Neutrinos at the High Energy Frontier

Neutrinos at the High EnergyFrontier

MOTIVATION The onlyknown BSM physics at the particlephysicslevelis the existence of neutrino masses -- There is no unique solution for mass terms: Diraconly? Majoranaonly? Both? -- if Both, existence of (2 or 3) families of massive right-handed (~sterile) i ,i neutrinos ispredicted («see-saw» models) masses are unknown (<eV to >1010GeV) -- Arguably, right handed neutrinos are the mostlikely ‘new physics’ thereis -- can high energyparticlephysicsexperimentsparticipate to the search?

Adding masses to the Standard model neutrino 'simply' by adding a Dirac mass term impliesadding a right-handedneutrino (new particle) No SM symmetrypreventsaddingthen a termlike and thissimplymeansthat a neutrino turnsinto a antineutrino (the charge conjugate of a right handed antineutrino is a lefthanded neutrino!) It isperfectlyconceivablethatbothterms are present ‘see-saw’

See-saw in the mostgeneralway : MR 0 mD  0 Dirac + Majorana mass terms MR 0 mD  0 Dirac + Majorana L NR R NL ½ 0 ½ 0 4 states , 2 mass levels MR = 0 mD  0 Dirac only, (like e- vs e+): L R R L ½ 0 ½ 0 4 states of equal masses MR 0 mD = 0 Majorana only L R ½ ½ 2 states of equal masses m m m Iweak= Iweak= Iweak= Some have I=1/2 (active) Some have I=0 (sterile) All have I=1/2 (active) m1 have I=1/2 (~active) m2 have I=0 (~sterile)

Neutrinos : the New Physicsthereis… and a lot of it! Mass hierarchies are all unknownexcept m1 < m2 Preferred scenario has bothDirac and Majoranaterms … … a bonanza of extremeexperimental challenges

Note thatthisis not necessary as we have no ideaof mD and MR !

= has been invoked to explain the smallness of active neutrino masses (maybe)  is a pretty large hierarchyproblemis’ntit? ... but we dont really know thatthisimplies M  MGUT northat the see-sawmixingissmall norwhatis the familydependence of thisreasoning.

Manifestations of right handedneutrinos = light mass eigenstate N = heavy mass eigenstate  which couples to weak interaction cos -  for onefamily see-saw   (mD/M) c sin -- mixingwith active neutrinos leads to various observable consequences -- if very light (eV) , possible effect on neutrino oscillations -- if mixing in % or permillevel, possiblymeasurableeffects 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 whoknows?) and generally out of reach of hadron colliders -- how about high statisticse+e- ?

Back to the future 30 yearslater and withexperiencegained on LEP, LEP2 and the B factories wecan propose a Z,W,H,tfactory of 1000 times the luminosity of LEP2 CERN islaunching a 5 years international design study of CircularColliders 100 TeV pp collider (VHE-LHC) and high luminositye+e- collider (TLEP) -- kick-off meeting 12-15 February 2014 in Geneva --

IPAC’13 Shanghai http://arxiv.org/abs/1305.6498. Z WW ZH tt CONSISTENT SET OF PARAMETERS FOR TLEP TAKING INTO ACCOUNT BEAMSTRAHLUNG Will consideralso : x10 upgrade withe.g. charge compensation? (suppressesbeamstrahlung and beam-beamblow up)

Goal performance of e+ e- colliders complementarity Combined know-how {LEP, LEP2 and b-factories} applied for large e+e- ring collider High Luminosity + Energyresolution and Calibration  precision on Z, W, H, t • 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…)

STATISTICS(e+e- ZH, e+e- →W+W-, e+e- →ZH,[e+e-→t ) 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 ) -- exquisteenergy calibration up and above WW threshold targetprecisions Also -- sin2 W10-6 -- S= 0.0001 from W and Z hadronicwidths -- orders of magnitude on FCNCs and rare decayse.g. Z , e, e in 1011 Zlleventsetc. etc. Design study to establishpossibility of theoreticalcalculations of correspondingprecision.

NB without TLEP the SM line would have a 2.2 MeV width in otherwords .... ()=  610-6 +several tests of sameprecision

Neutrino counting In October 1989 LEP determinedthat the number of neutrino familieswas 3.110.15 In Feb 1990 Cecilia Jarlskogcommentedthatthisnumbercouldsmallerthan 3 if the lefthanded neutrino(s) has a component of (a) heavysterile neutrino(s) whichiskinematicallysuppressed or forbidden

Atthe end of LEP: Phys.Rept.427:257-454,2006 N = 2.984 0.008 - 2  :^) !! Test of the unitarity of the PMNS matrix This isdeterminedfrom the Z line shape scan and dominated by the measurement of the hadronic cross-section at the Z peakmaximum  The dominant systematicerroris the theoretical uncertainty on the Bhabha cross-section (0.06%) whichrepresents 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!

Another solution: determine the number of neutrinos from the radiative returns e+e-   Z ( vv ) in its original form (Karlen) the methodonlycounts the ‘single photon’ events and isactuallyless sensitive thanclaimed. It has poorerstatistics and requires running ~10 GeVabove the Z pole. Systematics on photon selection are not small. presentresult: Nv= 2.920.05

Neutrino countingat TLEP given the very high luminosity, the followingmeasurementcanbeperformed • The common tag allowscancellation of systematics due to photon selection, luminosity • etc. The others are extremelywellknown due to the availanbility of O(1012 ) Z decays. • The full sensitivity to the number of neutrinos isrestored , and the theoryuncertainty • on is veryverysmall. • A good measurementcanbe made from the data accumulatedat 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 higherluminosity)   =0.0004? • understudy.

ILC Z – tagging by missing mass total rate  gHZZ2 ZZZ final state  gHZZ4/ H  measure total widthH emptyrecoil = invisible width ‘funnyrecoil’ = exoticHiggsdecay easy control belowtheshold e- H Z* Z e+

best-of FCC/TLEP #1: Higgsfactory (constrained fit including ‘exotic’) 4 IPs (2 IPs) 2 106 ZH events in 5 years «A taggedHiggsbeam». sensitive to new physics in loops Best across the board invisible width = (darkmatter?) also (but betterdone at the hadron colliders HL-LHC, VHE-LHC: 0.6% 28% 13% total width HHH Htt fromeffect on HZ threshold arXiv:1312.3322v1 fromeffectonttthreshold

Higgs Decay into nu + N Chen, He, Tandean, Tsai (2011)

arxiv:1208.3654 LEP2 limits (DELPHI) (projected)

Conclusion and invitation The study of Future CircularCollidersisstarting (CERN, China), including high luminosity e+e- collider. Precisemeasurements of the invisible Z and Higgswidthscanbe made usingtagging: e+e-  Zande+e-  ZH There are certainlymany more variables thatwillbe sensitive to the existence of heavy right handedneutrinos What about an ‘invisible’ phenomenologyworking group for the FCC study?

Neutrinos at the High Energy Frontier