Transcript Document

Fifty years after the Neutrino experimental discovery
III International Workshop on:
"Neutrino Oscillations in Venice"
New Horizons
Carlo Rubbia
1
Cosmology: a few established facts
Visible stars are beautiful to see and
without stars there would be no
astronomy: but they represent as a whole
a mere Stars ≈ 0.005 ± 0.002.
The total density of the Universe is now
firmly established to be o = 1.02 ± 0.02.
Total matter density M = 0.27 ± 0.04
Total dark energy density L = 0.73 ±
0.04: Vacuum is not “empty”
M + L ≈ 0 :cosmic agreement !
Ordinary matter (nuclei) are believed to
come from the so called Big Bang Nucleosynthesis (BBN), 3 minutes after
BBN is set to BBN = 0.044 ± 0.004.
We need additional “dark” matter, since
M - BNN ≈ 0.226 ± 0.06 !
What is the origin of such a difference ?
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Matter density of Universe
Slide# : 2
Now
Then
Cosmic microwave background (CMB)
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Slide# : 3
Direct cosmological measurements from WMAP
 First peak shows the universe is
close to spatially flat. Shape and
position are in beautiful
agreement with predictions from
standard cosmological models
 Constraints on the second peak
indicate substantial amounts of
baryonic matter
 Third peak will measure the
physical density of the overall
matter
 Damping tail will provide
consistency checks of underlying
assumptions
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Slide# : 4
Overall Matter in the Power Spectrum
Raising the overall matter density
reduces the overall amplitude of the
peaks.
 Lowering the overall matter density
eliminates the baryon loading effect so
that a high third peak is an indication
of dark matter.
 With three peaks, its effects are
distinct from the one due to the
baryons

Parameter
Baryon Density
Matter Density
Hubble Constant
Baryon Density/Critical Density
Matter Density/Critical Den sity
Age of the Unive rse
Matter Density : mh2 = 0.14 ± 0.02
Value
bh2 = 0.024 ± 0.001
mh2 = 0.14 ± 0.02
h = 0.72 ± 0.05
b = 0.044 ± 0.004
m = 0.27 ± 0.04
to = 13.7 ± 0.2
Dark matter density
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Slide# : 5
Baryons in the Power Spectrum
Baryon Density: bh2 = 0.024 ± 0.001
 The odd numbered acoustic peaks
in the power spectrum are
enhanced in amplitude over the
even numbered ones as we
increase the baryon density of the
universe.
Baryon density
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Slide# : 6
Direct evidence for Dark matter ?
 A large amount of evidence is accumulating on Dark Matter, both from the
theoretical and the experimental point of view.
Observations
Galactic Rotation Curves
M-r
Hot Gas in Ellipticals and
Clusters Gravitational
Lensing
Large Scale Velocity fields
Theory
Inflation total = 1
Growth of Den sity
Fluctuations
Big Bang
Nucleosynthesi s: B <
0.09
SN Ia
 Galactic Rotation Curves: Doppler
measurements in spiral galaxies. Observe: v(r)
 if v is constant,then: M ≈ r
 Need for “dark matter”
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It confirms WMAP result
Slide# : 7
Gravitational Lensing
Gravitational mass of the
galaxy is measured from the
focussing effect induced by a
distant, passing star
It confirms WMAP result
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Slide# : 8
Ordinary matter from BB Nucleosynthesis (baryons)
 Big−Bang Nucleosynthesis
depends sensitively on the
baryon/photon ratio, and we
know how many photons there
are, so we can constrain the
baryon density.
 Result:
baryon  0.05
 [Burles, Nollett & Turner]
BBN = 0.044 ± 0.004

It confirms WMAP result
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Slide# : 9
Open questions
 There now cosmic concordance with 0 = 1 and full agreement for:
Matter: 27%, of which: Baryons: < 5%, Neutrinos: <0.5%
Energy: 73%
 Only 5% of the Universe is made of quarks and leptons: the rest is invisible
(dark matter + dark energy) and totally unknown.
 Some very naïve questions come about:
Dark energy and dark matter have both a common origin or are they two
completely unrelated phenomena ?
Is each of them describable as classical (gravitational) or as quantum
mechanical phenomenon ?
Cold dark matter is well detected gravitationally: but does it have other
interactions, in particular an electro-weak coupling to ordinary matter?
 If it has electro-weak properties, how can it be so (very) massive and so
stable as to have survived for at least 13.7 billion years ?
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Slide# : 10
L ≠ 0: a huge Pandora box
 The energy density L is not larger than the critical cosmological density
o ≈ 1, and thus incredibly small by particle physics standards.
 This is a profound mystery, since we expect that all sorts of vacuum
energies contribute to the effective cosmological constant. In particular
the quantum aspects are very serious, since they predict invariably values
for L-term which are up to very many orders of magnitude larger than the
experimental value, L= 0.7. How can we reconcile such huge difference ?
 A second puzzle: since vacuum energy constitutes the missing 2/3 of the
present Universe, we are confronted with a cosmic coincidence problem.
 The vacuum energy density is constant in time, while the matter density
decreases as the Universe expands. It would surprising that the two
would be comparable just at about the present time, while their ratio was
tiny in the early Universe and would become very large in the future.
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Slide# : 11
Origin of dark matter
 This has been the Wild, Wild West of particle physics: axions, warm
gravitinos, neutralinos, Kaluza-Klein particles, Q balls, wimpzillas,
superWIMPs, self-interacting particles, self-annihilating particles, fuzzy
dark matter,…
 Masses and interaction strengths span many orders of magnitude, but in
all cases we expect new particles with electroweak symmetry breaking,
 Particle physics provides an attractive solution to CDM: long lived or
stable neutral particles:
Neutrino ( but mass ≈ 30 eV !)
Axion (mass ≈ 10-5 eV)
SUSY Neutralino (mass > 50 GeV)
 Axion and SUSY neutralino are the most promising particle dark matter
candidates, but they both await to be discovered !
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Slide# : 12
Standard Model and beyond
 Some of the most relevant questions for the future of Elementary
particles are related to the completion of the Standard model and of its
extensions.
 Central to the Standard Model is the experimental search of the Higgs
boson, for which a very strong circumstantial evidence for a relatively low
mass comes from the remarkable findings of LEP and of SLAC.
 However the shear experimental existence of an Higgs particle has very
profound consequences, provided it is truly elementary.
 [We remark that in other scenarios the Higgs may rather be “composite”,
requiring however some kind of new particles]
 Indeed, in the case of an elementary Higgs, while fermion masses are
“protected”, the Higgs causes quadratically divergent effects due to
higher order corrections.
 This would move its physical mass near to the presumed limit of validity of
quantum mechanics, well above the range of any conceivable collider.
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Slide# : 13
Cancellations ?
 In order to “protect” the Higgs mass, we may assume an extremely precise
graph cancellation in order to compensate for the residual divergence of
the “known” fermions.
 SUSY is indeed capable of ensuring such a cancellation, provided that for
each and every ordinary particle, a SUSY partner is present compensating
each other.
An observation of a low physical
mass of Higgs particle may imply
that the mass range of the SUSY
partners must be not too far away.
LEP
Running coupling constants are
modified above SUSY threshold,
and the three main interactions
converge to a common Grand
Unified Theory at about 1016 GeV
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Proton decay ?
1-1(Q)
With SUSY
2-1(Q)
3-1(Q)
Slide# : 14
SUSY also as the source of non-baryonic matter ?
 A discovery of a “low mass” elementary Higgs may become an important hint
to the existence of an extremely rich realm of new physics, a real blessing
for colliders.
 Such a doubling of known elementary particles, will be a result of gigantic
magnitude.
 However in order to be also the origin of dark mass, the lowest lying neutral
SUSY particle must be able to survive the 13.7 billion years of the Universe
The lifetime of an otherwise fully “permitted” SUSY particle decay is
typically ≈10-18 sec !
 We need to postulate some strictly conserved quantum number (Rsymmetry) capable of an almost absolute conservation, with a forbidness
factor well in excess of 4x10+17/ 10-18 =4x1035 !!!
 The relation between dark matter and SUSY matter is far from being
immediate: however the fact that such SUSY particles may also eventually
account for the non baryonic dark matter is therefore either a big
coincidence or a big hint.
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Slide# : 15
Direct relic DM detection underground
 Lest we become overconfident, we should remember that nature has many
options for particle generated dark matter, some of which less rich, but
also less “wasteful” than with SUSY.
 Therefore in parallel with the searches for new particles with colliders, a
search for relic decays of non-baryonic origin is an important,
complementary task which must be carried out in parallel with LHC.
 The overwhelming argument to pursue a search for dark matter should be
the assumption that dark matter has indeed electro-weak couplings with
ordinary matter (it behaves like a heavy neutrino).
Coherent
neutrino-like
Xsect, is
taken for
purpose of
illustration
MW = 200 GeV
Detection range
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Slide# : 16
Comparing DM with SUSY predictions ( LHC)
A promising method: liquid
Argon or eventually Xenon
These experiments are already capable to sample the SUSY models at a level
compatible with future accelerators constraints, such as CERN's LHC collider.
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Slide# : 17
Main backgrounds
 The flux from DM is known, once we assume we know its elementary
mass. It is typically of the order of 106 p/cm2/s.
 Although very large, it is negligibly small compared to solar neutrinos
which are 1012 p/cm2/s.
 NC induced nuclear recoils
due to neutrinos produce
an irreducible background.
 The more abundant CC
events are removed by the
signature of the detector.
 -background leaves open
a wide window for a WIMP
search
 The main background to fight against is due to residual neutrons which may
mimic a WIMP recoil signal (active shielding and WIMP directionality)
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Slide# : 18
Neutrino oscillations : CP violation in the leptonic sector
 Sacharov has pointed out that a strong CP violation in non-equilibrium conditions may
lead to matter over antimatter dominance shortly after the big-bang.
 If so, an equivalent CP violation may be present also in the leptonic sector. It can be
demonstrated experimentally studying neutrino oscillations, provided the unknown
angle 13 ≠ 0. Both e and  must not be “sterile”, i.e. energies of O(1GeV).
 The experimental programme is very costly and difficult and it requires two main
bold steps forward, namely:
 A new long distance, powerful low energy neutrino beam, capable of identifying e
and  neutrino species down to << 10-3. Under consideration are:
Super beams, in which an ordinary  beam is either off-axis or otherwise it has
a strongly e reduced background.
Beta-beams, in which a -decaying nucleus is accelerated and decays in an
appropriate storage ring pointing at the target, producing a very pure e beam.
.Muon beams, in which a cooled muon beam is accelerated and it decays in an
appropriate storage ring.
 A new detector of much greater mass and with a very high particle identification
capabilities. Liquid Argon is definitely the best choice at present.
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Slide# : 19
Neutrino oscillations:conventional methods
 Classic neutrino-mu production methods (horns) in order to enter in the
Precision Physics Era of neutrino oscillations require:
A very powerful proton accelerator of relatively low energy
Very precise control and rejection of the e contamination.
A long neutrino flight path, with sensitivity for 1 ÷ 2 MeV/km.
Oscillation peak at 295 Km
Flux • s (arbitrary unit)
 Assume for instance FNAL full energy
injector at 120 GeV:
 Limiting factor is power in target (2 MW)
 Decay path to Soudan is 730 km. The ->
e oscillation peak is at 1.8 GeV.
 Rate is of about 100 -> e events/year
for 13 = 3°with a 50 kton LAr detector
 .However the e beam contamination is also
of the same order. (≥ 0.4 ÷ 1 %)
2.5o
=2o
 2 

Flux  
2 2
1   
3o
0
=0o
1
T2K
2
2
E (GeV)
1 MeV/km
 At LNGS, also at 730 km, the real problem is the much more modest SPS
proton flux, corresponding to 4.5 x 1019 ppy, a factor ≈ 20 below FNAL.
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Slide# : 20
Beta beams
6He:
18Ne:
 = 100
 = 100
Neutrino
Source
Decay
Ring
SPS
PS

5x10 -2
 = 3°
4x10 -2
3x10 -2
 = - 90°
2x10 -2
 = 0°
1x10 -2
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Neutrino source
Acceleration
Probability muon
 Zucchelli has proposed a neutrino
beam from the -decay of a short
lived nucleus (He-6) followed by
acceleration and decay in a
dedicated high energy storage ring.
 The advantage of this method is
that a very pure e beam may be
produced, with a  contamination
nearly zero, O() ≤ 10-5.
 However e ’s introduce (f.i. via
neutral currents) a large number
O(1) of pions, indistinguishable in
the proposed 400 kton fiducial
water detector from the tiny
O(10-3) e ->  conversions due to
13 and CP violation effects.
0x10 0
0.3
1
 = 180°
 = 90°
10
MeV/km
Slide# : 21
Muon beams
 Neutrinos are produced by the decay in
flight of cooled and accelerated muons
from a high current proton target.
     
  e     e


  e O1    O10 
    O1    e O103 

3
e
 The simultaneous presence of e and  will
produce a large number of e+ and -.
 The interesting signal, due to e- and +.
must be identified by the sign of the
charge of the emitted lepton.
 Can one conceive a magnetic detector
(Gargamelle or LAr) with hundreds of
kton ? What about the huge stored
magnetic energy and cost ?
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1
Probability
e

e  e 
   
0.1


0.01
   e
e   
0.001
0.3
1
MeV/km
10 Slide# : 22
Proton decay
 At the big bang, matter has been created. Hence according to detailed balance
also the opposite process must occur, namely protons are not for ever.
 The lifetime depends on the mass for Grand unification. Rate ≈ M-4 and on
symmetry chosen.
 For M ≈ 1016 GeV, the expected window is around 1034÷1036 years. One hundred
kton, before experimental biases are 6x1034 nucleons.
 Both X and Y bosons and the associated Higgs particles may be present. The
decay modes are then:
 If IVB dominated, the main decay mode is V-A, with p->e++o, e++o etc.
 If Higgs is prevailing, the effective interaction is scalar and the heaviest decay
particles are largely favored, hence p-> K++  etc. are dominant.
1035 y
p  K+ 
1033 y
Liquid Argon TPC
65 cm
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Slide# : 23
To conclude….
Weearth,
do not
air,
fire, the
know
water
identity of
>95% of what
makes the
Universe
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baryons
neutrino
dark matter,
dark energy
Slide# : 24
Thank you !
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Slide# : 25