neutrinos at the high energy frontier

Alain Blondel Nuphys2013 2013-12-19

Neutrinos at the High Energy Frontier


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 Neutrino physics -- Alain Blondel

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 TLEP design study r-ECFA 2013-07-20

See-saw in the most general way :

MR 0mD 0Dirac + Majorana mass terms

MR = 0mD 0Dirac only, (like e- vs e+):

L R R L ½ 0 ½ 04 states of equal masses

m

Iweak=

Some have I=1/2 (active)Some have I=0 (sterile)

MR 0mD = 0Majorana only

L R ½ ½ 2 states of equal masses

m

Iweak=

All have I=1/2 (active)

MR 0mD 0Dirac + Majorana

L NR R NL ½ 0 ½ 04 states , 2 mass levels

m

Iweak=

m1 have I=1/2 (~active)m2 have I=0 (~sterile)

Alain Blondel TLEP design study r-ECFA 2013-07-20

Neutrinos : the New Physics there is… and a lot of it! SM Dirac mass term

only Majorana mass term only

Dirac AND Majorana Mass terms

L RI= ½ ½

L R R L ½ 0 ½ 0

L R ½ ½

NR NL 0 0L R ½ ½

X 3 Families X 3 Families X 3 Families X 3 Families

6 massless states 3 masses 12 states3 active neutrinos3 active antinu’s6 sterile neutrinos…3 mixing angles 1 CP violating phase

3 masses 6 active statesNo steriles3 mixing angles 3 CP violating phases0v

6 masses12 states6 active states 6 sterile neutrinos…More mixing angles and CPV phases0v 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


Note that this is not necessary as we have no idea of mD and MR !


= has been invoked to explain the smallness of active neutrino masses

(maybe)

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.


-- 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 ii

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- ?

cos -

Manifestations of right handed neutrinos

c sin

= light mass eigenstateN = heavy mass eigenstate which couples to weak interaction

for one family see-saw (mD/M)


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 --

Back to the future


http://arxiv.org/abs/1305.6498.

CONSISTENT SET OF PARAMETERS FOR TLEP TAKING INTO ACCOUNT BEAMSTRAHLUNG

IPAC’13 Shanghai

50 100 150 200 250 300 350 4001E+034

1E+035

1E+036

1E+037

Ecm (GeV)

TLEP Facility Luminosity

Luminosity/cm2/s

Z

WW

ZH

tt

Will consider also : x10 upgrade with e.g. charge compensation? (suppresses beamstrahlung and beam-beam blow up)

http://arxiv.org/abs/1305.6498

Alain Blondel Nuphys2013 2013-12-19 11

• 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…)

Goal performance of e+ e- colliders

Combined know-how {LEP, LEP2 and b-factories} applied for large e+e- ring colliderHigh Luminosity + Energy resolution and Calibration precision on Z, W, H, t

complementarity


STATISTICS(e+e- ZH, e+e- →W+W-, e+e- → ZH,[e+e-→ t )

TLEP-4 IP, per IP statisticscircumference 80 kmmax beam energy 175 GeVno. of IPs 4 Luminosity/IP at 350 GeV c.m. 1.3x1034 cm-2s-1 106tt pairsLuminosity/IP at 240 GeV c.m. 4.8x1034 cm-2s-1 2 106 ZH evtsLuminosity/IP at 160 GeV c.m. 1.6x1035 cm-2s-1 108 WW pairsLuminosity/IP at 90 GeV c.m. 5.6 1035 cm-2s-1 1012 Z decays

at the Z pole repeat the LEP physics programme in a few minutes…


to appear in JHEP


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

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 l l events etc. etc.

Design study to establish possibility of theoretical calculations of corresponding precision.

target precisions


NB without TLEP the SM line would have a 2.2 MeV width

in other words .... ()= 610-6 +several tests of same precision


In October 1989 LEP determined that the number of neutrino families was 3.110.15

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

Neutrino counting


N = 2.984 0.008

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 theoreticaluncertainty 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!

- 2 :^) !!

At the end of LEP:Phys.Rept.427:257-454,2006


Another solution: determine the number of neutrinos from the radiative returns

e+e- Z ( vv )

in its original form (Karlen) the method only counts the ‘single photon’ eventsand 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= 2.920.05


given the very high luminosity, the following measurement can be performed

Neutrino counting at TLEP

𝑵 𝒗=

𝜸 𝒁 (𝒊𝒏𝒗)𝜸 𝒁→𝒆𝒆 ,𝝁𝝁𝒆 , (𝑺𝑴 )

The common tag allows cancellation of systematics due to photon selection, luminosityetc. 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 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, =0.0011adding 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.

HF2012 summary Physics-- Alain Blondel 16-11-2012 Fermilab

e+

e-

Z*

Z

H

Z – tagging by missing mass

ILC

total rate gHZZ2

ZZZ final state gHZZ4/ H

measure total width H

empty recoil = invisible width‘funny recoil’ = exotic Higgs decayeasy control below theshold

best-of FCC/TLEP #1: Higgs factory

2 106 ZH events in 5 years

«A tagged Higgs beam».

invisible width = (dark matter?)

4 IPs (2 IPs)

total widthHHHHtt

0.6%28%13%

sensitive to new physics in loops

also (but better done at the hadron colliders HL-LHC, VHE-LHC:

Bes

t acr

oss t

he b

oard

from effect on HZ thresholdarXiv:1312.3322v1 from effect ontt threshold

(constrained fit including ‘exotic’)

24

Higgs Decay into nu + N

Chen, He, Tandean, Tsai (2011)

LEP2 limits (DELPHI)

(projected)

arxiv:1208.3654


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?

neutrinos at the high energy frontier

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