higgs production through sterile...

Higgs Production through Sterile Neutrinos

based on arXiv:1512.06035

Oliver FischerUniversity of Basel, Switzerland

[email protected]

IAS Conference, “The Future of High Energy Physics 2016”Hongkong, January the 19th, 2016

Motivation for sterile neutrinos

I Observation of neutrino oscillations requires at least two ofthe light neutrinos to be massive.

I Neutrino masses can be accounted for efficiently byright-handed or “sterile neutrinos”.

I Seesaw formula: (mν)αβ = −12v2EW(Y Tν ·M−1Yν

)αβ

The Seesaw Mechanism

I Näıve (1 νL, 1 νR) version: mν =12v2EW|yν |

2

MR

I More realistic example, the (2 νL, 2 νR) version:

Yν =

(O(yν) 0

0 O(yν)

),

(MR 0

0 MR + ε

)

⇒ mνi =v2EWO(y2ν )

MR(1 + ε)

⇒ Knowledge of mνi implies a relation between yν and MR .

Lowscale Seesaw

I This example uses a specific structure of the Yukawa and massmatrices that can be realised by symmetries (no fine tuning).

I A (2 νL, 2 νR) example:

Yν =

(O(yν) 0O(yν) 0

),

(0 MRMR ε

)

⇒ mνi = 0 + εv2EWO(y2ν )

M2R

⇒ In general: no fixed relation between yν and MR .⇒ Large yν are compatible with neutrino oscillations.

The Big Picture

GUT

Leptogenesis also

for larger masses

EW scale

models

ë

reactor

anomaly

ø

øø

warm Dark Matter

Lowscale Leptogenesis

mΝ2=Dmatm

2

mΝ2=Dmsol

2

eV keV MeV GeV TeV PeV EeV ZeV MGUT MPl

perturbativity

Ytop

Ye

10-5

10-7

10-9

10-11

Majorana Mass MR

Neu

trin

oY

ukaw

aco

upli

ng

y î

Symmetry Protected Seesaw Scenario

I Assumption: collider phenomenology dominated by two sterileneutrinos Ni with protective symmetry, such that

LN = −1

2N1RM(N

2R)

c − yναN1R φ̃† Lα + H.c.

I The active-sterile mixing parameter: θα =yναvEW√

2M

I The leptonic mixing matrix to leading order in θα

U =

Ne1 Ne2 Ne3 − i√2θe1√2θe

Nµ1 Nµ2 Nµ3 − i√2θµ1√2θµ

Nτ1 Nτ2 Nτ3 − i√2θτ √2θτ0 0 0 i√

21√2

−θ∗e −θ∗µ −θ∗τ − i√2(

1− θ22)

1√2

(1− θ22

)

Interactions between heavy neutrinos and the SM

I Charged current (CC):

j±µ =g

2θα ¯̀α γµ (−iN1 + N2)

I Neutral current (NC):

j0µ =g

2 cW

[θ2N̄2γµN2 + (ν̄i γµ ξα1N1 + ν̄i γµ ξα2N2 + H.c)

]I Higgs boson Yukawa interaction:

LYukawa =3∑

i=1

ξα2

√2M

vEWνiφ

0(N1 + N2

)I With the mixing parameters: ξα1 = (−i)N ∗αβ

θβ√2, ξα2 = i ξα1

Combination of present bounds

50 100 150 200

1

10-1

10-2

10-3

10-4

10-5

10-6

M @GeVD

Q2

50 100 150 200

1

10-1

10-2

10-3

10-4

M @GeVD

ÈyÈ

Direct searches

Delphi HZ pole searchesL 2Σ: ÈyÈ= ÚΑ yΝΑ2 , Q2=ÚΑÈΘΑ

2

LHC HHiggs decays*L 1Σ: ÈyÈ= ÚΑ yΝΑ2 , Q2=ÚΑÈΘΑ

2

Aleph He+e- ® 4 leptonsL 1Σ: ÈyÈ=ÈyΝe È, Q2=ÈΘe

2

Other Hglobal fitLÈyÈ= ÈyΝe È, Q

2=ÈΘe2

ÈyÈ= ÈyΝΜ È, Q2=ÈΘΜ

2

ÈyÈ= ÈyΝΤ È, Q2=ÈΘΤ

2

Antusch, OF; arXiv:1502.05915 (2015)

∗ Currently dominated by h → γγ.

Resonant mono-Higgs from sterile neutrinos

ν

W ν

hN

e+

e−

Z

ν

ν

h

N

e+

e−

I Generally: σhνν = σSMhνν + σ

Non-Uhνν + σ

Directhνν .

I σDirecthνν from on-shell production of sterile neutrinos.

? Interference with SM-background strongly suppressed.? W -exchange process effective at larger centre-of-mass

energies, but sensitive only to yνe .? s-channel production (Z boson) produces all flavours.

I σNon-Uhνν : indirect effect (via input parameters) from theinduced non-unitarity of the PMNS matrix.

Resonant mono-Higgs-production cross section

200 400 600 800 1000

10

20

30

40

50

M @GeVD

ΣhΝΝ

Direct HÈΘe

2L@fbD

200 400 600 800 1000

0.05

0.10

0.15

0.20

0.25

M @GeVD

ΣhΝΝ

Direct HÈΘΤ2L@fbD

Ecm @GeVD

240

350

500

1000

Antusch, Cazzato, OF, arXiv:1512.06035 (2015)

I Using present upper bounds at 68% Bayesian confidence level.

I Mono Higgs production cross section in the SM is ∼ 54 fb at250 and 350 GeV

Simulation, reconstruction and kinematic cuts

I Event simulation: WHIZARD 2.2.7

I Showering: PYTHIA 6.427

I Reconstruction: Delphes 3.2.0 (ILD card)

I Anaylsis: Madanalysis5

The Higgs Peak: |yνe | = 0.036 & M = 152 GeV, 10 ab−1

Ecm=240 GeV

100 105 110 115 120 125 1300

10000

20000

30000

40000

di-jet invariant mass @GeVD

EventsBin10ab-1

e+e-®ΝN®ΝΝh®jj

e+e-®ΝΝh SM®jj

e+e-®4f SM®jj


Our cuts (not fully optimised):

I Pre selection: Nj = 2,N` = 0, 110 < Mjj < 125 GeV

I For the example:Pjj > 70,�ET > 15 GeV

Event counts: (starting with pre selection)

BKG 548.584 → 18.627σDirecthνν 15.335 → 4.846

⇒ S√S+B' 30!

Contamination of SM parameters

150 200 250 300 350

0.001

0.002

0.005

0.010

0.020

0.050

0.100

M @GeVD

ΣhΝΝΣ

hΝΝ

SM-1

Ecm = 240 GeV

Ecm = 350 GeV

HΣbbΝΝH240 GeVL´10ab-1L-12

HΣbbΝΝH350 GeVL´3.5ab-1L-12


Standard cuts for Higgs events at lepton colliders:√s 240 GeV 350 GeV

Missing Mass [GeV] 80 ≤ Mmiss ≤ 140 50 ≤ Mmiss ≤ 240Transverse P [GeV] 20 ≤ PT ≤ 70 10 ≤ PT ≤ 140Longitudinal P [GeV] |PL| < 60 |PL| < 130Maximum P [GeV] |P| < 30 |P| < 60Di-jet Mass [GeV] 100 ≤ Mjj ≤ 130 100 ≤ Mjj ≤ 130Angle (jets) [Rad] α > 1.38 α > 1.38

Sensitivity of the mono-Higgs channel to neutrino mixing

Case I

150 200 250 300 350 400 450 5000.002

0.005

0.010

0.020

0.050

0.100

0.200

M @GeVD

ÈyΝeÈ

Ecm @GeVD

240, reconstructed

350, reconstructed

500, reconstructed

240, parton

350, parton

500, parton

Present upper bound


Considered:10 ab−1 for 240 GeV, 3.5 ab−1 for 350 GeV, 1 ab−1 for 500 GeV

Summary and conclusions

I Sterile neutrinos are well motivated extensions of the SM.

I Symmetry protected scenarios allow for large Yukawacouplings and masses in the interesting range.

I Higher center-of-mass energies lead to increasedmono-Higgs production cross sections from sterileneutrinos.

I√s = 350 GeV is even more sensitive than 240 GeV.

I A contamination of the Higgs sample can lead to a 3σdeviation of the SM parameters.

I Sensitivity to |yνe | down to 6× 10−3 is possible.? Important for understanding the data.? Complementarity to other searches for sterile Neutrinos.

I For other search channels, see: Antusch, OF; arXiv:1502.05915 (2015)

Thank you for your attention.

Backup I: Prospects of Sensitivity at the CEPC

L>10m CEPC

50 100 150 200 250

10-2

10-4

10-6

10-8

10-10

10-12

M @GeVD

Q2

L>10m CEPC

50 100 150 200 250

10-1

10-2

10-3

10-4

10-5

10-6

10-7

M @GeVD

ÈyÈ

Direct searches

Z pole search 2Σ: ÈyÈ= ÚΑ yΝΑ2 , Q2=ÚΑÈΘΑ

2

Higgs ®WW 1Σ: ÈyÈ= ÚΑ yΝΑ2 , Q2=ÚΑÈΘΑ

2

e+e-® h +MEHTL 1Σ: ÈyÈ=ÈyΝe È, Q2=ÈΘe

2

e+e-® lΝlΝ* 1Σ: ÈyÈ=ÈyΝe È, Q2=ÈΘe

2

Other

Precision constraints: ÈyÈ= yΝe2 + yΝΜ

2 , Q2=ÈΘe2+ÈΘΜ

2

Precision constraints: ÈyÈ=ÈyΝΤ È, Q2=ÈΘΤ

2

’’Unprotected’’ type-I seesaw

Antusch, OF; arXiv:1502.05915 (2015)

∗ Preliminary estimate using statistical uncertainty only.

Backup II: Higgs Boson Branching Ratio into Neutrinos

I From “indirect” tests andDelphi.

I O(1) branching ratiopossible.

⇒ Possible effect on Higgsdecay rates into StandardModel particles.

i=1«Θe

i=3«ΘΤ

i=2«ΘΜ

DELPHI

0 20 40 60 80 100 12010-6

10-5

10-4

0.001

0.01

0.1

1

M @GeVD

BrHh®ΝiNL

Antusch, OF; arXiv:1502.05915 (2015)

Backup III: Cross sections for SM background

Final state σSM@240 GeV σSM@350 GeV σSM@500 GeV

bb̄νν 146.492 134.614 183.594cc̄νν 88.0172 73.7956 82.7041jjνν 528.8 463.1 500.3bb̄bb̄ 81.2629 47.6152 25.5571bb̄cc̄ 146.566 87.6518 51.6446bb̄jj 6820.6 4259.5 2537.8bb̄e+e− 2080.87 2500.82 2920.9bb̄τ+τ− 34.1905 19.7975 11.0619cc̄τ+τ− 25.2553 15.0695 9.15227jjτ+τ− 116.0 72.4 37.6τ+τ−νν 235.89 163.851 119.989single top 0.012 63.3 1092tt̄ — 322. 574.

All cross sections in fb.

Backup IVa: High Energy Physics Time Scales

LEP

LHC

HL-LHC

Future collider

Today

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Proto

Construction

Physics

Backup IVb: High Energy Physics Time Scales

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LHC

HL-LHC

Future collider

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Happy years

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