11. GeoneutrinosAnti-neutrinos from the Earth – A new probe to study the interior of the Earth

APP 2013 – UOulu – 11.1 –

I What is the amount of uranium (U), thorium (Th) and kalium(40K) in the Earth?

I Test a fundamental geochemical paradigm: the Bulk SilicateEarth

I Determine the radiogenic contribution to terrestial heat flow

I A georeactor at the core of the Earth?

I Measured results from KamLAND (2005) and Borexino (2010)I needs a liquid scintillation detector (SNO+, LENA)

11. GeoneutrinosHeat production in the Earth

APP 2013 – UOulu – 11.2 –

I The total heat flow emitted by the Earth is approximately45 TW

I equivalent to the heat production of 15000 power plants of1000 MWel

I The heat flow has been measured at approximatey 25000locations at the surface of the Earth

I the map shows large variations (factor of 20) between thelocations

I The heat is generated, for example, by the natural radioacivityinside the Earth

I Uranium (U), Thorium (Th), and Potassium (K)

I The same radioactive decays are believed to be the sourceof geoneutrinos

11. GeoneutrinosThe Earth heat flow

APP 2013 – UOulu – 11.3 –

11. GeoneutrinosModels for the Earth

APP 2013 – UOulu – 11.4 –

11. GeoneutrinosModels for the Earth

APP 2013 – UOulu – 11.5 –

I The deepest drill hole approximately 12 kmI at Kola Peninsula, RussiaI initial aim 15 km, 12.261 km reached at 1989 (T = 180 ◦C)I difficult to drill much deeper due to high temperature and

pressure (15 km : T = 300 ◦C)I approximately one-third on the Baltic continental crust

I Information on the deeper parts obtained/derived fromI the speed, reflection and refraction of seismic wavesI the moment of inertia and precession motion of planetsI physical, chemical and minerological data obtained from

meteorites

I The most accepted model of the Earth composition is theBulk Silicate Earth model (BSE)

I direct and indirect information combinedI estimated radiogenic heat production of U, Th, and K in the

crust and mantle (r<3000 km) not explained correcly

11. GeoneutrinosAnti-neutrinos from the Earth

APP 2013 – UOulu – 11.6 –

I Uranium, thorium and potassium in the Earth release heat togetherwith anti-neutrinos

I 238U −→ 206Pb + 8· 4He + 6e− + 6ν

I 232Th −→ 208Pb + 6· 4He + 4e− + 4ν

I 40K −→ 40Ca + e− + ν (K1, 88.8 %)40K + e− −→ 40Ar + ν (K2, 11.2 %)

Decay chain Q t1/2 Emax εH εν[MeV] [109 yr] [MeV] [W/kg] [kg−1 · s−1]

U 51.7 4.47 3.26 0.95×10−4 7.41×107

Th 42.8 14.0 2.25 0.27×10−4 1.63×107

K1 1.32 1.28 1.31 0.36×10−8 2.69×104

11. GeoneutrinosAnti-neutrinos from the Earth – decay chains

APP 2013 – UOulu – 11.7 –

11. GeoneutrinosAnti-neutrinos from the Earth

APP 2013 – UOulu – 11.8 –

I High-energy part of neutrinos from U and Th are above the1.8-MeV threshold for inverse beta decay: ν + p −→ n + e+

I can be detected, for example, by liquid scintillation detector

I Different components may be distinguished due to differentenergy spectra: ν with highest energy comes from uranium

I Main source of background: neutrinos from nuclear reactorsI energy spectra not complete overlapping:

nuclear reactor neutrinos originate from fission fragments(geoneutrinos from the chains)

I neutrino oscillations (depends on energy and distance)

11. GeoneutrinosAnti-neutrinos from the Earth – the energy spectrum

APP 2013 – UOulu – 11.9 –

11. GeoneutrinosKamLAND – Kamioka Liquid scintillator Antineutrino Detector – 1 kton, depth 1 km

APP 2013 – UOulu – 11.10 –

11. GeoneutrinosKamLAND – measured geo-ν energy spectrum

APP 2013 – UOulu – 11.11 –

11. GeoneutrinosKamLAND – Results & Outlook

APP 2013 – UOulu – 11.12 –

I The total number of observed νe was 152 in the energy windowrelevant for geo-ν’s

I Background events: 127±13I reactor neutrinos: 80.4±7.2I radioimpurities of 210Pb: 42±11

(α-decay of 210Po: α + 13C −→ 16O + n)can be purified; result of Borexino =⇒ factor ∼150 lower

I Measuring time 749 days (∼2 years)

I Number of target protons 3.5×1031

I Estimated that geo-ν’s arrived in the distance of 200 km

I In Japan, large reactor neutrino background =⇒

11. GeoneutrinosReactor-ν vs geo-ν events – worldwide

APP 2013 – UOulu – 11.13 –

11. GeoneutrinosBorexino

APP 2013 – UOulu – 11.14 –

I Data collected between December 2007 and December 2009,corresponding to 537 days of live time

I 252 ton·yr fiducial exposure

I Approximately 10 events were associated to geo-neutrinos, with therate of approximately 4 per 100 kton per year

I The observed ν-spectrum above 2.6 MeV was compatible withbackground from European nuclear reactors (mean base line 1000 km)

I nuclear reactors do not exist in Italy

I The hypothesis of an active geo-reactor at the center of the Earthhaving a power greater that 3 TW was excluded at 95% CL

I Statistics not (yet) enought for accurate conclusionsI Measurement time of 4 time more is planned (1000 ton·yr)

11. GeoneutrinosBorexino – Geo-neutrino spectrum

APP 2013 – UOulu – 11.15 –

11. GeoneutrinosBorexino

APP 2013 – UOulu – 11.16 –

I Hints that all terrestial heat comes from radiogenic elements

11. GeoneutrinosReactor neutrino events per kiloton at Pyhasalmi

APP 2013 – UOulu – 11.17 –

11. GeoneutrinosLENA – Geo-neutrino spectrum in Pyhasalmi

APP 2013 – UOulu – 11.18 –

I Geo-ν events in Pyhasalmi ∼1300 per yearI nuclear reactor ν events ∼300I 210Pb events ∼10

I 2 TW hypothetical georeactor at the coreof the Earth could be identified after oneyear measurement

I 5 years measurementI red curve for Th,

blue curve for U

11. GeoneutrinosReactor neutrinos – Θ13

APP 2013 – UOulu – 11.19 –

I Θ12 ∼ 32.5 deg

I Θ13 ∼ 10 deg

I Θ23 ∼ 40 deg

I The third mixing angle Θ13 was measured by several experimentsduring a couple of last years

I allows δ(CP) to be determined with long baseline neutrino beams

11. GeoneutrinosReactor neutrinos – Θ13, Daya Bay, China

APP 2013 – UOulu – 11.20 –

I AD1 – AD6,AntiNeutrino detectors(liquid scintillationdetectors)

I quite small,some tens of tons

I D1, D2, L1–L4,nuclear reactors

I Plans to upgrade to20 kton

I measuring the MH

12. Proton DecayMotivation – Standard model of particle physics

APP 2013 – UOulu – 12.1 –

I The present particle physics uses the concepts of the model called theStandard Model of particle physics

I It describes the universe in terms of matter (fermions) and forces(bosons)

I uses 17 fundamental particles andtheir interactions=⇒ Higgs is predicted, and

observedI describes ∼200 particles and their

interactionsI gravity not included

I SM works well, it explains nearly allexperimental data collected so far,but not, for example

I matter-antimatter asymmetryI non-baryonic dark matterI neutrino oscillation (ν masses)

12. Proton DecayMotivation – Physics beyond the Standard model

APP 2013 – UOulu – 12.2 –

I Standard model is not wrong, it can be extendedI an extension to include neutrino masses is now needed

I More elaborated ideas, not yet experimentally verified, to extendthe Standard Model are

I supersymmetry (an idea to explain dark matter)I grand unified theories (an idea to unify electro-weak and strong

interactions)I supergravity (an idea to unify gravity into fundamental particles)I superstrings and M-theory (an idea to unify 4 forces in full quantum

theory)

I Some terminology

I Hadrons – particles made of quarks and anti-quarksI Baryons – particles made of three quarksI Mesons – made of a quark and a anti-quark

I Leptons - fundamental particles (e, µ, τ, ν’s)

12. Proton DecayGeneral – 1

APP 2013 – UOulu – 12.3 –

I General conservation laws – valid in all fields of physics – do notprevent proton of decaying

I energy, electric charge and (linear and angular) momentum

I Free neutron is unstable: n −→ p + e− + ν (τn ≈ 12 min)I neutron is heavier than proton

I Electron is stableI it is the lightest charged particle

I Most of the Grand Unified Theories (GUTs) predict that protonis unstable

I both Super-Symmetric and non Super-Symmetric modelsI τp ∼ 1033−37 years (upper limit)

I Proton decay has not been observed, the current limits of SK are(for non-SUSY channels)

I τp(p −→ e+ + π0) > 8.2× 1033 yearsI τp(p −→ µ+ + π0) > 6.6× 1033 years

12. Proton DecayGeneral – 2

APP 2013 – UOulu – 12.4 –

I An idea that proton may be unstable, Sakharov 1967I an explanation of the matter-antimatter asymmetry in the universe

requires CP violation and baryon number non-conservation (p-decay)

I The proton decay is a probe of fundamental interactions at extremelyshort distances (Planck scale) or high energies (”post-GZK”)

I an instrument for the investigation of the grand unification, ofPlanck-scale physics and of quantum gravity and string and M theories

=⇒ It is essential to construct new experiments to search for protondecay or improve the current limits

=⇒ LAGUNA

I Proton decay would perhaps be the most significant results of thefuture large-volume next-generation detectors (LAGUNA, Hyper-K,UNO, ...)

I unique test of GUTsI important also if not observed =⇒ ruling out models not correct

I Postulated at the first time 1974

12. Proton DecayGUT – Grand Unified Theories – 1

APP 2013 – UOulu – 12.5 –

I The Grand Unified Theories (GUTs) aim to unify electromagnetic,weak and strong interactions at high energies (small distances)

I E ∼ 1015−16 GeV (> 104 × GZK), R ∼ 10−32 mI experimental verification not possible with current colliders

(Epp,LHC ≈ 109 GeV) =⇒ proton decay

I Predicts that proton is unstableI two quarks in a proton transform into a lepton and an antiquarkI baryon and lepton number violation

I Simplest of the GUTs – minimal SU(5)I the dominant decay mode is p −→ e+ + π0 with τp ∼ 1031 years,

but this has already been ruled out by SK and others

I Supersymmetric GUTs (SUSY GUTs)I baryon and lepton number violation (but conserve B − L)I make life time longer and increase possible decay channelsI for p −→ e+ + π0, τp ∼ 5× 1035±1 years (WC)I for p −→ K+ + ν, the dominant SUSY-GUT decay channelτp ∼ (0.3− 3)× 1034 years (LSCI)

12. Proton DecayGUT – Grand Unified Theories – 2

APP 2013 – UOulu – 12.6 –

I In standard model, proton decay is not allowedI more a coincidence than a general principleI a bound neutron is stable against all decay modesI proton decay allowed in (many) standard model extensions

I In GUTs – if baryon number conservation is violated, neutroncan also decay

I the lifetime of a bound neutron would be comparable to thelifetime of a proton

I they would have different decay modes

I Theoretical predictions have large deviationsI no clear picture yetI large range of predicted τp and several possible decay channelsI some models already ruled out be experiments

I The physics of proton decay could also be linked to the excessof matter over antimatter in the Universe

I baryon number violationI evidence of asymmetry seen in the decay of K− and K+

12. Proton DecayGUT – Grand Unified Theories – Unification of forces

APP 2013 – UOulu – 12.7 –

I Running CouplingConstant =The strength of theinteraction (varyingas a function of theenergy)

I In the beginning ofthe Universe one forceonly

I separation due tocooling/expansion

12. Proton DecayGUT – Estimations for proton life times

APP 2013 – UOulu – 12.8 –

12. Proton DecayEstimation of the life time – Application of biology

APP 2013 – UOulu – 12.9 –

I An average human bodyI 80 kg, 60 % of H2OI 1 cm3 of H2O contains 1023 protons (of H2O)

consists of approximately ∼1028 protons

I If τp ∼1028 years would result in ∼1 decay·year−1

If τp ∼1026 years would result in ∼100 decays·year−1

I From this simple estimation it can be concluded that the lowerlimit of the proton life time can not be much lower than∼1027 years

I proton decay is a high-energy phenomena (∼1 GeV)=⇒ it would destroy thousands of molecules

I otherwise people would die on cancer in the age of teen-age oryoung adults

12. Proton DecayExperiments – General

APP 2013 – UOulu – 12.10 –

I Water Cerenkov detector – H2OLiquid scintillation detector – C16H18 (PXE)

I the free protons (two in H of water and 18 in H of PXE) and eightoxygen- and 6×16 carbon-protons are assumed to decay with equalprobability

I For the case of a free proton in hydrogen, the momenta of thedecay particles (e+, π0) or (µ+, π0) or (K+, ν), or ... are uniquelydetermined by two-particle kinematics

I For the bound protons (in oxygen and carbon), the decay-particlemomenta are no longer determined by simple two-particle kinematics.(Small) corrections from

I the Fermi motion of the protons (Fermi momentum, ∼250 MeV/c for pin 12C)

I the nuclear binding energy (m∗p = mp − Eb)

I the meson–nuclear interaction (in O and C)

should be considered

12. Proton DecayDecay signals – Water Cerenkov

APP 2013 – UOulu – 12.11 –

I Main channel: p −→ e+ + π0

I τ(π0) ≈ 8.4× 10−17 s

I B ∼ 98.8 %

12. Proton DecayDecay signals – Liquid scintillator

APP 2013 – UOulu – 12.12 –

I Main channel: p −→ K+ + ν

I τ(K+) ≈ 1.2× 10−8 s

I B(K+ −→ µ+ + νµ) ∼ 63 %B(K+ −→ π+ + π0) ∼ 21 %

I T(ν) ≈ 339 MeVT(K+) ≈ 105 MeV (Can be detected by LSCI)

12. Proton DecayThe IMB experiment (Irvine–Michigan–Brookhaven) – General

APP 2013 – UOulu – 12.13 –

I The first experiment dedicated to the proton decayI IMB – University of California (Irvine), University of Michigan,

Brookhaven National LaboratoryI C. McGrew et al., PRD59 (1999) 052004

Search for nucleon decay using the IMB-3 detector

I The IMB-3 detector situatedI at the Fairport salt mine, Ohio, operated by Morton InternationalI at depth 1900 feet (∼600 m) (−→ muon rate: Rµ ≈ 3 Hz)

I TankI dimensions: 17 m × 17.5 m × 23 m (∼cubic)I filled with ultrapure H2O of 2.5×106 gallons (≈10 milj. litres)I 2048 8-inch PMTs

I Fiducial mass (IMB-3): 3.3 kton

I Water Cerenkov detector

12. Proton DecayThe IMB experiment (Irvine–Michigan–Brookhaven) – The tank

APP 2013 – UOulu – 12.14 –

12. Proton DecayThe IMB experiment (Irvine–Michigan–Brookhaven) – Results

APP 2013 – UOulu – 12.15 –

I Did not observe proton decay, but detected (IMB-1) neutrinos fromSN1987A

I 851 days of exposureI 7.6 kton·year

(∼4.6×1033 nucleon·yr)I 935 contained events

observed

I Looked for 44 different modesof nucleon decay

I 18 for neutron and 26 forproton decay

I Saw no evidence for nucleondecay

I IMB-1 & IMB-3 : p −→ π0 + e+ (−→ γ + γ + e+):τp > 8.5× 1032 yr

12. Proton DecayProton decay in SK – 1

APP 2013 – UOulu – 12.16 –

I Super-Kamiokande is a 50 kton water Cerenkov detectorI at Kamioka Observatory, JapanI depth 1 km

12. Proton DecayProton decay in SK – 2

APP 2013 – UOulu – 12.17 –

I H. Nishino et al., PRL102 (2009) 141801Search for Proton Decay via p → e+ + π0 and p → µ+ + π0 in a LargeWater Cherenkov Detector

I SK-I and SK-III SK-I : April 2006 – September 2001 (11146 20-inch PMTs)I SK-II : October 2002 – October 2005 (5182 20-inch PMTs)I SK-III was completed in June 2006 (when all the PMTs were

reinstalled)

I Data from 91.7 kton·yr (SK-I) and 49.2 kton·yr (SK-II)I 1489 and 798 live days, respectively

I Results: no proton decays were observedI p → e+ + π0 =⇒ τp > 8.2× 1033 yr (prev τp > 1.6× 1033 yr, SK)I p → µ+ + π0 =⇒ τp > 6.6× 1033 yr (prev τp > 4.7× 1032 yr, IMB)

I SK-III – already three years of data collectedI predicted by theory: τp ∼ 5× 1035±1 years

12. Proton DecayLAGUNA

APP 2013 – UOulu – 12.18 –

I Three detector optionsI GLACIER – 100 kton, liquid argon TPCI LENA – 50 kton, liquid scintillatorI MEMPHYS – 600 kton, water Cerenkov

I DepthsI GLACIER – more than 1000 mwe (∼300 m)I LENA – more than 4000 mwe (∼1.4 km)I MEMPHYS – more than 3000 mwe (∼1.0 km)

I In LAGUNA detectors at most few proton-decay signals per yearI needs clear signal identificationI main background source is atmospheric neutrinos (νµ),

at shallow depths also cosmogenic background contributes

I Predicted τp ≈ 1033−36 years by most of the GUTsI this range is possible to study by LAGUNA detectorsI good sensitivity for different decay modes

12. Proton DecayLAGUNA – GLACIER

APP 2013 – UOulu – 12.19 –

I GLACIER – 100 kton liquid argon TPC, variable depths

I p −→ e+ + π0, π0 −→ 2γ’sI assuming perfect particle and track identification, a background

level of 1 event·Mton−1·year−1

I if no signal seen in 10 years =⇒ τp > 4× 1034 years

I p −→ K+ + ν, K+ −→ µ+ + νµ (63 %)−→ π+ + π0 (21 %)

I less than 1 % of the K ’s are mis-identified as protons (usingdE/dx vs R and applying Neural Network algorithm)

I good selection efficiency (atm-ν background less than oneevent·Mton−1·year−1)

I if no signal seen in 10 years =⇒ τp > 6× 1034 years

12. Proton DecayLAGUNA – LENA

APP 2013 – UOulu – 12.20 –

I LENA – 50 kton liquid scintillator, depth 4000 mwe

I p −→ e+ + π0, π0 −→ 2γ’sI produces a 938 MeV signalI e+ and π0 propagate approximately 4 metres (in opposite directions)

before being stopped=⇒ background rejection from atm-νµ’s

I If no signal seen in 10 years =⇒ τp > 1034 years

I p −→ K+ + ν, K+ −→ µ+ + νµ (63 %)−→ π+ + π0 (21 %)

I a monoenergetic signal of TK ≈ 105 MeV from K+, and a delayedsignal from its decay=⇒ coincidence signal ≈257 MeV (K + µ) or ≈459 MeV (K + π’s)

I background rate ≈0.064 year−1 by assuming coincidense signal andpulse shape analysis

I If no signal seen in 10 years =⇒ τp > 4× 1034 years

12. Proton DecayLAGUNA – MEMPHYS (or Hyper-K, one tank)

APP 2013 – UOulu – 12.21 –

I MEMPHYS – 600 kton water Cerenkov, depth > 3000 mwe

I p −→ e+ + π0, π0 −→ 2γ’sI estimated atm-ν background ∼2.25 event·Mton−1·year−1

I If no signal seen in 10 years =⇒ τp > 1035 years

I p −→ K+ + ν, K+ −→ µ+ + νµ (63 %)−→ π+ + π0 (21 %)

I a monoenergetic signal of TK ≈ 105 MeV from K+ can not bedetected, but its decay products can be detected=⇒ not favoured channel for WC

I If no signal seen in 10 years =⇒ τp > 2× 1034 years

12. Proton DecayLAGUNA – Comparison & Conclusion

APP 2013 – UOulu – 12.22 –

I GUTs =⇒ τp ∼ 1033−37 years (upper limit)I Hyper-K and LAGUNA detectors have possibilities to detect proton

decay if the current theories are correctI anyway, much better limits and ruling out of models obtained

13. Dark MatterEvidence for dark matter – Coma galaxy cluster

APP 2013 – UOulu – 13.1 –

I At the beginning of 1930’s F. Zwicky observed that galaxies inthe Coma cluster were moving too fast in order to remain(by gravity) in the cluster

I something else, that cannot be seen, must be holding thegalaxies together in the cluster

I More evidence until 40 years later (Vera Rubin)I the gas and stars in the outer parts of galaxies were moving

too fast with respect to the observed mass=⇒ rotation curve

13. Dark MatterEvidence for dark matter – Rotation curves

APP 2013 – UOulu – 13.2 –

I Rotation velocity measurements of star and galaxies as a functionof distance

I Spiral galaxy has most of the luminous material concentratedin a central hub and a thin disk

I If only luminous material exist, thenI for stars inside the hub M(< r) ∝ r 3 and therefore v ∝ rI for stars outside the hub M ∼ constant and v ∝ r−1/2

=⇒ Velocity should increase at small distances and decrease atlarge distances

I It is observed, on the contrary, that the rotation curves are quiteflat at large distances (halo)=⇒ the bulk of the galactic mass – typically 80–90% – would

be in the form of dark (i.e. non-luminous) matter in thehalo

13. Dark MatterEvidence for dark matter – Rotation curves of galaxy NGC6503

APP 2013 – UOulu – 13.3 –

13. Dark MatterEvidence for dark matter – Halo

APP 2013 – UOulu – 13.4 –

13. Dark MatterEvidence for dark matter – WMAP

APP 2013 – UOulu – 13.5 –

13. Dark MatterEvidence for dark matter – WMAP – results

APP 2013 – UOulu – 13.6 –

13. Dark MatterEvidence for dark matter – Planck

APP 2013 – UOulu – 13.7 –

13. Dark MatterEvidence for dark matter – Planck

APP 2013 – UOulu – 13.8 –

13. Dark MatterEvidence for dark matter – Conclusion

APP 2013 – UOulu – 13.9 –

I There is astrophysical and cosmological evidence that largequantities of dark matter must be hidden somewhere in theuniverse

I the dynamics of galaxies and galactic clusters can only beunderstood if the dominating part of the gravitation is causedby non-luminous matter

I What can the non-luminous matter be?

13. Dark MatterDark matter candidates – terminology

APP 2013 – UOulu – 13.10 –

I Baryonic dark matter

I Non-baryonic dark matter

I Baryonic dark matterI ordinary matter consisting of protons and neutronsI all that can or cannot be seen: interstellar dust, giant planets, ’old’

stars (white, red and brown dwarfs), black holes, ...I MACHOs – MAssive Compact Halo ObjectsI It is known to exist but it explains only a small part of dark

matter

I Non-baryonic dark matterclassified according to temperature in the early universe(decoupling)

I cold dark matterI warm dark matterI hot dark matter

13. Dark MatterDark matter candidates – non-baryonic dark matter

APP 2013 – UOulu – 13.11 –

I Hot dark matterI relativistic particlesI example candidate: neutrinos

=⇒ known to exist, but are hot=⇒ masses not heavy enough and number not large enough to

explain dark matter

I Warm dark matterI semi-relativistic particlesI example candidates: keV-mass sterile neutrinos and gravitons

=⇒ not yet experimentally known to exists

I Cold dark matterI non-relativistic particlesI example candidates: neutralinos, axions, WIMPZILLAs, solitons

(B-balls and Q-balls), etc

=⇒ the most popular hypothesis for dark matter: WIMPs(Weakly Interacting Massive Particles)

13. Dark Matterand Galaxy formation

APP 2013 – UOulu – 13.12 –

I The question of galaxy formation is closely related with theproblem of dark matter

I The models of galaxy formation depend very sensitively onwhether the the universe is dominated by hot or cold darkmatter

I models assume galaxies have originated from (quantum)fluctuations which have developed to larger gravitationalstructures

I two different scenarios can be distinguished:hot and cold dark matter

13. Dark Matterand Galaxy formation – hot dark matter

APP 2013 – UOulu – 13.13 –

I Low-mass and relativistic neutrinos could easily escape frommass structures

I Fluctuations below a certain critical mass would have notgrown to galaxies

I for neutrinos of 20 eV a critical mass of ∼1016 MSUN is requiredfor the structure formation to set in

I ’Top-down scenario’– first largest structures (superclusters), then clusters and galaxieslatest

I allows only small z values (z ≤ 1), but Hubble observationsshow that large galaxies exist for z ≥ 3

I This is one argument to exclude neutrinos as main dark mattercomponent

13. Dark Matterand Galaxy formation – cold dark matter

APP 2013 – UOulu – 13.14 –

I Massive, weakly interacting and mostly non-relativistic particleswill be gravitationally bound already to mass fluctuations ofsmaller sizes

I If cold dark matter dominate, the models show that initially smallmass structures collapse and can grow by further mass attractionsto form galaxies

I ’Bottom-up scenario’– the galaxies would then develop to galactic clusters and latersuperclusters

I cold dark matter then favours a scenario in which smallerstructures would be formed first and then develop into largerstructures

I confirmed by observations of, for example, COBE and WMAPsatellites

13. Dark MatterSupersymmetry – SUSY

APP 2013 – UOulu – 13.15 –

I In supersymmetric theories each fermion (half-integer spin) isassociated with a bosonic (integer spin) partner and each bosonhas a fermionic partner

I squark, slepton, ...I gluino, photino, zino, higgsino, neutralino, gravitino, ...I doubles the number of elementary particlesI no SUSY particles have been found

I From accelerator experiments =⇒ masses higher than 100 GeV(100mp)

I Massive SUSY particle would decay to lighter SUSY particles,and eventually to the lightest superparticle

I the lightest SUSY particle (LSP) would be stable

I The LSP is the most favourite candidate for WIMPsI neutralino

13. Dark MatterDark matter experiments – WIMPs

APP 2013 – UOulu – 13.16 –

I Direct or indirect experiments

I Direct experiments for dark matterI scattering of a WIMP inside the detector material is observedI results in a low-energy recoil nucleusI WIMP rate may be expected to exhibit time dependence

I Indirect experiments for dark matterI gravitational trapping of WIMPs close to a mass centre (the

core of the Sun or the Earth)I detection of the annihilation (or decay) products of WIMPs

(high-energy neutrinos)I large-volume liquid scintillation or water Cherenkov detector

13. Dark MatterIndirect experiments – LENA

APP 2013 – UOulu – 13.17 –

I 50 kton liquidscintillation detector

I Expected signal inLENA after 10 yearsin Pyhasalmi

I inverse beta decay

I For two values of darkmatter particles

I Discrete peak(s)

I Dashed lines describe background events (contributions from reactorneutrinos, DSNB, and atmospheric neutrinos)

13. Dark MatterDirect experiments – 1

APP 2013 – UOulu – 13.18 –

I The WIMP velocities are expected to be of the order of galacticexcape velocities, vχ ∼ 10−3c (non-relativistic)

I With mχ ∼ 100 GeV the maximum energy of the recoil nucleus(of A ∼50) of the detector is Er,max ∼50 keV

I uniform distribution between 0 and Er,max

I very low-energy recoil =⇒ difficult to observe

I Event rates in a detector varies depending whether the crosssection is spin-dependent (incoherent) of coherent

I R ∼ 1 event · kg−1 · day−1 for coherentI R ∼ 0.01 event · kg−1 · day−1 for incoherent

For coherent scattering it is required that A� 50, where A isthe detector nucleus mass number

I usually 76Ge or 131Xe =⇒ large A and incoherent scattering

13. Dark MatterDirect experiments – 2

APP 2013 – UOulu – 13.19 –

I Tens of experiments have been carried out and at least several arecurrently operational

I detector masses from few 100 grams to few kilogramsI most used also for double β-decay experimenst: MIBETA, EDELWEISS,

H&M, IGEX, CUORICINO, ...

I TechniquesI ionisation detectors (Ge), solid scintillation detectors (NaI/CsI),

gryogenic detectors (Ge), noble gases as liquids (Xe)

I Low counting rates =⇒ extra care for background substractionI high-energy neutrons

I Future experiments aims to several hundreds of kilos of detectormaterial

I GERDA, MAJORANA, EDELWEISS (Ge),ZEPLIN, XMASS-DM, XENON100 (LXe)

13. Dark MatterDirect experiments – CRESST

APP 2013 – UOulu – 13.20 –

I Cryogenic Rare Event Search with SuperconductingThermometer

I working temperature ∼15 mK

I WIMP elastic scattering on nuclei at the absorberI scintillating CaWO4 crystals (33 × 300 g modules)I low-activity copper and lead shielding

I Measures ∆T and scintillation lightI sensitive for very low-energy eventsI efficient background reduction

I Situates at Gran Sasso, Italy at ∼1.2 km

I 730 kg·days data taking in 2011 (with 8 modules)I 67 events in the acceptance window for WIMPsI 4σ significance that does not originate from four

major background source

I CDMS (Cryogenic Dark Matter Search), SoudanMine, Minnesota

I three events at 3σ

13. Dark MatterDirect experiments – CRESST at Gran Sasso

APP 2013 – UOulu – 13.21 –

13. Dark MatterCRESST – Results and comparison to other experiments (2012)

APP 2013 – UOulu – 13.22 –