Current Status of Neutrino Physics 2012 NRF workshop on Flavor
and Collider Physics Yonsei University June 8~9, 2012 Sin Kyu Kang
(Seoul-Tech )
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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
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Evidence for Neutrino Oscillation Solar neutrinos n e flux
deficit Atmospheric neutrinos A half of n m lost!
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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
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Those evidences are not enough to prove that neutrinos really
oscillate
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New standard solar model (SSM) (05) New SNO salt data (05)
These support neutrino oscillation as well as verify SSM
Confirmation of Neutrino Oscillation
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SNO II, III experiments 2008 Achieving precision measurements
of
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oscillation dip" L/E dependence smeared out! L/E distribution
of events KAMLAND & SK (2008) One period oscillation
observed
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Those developments may be enough to support that neutrinos
really oscillate
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Implications of neutrino oscillations Weak eigenstate Mass
eigenstate Neutrinos are massive Mass eigenstates are different
from weak eigenstates Pontecorvo-Maki-Nakagawa-Sakata (PMNS)
Matrix
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Neutrinos from backstage to center stage in particle physics
and cosmology Observation of neutrino oscillations
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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 !
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Neutrino oscillations can be significantly modified when the
neutrinos pass through matter Matter Effects MSW effect (Mikheyev,
Smirnov, Wolfestein)
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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
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- Solving solar neutrino problem - Probing inside the SUN -
Promoted to precision physics Pinning down solar n oscillation
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Koshino Results from Borexino (2011)
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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 :
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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%).
Slide 19
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First measurement of F (pep, 1.44 MeV) F pep in consistent with
F pep (SSM) (2011)
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Global fit of neutrino data Using all data from Latest SK(atm)
SNO salt data K2K, KamLAND Latest MINOS data (Maltoni et
al.2011)
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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
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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
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LSND (93-98) LSND observed oscillation at Dm 2 ~ 1 eV 2
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MinibooNE MiniBooNE reported first results of a search for n e
in a n m beam.
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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.)
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Consistent with LSND in a 2- mixing scheme. 2 excess ;
MinibooNE (2011)
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For E > 475 MeVFor full E range
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Old flux best fit f = 0.984, f = 1 within 1. New flux best fit
f = 0.942, f = 1 at 2.5: 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
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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
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3+1/3+2 fits to SBL data
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3(active) + 1(sterile) oscillation effectively 2- oscillation,
no CP violation. |U e4 | 2 (|U 4 | 2 ) constrained by the data on e
( ) disapperance Reactor anomaly Copp et al. (2011)
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3+1/3+2 fits to SBL data 3+2 oscillation Copp et al.
(2011)
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3 + 2 neutrino mixing scheme (with CP violation and two eV mass
neutrinos) provides a better fit to the global SBL data than the 3
+ 1 scheme. For both 3 + 1 and 3 + 2 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.
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Hint of CPT violation?
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MINOS E~ 3GeV Near Detector at 1.04 km Far Detector at 734
km
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n m disappearance
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Anti- n m disappearance
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Results Violation of CPT ?
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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 ?
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Cabibbo (1963)-Kobayashi-Maskawa (1973) Matrix: Experimental
steps: 12 23 13 ~13 ~2 ~0.2 ~65 1963198319902001 The smallest
mixing angle 13 is a crucial turning-point in doing precis ion
measurements, detecting CP violation and probing NP. Lessons from
Quarks ~45 ~33 ~10 ~??? 199820012012 20yy For leptons
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n e appearance MINOS Hints of nonzero q 13
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Allowed regions
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T2K results T2K
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Double Chooz
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Global fit to q 13 (Schwez (11))
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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
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near detector site RENO Experiment (2012)
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Summary of 3 mixing angles and m 2 From global fit including
reactor experiments (D.Forero, M.Tortola, J. Valle,
arXiv:1205.4018) 12 ~ 34 23 ~ 45 13 ~ 9.5
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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.
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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 4.... Tri-bimaximal Mixing (Harrison, Perkins, Scott
02)
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T. D. Lees Box (06) = YOY = 13 = 0 Tri-bimaximal mixing should
be modified because 13 has been measured no matter how small it is.
But,
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Typical Ideas to touch 13 : Usually 13 = 0 holds in the
symmetry limit. Ways to get 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
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A measurement of sin 2 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 13 Models based on leptonic flavor symmetries
predict small 13 A tabulation of predictions 13 (Albright, M. Chen,
06)
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Basic idea of Measuring CP violation : Observable : CP
Asymmetry Leptonic CP violation
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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 ?
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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
Slide 60
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)
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Degeneracies There are 8-fold degeneracy to resolve
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Masic Baseline L~7500km d dependence disappears Clean
measurement of mass hierarchy:
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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.
Slide 64
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
Slide 65
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
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Perspectives
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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
Slide 68
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
, 2,3 Super-Beams? Beta Beams? Neutrino Factory? m 2 12, 12 m 2 23
, 23 BorexinoOPERA 13, Sign (m 2 23 ) RENO, T2K, MINOS, Double
CHOOZ, NOVA, INO,
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What is precison neutrino physics good for? unique flavour
information tests models / ideas about flavour lessen: elimination
of SMA-MSW I
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Assuming 3 flavor neutrinos Giunti(11)
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Other possible indications on sterile n
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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 dont know