Testing Origin of Neutrino Mass at the LHC

Transcription

1 王凱 ( ワンカイ ) 東京大学数物連携宇宙研究機構 高エネルギー加速器研究機構理論系つくば, 2008 年 11 月 11 日 Tao Han, Biswarup Mukhopadhyaya, Zongguo Si and KW Phys. Rev. D 76, (2007) [arxiv: [hep-ph]] Pavel Fileviez Pére, Tao Han, Guiyu Huang, Tong Li and KW Phys. Rev. D 78, (2008) [arxiv: [hep-ph]]

2 Neutrino Mass: 1 st Evidence for Beyond SM Global Best Fit at 3σ level Schwetz ev 2 < m21 2 < ev 2 ; ev 2 < m31 2 < ev < sin 2 θ 12 < 0.40; 0.34 < sin 2 θ 23 < 0.67; sin 2 θ 13 < P i m i < 1.2 ev Something to keep in mind: Fermion mass

3 Lepton Number Violation (LNV) L Challenges: m t /m ν sin 2 θ 23 Dirac or Majorana nature of neutrino Global U(1) L or U(1) B L U(1) L as global symmetry in SM. Quantum gravity will break U(1) L and generate MAJORANA neutrino mass: llh u H u /M Pl ; m ν 10 5 ev

4 Global U(1) L or U(1) B L Broken Global Symmetry U(1) L Chikashige, Mohapatra, Peccei, 80 Majoron, Problem? U(1) B L is the leading candidate for extra U(1) gauge symmetry. Once imposing anomaly free condition, upto an overall normalization, U(1) Y is the uniquely dened. No [SU(3) C ] 2 U(1) B L or [SU(2) L ] 2 U(1) B L anomalies No [U(1) Y ] 2 U(1) B L or U(1) Y [U(1) B L ] 2 anomalies ONLY TRACE TrU(1) B L and Cubic [U(1) B L ] 3 SU(5) respect U(1) B L. One can gauge U(1) B L by adding just ONE SM singlet!

5 Models Assumption: SM Higgs Type I seesaw y D lν c H u + M R ν c ν c, L = 2 M R GeV, m ν MD 2 /M R Yanagida,79; Gell-Man et al.,79,glashow,80;mohapatra,senjanovic,80 Type II seesaw y ν l T iσ 2 l, L = 2 m ν = y ν v GeV Minikowski,77;Cheng,Li,80; Mohapatra,Senjanovic,81;Sha et al., 81 Zee-Babu model, generates neutrino mass at two-loop L = 2Zee 80, Babu, 88 Type III seesaw, etc...

6 Triplet Model (Type II seesaw) Y = 2 SU(2) L Triplet, Majorana Neutrino Mass from = 1 ( ) H + 2H H 0 H + y ν l T L C 1 iσ 2 l H ++ Wµ W ν : i 2g 2 2 v g µν ; H ++ l i l j : C 2Γ ++ ij P L

7 LNV Direct Test: 0νββ 1/M 4 W L y ν v /M 2 1/M4 W L m ν /M 2 y ν v M GeV 1 M > 0.1GeV

8 Other Bounds on Triplet Higgs Masses/Couplings VEV CDF/D 0 Search bound: m H ++ > 120 GeV (4 muons/muons+tau) Lepton Flavor Violation Br(µ e e + e + ) < ρ-parameter Gunion, et. al, 1990 Triplet vev breaks SU(2) L+R custodial symmetry ( ) 2 m W ρ = ; v < 1 GeV m Z cos θ W Or another real triplet to cancel. Georgi and Machacek, 1985

9 Triplet Model (Type II seesaw) Y = 2 SU(2) L Triplet = 1 ( ) H + 2H H 0 H + Breaking U(1) B L y ν l T L C 1 iσ 2 l + µh T iσ 2 H + h.c v = µ v 0 2 2M 2 H ++ l + l +, W + W + H + l + ν, W + h, W + Z, t b H 0 νν, ν ν, ZZ, W + W, H 1 H 1 (No tree level mass dierence among triplet Higgses. Otherwise H ++ H + W,H + H 2 W )

10 H ++ Decay BR: v vs yν Γ WW M 3 H (longitutinal); Γ ll M H

11 H + Decay BR

12 Neutrino and Triplet Leptonic Decay ( Y ν l T δ C iσ 2 l + h.c., where = + / 2 δ ++ δ 0 δ + / 2 ) No Majorana Phases sin θ 23

13 Doubly Charged (continued)

14 Neutrino Spectrum normal hierarchy inverted hierarchy (m 3 ) 2 (m 2 ) 2 (m 1 ) 2 ( m 2 ) sol ν e ( m 2 ) atm ν µ ( m 2 ) atm ν τ ( m 2 ) sol (m 2 ) 2 (m 1 ) 2 (m 3 ) 2

15 Majorana Phase Singly Charged Higgs BR is independent of Majorana phases.

16 Majorana Phase: a close look Γ + = cos θ + m diag ν V PMNS, Γ ++ = V v PMNS mdiag ν V PMNS 2 v Y j + = 3X Γ ij + 2 v, 2 Y ++ = 2v Γ ++ i=1 0 B V PMNS c 12 c 13 c 13 s 12 e iδ s 13 c 12 s 13 s 23 e iδ c 23 s 12 c 12 c 23 e iδ s 12 s 13 s 23 c 13 s 23 s 12 s 23 e iδ c 12 c 23 s 13 c 23 s 12 s 13 e iδ c 12 s 23 c 13 c 23 1 C A diag(e i Φ 1 /2, 1, e i Φ 2 /2 )

17 Singly Charged

18 Decay length of H ++ v 10 4 GeV: secondary vertex; Not longlived

19 Distinguish Spectrum via LNV Higgs Decay

20 Part II Phenomenology Searching at the Large Hadron Collider

21 Production of Triplet Higgses q(p 1 ) + q(p 2 ) H ++ (k 1 ) + H (k 2 ) q(p 1 ) + q (p 2 ) H ++ (k 1 ) + H (k 2 ) q(p 1 ) + q (p 2 ) H + (k 1 ) + H 2 (k 2 ) Tree Level Cross-section of Triplet Higgses Production

22 Remarks on Production triplet vev v suppresion phase space suppression Gauge cancellation among diagrams (Longitutinal W)

23 Remarks on Production (continued) QCD correction for this mass range 25% (NLO K -factor 1.25) real photon emission (γγ H ++ H ) 10% σ(fb) 10 2 σ(fb) M ++ H (GeV) M H ++ (GeV)

24 Photon-Photon σ γγ = σ elastic + σ inelastic + σ semi elastic σ elastic = σ inelastic = σ semi elastic = Z 1 Z 1 dz 1 dz 2 f γ/p (z 1 )f γ/p (z 2 )σ(γγ H ++ H ) τ τ/z 1 Z 1 Z 1 Z 1 Z 1 dx 1 dx 2 dz 1 τ τ/x 1 τ/x 1 /x 2 τ/x 1 /x 2 /z 1 dz 2 f q (x 1 )f q (x 2)f γ/q (z 1 )f γ/q (z 2 )σ(γγ H ++ H ) Z 1 Z 1 Z 1 dx 1 dz 1 dz 2 f q (x 1 )f γ/q (z 1 )f γ/p (z 2 )σ(γγ H ++ H ) τ τ/x 1 τ/x 1 /z 1 τ = 4m2 S Drees, Godbole 94

25 Search via Leptonic Decays Small vev limit v < 10 4 GeV All LNV, but not observable except for H ++ H ++ l + l + ; H + l + ν l ; H 2 νν µ,e and τ respectively H 2 invisible and always produced via H ± H 2, another missing ν from H +, impossible to reconstruct. pp H ++ H l + l + l ν, l + l + τ ν (l = e, µ) pp H ++ H l + l + l l, l + l + τ τ (l = e, µ)

26 4 Lepton (no τ nal state) p T (l max ) > 30 GeV and p T (l) min > 15 GeV η(l) < 2.5 R ll > 0.4 SM Background if there exists same avor, opposite sign dilepton ZZ/γ l + l l + l Veto events of M l + l M Z < 15 GeV After reconstruction, purely event counting

27 Trilepton (no τ nal state) p T (l max ) > 30 GeV and p T (l) min < 15 GeV η(l) < 2.5 R ll > 0.4 E T > 40 GeV SM Background if there exists same avor, opposite sign dilepton W ± Z/γ l ± νl + l, W ± W ± W l ± l + l + E T Veto events of M l + l M Z < 15 GeV

28 Trilepton M T = (E l T + E T ) 2 ( p l + p) 2 T

29 τ Reconstruction No other E T in nal state: pp H ++ H l + l + τ τ, l + l + µ τ, l + τ + τ τ Highly Boosted τ p invisible = κ p l ; each τ corresponds to one unknown Σ p T invisible = p T 2 independent equations M l + l + = Mrec τ τ ; 1 more equation UPTO THREE τs

30 µµττ and µµµτ

31 τ Identication Very dierent from τ ± from Lepton Number Conserving H ± decay. τ ± behaves just like τ ± from SM W ±. H τ ν (W τ ν τ ) : τ left-handed H + τ + ν (W + τ + ν τ ): τ + right-handed τ + R π+ ν τ τ L π ν τ pions are soft.

32 τ Leptonic decay H + τν l + E T Lepton p T H + l + E T l from H + Jaccobian Peak around M H /2 (may change due to boost) l from τ, purely boost eect, softer pt l selection (GeV) l misidentication rate 2.9% 9.4% 17.6% 4.6% 12.4% 22.2% τ survival probability 57.0% 69.8% 78.8% 62.8% 75.7% 83.7% τ selection: p T < 100 GeV (for M + H = 300 GeV) p T < 200 GeV for M + H = 600 GeV

33 Measuring BR knowns: N, L (Integrate luminosity) indirect: reconstructed M σ(h ++ H ) N 4µ = L σ(pp H ++ H ) BR 2 (H ++ µ + µ + ) N 3µτ = L σ(pp H ++ H ) BR(H ++ µ + µ + )BR(H ++ µ + τ + )

34 Once the BRs are measured,... Even the Phase.

35 Conclusion We propose one scenario that the Triplet models for neutrino mass generation can be directly tested at the LHC. It predicts dierent phenomenology like doubly charged scalars that can decay into same sign dilepton. If the doubly charged Higgs and its LNV decay has been discovered, we will be able to extract information of neutrino mass and mixing from BR of triplet Higgses. Thank you!