1 new horizons carlo rubbia fifty years after the neutrino experimental discovery iii international...

1

New Horizons

Carlo Rubbia

Fifty years after the Neutrino experimental discovery

III International Workshop on:

"Neutrino Oscillations in Venice"

Venice,Feb06 Slide# : 2

Cosmology: a few established facts

Energ

y d

ensi

ty o

f U

niv

ers

e

Matter density of Universe

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 ± 0.04Total dark energy density = 0.73 ± 0.04: Vacuum is not “empty” M + ≈ 0 :cosmic agreement !Ordinary matter (nuclei) are believed to come from the so called Big Bang Nucleo-synthesis (BBN), 3 minutes afterBBN 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 ?


Cosmic microwave background (CMB)

Th

en

Now


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


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 ValueBaryon Density bh

2 = 0.024 ± 0.001Matter Density mh2 = 0.14 ± 0.02Hubble Constant h = 0.72 ± 0.05Baryon Density/Critical Density b = 0.044 ± 0.004Matter Density/Critical Density m = 0.27 ± 0.04Age of the Universe to = 13.7 ± 0.2

Dark matter density

Matter Density : mh2 = 0.14 ± 0.02

Matter Density : mh2 = 0.14 ± 0.02


Baryons in the Power Spectrum

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

Baryon Density: bh2 = 0.024 ± 0.001

Baryon Density: bh2 = 0.024 ± 0.001


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 TheoryGalactic Rotation CurvesM r

I nflation total = 1

Hot Gas in Ellipticals andClusters GravitationalLensing

Growth of DensityFluctuations

Large Scale Velocity fields Big BangNucleosynthesis: B <0.09

SN I a

Galactic Rotation Curves: Doppler measurements in spiral galaxies. Observe: v(r)

if v is constant,then: M ≈ r Need for “dark matter”

It confirms WMAP resultIt confirms WMAP result


Gravitational Lensing

Gravitational mass of the galaxy is measured from the focussing effect induced by a

distant, passing star

Gravitational mass of the galaxy is measured from the focussing effect induced by a

distant, passing star



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.

baryon 0.05

Result:

[Burles, Nollett & Turner]

BBN = 0.044 ± 0.004



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 ?


≠ 0: a huge Pandora box

The energy density 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 -term which are up to very many orders of magnitude larger than the experimental value, = 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.


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 !


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.


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.

Without SUSY

1-1(Q)

2-1(Q)

3-1(Q)

With SUSY

LEPAn 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.

Running coupling constants are modified above SUSY threshold, and the three main interactions converge to a common Grand Unified Theory at about 1016 GeV

Proton decay ?


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 (R-symmetry) 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.


Direct relic DM detection underground

MW = 200 GeV

Detection range

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


Comparing DM with SUSY predictions ( LHC)

These experiments are already capable to sample the SUSY models

at a level compatible with future accelerators constraints, such as

CERN's LHC collider.

A promising method: liquid Argon or eventually Xenon

A promising method: liquid Argon or eventually Xenon


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)


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.


Neutrino oscillations:conventional methods

0 1 2

2

221

2

Flux

Flu

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Flu

x •

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ry u

nit

) (

arb

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)

=2o

2.5o

3o

Oscillation peak at 295 KmOscillation peak at 295 Km

=0o

T2KT2K

E (GeV)

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 energyVery precise control and rejection of the e contamination.A long neutrino flight path, with sensitivity for 1 ÷ 2 MeV/km.

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 %)

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.


Beta beams 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 tinyO(10-3) e -> conversions due to 13 and CP violation effects.

Neutrino

Source

Decay Ring

SPS

PS

Acceleration Neutrino source

0x100

1x10-2

2x10-2

3x10-2

4x10-2

5x10-2

0.3 1 10

Pro

babi

lity

muo

n

MeV/km

= 0°

= 90°

= - 90°

= 180°

= 3°

6He: = 100 18Ne: = 100


Muon beams Neutrinos are produced by the decay in

flight of cooled and accelerated muons from a high current proton target.

e e

O 1 e O 10 3 `

e e O 1 è O 10 3

0.001

0.01

0.1

1

0.3 1 10

Pro

babi

lity

MeV/km

è e

e

è

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 ?


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.

65 cm

p K+ 1033 y

1035 y

Liquid Argon TPCLiquid Argon TPC


earth, air,

fire, water

baryonsneutrino

dark matter, dark energy

To conclude….

We do not know the identity of >95% of what makes the Universe


Thank you !

1 new horizons carlo rubbia fifty years after the neutrino experimental discovery iii international...

Documents

overall matter density

total matter density

total density

matter densitycritical

matter density mh2

physical density

baryonsmatter density

total dark energy density