LHC and the origin of neutrino mass Goran Senjanovi c ICTP B. - - PowerPoint PPT Presentation

• G. Senjanovi´

c

LHC and the origin of neutrino mass

Goran Senjanovi´ c ICTP

• B. Bajc, G. S., 06

B.Bajc, M. Nemevˇ sek, G. S., 07 In progress with A. Arhrib, B. Bajc, D. Ghosh, T. Han, G.-Y. Huang, I. Puljak,

Neutrino 08-Christchurch 1

• G. Senjanovi´

c

With the degrees of freedom of the SM ν masses parametrized by Weinberg d = 5 effective operator L = Yij LiHHLj M v2 M Y = UP MNS mdiag

ν

U T

P MNS

neutrino mass - Majorana M signals the appearence of new physics

Neutrino 08-Christchurch 2

• G. Senjanovi´

c

Violation of lepton number: ∆L = 2

• neutrino-less double beta decay ν0ββ

a text-book fact

• same sign charged lepton pairs in colliders

Keung, G.S., 83

Neutrino 08-Christchurch 3

• G. Senjanovi´

c

• If M is huge, no hope of direct observation of new physics
• M = 1013GeV − 1014GeV corresponds to Y of order one
• However, small Yukawas are natural in a sense of being

protected by symmetries.

• Keep M free and look for theoretical predictions (grand

unification)

Neutrino 08-Christchurch 4

• G. Senjanovi´

c

Only 3 ways of producing the Weinberg operator By exchange of heavy

• fermion singlet (1C, 1W , Y = 0)

TYPE I SEESAW Minkowski, 77 Mohapatra, Senjanovi´ c, 79 Gell-Mann et al, 79 Glashow, 79 Yanagida, 79

• boson weak triplet (1C, 3W , Y = 2)

TYPE II SEESAW Lazarides et al, 80 Mohapatra, Senjanovi´ c, 80

• fermion weak triplet (1C, 3W , Y = 0)

TYPE III SEESAW Foot et al, 86

Neutrino 08-Christchurch 5

• G. Senjanovi´

c

I and II very well studied, III almost ignored in the past

Neutrino 08-Christchurch 6

• G. Senjanovi´

c Neutrino 08-Christchurch 7

• G. Senjanovi´

c Neutrino 08-Christchurch 8

• G. Senjanovi´

c

All this by itself not more useful than just Weinberg operator unless

• we can reach the scale M, interesting only for low M
• we have a theory of these singlets, triplets (GUT for example)

Neutrino 08-Christchurch 9

• G. Senjanovi´

c

This reminiscent of the Fermi theory of low energy weak interactions: saying that the four fermion interactions can be described by the exchange of a new particle (W boson) not useful except

• when you can reach the new scale (MW )
• you have a theory of this new particle: SU(2)L×U(1) Standard

Model gauge theory that correlates different processes at low energies E << MW

Neutrino 08-Christchurch 10

• G. Senjanovi´

c

ν mass window to new physics - if Majorana

• Dirac case complete - new physics not necessary
• SM with Majorana neutrino not complete
• Majorana case connects mν to different new phenomena like

ν0ββ decay

Neutrino 08-Christchurch 11

• G. Senjanovi´

c Neutrino 08-Christchurch 12

• G. Senjanovi´

c

in general mν not directly connected to ν0ββ decay: depends on the completion Example: LR symmetry with low WR, νR masses has a nonzero ν0ββ decay even with yD, mν → 0

Neutrino 08-Christchurch 13

• G. Senjanovi´

c Neutrino 08-Christchurch 14

• G. Senjanovi´

c

This is why it is important for the see-saw to be traced in colliders: measure ∆L = 2 operators not only in ν0ββ decays, but also in colliders Keung, Senjanovi´ c, 83

Neutrino 08-Christchurch 15

• G. Senjanovi´

c

L-R symmetric theories: SU(2L)×SU(2)R×U(1) gauge theory

• νL implies νR
• Type I seesaw: connects neutrino mass to scale of parity

restoration

• colliders: produce WR through Drell-Yan

Neutrino 08-Christchurch 16

• G. Senjanovi´

c Neutrino 08-Christchurch 17

• G. Senjanovi´

c

• direct test of parity restoration
• direct test of lepton number violation
• determination of WR and N masses

Ferrari et al, 99 Gninenko et al, 07 LHC easily probes WR up to 3-4 TeV and νR in 100 - 1000 GeV

Neutrino 08-Christchurch 18

• G. Senjanovi´

c

L-R theory: also type II Type II: pair production of doubly charged Higgses, which decay into same sign lepton (anti lepton) pairs Mν = Y∆v∆ probe directly Mν if no type I Kadastik, Raidal, Rebane,07 and references therein

Neutrino 08-Christchurch 19

• G. Senjanovi´

c Neutrino 08-Christchurch 20

• G. Senjanovi´

c

Datta, Guchait, Pilaftsis, 93 Datta, Guchait, Roy, 93 Ferrari et al, 99 Han, Zhang, 06 Gninenko et al, 07 del Aguila, Aguilar-Saveedra, Pittau, 07 del Aguila, Aguilar-Saveedra, 07 Han et al, 07 Akeroyd, Aoki, Sugiyama, 07 Fileviez Perez et al, 07 Kadastik, Raidal, Rebane,07

Neutrino 08-Christchurch 21

• G. Senjanovi´

c

Kersten and Smirnov, 07 Chao et al, 08 Franceschini, Hambye, Strumia, 08 Fileviez Perez et al, 08 many more in type I and also type II

Neutrino 08-Christchurch 22

• G. Senjanovi´

c

Interesting theories: mDirac ≪ MνR (see-saw) MνR, MWR ∼ O(1 − 10) TeV

Neutrino 08-Christchurch 23

• G. Senjanovi´

c

Handle on a see-saw scale form grand unification : SO(10) theory

• SO(10) unifies a family of fermions and postulates right-handed

neutrinos

• has L-R symmetry in a form of charge conjugation of Dirac
• naturally both type I and II seesaw

Neutrino 08-Christchurch 24

• G. Senjanovi´

c

• usually no low scale from running
• typically YDirac ∼ Ytop: fits with MR ∼ 1014GeV

Such theories have a natural see-saw mechanism (mν and ν0ββ well described) but no low see-saw scale (no ∆L = 2 in colliders)

Neutrino 08-Christchurch 25

• G. Senjanovi´

c

Take for example the SO(10) model with Yukawas LY = 16i

F

• Y ij

1010H + Y ij 126126H

• 16j

F

Lazarides, Shafi, Wetterich, 81 Babu, Mohapatra, 92 Bajc, Senjanovi´ c, Vissani, 02 Only two 3 × 3 symmetricYukawa matrices Y10 and Y126 to describe all light fermions (md, mu, me, mν)

Neutrino 08-Christchurch 26

• G. Senjanovi´

c

Full theory with such Yukawas for example in the minimal renormalizable supersymmetric SO(10):

• three copies of 16F
• 210H, 126H, 126H, 10H

Clark, Kuo, Nakagawa, 83 Aulakh, Mohapatra, 83 Aulakh, Bajc, Melfo, Senjanovi´ c, Vissani, 04 The theory over constrained and quite predictive

Neutrino 08-Christchurch 27

• G. Senjanovi´

c

Some evidence that constraints from Higgs sector and Yukawa sector are in contradiction Aulakh, 05, 06 Bajc, Melfo, Senjanovi´ c, Vissani, 05 Bertolini, Malinsky, Schwetz, 06 Although some new hope for consistent fit comes from recent (yet unpublished) results Dorˇ sner, Nemevˇ sek, to appear possibility: relate proton decay branching ratios to neutrino masses and mixings.

Neutrino 08-Christchurch 28

• G. Senjanovi´

c

Even with new physics - only indirect Simple predictive GUT candidate with measurable seesaw?

Neutrino 08-Christchurch 29

• G. Senjanovi´

c

MINIMAL SU(5) The minimal Georgi-Glashow model ruled out because Minimal: 24H + 5H + 3(10F + 5F )

• 1. gauge couplings do not unify
• 2 and 3 meet at 1016 GeV (as in susy),
• but 1 meets 2 too early at ≈ 1013 GeV
• 2. neutrinos massless (as in the SM)

Neutrino 08-Christchurch 30

• G. Senjanovi´

c

Add just one extra fermionic 24F

New Yukawa terms (higher dimensional operators a must as in the minimal model) LY ν = yi

0¯

5i

F 24F 5H + 1

Λ ¯ 5i

F

• yi

124F 24H + ...

• 5H + h.c.

Under SU(3)C×SU(2)W ×U(1)Y decomposition 24F = (1, 1)0 + (1, 3)0 + (8, 1)0 + (3, 2)5/6 + (¯ 3, 2)−5/6

Neutrino 08-Christchurch 31

• G. Senjanovi´

c

singlet S = (1, 1)0 triplet T = (1, 3)0 LY ν = Li

• yi

T T + yi SS

• H + h.c.

Mixed Type I and Type III seesaw: (Mν)ij = v2

• yi

T yj T

mT + yi

Syj S

mS

• → one massless neutrino

Neutrino 08-Christchurch 32

• G. Senjanovi´

c

The only possible pattern: m3 ≪ m8 ≪ m(3,2) ≪ MGUT A solution m3 = 102GeV m8 = 107GeV m(3,2) = 1014GeV MGUT = 1016GeV

Neutrino 08-Christchurch 33

• G. Senjanovi´

c

1-loop result:

For MGUT ∼ > 1015.5 GeV (p decay) → m3 ∼ < 1TeV Prediction of the model

Neutrino 08-Christchurch 34

• G. Senjanovi´

c

mmax

3

− MGUT at two loops

15.6 15.7 15.8 15.9 16 2.25 2.5 2.75 3 3.25 3.5 3.75

log10

• MGUT

GeV

• log10

mmax

3

GeV

• Neutrino 08-Christchurch

35

• G. Senjanovi´

c

T at LHC ? T 0,± weak triplet → produced through gauge interactions (Drell-Yan)

pp → W ± + X → T ±T 0 + X pp → (Z or γ) + X → T +T − + X

Neutrino 08-Christchurch 36

• G. Senjanovi´

c Neutrino 08-Christchurch 37

• G. Senjanovi´

c

10-4 10-3 10-2 10-1 100 101 100 200 300 400 500 600 700 800 900 1000 cross section (pb) mT (GeV) pp -> T+- T0 + X at LHC T+ T0 T- T0

Neutrino 08-Christchurch 38

• G. Senjanovi´

c

ΓT ≈ mT|yT|2

The best channel is like-sign dileptons + jets BR(T ±T 0 → l±

i l± j + 4 jets) ≈ 1

20 × |yi

T |2|yj T |2

(

k |yk T |2)2 Neutrino 08-Christchurch 39

• G. Senjanovi´

c

Same couplings yi

T contribute to

• ν mass matrix and
• T decays

Neutrino 08-Christchurch 40

• G. Senjanovi´

c

Normal hierarchy:

vyi∗

T

√ 2 = i√mT

• Ui2
• mν

2 cos z ± Ui3

• mν

3 sin z

• Inverse hierarchy:

vyi∗

T

√ 2 = i√mT

• Ui1
• mν

1 cos z ± Ui2

• mν

2 sin z

• U = PMNS matrix, z = arbitrary complex number

Ibarra, Ross, 03 Measuring T decays → constraints on z (θ13, phases)

Neutrino 08-Christchurch 41

• G. Senjanovi´

c

• exp. limit: mT ∼

> mZ Total decay width of T ±, T 0 ΓT = mT 32π

• k
• yk

T

• 2

2f1 mW mT

• + f1

mZ mT

• + f0

mH mT

• fn(x) = (1 − x2)2(1 + 2nx)

From the general parametrization above

• k
• yk

T

• 2

≥ mT v2

• ∆m2

S

(normal hierarchy)

• k
• yk

T

• 2

≥ mT v2

• ∆m2

A

(inverse hierarchy)

Neutrino 08-Christchurch 42

• G. Senjanovi´

c

Upper limit on total triplet lifetime τT ∼ < 2 100 GeV mT 2 mm (normal hierarchy) (and

• ∆m2

A/∆m2 S ≈ 5 times smaller for inverse hiearchy)

Measure lifetime? But should be easier to measure

• slower decay modes
• branching ratios

Neutrino 08-Christchurch 43

• G. Senjanovi´

c

|yk

T | from τ(T → lkjj) are partially correlated (connected by

unknown complex z and not yet measured θ13 and phases δ, Φ in UP MNS)

Neutrino 08-Christchurch 44

• G. Senjanovi´

c

Scanning over whole parameter space normal hierarchy inverse hierarchy

Neutrino 08-Christchurch 45

• G. Senjanovi´

c

Assuming Majorana phase Φ = 0 normal hierarchy inverse hierarchy

Neutrino 08-Christchurch 46

• G. Senjanovi´

c

SM background: in ideal detectors is 0 (no ∆L = 2 in SM) But real life not ideal

Neutrino 08-Christchurch 47

• G. Senjanovi´

c

Background mainly from

• t¯

tnj: t → W +b ¯ t → W −(¯ b → W +¯ q)

• b¯

bnj: b → W −(q → W +q′) ¯ b → W +¯ q′′ W + → l+ν produce final states → l+l+4j+ missing energy Cross sections huge (QCD), but phase space fortunately small

Neutrino 08-Christchurch 48

• G. Senjanovi´

c

• neutrinos must carry small transverse energy
• a lepton and two jets near a hypothetical mT

Other important non-QCD modes

• W +W +nj
• W +Znj

Z → q(¯ q → W +¯ q′)

Neutrino 08-Christchurch 49

• G. Senjanovi´

c

Some estimates: with just very loose cuts: σbackground ≈ O(10 − 100) fb Different for different final states (e+, µ+ or τ +) Del Aguila, Aguilar-Saavedra, 07 Seems under control (σbackground ∼ < 1 fb) with better cuts Franceschini, Hambye, Strumia, 08 Cuts in general influence the signal as well

Neutrino 08-Christchurch 50

• G. Senjanovi´

c

Incremental increase of cuts on the signal (mT = 400 GeV): σsignal = 34.37 fb without any cuts Cuts ⇓ σsig.(fb) pT (ℓ) > 30(GeV) 33.50 pT (jets) > 20 (GeV) 21.96 | η(ℓ) |< 2.5 19.68 | η(jets) |< 3 18.57 ∆Rℓℓ > 0.3 18.42 ∆Rℓj > 0.4 17.20 ∆Rjj > 0.7 7.33 Arhrib, Bajc, Ghosh, Han, Huang, Puljak, Senjanovi´ c, to appear

Neutrino 08-Christchurch 51

• G. Senjanovi´

c

Conclusions

• experimental probe of (Majorana) neutrino mass origin: lepton

number violation at LHC (same sign dileptons), a high energy analogue of neutrino-less double beta decay

• an explicit example of predictive GUT theory: ordinary

minimal SU(5) with extra fermionic adjoint

• weak fermionic triplet predicted in the TeV range (type III)
• its decay connected with neutrino mass
• good chances to find it at LHC
• possible even to get information on unmeasured neutrino

parameters

Neutrino 08-Christchurch 52

• G. Senjanovi´

c R measures separations R = [(∆φ)2 + (∆η)2]1/2 where ∆φ and ∆η are the azimuthal angular separation and (pseudo) rapidity difference between two particles Neutrino 08-Christchurch 52-1