Alain Blondel Right handed Neutrinos at the FCC
Alain Blondel Right handed Neutrinos at the FCC Clermont 2015 11. 06. 2021 The Hunt for Heavy Neutrinos at the FCC Alain Blondel University of Geneva courtesy J. Wenninger with many thanks to S. Ganjour, M. Mitra, S. Pascoli, E. Graverini, P. Mermod, N. Serra, M. Shaposhnikov 1
Future Circular Collider Study - SCOPE CDR and cost review for the next ESU (2018) International collaboration to study: • 100 Te. V 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 11. 06. 2021 Alain Blondel Right handed Neutrinos at the FCC Clermont 2015 2
possible long-term strategy PSB PS (0. 6 km) SPS (6. 9 km) LEP LHC (26. 7 km) HL-LHC FCC-ee (80 -100 km, e+e-, 90 -350 Ge. V Interm. step FCC-hh (pp, up to 100 Te. V c. m. ) Ultimate goal & e± (120 Ge. V)–p (7, 16 & 50 Te. V) collisions FCC-eh) ≥ 60 years of e+e-, pp, ep/A physics at highest energies 11. 06. 2021 3
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 (1 mm vs 5 cm at LEP) much shorter lifetime (few minutes) top up continuously with booster ==> increase operation efficiency Increase SR beam power to 50 MW/beam 50 5 4 1000 at ZH threshold in LEP/LHC tunnel X 4 in FCC tunnel X 4 interaction points EXCITING! 11. 06. 2021 4
beam commissioning will start in 2016 K. Oide 11. 06. 2021 5
93 km option – current baseline LHC P 1/P 8 extraction (avoids Jura limestone) Deepest shaft 10, 500 m close to 400 m 11. 06. 2021 (not optimized) 6
Goal performance of e+ e- colliders WOW! complementarity with ILC/CLIC complementarity • Luminosity : Crossing point between circular and linear colliders ~ 4 -500 Ge. V As pointed out by H. Shopper in ‘The Lord of the Rings’ (Thanks to Superconducting RF…) Combined know-how {LEP, LEP 2 and b-factories} applied for large e+e- ring collider High Luminosity + Energy resolution and Calibration precision on Z, W, H, t 11. 06. 2021 7 CAN WE DO IT? Many accelerator and experimental challenges!
Beam polarization and E-calibration @ FCC-ee Precise meast of Ebeam by resonant depolarization ~100 ke. V 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 Ge. V) in March 1994 Polarization in collisions was observed (40% at BBTS = 0. 04) At LEP beam energy spread destroyed polarization above 60 Ge. V E E 2/ At FCC-ee transverse polarization up to at least 80 Ge. V 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 ke. V beam energy calibration around Z peak and W pair threshold. 11. 06. 2021 m. Z ~0. 1 Me. V, m. W ~ 0. 5 Me. V 8
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circumference max beam energy no. of IPs Luminosity/IP at 350 Ge. V c. m. Luminosity/IP at 240 Ge. V c. m. Luminosity/IP at 160 Ge. V c. m. Luminosity/IP at 90 Ge. V c. m. TLEP-4 IP, per IP 80 km 175 Ge. V 4 1. 3 x 1034 cm-2 s-1 6. 0 x 1034 cm-2 s-1 1. 6 x 1035 cm-2 s-1 2. 1035/36 cm-2 s-1 statistics 106 tt pairs 2 106 ZH evts 108 WW pairs 1012/13 Z decays at 11. 06. 2021 the Z pole repeat the LEP physics programme in a few minutes… 10
First look at the physics case of TLEP, ar. Xiv: 1308. 6176 v 3 scoped the precision measurements: -- Model independent Higgs couplings and invisible width -- Z mass (0. 1 Me. V), W mass (0. 5 Me. V) top mass (~10 Me. V), sin 2 Weff , 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 11. 06. 2021 11 http: //cern. ch/FCC-ee precision event generators (Jadach et al)
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 6/11/2021
Is it the end? 6/11/2021
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 6/11/2021
Nima 11. 06. 2021 15
Nima At higher masses -- or at smaller couplings? 11. 06. 2021 16
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 (me. V to Ze. V), nearly impossile to find. . . but could perhaps explain all: DM, BAU, -masses 17 11. 06. 2021
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. B 631: 151 -156, 2005 ar. Xiv: hep-ph/0503065 11. 06. 2021 18
Electroweak eigenstates R L L I = 1/2 L R R R Q= -1 Q= 0 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? -- 11. 06. 2021 19
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) 11. 06. 2021 Neutrino physics -- Alain Blondel
Mass eigenstates See-saw in a general way : MR = 0 m. D 0 Dirac only, (like e- vs e+): m L R R L Iweak= ½ 0 4 states of equal masses Some have I=1/2 (active) Some have I=0 (sterile) 11. 06. 2021 MR 0 m. D 0 Dirac + Majorana mass terms m MR 0 m. D = 0 Majorana only L R ½ Iweak= ½ 2 states of equal masses All have I=1/2 (active) M R > m. D 0 see-saw Dirac + Majorana m R NL Iweak= ½ 0 4 states , 2 mass levels dominantly: L NR m 1 have ~I=1/2 (~active) 21 m 2 have ~I=0 (~sterile)
There even exists a scenario that claims to explain everything: the MSM Shaposhnikov et al Te. V N 2, N 3 Ge. V Me. V N 1 ke. V me. V 11. 06. 2021 3 2 1 can generate Baryon Asymmetry of Universe if m. N 2, N 3 > 140 Me. V constrained: mass: 1 -50 ke. V mixing : 10 -7 to 10 -13 decay time: N 1 > Universe N 1 v soon excluded? 22
Manifestations of right handed neutrinos what is produced in W, Z decays is: 11. 06. 2021 23
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. . . 11. 06. 2021 24
Indirect constraints from lepton flavour violation are weak arxiv: 1208. 3654 LEP 2 limits (DELPHI) LEP 1 limits (DELPHI) (projected) 11. 06. 2021 25
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 250 Ge. V by reconfiguration after 500 Ge. V running; under discussion) FCC-ee (crab waist) 11. 06. 2021 26
-- invisible widths -- FCNC -- direct search of heavy neutrino decays 11. 06. 2021 27
At the end of LEP: Phys. Rept. 427: 257 -454, 2006 N = 2. 984 0. 008 - 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 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! 11. 06. 2021 28
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Neutrino counting at TLEP given the very high luminosity, the following measurement can be performed 11. 06. 2021 30
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) 11. 06. 2021 Htt (best at FCC-hh) <1% 28% 13% from HZ thresh from tt thresh 31
Lepton flavour violating Z decays with 1013 Z decays A. Abada et al, ar. Xiv: 1412. 6322 Indirect searches for sterile neutrinos at a highluminosity Z-factory A. Abada, V. De Romeri, S. Monteil, J. Orloff, A. M. Teixeira 11. 06. 2021 32
RHASnu’s production in Z decays Production: multiply by 2 for anti neutrino and add contributions of 3 neutrino species (with different |U| 2 ) Decay length: cm NB CC decay always leads to 2 charged tracks Backgrounds : four fermion: 11. 06. 2021 e+e- W*+ W*- e+e- Z*(vv) + (Z/ )* 33
Order-of-magnitude extrapolation of existing limits 4 106 Z decays BAU 11. 06. 2021 see-saw maybe achievable with 1010 - 1013 Z decays? 34
Search for heavy neutral leptons search e+ e- v N N v( /Z)* monojet Find: one event in 4 x 106 Z: e +e e+ * e 11. 06. 2021 Z* 35
Decay length |U|2 Interesting region ~ 10 -9 to 10 -12 @ 50 Ge. V L=1 mm L=10 m ~1 evt with 1013 Zs 20 50 heavy neutrino mass ~ M 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 11. 06. 2021 36 100 + N W- qq
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NZ = 1012 1 mm<L<1 m region of interest FCC-ee sensitivity A. B, Elena Graverini, Nicola Serra, Misha Shaposhnikov 11. 06. 2021 38
NZ = 1012 1 mm<L<1 m region of interest FCC-ee sensitivity 11. 06. 2021 39
NZ = 1012 1 mm<L<1 m region of interest FCC-ee sensitivity 11. 06. 2021 40
SHIP NZ = 1012 1 mm<L<1 m region of interest FCC-ee sensitivity NB very large detector caverns for FCC-hh may allow very large FCC-ee detector (R=15 m? ) leading to improved reach at lower masses. 11. 06. 2021 41
-- also search for same sign muons or electrons at the LHC (e. g. CMS: ) ATLAS ar. Xiv: 1203. 5420. CMS ar. Xiv: 1207. 6079. ar. Xiv: 1501. 05566 11. 06. 2021 limits at |U|2 ~ 10 -2 -5 level 7 Ge. V run papers on 8 Ge. V run in preparation 42
Preliminary projection for LHC (P. Mermod, very preliminary) 11. 06. 2021 43
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 Te. V 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. . . 11. 06. 2021 44
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 Te. V 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. 11. 06. 2021 45
SPARES 11. 06. 2021 46
Higgs Decay into nu + N Chen, He, Tandean, Tsai (2011) 11. 06. 2021 47
arxiv: 1208. 3654 H-> v. N or Z-> v. N LEP 2 limits (DELPHI) (projected) ? TLEP-Z ? 11. 06. 2021 48
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 Ge. V above the Z pole. Systematics on photon selection are not small. present result: Nv= 2. 92 0. 05 11. 06. 2021 49
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