensitive to new physics in loops
invisible width = (dark matter?)
also (but better done at the
hadron colliders HL-LHC, VHE-LHC:
total width
HHH
Htt
0.6%
28%
13%
from effect on HZ threshold
arXiv:1312.3322v1
from effect ontt threshold
Higgs Decay into nu + N
Chen, He, Tandean, Tsai (2011)
24
arxiv:1208.3654
LEP2 limits (DELPHI)
(projected)
Conclusion and invitation
The study of Future Circular Colliders is starting (CERN, China), including high luminosity
e+e- collider.
Precise measurements of the invisible Z and Higgs widths can be made using tagging:
e+e-   Z and e+e-  ZH
There are certainly many more variables that will be sensitive to the existence of
heavy right handed neutrinos
What about an ‘invisible’ phenomenology working group for the FCC study?
Alain Blondel Nuphys2013 2013-12-19