The Hunt for Heavy Neutrinos at the FCC Alain Blondel Right handed Neutrinos at the FCC Clermont 2015 Alain Blondel University of Geneva with many thanks to S. Ganjour, M. Mitra, S. Pascoli, E. Graverini, P. Mermod, N. Serra, M. Shaposhnikov courtesy J. Wenninger 19.09.2018

Future Circular Collider Study - SCOPE CDR and cost review for the next ESU (2018) International collaboration to study: 100 TeV pp-collider (FCC-hh) Ultimate goal  defining infrastructure requirements e+e- collider (FCC-ee) as potential intermediate step p-e (FCC-he) option 80-100 km infrastructure in Geneva area 19.09.2018 Alain Blondel Right handed Neutrinos at the FCC Clermont 2015

possible long-term strategy FCC-ee (80-100 km, e+e-, 90-350 GeV Interm. step LEP PSB PS (0.6 km) LHC (26.7 km) HL-LHC SPS (6.9 km) FCC-hh (pp, up to 100 TeV c.m.) Ultimate goal & e± (120 GeV)–p (7, 16 & 50 TeV) collisions FCC-eh) ≥60 years of e+e-, pp, ep/A physics at highest energies 19.09.2018

1000 50 5 4 at ZH threshold in LEP/LHC tunnel X 4 in FCC tunnel Original motivation (end 2011): now that m_H and m_top are known, explore EW region with a high precision, affordable, high luminosity machine  Discovery of New Physics in rare phenomena or precision measurements ILC studies  need increase over LEP 2 (average) luminosity by a factor 1000 How can one do that without exploding the power bill? Answer is in the B-factory design: a low vertical emittance ring with small *y (1mm vs 5cm at LEP)  much shorter lifetime (few minutes)  top up continuously with booster ==> increase operation efficiency Increase SR beam power to 50MW/beam 50 5 4 1000 at ZH threshold in LEP/LHC tunnel X 4 in FCC tunnel X 4 interaction points EXCITING! 19.09.2018

beam commissioning will start in 2016 K. Oide 19.09.2018

93 km option – current baseline LHC P1/P8 extraction (avoids Jura limestone) Deepest shaft close to 400 m (not optimized) 10,500m 19.09.2018

Goal performance of e+ e- colliders WOW! complementarity with ILC/CLIC 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 + Energy resolution and Calibration  precision on Z, W, H, t CAN WE DO IT? Many accelerator and experimental challenges! 19.09.2018

Beam polarization and E-calibration @ FCC-ee Precise meast of Ebeam by resonant depolarization ~100 keV each time the meast is made At LEP transverse polarization was achieved routinely at Z peak. instrumental in 10-3 measurement of the Z width in 1993 led to prediction of top quark mass (179+- 20 GeV) in March 1994 Polarization in collisions was observed (40% at BBTS = 0.04) At LEP beam energy spread destroyed polarization above 60 GeV E  E2/  At FCC-ee transverse polarization up to at least 80 GeV to go to much higher energies requires spin rotators and siberian snake FCC-ee: use ‘single’ bunches to measure the beam energy continuously no interpolation errors due to tides, ground motion or trains etc… but saw-toothing must be well understood! require Wigglers to speed up pol. time << 100 keV beam energy calibration around Z peak and W pair threshold. mZ ~0.1 MeV, Z ~0.1 MeV, mW ~ 0.5 MeV 19.09.2018

PUBLISHED 19.09.2018

TLEP: PARAMETERS & STATISTICS (e+e- -> ZH, e+e- → W+W-, e+e- → Z,[e+e-→ t 𝑡 ] ) TLEP-4 IP, per IP statistics circumference 80 km max beam energy 175 GeV no. of IPs 4 Luminosity/IP at 350 GeV c.m. 1.3x1034 cm-2s-1 106tt pairs Luminosity/IP at 240 GeV c.m. 6.0x1034 cm-2s-1 2 106 ZH evts Luminosity/IP at 160 GeV c.m. 1.6x1035 cm-2s-1 108 WW pairs Luminosity/IP at 90 GeV c.m. 2. 1035/36 cm-2s-1 1012/13 Z decays at the Z pole repeat the LEP physics programme in a few minutes… 19.09.2018

-- Model independent Higgs couplings and invisible width First look at the physics case of TLEP, arXiv:1308.6176v3 scoped the precision measurements: -- Model independent Higgs couplings and invisible width -- Z mass (0.1 MeV), W mass (0.5 MeV) top mass (~10 MeV), sin2Weff , Rb , N etc...  powerful exploration of new physics with EW couplings up to very high masses  importance of luminosity and Ebeam calibration by beam depolarization up to W pair So far: simulations with CMS detector (Higgs) -- or «just» paper studies. Snapshot of novelties appeared in recent workshops Higher luminosity prospects at W, Z with crab-waist  sensitivity to right handed (sterile) neutrinos  s-channel e+e-  H(125.2) production almost possible (  monochromators)  rare Higgs Z W and top decays, FCNCs etc...  discovery potential for very small couplings  precision event generators (Jadach et al) 19.09.2018 http://cern.ch/FCC-ee

Englert and Higgs get Nobel Prize 1997-2013 Higgs boson mass cornered (LEP H, MZ etc +Tevatron mt , MW) Higgs Boson discovered (LHC) Englert and Higgs get Nobel Prize (c) Sfyrla 9/19/2018

Is it the end? 9/19/2018

-- Baryon Asymmetry in Universe -- Neutrino masses Is it the end? -- Dark matter -- Baryon Asymmetry in Universe -- Neutrino masses -- and... why are the charges of e and p identical to 21 significant digits? are experimental proofs that there is more to understand. We must continue our quest 9/19/2018

Nima 19.09.2018

At higher masses -- or at smaller couplings? Nima At higher masses -- or at smaller couplings? 19.09.2018

But at least 3 pieces are still missing THE STANDARD MODEL IS COMPLETE ..... But at least 3 pieces are still missing neutrinos have mass... and this very probably implies new degrees of freedom  Right-Handed, Almost «Sterile» (very small couplings) Neutrinos completely unknown masses (meV to ZeV), nearly impossile to find. .... but could perhaps explain all: DM, BAU,-masses 19.09.2018

FCC design study and FCC-ee http://cern.ch/fcc-ee some REFERENCES arxiv:1308.6176 arxiv:1208.3654 FCC design study and FCC-ee http://cern.ch/fcc-ee and presentations at FCC-ee physics workshops http://indico.cern.ch/category/5684/ Phys.Lett.B631:151-156,2005 arXiv:hep-ph/0503065 19.09.2018

Electroweak eigenstates 𝒆 𝒗 𝒆  𝒗   𝒗  𝒆   Q= -1 R R R L L L  𝒆     Q= 0 R R R I = 1/2 I = 0 Right handed neutrinos are singlets no weak interaction no EM interaction no strong interaction can’t produce them can’t detect them -- so why bother? -- 19.09.2018

Adding masses to the Standard model neutrino 'simply' by adding a Dirac mass term (Yukawa coupling) 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 (‘natural’?) that both terms are present  ‘see-saw’ B. Kayser, the physics of massive neutrinos (1989) 19.09.2018

See-saw in a general way : MR  0 mD  0 Dirac + Majorana mass terms Mass eigenstates See-saw in a general way : MR  0 mD  0 Dirac + Majorana mass terms MR > mD  0 Dirac + Majorana L NR R NL ½ 0 ½ 0 4 states , 2 mass levels see-saw 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 dominantly: 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) 19.09.2018

There even exists a scenario that claims to explain everything: the MSM Shaposhnikov et al TeV N2, N3 can generate Baryon Asymmetry of Universe if mN2,N3 > 140 MeV GeV MeV constrained: mass: 1-50 keV mixing : 10-7 to 10-13 N1 keV decay time: N1 > Universe eV 3 2 N1 v  meV 1 soon excluded? 19.09.2018

Manifestations of right handed neutrinos 𝒗 = light mass eigenstate N = heavy mass eigenstate  𝒗𝑳 , active neutrino which couples to weak inter. and  NR, which does’nt. 𝒗= 𝒗𝑳 cos - 𝑵𝒄 𝑹 𝐬𝐢𝐧 one family see-saw :   (mD/M) 𝒎𝒗  𝒎𝑫𝟐 𝑴 mN  M |U|2  2  𝒎𝒗 / mN can be larger with 3 families 𝑵= 𝑵 𝑹 cos+ 𝒗𝑳 c sin what is produced in W, Z decays is: 𝒗𝑳= 𝒗 cos + 𝑵 𝐬𝐢𝐧 -- mixing with active neutrinos leads to various observable consequences -- if very light (eV) , possible effect on neutrino oscillations (short baseline) -- if in keV region (dark matter), monochromatic photons from galaxies with E=mN/2 -- possibly measurable effects at High Energy If N is heavy it will decay in the detector (not invisible)  PMNS matrix unitarity violation and deficit in Z «invisible» width  Higgs, W, Z exotic decays H ii and Z ii , W-> li i  also in charm and b decays via W*-> li i  violation of unitarity and lepton universality in Z, W or  decays -- etc... etc... -- Couplings are small (𝒎𝒗 / mN) (but who knows?) and generally out of reach of hadron colliders (but this deserves to be revisited for detached vertices @LHC, HL-LHC, FCC-hh) 19.09.2018

by virtual neutrino exchange and to flavour violation Indirect effects -- neutrino Majorana mass term can lead to lepton number violating processes by virtual neutrino exchange and to flavour violation -- neutrinoless double beta decay (the most powerful one) -- FCNC (e) etc... -- at a Z factory : Z  Z e Z->  ,      e etc... 19.09.2018

Indirect constraints from lepton flavour violation are weak arxiv:1208.3654 LEP2 limits (DELPHI) LEP1 limits (DELPHI) (projected) 19.09.2018

Goal performance of e+ e- colliders FCC-ee as Z factory: 1012 Z (possibly even 1013 with crab-waist) (few years) possible upgrade complementarity ww NB: ideas for lumi upgrades: ILC arxiv:1308.3726 (not in TDR. Upgrade at 250GeV by reconfiguration after 500 GeV running; under discussion) FCC-ee (crab waist) 19.09.2018

-- direct search of heavy neutrino decays -- invisible widths -- FCNC -- direct search of heavy neutrino decays 19.09.2018

At the end of LEP: N = 2.984 0.008 Phys.Rept.427:257-454,2006 - 2  :^) !! 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! 19.09.2018

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Neutrino counting at TLEP given the very high luminosity, the following measurement can be performed     19.09.2018

incl. invisible = (dark matter?) Higgs factory (constrained fit including ‘exotic’) 4 IPs (2 IPs) 2 106 ZH events in 5 years «A tagged Higgs beam». sensitive to new physics in loops incl. invisible = (dark matter?) NB will improve with inclusion of ZH-> qq H tagging  total width HHH (best at FCC-hh) Htt (best at FCC-hh) <1% 28% 13% from HZ thresh from tt thresh 19.09.2018

Lepton flavour violating Z decays with 1013 Z decays A. Abada et al, arXiv:1412.6322 Indirect searches for sterile neutrinos at a high-luminosity Z-factory A. Abada, V. De Romeri, S. Monteil, J. Orloff, A. M. Teixeira 19.09.2018

RHASnu’s production in Z decays multiply by 2 for anti neutrino and add contributions of 3 neutrino species (with different |U|2 ) Decay Decay length: cm NB CC decay always leads to  2 charged tracks Backgrounds : four fermion: e+e-  W*+ W*- e+e-  Z*(vv) + (Z/)* 19.09.2018

Order-of-magnitude extrapolation of existing limits 4 106 Z decays maybe achievable with 1010 - 1013 Z decays? BAU see-saw 19.09.2018

search e+ e- v N N v(/Z)* monojet Find: one event in 4x106Z: e+e- Search for heavy neutral leptons search e+ e- v N N v(/Z)* monojet Find: one event in 4x106Z: e+e- e+ * Z* e- 19.09.2018

Decay length ~1 evt with 1013Zs Interesting region |U|2 ~ 10-9 to 10-12 @ 50 GeV Decay length L=1mm L=1m L=10m ~1 evt with 1013Zs 20 50 100 heavy neutrino mass ~ M  N + W-qq a large part of the interesting region will lead to detached vertices ... very strong reduction of background! Exact reach domain will depend on detector size and details of displaced vertex efficiency & background 19.09.2018

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A.B, Elena Graverini, Nicola Serra, Misha Shaposhnikov NZ = 1012 1mm<L<1m region of interest FCC-ee sensitivity A.B, Elena Graverini, Nicola Serra, Misha Shaposhnikov 19.09.2018

NZ = 1012 1mm<L<1m NZ = 1013 100𝒎 <L<5m region of interest FCC-ee sensitivity 19.09.2018

NZ = 1012 1mm<L<1m NZ = 1013 100𝒎 <L<5m region of interest FCC-ee sensitivity 19.09.2018

SHIP NZ = 1012 1mm<L<1m NZ = 1013 100𝒎 <L<5m region of interest FCC-ee sensitivity NB very large detector caverns for FCC-hh may allow very large FCC-ee detector (R=15m?) leading to improved reach at lower masses. 19.09.2018

-- also search for same sign muons or electrons at the LHC (e.g. CMS: ) ATLAS arXiv:1203.5420. CMS arXiv:1207.6079. arXiv:1501.05566 7 GeV run papers on 8 GeV run in preparation limits at |U|2 ~ 10-2-5 level 19.09.2018

Preliminary projection for LHC (P. Mermod, very preliminary) 19.09.2018

Comment/Outlook for FCC-hh We have seen that the Z factory offers a clean method for detection of Heavy Right-Handed neutrinos Ws are less abundant at the lepton colliders At the 100 TeV hadron machine the W is the dominant particle. There is a lot of /pile-up/backgrounds/lifetime/trigger issues which need to be investigated. BUT.... in the regime of long lived HNLs the simultaneous presence of -- the initial lepton from W decays -- the detached vertex with kinematically constrained decay allows for a significant background reduction. But it allows also a characterization both in flavour and charge of the produced neutrino, thus information of the flavour sensitive mixing angles and a test of the fermion violating nature of the intermediate (Majorana) particle. VERY interesting... 19.09.2018

Conclusions 1. H, Z factory will investigate invisible widths with exp precision of < 0.15% (Higgs) and < 0.0004  2. The direct quest for the «Right-Handed-Almost-Sterile-See-saw-partners neutrinos» (dextrinos? RHASnus? Heavy Neutral Leptons? Shaposhninos? heavinos?) is not desperate at all for Majorana mass at weak scale. In particular it may lead to spectacular ‘detached vertex’ signatures in a beam dump experiment (SHIP) or in Z-> neutrino decays at a Tera-Z factory like FCC-ee, Observation in W decays at hadron colliders with enough energy and luminosity (100 TeV FCC-hh), would allow charge and flavour identification (mixing angles!) ... be very interesting! But here a detached vertex trigger and some way to reduce the hadron interaction background will be needed. 19.09.2018

SPARES 19.09.2018

Higgs Decay into nu + N Chen, He, Tandean, Tsai (2011) 19.09.2018

H-> vN or Z-> vN arxiv:1208.3654 LEP2 limits (DELPHI) (projected) ? TLEP-Z ? 19.09.2018

determine the number of neutrinos from the radiative returns 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 19.09.2018

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