A New Theory of Neutrino Oscillations Netta Engelhardt

A New Theory of Neutrino Oscillations Netta Engelhardt 8. 19. 2009

Presentation Outline The Standard Model of Particle Physics n Neutrinos in the Standard Model n Neutrino mass n Standard theory of neutrino oscillation n LSND and Mini. Boo. NE anomalies n A New Theory: U(1)B-L Gauge Symmetry n MINOS n Summary n

Standard Model of Particle Physics Describes 3 of the 4 fundamental forces n Strong force, mediated by gluons n Electromagnetic force, mediated by the photon n Weak force, mediated by W and Z bosons n

SM: Families of Particles Bosons: have integer spin, are either elementary (gauge bosons or Higgs), or composite (mesons). Gauge bosons are force mediators. n Fermions (matter particles): have spin in multiples of ½, are either elementary (quarks – colored, or leptons – colorless) or composite n

6 leptons, Generations 6 antileptons Lepton n n Classified by quantum number flavor: electron, muon, tau.

Neutrinos in the Standard Model n n Electromagnetically neutral leptons Handedness (chirality): no right-handed neutrinos Higgs field => neutrinos are massless Interact only via the weak interaction

Neutrino Mass through Neutrino Oscillation n Experimental fact: a neutrino of one flavor at t=0 may be observed to have another flavor at t=t’.

Neutrinos have Mass If not, then the Hamiltonian is diagonal in the flavor basis n => Flavors are stationary states n => Probability of oscillation = 0 n So neutrinos have nonzero mass n H is diagonal in the mass basis (always) n Mass and flavor are not simultaneously diagonalizable n

Standard Theory of Neutrino Oscillation

Oscillation Probability For a simplified 2 x 2 case: So the standard oscillation probability has a periodic dependence on L/E and , but no dependence on chirality or L and E independently.

LSND and Mini. Boo. NE n n LSND produced mu antineutrinos and detected e antineutrinos at a baseline of 30 meters. They saw an excess of e antineutrino events beyond what is predicted by the standard theory. Explanation for LSND: add a fourth mass eigenstate and otherwise keep theory the same. Mini. Boo. NE accelerated mu neutrinos and detected e neutrinos at a baseline of 541 meters while keeping L/E the same as LSND’s. Since would be the same, L/E would be the same, and the mass squared difference would be the same, Mini. Boo. NE was expected to see the same sort of excess as LSND.

LSND and Mini. Boo. NE, cont. No such excess was seen at Mini. Boo. NE. n However, Mini. Boo. NE saw an unexplained excess of e neutrinos at very low energies. n

A New Neutrino Theory Reconciling LSND and Mini. Boo. NE n Energy n Baseline n Chirality n n Baryon and lepton quantum numbers – conservation (SM), and violation

A 5 th Fundamental Force n n n n A new gauge interaction mediated by a new gauge boson called the paraphoton. Requires neutrinos to be Majorana particles Generates a B-L (baryon # - lepton #) dependent potential This potential, VB-L, is sensitive to the chirality of a neutrino. Sensitive to L and E. Weaker than the weak interaction Requires 3 additional flavorless neutrinos called sterile neutrinos, which have a negative B-L potential.

A Minimalistic 3+1 Model n 1 sterile mixing neutrino (the miscetrino) and 2 sterile non-mixing neutrinos. Oscillation probability dependent on L and E. n What about long baseline?

MINOS n n n MINOS is a long-baseline (734 km) neutrino oscillation experiment Preliminary MINOS data indicates good agreement with this model. Our model is able to provide an explanation for the otherwise contradictory results of LSND neutrinos, LSND antineutrinos, Mini. Boo. NE preliminary antineutrino data, preliminary MINOS neutrinos and antineutrinos data.

Numerical Analysis n 2 = 90/(49 DOF) at best fit point

Summary The addition of a spontaneously broken B-L symmetry is able to reconcile provide a better explanation neutrino oscillation data. n The full 3+3 model is expected to find an even better fit (more parameters). n We still need names for the sterile neutrinos. n

Acknowledgments I would like to express my sincere thanks to my advisor, Ann Nelson, and to Jonathan Walsh for guidance and support throughout the duration of this project. Additional thanks are due to Andrew Lytle for helpful conversations and to Jenna Walrath for bright ideas.