1 Visible and Invisible Universe: A short commentary Carlo Rubbia CERN Geneva, Switzerland and INFN/LNGS, Assergi, Italy

1

Visible and Invisible Universe: A short

commentary Carlo Rubbia

CERN Geneva, Switzerland and

INFN/LNGS, Assergi, Italy

Venice, April 16, 2008 Slide# : 2

Luminous matter and Astronomy directly account for only a tiny fraction (0.5 %) of the total mass density budget of the Universe and only about a tenth of the ordinary matter (baryons). As we have known for several decades, the bulk of the matter and energy in the Universe are dark and therefore only indirectly observable through their induced effects.

But there is more: Naively, one would expect the Universe to be synonym of ordinary matter. This intuition is grossly wrong. Discoveries of such so far completely unknown phenomena in the Laboratory will be of extraordinary importance.

We have for the first time a complete and self-consistent accounting both for mass and energy in the Universe (W0 ≈ 1)!

A finite cosmological constant has profound consequences for fundamental physics. By any standard, it is even more exotic and more poorly understood than dark matter.


One of the most exciting cosmological results is the now solid experimental evidence of a cosmic concordance, o = 1.02 ± 0.02 of a mixture of about 2:1 between dark energy and matter.

These results are to be compared with the also firmly established Big Bang Nucleo Synthesis, BBN = 0.044 ± 0.004, i.e. ordinary hadronic matter is only a few % of o.

There is therefore strong, direct cosmological support for a so-far unknown non hadronic matter M - BNN ≈ 0.226 ± 0.06

The experimental detection of a such new form of dark matter is an extremely exciting programme.

Ordinary matter is the source of all inanimate and living things we know of and it had an immense evolutionary role over the 13.7 billion years from the big bang :what about the role of the otherwise dominant dark matter ?


Cosmology: a few established facts

Energ

y d

ensi

ty o

f U

niv

ers

e

Matter density of Universe

M + ≈ 0

BBN is firmly set to BBN = 0.044 ± 0.004

Need for Dark, non baryonic matter, sinceM - BNN ≈ 0.226 ± 0.06 !

What is the origin of such a difference ?

Neutrino’s contribution insufficient (0.0005 < h2 < 0.0076)

Cold dark matter hypothesis preferred by cosmological considerations

But Cold + Warm dark matters not excluded


WMAP power spectrum vs. dipole moment


Baryons in the WMAP 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


Overall Matter in the WMAP 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 baryons

Matter density

Matter Density : mh2 = 0.14 ± 0.02

Matter Density : mh2 = 0.14 ± 0.02


WMAP results

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


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

It confirms WMAP result for a so-far unknown

additional matter

It confirms WMAP result for a so-far unknown

additional matter

Focussing of

gravitational lensing


Weak lensing observations of cluster merger

Shown in green contours in both panels are the weak lensing reconstruction with the outer contour level at = 0.16 and increasing in steps of 0.07. The white contours show the errors on the positions of the peaks and correspond to 68:3%, 95:5%, and 99:7% confidence levels. The white o show the location of the centers of the masses of the plasma clouds.

The gravitational potential does not trace the plasma distribution, the dominant baryonic mass component, and thus proves that the majority of the matter in the system is unseen.

Clowe, Bradac et al.


Evidence of Ω ≠ 0

Redshift measurements of Type 1A SN indicate an accelerated expansion at large z

Regression velocity of Type 1A SN

Constant expansion rate

White Dwarf Giant Companion

Accretion Disk

SN explosion occurs when the white dwarf reaches a specific mass


There is also evidence of a significant (actually dominant) contribution to the matter / energy content of the Universe due to some form of energy characterized by negative pressure: Dark Energy.

Can be accommodated into the Einstein’s equation in the form of Cosmological Constant:

Very difficult to interpret in the framework of particle physics (v.e.v. some 1050 larger than the actual value of ) and also in terms of cosmological arguments (the observed quasi-equality between Dark Energy and Matter densities hard to justify on the basis of general arguments).

... and Dark Energy

8 G T R 1

2R g

g


Dark Matter Candidates ? Despite the impressive amount of

astrophysical evidence, the exact nature of Dark Matter is still unknown.

All present evidence is now limited to gravitational effects. The main question is that if other types of interactions may be also connected to DM. A key question is the presence of a electro-weak coupling to ordinary matter.

Elementary particle physics provides a number of possible candidates in the form of long lived, Weakly Interacting Massive Particles (WIMPs).

Good bets are, at the moment, the lightest SUSY particle (the Neutralino) and the Axion.

•Kaluza-Klein DM inUED•Kaluza-Klein DM in RS •Axion•Axino•Gravitino•Photino•SM Neutrino•Sterile Neutrino•Sneutrino•Light DM•Little Higgs DM•Wimpzillas•Q-balls•Mirror Matter•Champs (charged DM)•D-matter•Cryptons•Self-interacting•Superweakly interacting•Braneworls DM•Heavy neutrino•NEUTRALINO•Messenger States in GMSB•Branons•Chaplygin Gas•Split SUSY•Primordial Black Holes


Will LHC find the keys ? 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 observation of the Higgs boson, for which a very strong evidence for a relatively low mass comes from the remarkable findings of LEP and of SLAC.

In the case of an elementary Higgs, while fermion masses are “protected”, the Higgs mass becomes quadratically divergent due to higher order fermion corrections. This would move its physical mass near to the presumed limit of validity of quantum mechanics.

Therefore in order to “protect” the mass of the Higgs, we need an extremely precise graph cancellation in order to compensate for the divergence of the known fermions.

SUSY is indeed capable of ensuring such a symmetric cancellation, with a SUSY partner yet to be discovered for each and every ordinary particle.

A low Higgs mass tells us that the mass range of the SUSY partners must be not too far away.


Running coupling constants

Running coupling constants are modified above SUSY threshold, and the three main interactions converge to a common Grand Unified Theory at about 1016 GeV but provided that SUSY is there at a not too high masses

Without SUSY

1-1(Q)

2-1(Q)

3-1(Q)

With SUSY

LEP

Proton decay ? 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 LHC.

A doubling of the number of elementary particles, is a result of gigantic magnitude.


SUSY as the source of non-baryonic matter ?

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.

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 experimental signature of a SUSY type particle is generally very characteristic and it deeply affects the number and the kinematical configuration of large p events.

Colliders as sources of SUSY

2 leptons p>15 GeV+ Emiss> 100 GeV

Standard model(background)

SUSY signalLeptonLepton(s)

mo = 200 GeVm1/2 = 160 GeVtg = 2Ao = 0µ < 0


Relic WIMP as the source of non-baryonic matter ? A first, most relevant question is if DM, besides gravitational effects also

couples quantum-mechanically with electroweak interactions. If this is so at some level one might expect collisions in the laboratory between DM and ordinary particles, like for instance the so called WIMP particles.

MW = 200 GeV

Detection range

Coherent neutrino-like Xsect, is taken for purpose of illustration

Lest we become overconfident, we should remember that nature has many options for particle generated dark matter, some of which less rich than with SUSY.

With sufficiently sensitive searches we may confirm or exclude the electroweak coupling. Indeed DM may be an exclusive realm of gravitation.

QuickTime™ and a decompressor

are needed to see this picture.

Galactic speed


10-46 cm2

Predictions of relic Susy/WIMP

Typical recoil threshold for elastic nuclear recoils > 30 keV


Methods of direct detection

Earlier experiments identify in a well shielded, underground laboratory (LNGS) the presence of a very small seasonal variation in the otherwise very huge background due to ordinary, low energy (≤ 6 keV) electron-like events. Such a tiny variation is interpreted as due to the WIMP signal. (DAMA)

More recent experiments (CDMS and EDELWEISS) , in order to detect directly a WIMP signal above background make use of a very low temperature (12-50 milliK) Ge target, in which the slow thermal energy of the recoiling WIMP associated atom is detected by an electric signal sensitive to the phonons (local heating) of the recoil.

These detectors are capable of a good discrimination but they suffer from the very low integrated mass sensitivity: 32 kg x day for EDELWEISS(Frejus) AND 38 kg x day for CDMS(Soudan).

A new kind of detector, ultimately capable of many tens of tons of sensitive mass has been developed based on the use of a ultra-pure Noble liquid (earlier Xenon, now Argon) at standard temperature with the simultaneous detection of the scintillation and ionisation signals in order to identify, with an adequate selectivity, a WIMP recoil signal from ordinary backgrounds.


Discrimination Methods1) New generation detectors must effectively discriminate between

Nuclear Recoils (Neutrons, WIMPs)Electron Recoils (gammas, betas)

recoil energy

Light

Charge Heat

CDMS, EDELWEISS

CRESST

ZEPLINXMASSXENONArDMWARP

Cryogenic, 30 milliK

Liquid Argon, Xenon


Competition

DAMA/LIBRA

CUORICINO

WARP

UK

Canada

Germany

Japan

Spain

USA

ItalyItaly

Russia

USA

ANAIS ROSEBUD

IGEX

MAJORANA (DM)XENON

CDMS II

DRIFT I

ZEPLIN I

ZEPLIN III

ZEPLIN II

NaIAD CRESST II

EDELWEISS II

France

HDMS/GeninoBubble

ChamberPICASSO

XMASS (DM) LiF

ELEGANTS V & VI

More than 20 experiments running or in constructionMore than 20 experiments running or in construction

ArDM


Neutrino-induced background nuclear recoil Neutral current induced

nuclear recoils due to solar and cosmic ray neutrinos produce an irreducible background.

The more abundant electron related neutrino events are removed by the signature of the detector

For cosmic ray neutrinos, which exhibit an essentially flat recoil energy distribution, an upper limit ER < 80 keV has been introduced.

The Argon neutrino background within 30 keV ≤ ER ≤ 80 keV is ≈ 0.033 ev/kton/day, just below the parameter independent WIMP limit, > 0.1 ev/kton/day.

Therefore the neutrino background leaves open a wide rate window over which a search for a WIMP signal may be experimentally conducted.

0.4210 44 N 2 p1 MeV

2


Dama/Libra 2008

December30 km/s

~ 232 km/s60°

June

30 km/s

DAMA/NaI (7 years) + DAMA/LIBRA (4 years)total exposure: 0.82 tonyr

2-6 keV

6-14 keV

2-6 keV

6-14 keV

Evans power law

100-120 GeV


experimental single-hit residuals rate vs time and energy DAMA/NaI (7 years) + DAMA/LIBRA (4 years) Total exposure: 300555 kgday = 0.82 tonyr

2-5 keV

2-6 keV

A=(0.0215±0.0026) cpd/kg/keV

2/dof = 51.9/66 8.3 C.L.

2-4 keV

A=(0.0176±0.0020) cpd/kg/keV

2/dof = 39.6/66 8.8 C.L.

A=(0.0129±0.0016) cpd/kg/keV

2/dof = 54.3/66 8.2 C.L.

Absence of modulation? No

2/dof=117.7/67 P(A=0) = 1.310-4


2/dof=116.1/67 P(A=0) = 1.910-4


2/dof=116.4/67 P(A=0) = 1.810-4

ROM2F/2008/07

Acos[(t-t0)] ; continuous lines: t0 = 152.5 d, T = 1.00 y


Passive neutron and gamma shieldPassive neutron and gamma shield

Active VetoActive Veto

100 liters 100 liters ChamberChamber

Detector under construction at LNGS - 140 kg active target, will possibly allow to reach sensitivity up to 10-45 cm2 WIMP nucleon cross section (covering the most critical part of SUSY parameter space)

Complete neutron shield4π active neutron veto (8 tons

Liquid Argon, 300 PMTs)3D event localization and definition

of fiducial volume for surface background rejection

Cryostat designed to allocate a possible 1400 kg detector

S-WARP of > 10 tons under consideration for the LNGS with Ar-39 depleted cryogenic liquid

The WARP detector at GranSasso Laboratory


WARP after positioning in Hall-B (Jul.’07), inside the sustaining structure


A few comments about Dark Energy. Several increasingly accurate Astronomical observations have

strengthened the evidence that today’s Universe is dominated by an exotic nearly homogeneous energy density with negative pressure. The empty space still contains lots of invisible energy.

The simplest candidate is a cosmological term in Einstein's field equations. Independently of the nature of this energy, the constant is not larger than the critical cosmological density ≈ 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.

Since the vacuum energy density is constant in time, while the matter energy density decreases as the Universe expands, why are the two comparable at about the present time, tiny in the early Universe and very large in the distant future ?

The problem of the value of is one of the greatest questions of the Universe, all along from its introduction in 1917 by Einstein: it has now become widely clear that we are facing a deep mystery and that the problem will presumably stay with us for along time.


earth, air,

fire, water

baryonsneutrino

dark matter, dark energy

To conclude….

We do not know the identity of >95% of what makes the Universe: just“dull particles” or something much richer ?


Thank you !

Documents

1 Visible and Invisible Universe: A short commentary Carlo Rubbia CERN Geneva, Switzerland and INFN/LNGS, Assergi, Italy