Neutrino non-standard interactions : a possible solution to theNOvA and T2K tension
Sabya Sachi Chatterjee

Twentieth Lomonosov Conference on Elementary Particle
Physics, Moscow 2021
Based onPRL 126, 051802 (ArXiv: 2008.04161) by S.S. Chatterjee, & A. Palazzo

25.08.2021

A Few Known Unknowns in Neutrino Physics
1. Whether neutrino is Dirac or Majorana particle.
2. Absolute masses () of neutrinos are unknown. We know themagnitude of mass squared differences ().
3. The sign of the solar mass splitting () is known that is +ve that is m2 >m1.

But the sign of the atmospheric mass splitting () is unknown. This is known as
mass hierarchy problem.
, called normal hierarchy, andcalled inverted hierarchy.
4. The magnitude of the atmospheric mixing angle (rise famous octant ambiguity.

) is unknown. This also gives

5. No confirmation yet about the CP-violation in leptonic sector.

New Physics ?
Presence of sterile neutrino, long-range forces, non-unitary nature of PMNS matrix,
CPT violation, non-standard neutrino interactions, and many others.

2Over the past few years tremendous efforts and invaluable contributions from the neutrino
experiments established the standard three-neutrino framework beyond any doubt.

However the standard interpretation of that framework might not be the ultimate picture.
There may exist many new physics scenarios for which we will need to invoke newinterpreation on top of the standard interpreation.

One of the most popular new physics scenarios is the non-standard interactions ofneutrinos (NSI).

In this work we explore the impact of NSI in the interpretation of current T2K and NOvAtension.

See also 2008.01110 by P. B. Denton, J. Gehrlein, and R. Pestes

3Current status ofKnown very precisely

Most unknown

Sign is +ve (m1 < m2)

parameters (uncertainties)

Known quite precisely

Most unknown

Sign is unknown

ArXiv: 2006.11237 by P. Salas et al., arXiv: 2007.14792 by Esteban et al., andarXiv: 2107.00532 by F. Capozzi et al.

4

NSI and its presence in the oscillation framework
The effect of the effective 4-Fermi flavor changing neutral current non-standard
interactions (NSI) in neutrino oscillation physics is realized through this Lagrangian :N is the number
density of fermionsStrength of NSIs
5

L. Wolfenstein PRD 17, 2369 (1978)

CC-interaction

NC-interaction

Neutrino flavor eigenstates are related to the mass eigenstates as

Where,

6

The time evolution Schrödinger equation for the neutrino flavor eigenstates in vacuum
is given by…………...(I)Similarly, in matter this is given by…………...(II)Charge current potential for neutrino
Neutral current potential for neutrino
For antineutrino,and7

Now, the time evolution equation for the neutrino flavor eigenstates in presence of NSI
is given by…………...(III)
Where,andThe probability for one flavor

transforming to another flavor

is calculated as

In our analysis we assume one NSI parameter at a time and we have mainly
considered the impact of two NSI parametersrespectively.

8

In presence of NSI, thetransition probability can be written approximately as,

9Limits from the IceCube preliminary (90% C.L.)

See the talk by T. Ehrhardt presesented atPPNT, Uppsala (2019)
For more details please see ArXiv: 2106.07755

10Brief description of the experimental setup T2K
T2K (Tokai to Kamioka)
Baseline

295 KM

Detector mass

22.5 Kt

Proton Energy

30 GeV515 kW stable operationachieved

POTPOT

Talk by P. Dunne at Neutrino 2020

11Brief description of the experimental setup NOvA
NOvA (Fermilab to Minnesota)
Baseline

810 KM

Detector mass

14 Kt

Proton Energy

120 GeV
Beam Power
Typically ~ 700 kW

POTPOT

12

T2K Dataset

00.6
1.2
Reconstructed neutrino energy (GeV)

000.6
1.2
Reconstructed neutrino energy (GeV)

1.0
Reconstructed neutrino energy (GeV)

2.000.8
1.20.4
Reconstructed neutrino energy (GeV)

1.0
Reconstructed neutrino energy (GeV)

Talk by Patrick Dunne at Neutrino 2020 conference

2.013

NOvA Dataset

33 events

82 events

211 events, 8.2 bg

0

1234

Reconstructed neutrino energy (GeV)

5105 events, 2.1 bg

01234

Reconstructed neutrino energy (GeV)

Please see the talk by Alex Himmel at Neutrino 2020

5 14

Results from the Collaborations

Prefers maximal CP-violation

No CP-violation

15

Talk by P. Dunne and A. Himmel at neutrino 2020

68% and 90% C.L. contours at 2 d.o.fMore than 90% C.L. disagreement
between T2K and NovA in the measurementof CP-phase

No discrepancy

16

IO is preferredover NO instandard oscillation

However NO ispreferred over IO inPresence of NSI

17

Combined analysis of T2K and NOvA

Allowed regions of NSI parameters

18

NSI with e-mu sector (NO) is better preferred over e-tau sector (NO) !

IceCube bounds
are compatible !

19

Tension resolved !

20

NSI, NO is preferredover NSI, IO

No discrepancy !

21

Strong constraints on NC-NSI from the non-observation of charged lepton flavor violation
Possible to avoid these bounds:
1. Model with neutral light mediators
2. Heavy mediators models arising in radiative neutrino mass model
3. Models with two mediators in the framework of dimension-8 operators

For references please see:Y. Farzan 1505.06906, Y. Farzan, I. Shoemaker 1512.09147,
Y. Farzan, M. Tortola 1710.09360,
M. Gavela, D. Hernandez, T. Ota, and W. Winter 0809.3451,
K.Babu, P. B. Dev, S. Jana, and A. Thapa 1907.09498,
D. Forero and W. Huang 1608.04719
U. Dey, N. Nath and S. Sadhukhan 1804.05808
And many more.
For overview see, 1907.00991

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Conclusion
We have investigated the impact of NSI on the current data of T2K and NOvA.
More than 90% C.L. disagreement between T2K and NovA in the measurementof the Standard Model CP-phase. It can be resolved if one considers the presenceof NSI of typeor
Our result also shows that the NO is preferred over IO in presence of NSI, also
is preferred slightly more than
Future data from T2K and NOvA, and future experiments like T2HK, DUNE andatmospheric current and future data is expected to confirm the presence of NSI andwill help resolving this ambiguity.
Our work also evidences the importance of JUNO like experiment to determine NMO
unambigiously, irrespective of the presence of NSI.
Might be a hint of Physics Beyond the Standard Model !

Thank you!

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For antineutrinos (inverse beta-decay)

In Liquid Ar detector
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25

Bievent plots for NO

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Bievent plots for IO