Current Status of Neutrino Physics 2012 NRF workshop on Flavor and Collider Physics Yonsei University June 8~9, 2012 Sin Kyu Kang (Seoul-Tech )

Outline What we have observed for neutrinos - Evidence for neutrino oscillations - Confirming neutrino oscillations Recent developments of solar n experiments - Pinning down true solution to solar neutrino problem Anomalies in Neutrino Experiments - Hints of sterile neutrinos & CPT violation or not Discovery of nonzero q 13 Theoretical Challenges Perspective on Leptonic CP violation Conclusion

Evidence for Neutrino Oscillation Solar neutrinos n e flux deficit Atmospheric neutrinos A half of n m lost!

Evidence for Neutrino Oscillation Reactor neutrinos e + p e + + n  Confirming solar neutrino oscillation n e flux deficit Beam neutrinos (KamLAND 03) (K2K 04, MINOS 06) Energy spectrum of events in K2KEnergy spectrum of events in MINOS Beam n m disappearance

Those evidences are not enough to prove that neutrinos really oscillate

 New standard solar model (SSM) (05)  New SNO salt data (05) These support neutrino oscillation as well as verify SSM Confirmation of Neutrino Oscillation

SNO II, III experiments 2008 Achieving precision measurements of

oscillation „dip" L/E dependence smeared out! L/E distribution of events KAMLAND & SK (2008) One period oscillation observed

Those developments may be enough to support that neutrinos really oscillate

Implications of neutrino oscillations Weak eigenstate Mass eigenstate  Neutrinos are massive  Mass eigenstates are different from weak eigenstates Pontecorvo-Maki-Nakagawa-Sakata (PMNS) Matrix

Neutrinos from backstage to center stage in particle physics and cosmology Observation of neutrino oscillations

What determined from oscillation exp. Neutrino mixing (PMNS) matrix can be parametrized by unknown Solarreactor and/or accelerator 0  Atmospheric  23 ~ 45°  12 ~ 34°  13 = ?  13 is the gateway of CP violation in lepton sector !

 Neutrino oscillations can be significantly modified when the neutrinos pass through matter Matter Effects – MSW effect (Mikheyev, Smirnov, Wolfestein)

 MSW effect modifies the e survival probability  For production in matter with electron density n e :  Simple (and useful) limiting cases: Below critical energy, vacuum oscillations dominate Above critical energy matter effects dominate  Critical energy ~1.8 MeV for LMA, 8 B  Goes as 1/  m 2 Solar neutrinos affected by MSW

- Solving solar neutrino problem - Probing inside the SUN - Promoted to precision physics Pinning down solar n oscillation

Koshino Results from Borexino (2011)

► Low background liquid scintillator detector. ► New Prec. Measurement of 7 Be neutrinos via n -e scattering. ► First real time spectral measurment of sub-MeV solar n. ► Observed rate : cf. expected rate without oscillation :

Day-Night Asym. from Borexino Measurement of A ND in the event rate due to F ( 7 Be) In general, the flux rate in Night should be higher than Day because of the regeneration effect due to matter. In the 7 Be energy region, no significant effect expected in MSW-LMA region, but large in MSW-LOW region (~20%).

First measurement of F (pep, 1.44 MeV) F pep in consistent with F pep (SSM) (2011)

Global fit of neutrino data Using all data from Latest SK(atm) SNO salt data K2K, KamLAND Latest MINOS data (Maltoni et al.2011)

Mixing angle q 13 CP violation in neutrinos Neutrino Mass hierarchy Existence of sterile neutrinos Majorana or Dirac ? Absolute neutrino mass scale …….. Although we are sure that neutrinos oscillate and further experiments precisely measure neutrino oscillation parameters, Still, there are several unknown about n

Hints of sterile neutrinos? Anomalies in Neutrino Experiments A number of “hints” (they do not make an evidence but pose an experimental problem that needs clarification ; Altarelli(11) ) LSND and MiniBoone Reactor flux & anomaly Gallium anomaly Neutrino counting from cosmology

LSND (93-98)  LSND observed oscillation at Dm 2 ~ 1 eV 2

MinibooNE  MiniBooNE reported first results of a search for n e in a n m beam.

MinibooNE  E n > 475 MeV data in good agreement with background prediction - 2-neutrino fit excluded LSND at 90% CL (CPC) - consistent with no oscillations  However, an excess of events observed for En < 475 MeV.  can not be explained by two neutrino oscillation but 3+2 scheme (Maltoni et al.)

Consistent with LSND in a 2-ν mixing scheme. ∼ 2σ excess ; MinibooNE (2011)

For E > 475 MeVFor full E range

Old flux best fit f = 0.984, f = 1 within 1σ. New flux best fit f = 0.942, f = 1 at 2.5σ: This implies that all reactor neutrino experiments with L < 100m have observed a deficit of e events compared to the theory prediction, at 98.6% C.L. Reactor neutrino ( ) anomaly

Do not really agree !! Gallium n e disappearance (GALLEX, SAGE) Deficit in the observed rate due to a radioactive source with known intensity in the Gallium experiments (Giunti, Laveder, 2010)  Gallium anomaly

3+1/3+2 fits to SBL data

3(active) + 1(sterile) oscillation effectively 2-ν oscillation, no CP violation. |U e4 | 2 (|U μ4 | 2 ) constrained by the data on ν e ( ν μ ) disapperance Reactor anomaly Copp et al. (2011)

3+1/3+2 fits to SBL data 3+2 oscillation Copp et al. (2011)

3 + 2 neutrino mixing scheme (with CP violation and two eV mass neutrinos) provides a better fit to the global SBL data than the scheme. For both and schemes there is a strong tension between the description of the “appearance” data and limits from the “appearance” and “disappearance” data. Only a relatively small active-sterile neutrino transition probability is allowed by the data.

Hint of CPT violation?

MINOS E~ 3GeV Near Detector at 1.04 km Far Detector at 734 km

n m disappearance

Anti- n m disappearance

Results Violation of CPT ?

Non-zero q 13 Towards Unknown for Neutrinos Accomplishment of 3 mixing angles in U PMNS A hope to observe CPV in lepton sector. Sensitive to theoretical models, so we can test lots of theoretical models. Sets a bound of accuracy to probe new physics. Why measurement of q 13 important ?

Cabibbo (1963)-Kobayashi-Maskawa (1973) Matrix: Experimental steps: θ 12 → θ 23 → θ 13 → δ ~13° ~2° ~0.2° ~65° The smallest mixing angle θ 13 is a crucial turning-point in doing precis ion measurements, detecting CP violation and probing NP. Lessons from Quarks ~45° ~33° ~10° ~??? yy For leptons

n e appearance MINOS Hints of nonzero q 13

Allowed regions

T2K results T2K

Double Chooz

Global fit to q 13 (Schwez (11))

Daya Bay Experiment (2012) 4 reactor cores, 11.6 GW 2 more cores in 2011, 5.8 GW Mountains near by, easy to construct a lab with enough overburden to shield cosmic-ray backgrounds Discovery of non-zero  13

near detector site RENO Experiment (2012)

Summary of 3 mixing angles and  m 2 From global fit including reactor experiments (D.Forero, M.Tortola, J. Valle, arXiv: )  12 ~ 34°  23 ~ 45°  13 ~ 9.5°

Theoretical challanges Observations for three mixing angles (a) q 23 is large and close to  /4, suggestive of something? (b) q 12 is large and close to 35°. (c) q 13 is not large and close to 10°. Why q 12 q 23 large and close to 2 special values ? Why q 13 small ? Very strong hints at a certain (underlying) flavor symmetry.

Before measuring  13, neutrino mixing matrix is consistent with Tri-bimaximal mixing pattern Tri-bimaximal mixing pattern has been very popular because it can be derived from discrete symmetries such as A 4, S Tri-bimaximal Mixing (Harrison, Perkins, Scott 02)

T. D. Lee’s Box ’ (06)  =  YOY =θ 13 = 0 Tri-bimaximal mixing should be modified because  13 has been measured no matter how small it is. But,

Typical Ideas to touch θ 13 :  Usually θ 13 = 0 holds in the symmetry limit.  Ways to get θ 13  0 : (A) Starting from Flavor Symmetries: Z 2, Z 3, S 3, S 4, A 4, D 5, L e – L  – L , … GUT models: SO(10), E 6, left-right, string-inspired, …. - Explicit symmetry breaking at the model scale; - Radiative corrections from a super-high scale to low scales. (B) Others : - Lepton-Quark Complementarity: CKM-MNS correlation - Texture Zeros: seesaw, non-seesaw, etc

A measurement of sin 2 θ 13 at the sensitivity level of 0.01 can rule out at least half of the models!  Models based on GUT generally give relatively large θ 13  Models based on leptonic flavor symmetries predict small θ 13  A tabulation of predictions θ 13 (Albright, M. Chen, 06)

Basic idea of Measuring CP violation : Observable : CP Asymmetry Leptonic CP violation

Complete determination of U PMNS CPV in lepton sector may play a crucial role of baryogenesis It may furnish some hint of quark-lepton symmetry or grand unification Why measurement of  CP violation important ?

 CP asymmetry could be large ~5% in several models, measurable in future experiments  However, there is contamination due to matter effects that make it difficult to see CPV  Golden Channel Probing oscillation between e and  Neutrino Factory (e.g. Fermilab  Minesota Fermilab  Gran Sasso)  How to detect Since CP violation causes small changes in probability, large data samples are required to measure them

Probability for Appearance Channels  Complicated, but all interesting information there:  13,  CP, mass hierarchy (via A) (Cervera et al. 2000; Freund, Huber, Lindner, 2000; Freund, 2001)

Degeneracies There are 8-fold degeneracy to resolve

Masic Baseline L~7500km d dependence disappears Clean measurement of mass hierarchy:

CP violation and mass hierarchy L ~ 1500 – 6000 km good for CP violation (large  13 ) L > 6000 km necessary for mass hierarchy (if small  13 ) Use 4000 and 7500 km (“magic baseline”) as standard baselines CP violation Mass hier.

Conclusion Revolutions in neutrino physics The solar and atmospheric neutrino problem solved! Small but finite neutrino mass: –Probes physics beyond the standard model –New insights into the origin of flavor –Interesting interplay between neutrinos and cosmos Hints of sterile neutrinos/ CPT violation ? Nonzero q 13 has been measured. A lot more to learn in the next few years

 What we have learnt  Neutrinos are massive particles  Neutrino mix a lot discovery of two large mixing angles  Very different from quarks  The first phase of studies of neutrino mass and mixing is essentially over and new phase just started The first evidence for demise of the minimal standard model

Perspectives

future neutrino oscillations improving measuring Aims:  improved precision of the leading 2x2 oscillations  detection of generic 3-neutrino effects:  13, CP violation  precision neutrino physics

Three Generations of Experiments Needed 0. Only three or more ? SBL+Cosmology I. Precision measurements for Solar & Atm. Sector II. Connection between both Sectors III. CP-Violating Interference δ,  2,3 Super-Beams? Beta Beams? Neutrino Factory? Δ Δm 2 12, θ 12 │Δm 2 23 │, θ 23 BorexinoOPERA θ θ 13, Sign (Δm 2 23 ) RENO, T2K, MINOS, Double CHOOZ, NOVA, INO, …

What is precison neutrino physics good for?  unique flavour information  tests models / ideas about flavour  lessen: elimination of SMA-MSW I

Assuming 3 flavor neutrinos Giunti(11)

Other possible indications on sterile n

What is the sign of  m 2 32 Neutrino mass spectrum : Are 3 flavor oscillations enough ? Is the CP phase non-zero? Is  23 maximal ? If not, what is the octant? Are Neutrinos Majorana ? What we don’t know