1. The unknown part of the universe, dark matter
Krasznahorkay Attila
MTA Atomki, Debrecen

2. ATOMKI, Debrecen
The „Institute for Nuclear Research” in the downtown of Debrecen!
4 main divisions:
Nuclear Physics Division
Atomic Physics Division
Applied Physics Division
Accelerator Centre
Size: 100 scientists, 100 other staff

3. Our visible world is beautiful
Our visible world is beautiful. With our vision we can learn about the surrounding world, recognize the laws of nature, and use them to facilitate our lives.
However, our observations with the naked eye have limitations ...

4. Our visible and invisible world
Bacteria (1674, 1865) Viruses (1892)
Too small objects 
Microscope
Too far objects 
telescopes
Radioactive radiations

5. Discovering a new invisible micro-world
Philippe Lenard, examination of cathode rays 1886, phosphorescent screen, thin foil publ  Nobel Prize 1905
J.J. Thompson, 1897 Discovering the Electron  Nobel Prize in 1906
W.C. Rontgen.: Discovering X-rays, later they are called Röntgen-rays. Wilhelm Conrad Rontgen was first awarded the Nobel Prize in Physics in 1901.
A new device for detecting invisible radiation, the Fotoemulsion Becquerel, 1899 α, β, γ radiation  Nobel Prize 1903
Rutherford, the structure of the atoms, the nucleus  Nobel Prize in 1908 Electronic detectors, particle accelerators  new particles

6. The first motivation to research the dark matter
Study of the velocity of stars as a function of distance
Dark halo around the galaxies
Andromeda galaxy
Mass: 370 billion M☉
Distance: 2.5 million Light year
In grammar school we learned that the movements of planets around the Sun can be interpreted precisely with the Newton's laws .
Census in the Universe
Stars and galaxies: 0.5 %
Visible matter: 5 %
Dark matter: ≈ 30 %
Dark energy: ≈ 65 %
Gravitational lensing
Dark galaxies

7. What do we know and what we do not about dark matter?
We observe its gravitational effect on the visible stars. Their contribution to the mass of the Universe is huge (95%)
We are searching diligently for the associated particles with more and more sensitive detectors.     
We can not turn it on What particle (s) are they?
What (new) interactions affect these particles?

8. Searching from the basement to the attic already for 30 years, every corner with tremendous strength ...
With state-of-the-art underground detectors,
with high-sensitivity spectrometers built in space

9. The physicists of the world's largest accelerator laboratory, the Large Hadron Collider (LHC), built at CERN, are also involved in the search.
Lake Genova
Jura
LEP/ LHC
France
SPS
Switzerland PS

10. The nucleus as a discovery machine
The LHC was built on a discovery machine where the collisions of high-energy protons are being investigated. These protons are in the nucleus, too. We investigate the properties and transformations of nuclear nuclei in the Institute of Nuclear Research of the Hungarian Academy of Sciences. In fact, however, the nucleus is also a discovery machine like LHC, with only minor energies. Which perhaps all the interactions of nature are present. Of the four currently known interactions, two were discovered in the nucleus. These are strong and weak interactions. What are they good for? The strong interaction results in the very large binding energy of the nucleus, which is liberated by the nuclear reactors. Without the weak interaction, the Sun would not bake. We started searching the dark matter in the nucleus.
The nucleus as a discovery machine
A The LHC was built on a discovery machine where the collisions of high-energy protons are being investigated. These protons are in the nucleus, too.
We investigate the properties and transformations of atomic nuclei in the Institute of Nuclear Research of the Hungarian Academy of Sciences.
In fact, however, the nucleus is also a discovery machine like LHC, with only smaller energies. Which perhaps all the interactions of nature are present.
Of the four currently known interactions, two were discovered in the nucleus. These are strong and weak interactions. What are they good for? The strong interaction results in the very large binding energy of the nucleus, which is liberated by the nuclear reactors. Without the weak interaction, the Sun would not shine.
We started searching for the dark matter in the nucleus.

11. The dark force and the dark photon
In our visible world, photons, quantums of the light, mediate electromagnetic interaction.
In the dark world, light is the equivalent of dark radiation, the quantum of which is the dark photon (2008).
Big experiments are under way to detect the dark photon around the world.
Under the aforementioned theory, there could be dark atoms and we could start thinking about dark chemistry ....
Features of the Dark Photon:
Well defined (short) life time
Decomposition to electron-positron pair

12. Searching for the e+ e- decay of the dark photon in nuclear transitionsJπ e+ e+ e+ e– Jπ e– e– e–
So if we measure the angles between the e- and e+ particles that are generated in succession for many events, and sketch the angular frequency, the so-called angular correlation, we expect a typical peak.

13. Creation and decay of 8Be*
Decay with proton emission: B(p + 7Li) ≈ 100%
With γ-radiation: B(8Be + g) ≈ 1.5 x 10-5
With internal pair creation: B(8Be + e+ e-) ≈ 5.5 x 10-8
 Smooth, gradually decreasing angular correlation
Creating a dark photon: B(8Be + X) ≈ 5.5 x 10-10
finding a peak on the curve

14. Seeing the invisible (detectors)
Multy Wire Proportional Chamber (MWPC):

15. Two dimensional MWPC readout with the help of induced charges on the cathode strips
Charpak and Shauli, Nobel Prize 1973

16. Scintillation detectors
Scintillating materials:
At the deexcitation of excited atoms "scintillation light" is generated.
Inorganic crystals (ZnS(Ag), NaI(Tl), CsI(Tl)…)
Organic materials (plastics, liquids…)
Gases
The resulting light is transferred to the photoelectron multiplier by a light guide (Plexiglas, light guide fibers ...).
A photomultiplier

17. Electrostatic Van de Graaff accelerator
A ribbon charged up with needles takes up the charges to a hemisphere that is charged to high voltage.
Production of acceleration field with many electrodes with increasing voltage. Among them is a resistance divider.

18. Typical high energy γ-ray spectrum

19. Our electron-positron spectrometer

20. Our experimental results and their interpretation
Interpretation of our results for the electron-positron angular correlation by assuming the creation and decay of a new particle.
Experiment points: red points with errors Theoretical curve: dashed line
Spectrometer check: empty circles with errors
Curves calculated with the assumption of a new particle
 m0c2= 16.6 MeV, X(16.6)

21. Phys. Rev. Lett. 117, 071803 Egy kis statisztika:
Szinte minden ország újságai hírül adták
Több mint 200 ezer letöltés a világhálóról
2016-ban 17 nemzetközi konferencia meghívást kaptam

22. Our result is on the international list
Our results will be checked in many of the world's large laboratories.
Results are expected in a few years time.
CERN experiment in September

23. To 8Be continued… More telescopes bigger efficiency
Position Sensitive Si Detectors for determining the momentum vectors for electrons and positrons.
Precise determination of the invariant mass.
Do we see anything in the 17.6 MeV transition? (Predictions of the protofobic model)
Measuring the life time of the particle.
In E1 transition (11B (p,γ)12C) do we see anything? (does parity conserved in the interaction?)
Investigating the two γ decay of the particle.

24. Our first results at the new accelerator
New Si DSSD detectors
New data acquisition system
Published data
New data
We could reproduce the published anomaly!!!

25. We live in a fantastic age
We live in a fantastic age. Our physical understanding of the world in the coming years will probably be fundamentally changed. Take part in this process!