Determining the Majorana nature of neutrino through patterns of |∆B|=2 processes

Xinshuai YanDepartment of Physics and Astronomy

University of Kentucky Lexington, KY

6th PIKIOMeetingUniversityofNotreDame

Oct6,2018

BasedontwopapersincollaborationwithSusanGardner:[S.Gardner andX.Y.,arXiv:1808.05288 andPRD97056008 (2018) arXiv:1710.09292]

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B-L violationØ In the Standard Model (SM), neither baryon number (B) nor lepton

number (L) is conserved, but B-L is. Thus the observation of B-L violation reveal the existence of physics BSM.

q Inleptonsector: Observation ofneutrinoless double(0𝜐𝛽𝛽) decayshowsthatLisbrokenbytwounits.That istosaythatneutrinohasaneffectiveMajorana mass.

q Inquarksector:

B-Lviolation:

• Neutron-antineutron oscillation ---- Spontaneous.• Dinucleon decay(innuclei) --- limited byfinitenucleidensity.• Nucleon-antinucleon conversion ----Mediatedbyanexternalsource.

[Susan Gardner andX.Y.,PRD(2018)]

[Marshak andMohapatra (1980)]

[J.Schechter andJ.W.Valle (2012)]

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Scalar-fermion interactions with no proton decay

[Arnold, Fornal, andWise (2013)Susan Gardner andX.Y.(2018)]

Treelevelprotondecaydiagrams

E.g.,

Possible interactions between scalar particle X and SM fermions:

[Arnold, Fornal, andWise (2013)]Notethese interactions donotbreakBandL!

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Minimal interactions that break B and/or L

Appearedin[Arnold,Fornal,andWise(2013)]

[Susan Gardner andX.Y.(2018)]

𝑛 − 𝑛(oscillation

∆𝐿 = 2, ∆𝐵 = 0

𝑛𝑢𝑐𝑙𝑒𝑜𝑛 − 𝑎𝑛𝑡𝑖𝑛𝑢𝑐𝑙𝑒𝑜𝑛conversion

Newconversion

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Quarklevel𝑛 − 𝑛( oscillationØ There are 4 independent quarklevel𝑛 − 𝑛( oscillation operators that

respect SM gauge symmetry:[Raoand Shrock (1982)W.Caswell etal(1983)M.Buchoff etal(2012)]

q Note: M1 yields the operator (𝒪2)RRR, M2 yields (𝒪3)LLR, M3 yields (𝒪1)RRR.

[Raoand Shrock (1982)]

Quark level𝑛 − 𝑛(oscillation operators with SU(3)⨂Uem 1 .

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Mechanismsof0𝜐𝛽𝛽 decay

q (a)-(c): A light neutrino is exchanged --- “long-range” diagrams;q (d): Mediated by heavy particles --- “short-range” diagram.

[Bonnetetal(2013)]

OnlymodelsA,B,andCcanproduce𝜋?𝜋? → 𝑒?𝑒? decay,whichcorrespondtothesecondcaseofdecaytopology“T-II-3”inBonnetetal(2013).

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Processesofinterestgeneratedbythemodels

Welistthe ∆𝐿 = 2𝑎𝑛𝑑 ∆𝐵 = 2 processesgeneratedbythemodelsinwhich onlyfirst-generationfermionareinvolved.

(*)indicates thataweakisospin triplet of ∆𝐿 = 2 processes canappear.

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Patternsof|∆B|=2 & Majorana neutrino

q We have showed that 𝑒?𝑛 → 𝑒?𝑛( can not appear if 𝑛 − 𝑛( oscillation is mediated through (𝒪1)RRR. Distinguish M3 from M1 and M2

[Susan Gardner andX.Y.,PRD(2018)]

• M3 has scalar content X7 and X8 ;• 𝑒?𝑝 → 𝑒D�̅� only => M10, M12, or

M15. Common scalar content: X1

One example: No 𝑒?𝑛 → 𝑒?𝑛(& Yes 𝑛𝑛(,

𝜋?𝜋? → 𝑒?𝑒? decayA

M3 X7X7X8 M10 X7X8X8X1

M12 X5X5X8X1

A X1X8𝑋HI M15 X4X4X8X1

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Summary• Motivated by search for new physics, we explore simple BSM scalar

models with B, L, and B-L violation. For phenomenological viability, we permit no proton decay for these models.

• Various ∆𝐵 = 2 and ∆𝐿 = 2 processes,suchas𝑛𝑛( oscillationandnucleon-antinucleonconversionand0𝜐𝛽𝛽 decay, canbestudiedwithinthesemodels.

• We show that the observation of 𝑛𝑛( oscillations and of particular nucleon-antinucleon conversion processes can reveal the Majorananature of the neutrino.

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Backup Slides

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[Bonnet etal(2013)]

The two basic tree-level topologies realizing d=9 0𝜐𝛽𝛽 decay operator

Simple BSM scalar models with no proton decay

v Hasneverbeenobserved!v Imposesevereconstraints onnewphysics,e.g.,protonlifetime for𝑝 → 𝑒D𝜋Jmode8.2X1033 yr.

Developsimplemodelswithnewscalargaugebosonswhoseinteractions:

andstudytheirvariousphenomenology.

ØRespect SU(3)XSU(2)XU(1)symmetry ---- SMsymmetry;ØHavemassdimension 3and4---- Renormalizable;ØBreakBor/andL;ØDonotpermit protondecay attree level;

Protondecay:

[H.Nishino etal.(Super-K) (2009)]

ThistalkisbasedontwopapersincollaborationwithSusanGardner:[S.Gardner andX.YarXiv:1808.05288, PRD 97056008 (2018)]

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