Heavy Neutrinos and (Safe) Jet Vetoes 1 University of Birmingham - PowerPoint PPT Presentation

Heavy Neutrinos and (Safe) Jet Vetoes 1 University of Birmingham Richard Ruiz Institute for Particle Physics Phenomenology, University of Durham, UK 2 13 June 2018 1 with Silvia Pascoli and Cedric Weiland [1805.09335, 180X.YYYYY] 2 IPPP → CP3, Universite Catholique de Louvain, Belgium (Fall ’18) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 1 / 33

The Challenge Brief history: 2 years ago asked if possible to improve LHC searches for leptonic decays of heavy neutrinos, N → ℓ 1 W → ℓ 1 ℓ 2 ν “improve” ̸ = MVA or BDT but a qualitatively new pheno analysis ℓ ± 3 W ± ν ℓ N 1 , 2 u i W ±∗ ℓ ∓ 2 ℓ ± d j 1 The impetus : new channels ( W γ fusion), new technology (automated NLO+PS), unclear if lepton number violating ℓ ± 1 ℓ ± 2 + nj is observable An idea : heavy N events typically contain fewer jets than backgrounds The question : can jet activity be used to improve heavy N searches? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 2 / 33

Money Plot: Pushing the reach of the LHC The result: 1 CMS 95% CL upper limit on |V | 2 eN -1 13 TeV, 35.9 fb [1802.02965] − 1 10 95% CL, 2 → | -1 150 fb 4 → -1 τ 95% CL, 3 ab = |V − 2 10 2 2 95% global upper limit on |V | [1605.08774] | 3 e4 − 10 e4 |V Veto,b Standard Analysis (p = 25 GeV) T − 4 10 Veto,j l Safe Veto Analysis (p = p ) 1 T T ± 2 LHC 14 τ ± e l |V | =0 µ 4 h X 5 − 10 200 400 600 800 1000 m [GeV] N [1805.09335] Plotted : LHC 14 sensitivity to active-sterile neutrino mixing (coupling) vs heavy neutrino mass in the τ ± h e ∓ ℓ X ( ℓ X = e , µ, τ h ) final state Dash = standard search with b -jet veto (mirrors 13 TeV CMS for e /µ ) Solid = “improved” analysis with special type of jet veto . . . . . . . . . . . . . . . . . . . . Improved sensitivity up to 10 − 11 × with L = 3 ab − 1 . Now for the details! . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 3 / 33

Heavy Neutrinos and (Safe) Jet Vetoes A philosophically new approach to heavy N searches at colliders has increased LHC sensitivity by an order of magnitude (in coupling space) New channels, new tools/machinery, new understanding of jets Today: 1 Why heavy neutrinos? 2 Heavy neutrino production at colliders 3 Safe Jet Vetoes 4 Monte Carlo Campaign (an ongoing fight!) 5 Results ✓ 6 Outlook for future colliders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 4 / 33

Motivation for new physics from ν physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 5 / 33

In neutrino fixed-target experiments, ν µ beams are prepared from π ± , then studied at near and far detectors (reminiscent of early SLAC DIS expts) 20 Prediction × 20 NOvA 6.05 10 POT-equiv. Deficit/disappearance of expected ν µ σ 1- syst. range Max. mix. pred. 15 (+apperance of ν e /ν τ ) interpreted Backgrounds Data Events successfully as ν ℓ 1 → ν mass → ν ℓ 2 10 transitions/oscillations 5 [E.g. NO ν A ν µ disapp., 1701.05891] 0 oscillations 1.5 Ratio to no Reconstructed Neutrino Energy (GeV) 012345 1 0.5 = ⇒ ν have mass! 0 0 1 2 3 4 5 . . . . . . . . . . . . . . . . . . . . Reconstructed neutrino energy (GeV) . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 6 / 33

So, neutrinos have masses ≲ O ( 0 . 1 ) eV. Is this a problem? Yes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 7 / 33

Neutrinos Masses and the Standard Model (SM) To generate ν masses similar to other SM fermions, we need N R ) ( ⟨ Φ ⟩ + h ) ( L ν Yuk . = − y ν L ˜ Φ N R + H . c . = − y ν ν L ℓ L N R + H . c . 0 = ⇒ m D ν L N R , where m D = y ν ⟨ Φ ⟩ and y ν is the neutrino’s Higgs Yukawa coupling. However, N Ri do not exist in the SM, implying m D = 0 Nonzero neutrino masses implies new degrees of freedom exist [Ma’98]: m ν � = 0 + LH currents LH Majorana Mass : m L ν ν L ν c and / or Dirac Mass : m D ν ν L N R L m L m D ν = y � ∆ � or strong dynamics ν = y � Φ SM � . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 8 / 33

Collider Connection to Neutrino Mass Models 3 Neutrino mass models (aka Seesaw models) hypothesize new particles of all shapes, spins, charges, and color: N (Type I) , T 0 , ± (Type III) , Z B − L , H ± , ±± (Type I+II) , . . . R Through gauge couplings and mixing, production in ee / ep / pp collisions DY : qq → γ ∗ / Z ∗ → T + T − qq ′ → W ± R → N ℓ ± and WBF : W ± W ± → H ±± GF : gg → h ∗ / Z ∗ → N ν ℓ u m u � p u d n d u W ∗ e − R W − H −− N u i W R ℓ 2 W − e − ℓ 1 d j d � p u u u 3 Review on ν mass models at colliders, Y. Cai, T. Li, T. Han, RR [1711.02180] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 9 / 33

Collider Connection to Low-Scale Neutrino Mass Models 4 Seesaw particles then decay to SM particles that are observed/inferred by detector subsystems T ± → W ± ν, Z ℓ ± , h ℓ ± R → N ℓ ∓ → ℓ ± W ± 1 ℓ ± and/or 2 + nj , Identification of particles and properties through reconstruction of final-state kinematics, e.g., invariant mass peaks and angular distributions (5 TeV, 0.4 /dm [1 / 30 GeV] (M ,m ) = 500 GeV) W N R (3 TeV, 150 GeV) (4 TeV, 0.3 (3 TeV, 400 GeV) 30 GeV) (3 TeV, 0.2 300 GeV) σ d 0.1 σ 1/ 0 0 100 200 300 400 500 600 m [GeV] j N 4 Review on ν mass models at colliders, Y. Cai, T. Li, T. Han, RR [1711.02180] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 10 / 33

II: Heavy Neutrinos and Colliders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 11 / 33

(Heavy) Neutrino Mixing for Non-experts After EWSB, ν ℓ and N R are singlets under SU ( 3 ) c ⊗ U ( 1 ) EM = ⇒ mixing! Neutrino oscillations already tell us mass states ̸ = flavor states Example : In a two-state system, mixing between chiral eigenstates and mass eigenstates is given by unitary transformation/rotation ( ν L ( cos φ ) ) ( ν 1 ) sin φ = N c − sin φ cos φ N 2 R � �� � � �� � chiral basis mass basis Decompose chiral states in an interaction theory into mass states by making the replacement: φ ≪ 1 ≈ ( 1 − 1 2 φ 2 ) | ν 1 ⟩ + φ | N 2 ⟩ | ν L ⟩ = cos φ | ν 1 ⟩ + sin φ | N 2 ⟩ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 12 / 33

(Heavy) Neutrino Mixing for Non-experts After EWSB, ν ℓ and N R are singlets under SU ( 3 ) c ⊗ U ( 1 ) EM = ⇒ mixing! Neutrino oscillations already tell us mass states ̸ = flavor states Example : In a two-state system, mixing between chiral eigenstates and mass eigenstates is given by unitary transformation/rotation ( ν L ( cos φ ) ) ( ν 1 ) sin φ = N c − sin φ cos φ N 2 R � �� � � �� � chiral basis mass basis Decompose chiral states in an interaction theory into mass states by making the replacement: φ ≪ 1 ≈ ( 1 − 1 2 φ 2 ) | ν 1 ⟩ + φ | N 2 ⟩ | ν L ⟩ = cos φ | ν 1 ⟩ + sin φ | N 2 ⟩ Simplify : Like CKM, messy for n > 1 gen., so parameterize [0901.3589]: Large active-light as | U ℓν m | 2 ∼ 1 − ( m ν / m N ) Small active-heavy/active-sterile as | V ℓ N m ′ | 2 ∼ ( m ν / m N ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ruiz - IPPP Heavy N and (Safe) Jet Vetoes - Birmingham 12 / 33