Visible and Invisible Universe: A short commentary Carlo Rubbia CERN Geneva, Switzerland and INFN/LNGS, Assergi, Italy.
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Visible and Invisible Universe: A short commentary Carlo Rubbia CERN Geneva, Switzerland and INFN/LNGS, Assergi, Italy 1 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. Venice, April 16, 2008 Slide# : 2 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 sofar 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 ? Venice, April 16, 2008 Slide# : 3 Cosmology: a few established facts BBN is firmly set to BBN = 0.044 ± 0.004 Need for Dark, non baryonic matter, since M - 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 M + ≈ 0 Matter density of Universe Venice, April 16, 2008 Slide# : 4 WMAP power spectrum vs. dipole moment Venice, April 16, 2008 Slide# : 5 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: bh2 = 0.024 ± 0.001 Baryon density Venice, April 16, 2008 Slide# : 6 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 : mh2 = 0.14 ± 0.02 Matter density Venice, April 16, 2008 Slide# : 7 WMAP results Parameter Baryon Density Matter Density Hubble Constant Baryon Density/Critical Density Matter Density/Critical Den sity Age of the Unive rse Venice, April 16, 2008 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 Slide# : 8 Gravitational lensing Gravitational mass of the galaxy is measured from the focussing effect induced by a distant, passing star Focussing of gravitational lensing It confirms WMAP result for a so-far unknown additional matter Venice, April 16, 2008 Slide# : 9 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. Venice, April 16, 2008 Slide# : 10 Evidence of Ω ≠ 0 Regression velocity of Type 1A SN Accretion Disk White Dwarf Giant Companion SN explosion occurs when the white dwarf reaches a specific mass Redshift measurements of Type 1A SN indicate an accelerated expansion at large z Constant expansion rate Venice, April 16, 2008 Slide# : 11 ... and Dark Energy 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: 1 8 G T R R g g 2 Very difficult to interpret in the framework of particle physics (v.e.v. some 1050 larger than the actual value of ) arguments (the observed also in terms of cosmological and quasi-equality between Dark Energy and Matter densities hard to justify on the basis of general arguments). Venice, April 16, 2008 Slide# : 12 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 electroweak 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. Venice, April 16, 2008 •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 Slide# : 13 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. Venice, April 16, 2008 Slide# : 14 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 LEP 1-1(Q) With SUSY 2-1(Q) 3-1(Q) 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. Venice, April 16, 2008 Slide# : 15 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 !!! Venice, April 16, 2008 Slide# : 16 Colliders as sources of SUSY 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. 2 leptons p>15 GeV+ Emiss> 100 GeV mo = 200 GeV m1/2 = 160 GeV tg = 2 Ao = 0 µ<0 Standard model (background) Lepton(s) Venice, April 16, 2008 Lepton SUSY signal Slide# : 17 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. Galactic speed QuickTime™ and a decompressor are needed to see this picture. Coherent neutrino-like Xsect, is taken for purpose of illustration 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 than with SUSY. With sufficiently sensitive searches we may confirm or exclude the electroweak coupling. Indeed DM may be an exclusive realm of gravitation. Venice, April 16, 2008 Slide# : 18 Predictions of relic Susy/WIMP 10-46 cm2 Venice, April 16, 2008 Typical recoil threshold for elastic nuclear recoils > 30 keV Slide# : 19 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. Venice, April 16, 2008 Slide# : 20 Discrimination Methods 1) New generation detectors must effectively discriminate between Nuclear Recoils (Neutrons, WIMPs) Electron Recoils (gammas, betas) ZEPLIN XMASS XENON ArDM WARP Liquid Argon, Xenon Light CRESST recoil energy Charge Heat Cryogenic, 30 milliK CDMS, EDELWEISS Venice, April 16, 2008 Slide# : 21 Competition More than 20 experiments running or in construction DAMA/LIBRA CRESST II NaIAD WARP Italy EDELWEISS II UK ZEPLIN I ZEPLIN III ZEPLIN II DRIFT I CUORICINO Germany France Bubble Chamber USA HDMS/Genino Russia Japan PICASSO USA XMASS (DM) Canada CDMS II ELEGANTS V & VI IGEX XENON MAJORANA (DM) LiF Spain ANAIS ROSEBUD ArDM Venice, April 16, 2008 Slide# : 22 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 2 p 0.421044 N 2 1 MeV 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. Venice, April 16, 2008 Slide# : 23 Dama/Libra 2008 DAMA/NaI (7 years) + DAMA/LIBRA (4 years) total exposure: 0.82 tonyr December 60 ° 2-6 keV June 6-14 keV 100-120 GeV Evans power law Venice, April 16, 2008 Slide# : 24 DAMA/NaI (7 years) + DAMA/LIBRA (4 years) Total exposure: 300555 kgday = 0.82 tonyr experimental single-hit residuals rate vs time and energy Acos[w(t-t0)] ; continuous lines: t0 = 152.5 d, T = 1.00 y 2-4 keV A=(0.0215±0.0026) cpd/kg/keV 2/dof = 51.9/66 8.3 C.L. Absence of modulation? No 2/dof=117.7/67 P(A=0) = 1.310-4 2-5 keV A=(0.0176±0.0020) cpd/kg/keV 2/dof = 39.6/66 8.8 C.L. Absence of modulation? No 2/dof=116.1/67 P(A=0) = 1.910-4 2-6 keV A=(0.0129±0.0016) cpd/kg/keV 2/dof = 54.3/66 8.2 C.L. Absence of modulation? No 2/dof=116.4/67 P(A=0) = 1.810-4 Venice, April 16, 2008 Slide# : 25 detector Detector The underWARP construction at LNGSat140 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) GranSasso Laboratory 100 liters Chamber Complete neutron shield 4π active neutron veto (8 tons Liquid Argon, 300 PMTs) 3D event localization and definition of fiducial volume for surface background rejection Active Veto Cryostat designed to allocate a possible 1400 kg detector S-WARP of > 10 tons under consideration for the LNGS with Ar39 depleted cryogenic liquid Venice, April 16, 2008 Passive neutron and gamma shield Slide# : 26 WARP after positioning in Hall-B (Jul.’07), inside the sustaining structure Venice, April 16, 2008 Slide# : 27 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. Venice, April 16, 2008 Slide# : 28 To conclude…. We do earth, not know air, fire, the identity of water >95% of what makes the Universe: just “dull particles” or something much richer ? Venice, April 16, 2008 baryons neutrino dark matter, dark energy Slide# : 29 Thank you ! Venice, April 16, 2008 Slide# : 30