Measuring the Gravitational Acceleration of Antimatter: The AEgIS Experiment Torkjell Huse (for Nicola Pasifico) – University of Oslo On behalf of the AEgIS collaboration 22/05/2015CIPANP 20151

Outline  Motivation of the AEgIS experiment  AEgIS overview  Antihydrogen production  Antiproton cooling  Positron system  Traps  Charge exchange reaction with positronium  The FACT detector and gravity module  Antihydrogen detector  Gravity module  Deflectometer  Free fall detector  Conclusions 22/05/2015CIPANP 20152

Stefan Meyer Institute CERN Czech Technical University ETH Zurich University of Genova University of Milano University of Padova University of Pavia University College London Politecnico di Milano Max-Planck Institute Heidelbert Institute of Nuclear Research of the Russian Academy of Science University of Bergen University of Bern University of Brescia Heidelberg University University of Trento University of Paris Sud University of Oslo University of Lyon 1 INFN sections of: Genova, Milano, Padova, Pavia, Trento A E g I S collaboration 22/05/2015CIPANP 20153

Scientific motivation  General relativity is a classic (non quantum) theory  EEP violations may appear in some quantum theories  New quantum scalar and vector fields are allowed in some models (Kaluza Klein…)  Einstein field:Tensor graviton (spin 2) + Gravi – vector (spin 1) + Gravi – scalar (spin 0)  These fields may mediate interactions violating the equivalence principle (M. Nieto and T. Goldman - Phys. Rep. 205, (1992)  Scalar: “charge” of particle equal to “charge” of antiparticle (attractive force)  Vector: charge of particle opposite to charge of antiparticle (repulsive/attractive force)  Cancellation between vector and scalar components is possible for matter! 22/05/2015CIPANP 20154

Einstein Equivalence Principle  The Einstein Equivalence Principle is summarised by the following 3 principles  Weak Equivalence Principle (m i =m g ) +  For any non-gravitational experiment  Lorentz Local Invariance (independence from any free falling frame of reference) +  Local Position Invariance (independence from position in the universe)  Verified e.g. through gravitational red shift 22/05/2015CIPANP 20155

WEP and matter  Verification of the WEP for matter attained to  No precise verification to date for antimatter. 22/05/2015CIPANP 20156

We cannot build an tension pendulum made of antimatter  We have to “borrow” another way of doing the WEP measurement from atomic physics Split and recombine the atomic wave function in presence of gravity Quantum interference if Very cold atoms are needed with a very collimated beam A. Peters et al, Nature 400 (1999) /05/2015CIPANP 20157

The AEgIS way  We cannot get to μ K / nK temperatures required for quantum interference  Difficult to have good collimation  Using classical interference:  Use a two grating configuration with classical interferometry (grating pitch ~ 40 um)  Aiming at an initial accuracy of 1%  Good collimation of the beam is not necessary for physics (only for statistical reasons) 22/05/2015CIPANP 20158

Measurement sensitivity  1% sensitivity achievable with ~ 600 annihilations  Measurement resolution ~ 3 um  Cold antihydrogen necessary for bigger deflection and lower beam divergence. 22/05/2015CIPANP 20159

AEgIS experiment layout Aims:  Measure the gravitational acceleration for antihydrogen in Earth’s gravitational field  Hyperfine Spectroscopy of antihydrogen  Spectroscopy of 1s->2s transition 22/05/2015CIPANP

Antihydrogen production in a glance 22/05/2015CIPANP  5.3 MeV antiprotons energy-degraded down to few keV  Trapping in a Penning- Malmberg trap  Antihydrogen production through charge-exchange reaction with Rydberg- state positronium (see next slide)  1 st ever attempt at producing a pulsed antihydrogen beam!

Antiproton cooling  Bring the traps to 100 mK through dilution cooling (exploiting a phase separation of a He3-He4 mixture)  Electrons cooled down by a resonant circuit subtracting axial energy from the electrons  Other forms of cooling under consideration are evaporative cooling, ion cooling, sysiphus cooling (currently being researched by AEgIS collaboration members) [see New. J. Phys 8 45 (2006) and Phys. Rev. A 89, (2014)]. 22/05/2015CIPANP )Kinetic energy  potential energy 2)Dissipative ”Sisyphus transfer step” 3)Molecule back in position 4)Original internal state

Positron system 22/05/2015CIPANP  Surko-type accumulator:  radioactive source,  solid neon moderator  buffer gas  Source activity (now)= 14 mCi  we expect e+ with 50 mCi source e+ accumulator e+ first trap

Charge exchange and Stark acceleration  Positrons incoming from a β + source hit a silicon microporous target, where they capture an electron and Positronium (Ps) is created.  Positronium is excited in Rydberg states with laser light (Ps*)  Antiprotons coming at ~5 MeV are slowed down by degraders to ~100 keV and a fraction is trapped in a penning trap.  Several bunches can collected in the trap to increase the spatial density.  Antiprotons in the trap take the positrons from Ps* through charge- exchange reaction and form Rydberg anti-H  Antihydrogen is then accelerated forward through Stark acceleration First production ever of pulsed antiH beam!!! 22/05/2015CIPANP

The trap system 22/05/2015CIPANP Hbar production trap Off-axis trap (positrons) On-axis trap (antiprotons) Ps Production target

The Fast Annihilation Cryogenic Tracking (FACT) detector 22/05/2015CIPANP Purpose: detect antihydrogen annihilations in the trap (proof of antihydrogen formation) 800 scintillating fibers (4 layers 1mm diameter) coupled to clear fibers z sensitivity (beam formation): 2.1 mm resolution Read out by Multi Pixel Photon Counters (MPPC) Operated at 4 K, 1 Tesla, dissipation 10W Volume with vacuum separated from the main trap vacuum Counts thousands annihilations in about 1ms J. Storey et al (AEgIS Coll.) NIMA (2013)

The gravity module 22/05/2015CIPANP Emulsion Readout ASICs 77 (or 4) K vessel Strip detector (25 um pitch, 50 um thickness) moire deflectometer Low energy 4K/100mK ~0.5 m Scintillating fiber Detector

22/05/2015CIPANP Probing the deflectometer with antimatter  Measuring forces using “slow” antiprotons (~ 100 keV)  Deflectometer prototype on small distances, using emulsions for detecting antiprotons  Force measured from deflection of antiproton fringe pattern from light fringe pattern

Silicon detector 22/05/2015CIPANP  First ever use of silicon to detect direct on-sensor annihilations  Cryogenic operation, vacuum separation window (UHV to OVC)  Strip detector with 50 um thickness, 25 um strip pitch. Resolution down to ~7 um  Sensors produced by SINTEF, Norway  Custom self-triggering readout ASIC from IDE AS - Norway

Detector tests 22/05/2015CIPANP  A secondary beamline has been dedicated to detector tests (silicon and emulsions) and deflectometer studies  The annihilation events can be identified as “star shaped”, where the prongs derive from the annihilation products.

Conclusions 22/05/2015CIPANP  AEgIS is in commissioning phase. Trap systems are ready.  Work is in progress to improve antihydrogen cooling  The deflectometer has successfully been tested for the first time with antimatter beams. Further tests are foreseen this year  Detector tests were successful. Design of the gravity module to be started soon.  Positronium spectroscopy studies can be started immediately