1. Angela Gligorova on behalf of the AEgIS and Medipix collaborations
Measurements of antiproton annihilations using GRACE: a new facility for the extraction of low energy antiprotons at the CERN AD
Angela Gligorova on behalf of the AEgIS and Medipix collaborations
5th Beam Telescopes and Test Beams Workshop 2017
24-27 January, Barcelona

2. Outline The AEgIS experiment at CERN
Indirect and direct detection of antiproton annihilations
GRACE-a new facility for extraction of low energy antiprotons
Commissioning and some test beam results - Timepix3 as a direct annihilation detector
Other detector technologies tested in GRACE
Summary 2

3. AEgIS-Antimatter experiment: gravity, interferometry, spectroscopy
Primary scientific goal: To measure gravitational acceleration for antihydrogen -> test the Weak Equivalence Principle for antimatter. 3

4. Antihydrogen formation in AEgIS
Catching and cooling to sub-kelvin temperatures of 5.3 MeV antiprotons from the Antiproton Decelerator (AD);
Accumulation of positrons from 22Na source;
Formation of positronium (Ps) and laser excitation to Rydberg state (n=20-30);
Antihydrogen production by resonant charge exchange reaction.
Formation of antihydrogen beam by Stark acceleration.
Detection of the free fall of antihydrogen with position detector. 4

5. Detection of the antihydrogen free fall
Position detector
Silicon position detector, where the annihilation of antihydrogen takes place (~10 μm resolution) .
Emulsion detector, for more precise reconstruction of the annihilation point (~1 μm).
Fibre time-of-flight for timing information on the emulsion detector. 5

6. Indirect and direct detection of antiproton annihilations
Antiproton-proton and antiproton-nucleus interactions
Pions and kaons
(charged and neutral)
X: nuclear recoils, p, t, n, α, 3He, 4He, 6He, 8He, Li...
Indirect detection: as in HEP, reconstruction of the annihilation point through detection of the annihilation products (e.g. ATHENA, Si strip+CsI crystal hodoscope, 4 mm resolution on the vertex).
Direct detection: using the actual detector as an annihilation plane and for detection of annihilation prongs. 6

7. Antiproton Decelerator
GRACE-a facility for extraction of low energy antiprotons at the AD at CERN
Antiproton Decelerator
GRACE 7

8. Electrostatic optics of GRACE
5.3 MeV antiprotons (~200 ns bunches) every 100 s from the AD.
Al degrader (46 um) to slow them to keV energy.
Delivery of low (tunable) energy antiprotons, 0-10 keV.
Fully electrostatic optics: 2 Einzel lenses + Electrostatic deflector (Beam optics simulation with IBSimu).
Vacuum down to 1e-7 mbar. 8

9. Commissioning of GRACE using Timepix3 detector
Developed by the Medipix collaboration at CERN.
Hybrid pixel detector, 55 um pixel pitch, 256x256 pixels.
Simultaneous measurement of ToT and ToA.
40 MHz readout, additional 640 MHz fast clock for fine tuning of the ToA- down to 1.6 ns resolution.
Wide dynamic range: up to ~500keV/pixel.
Bonded to 500 um and 675 um thick Si sensors for our application. 9

10. Commissioning of GRACE using Timepix3 detector
Background (fast gaussian, pions and fast fragments from beam annihilations on chamber walls and moderators) before the arrival of the slow bended antiprotons.
Time delay of the slow antiprotons - indication for their energy. E.g. 500 ns delay - 40 keV; 1 us - 10 keV; 2 us keV. 10

11. Energy tuning of the antiprotons in GRACE
Estimation of the energy of the antiprotons from the time-of-flight (the time delay from the fast gaussian). 11

12. The journey of one bunch of antiprotons in GRACE, recorded with Timepix312

13. Comparison of the energy of antiprotons between data and simulations*
GEANT4 simulations of the beam propagation in GRACE.
Scans with different voltages applied on deflecting electrodes and on the Einzel lenses.
Depending on the selected energy, up to couple of tens of low energy antiprotons delivered for tests (good agreement between data and simulations).
D1=0; D2=1.5 kV; E1=2 kV; E2=3 kV
D1=0; D2=3 kV; E1=4 kV; E2=3 kV
PRELIMINARY 13
*Courtesy of Helga Holmestad

14. Reconstruction of the annihilation vertex and antiproton tagging
Tagging of the antiproton annihilation events through identification of tracks from pions and heavy fragments.
Use of a thick (675 um) Si sensor to increase the length of the tracks produced by the annihilation prongs.
Tracks longer several mm are observed for many annihilation events.
Clustering and vertex fitting algorithm are currently being developed.
pions 14

15. 3D reconstruction capabilities
Reconstruction of an annihilation event and estimation of the annihilation depth using ToA information from Timepix3
<-XY plane
YZ plane->
<-XZ plane
3D view-> 15

16. Other detector technologies employed in GRACE
Detection of antiproton annihilations with:
Emulsion (fragmentation studies in different materials)
CsI crystals and
Cr-39 solid state nuclear track detector
Si strip detector
Analysis in progress 16

17. Cold tests with Timepix3 - detection of antiprotons at -85C
Cryo tests in lab down to -150C (temperature of the chip)
Detection of 5 keV antiprotons at -85C in GRACE
Issues with cooldown in GRACE-more data to be taken this year 17

18. Summary
A new extraction beamline at CERN AD, capable of selecting antiprotons of a given energy (up to 10 keV).
Reliable and reproducible results in terms of flux/energy of the delivered antiprotons.
Timepix3 detector offers excellent capabilities for direct detection of low energy antiprotons, including operation in cold environment.
Easy installation (within couple of hours) and possibility for measurements with different detector technologies.
More cryo tests with Timepix3 to be performed this year.
Some technical upgrades (cables, HV feed-throughs) are foreseen to provide antiprotons at even higher energies.
The beam line could be put on disposal to external users (from May onwards). 18

19. Thank you :) 19