Experiments with low energy antimatter Giovanni Consolati, on behalf of the AEGIS collaboration Politecnico di Milano and Istituto Nazionale Fisica Nucleare - Milano Introduction to cold antimatter Experiments and Milestones The Aegis experiment Conclusions and Outlook
Brief antimatter history 1928: relativistic equation of the ½ spin electron (Dirac) 1929: electron sea and hole theory (Dirac) 1931: prediction of antimatter (Dirac, Oppenheimer, Weyl) Positrons 1932: discovery of positron in cosmic rays (Anderson) 1933: discovery of e-/e+ creation and annihilation (Blackett, Occhialini) 1937: symmetric theory of electrons and positrons 1955: antiproton discovery (Segre, Chamberlain, Wiegand) Other Antiparticles 1956: antineutron discovery (Cork, Lambertson, Piccioni, Wenzel) 1995: creation of high-energy antihydrogen (CERN, Fermilab) 2002: creation of 10 K antihydrogen (Athena, Atrap) 2011: antihydrogen confinement (Alpha) 2013: preliminary Hbar gravity measurement (Alpha) 2013: first Hbar beam (Asacusa) Cold Neutral Antimatter
From Hot (GeV) to Cold (< mev) Antimatter Why cold? The lower the energy, the higher the sensitivity for tests on elementary constituents. Spectroscopy of anti-atoms can be studied only at very low energies Charged or Neutral? Significant limits have been obtained on CPT violation with antiparticles. However, neutral systems are the only candidates for the study of antimatter gravity, whose measurement on charged antimatter is very challenging owing to its sensitivity to electromagnetic (stray) fields.. 24-26 Sep 2014 - Messina
Test on CPT symmetry Test on the Weak Equivalence Principle 10-18 WEP tests on matter system 10-16 10-14 10-12 10-10 10-8 10-6 10-4 10-2 09/28/14 1700 1800 1900 2000
AD (Antiproton Decelerator) at CERN AD slows down antiprotons to 5.3 MeV by stochastic and electron cooling. Antiproton rate (roughly): 3x107 /200 s (100 ns pulse width)
Cold antihydrogen production ALPHA ATRAP ASACUSA
Milestones on cold antimatter ATHENA-ATRAP 2002 - Production of ~10 K Antihydrogen ATHENA apparatus ATHENA M. Amoretti et al. Nature 419 (2002) 456. ATRAP G. Gabrielse et al. Phys. Rev. Lett. 89 (2002) 213401 Double nested potential well -125 antiprotons -100-75 -50 0 2 4 6 8 Length (cm) 10 12 Confinement of antiprotons and positrons in Penning Traps. Antihydrogen formed escapes from the trap and is detected: by gammas and pions (ATHENA); or by field ionization method (ATRAP) 24-26 Sep 2014 - Messina
Milestones ALPHA 2011 - Antihydrogen Confinement Antihydrogen formation and Confinement (1000 sec) in an Octupolar Magnetic Field Andresen et al. Nature 7 (2011) 558. Amole et al. Nature 483 (2012) 439. ALPHA 2013 Preliminary gravity measurement on antih - 434 anti-h trapped in the Alpha magnetic configuration. - B field is switched off. - Anti-H get released - Up-down asymmetry in the annihilation measures the gravitational pull ALPHA Nature Communications DOI: 4 (2013) 1785 10.1038/ncomms2787 F = mg mi < 75 F = 100
Milestones ASACUSA 2013 - First Antihydrogen Beam ASACUSA N.Kuroda et al. Nature Communications DOI 10.1038/ncomms4089 Production of positrons and their storage in the CUSP trap Injection of antiprotons in the CUSP trap Detection of antihydrogen 2.7 m downstream in a magnetic field free environment
Milestones ATRAP 2013 Antiproton magnetic moment - p trapped in a Penning trap (B = 5 T) - Cyclotron: n,ms n+1,ms and spin-flip n,ms n,ms±1 transitions driven by antenna electrodes - Measurements of fc and fs - fs/fc = gpbar 2 - μpbar = (gpbar 2)μN - 4ppm uncertainties J. Di Sciacca et al, Phys.Rev. Lett. 110 (2013) 130801
AEgIS Spectroscopy Antimatter Interferometry Experiment Gravity Proposed : 2005 Approved by CERN : 2007 AEGIS: AD-6 Experiment at CERN Geneva (CH) http://aegis.web.cern.ch/aegis/
A E g I S collaboration CERN Czech Technical University ETH Zurich University of Milano University of Padova University of Pavia Politecnico di Milano University College London Stefan Meyer Institute University of Genova Institute of Nuclear Research of the Russian Academy of Science University of Bergen University of Lyon 1 INFN sections of: Genova, Milano, Padova, Pavia, Trento Max-Planck Institute Heidelbert University of Bern University of Oslo University of Brescia University of Paris Sud Heidelberg University University of Trento
AEGIS FIRST GOAL Test of WEP on antih in the Earth s gravitational field LONG TERM GOAL Spectroscopy with ultracold antih AEGIS EXPERIMENTAL STRATEGY 1) Produce cold antiprotons (100 mk) 2) Accumulate e+ and form Ps by interaction of e+ with a porous target 3) Laser excite Ps to get Rydberg Ps 4) Form Rydberg cold (100 mk) antihydrogen through the reaction: * p + ( Ps ) H + e * 5) Extract an antih beam using an inhomogeneous electric field 6) Pass the beam through a moirè deflectometer, which introduces a spatial modulation in the distribution of the antih arriving on a detector 7) Obtain g from this modulated distribution
Cold antiprotons production Antiprotons are caught in a cylindrical Penning trap, after energy degradation by Al foils, within a 5 T magnet, UHV, 4 K. e- cooling to a few K (final configuration 0.1 K) 5T Stacking several AD shots (104/105 sub-ev antiprotons) Transfer in the antih formation region (1 Tesla, 100 mk) p 1T 105 antiprotons ready for antih production 5 T magnet 4K 1 T magnet 0.1 K
Ps formation 1 T region Transfer line e+ generation, trapping and accumulation Vacuum A few 104 slow e+ generated by 22Na are trapped every 0.15 sec and sent to the accumulator. Up to 4 107 e+ are accumulated and transferred to the 1 T region to impinge a porous target. Ps is formed in the pores, cooled by collisions with the pore walls and emitted in vacuum. Solid Positron beam Ps Ps Ps Ps Positronium emission
Ps excitation Ps excited to Rydberg state by laser pulses. Two-steps laser excitation: UV laser (λ = 205 nm) for Ps excitation to n=3 IR laser (λ ~ 1670 nm) for Ps excitation from n=3 to Rydberg states n =25-35 Both lasers pumped by the same Nd:YAG source F. Castelli et al., Phys. Rev. A 78 (2008) 052512 S. Cialdi et al., NIM B 269 (2011) 1527
Antihydrogen formation Rydberg Ps interacts with the cloud of antiprotons in the 1 T region. AntiH formation: * p + ( Ps ) H + e * Cross section of the process: σ nps4 This accounts for the need of Rydberg Ps It is worth to note that also antih is in Rydberg state
Antihydrogen beam extraction and Rydberg atoms have large electric dipole moments. High sensitivity to electric fields. Possibility to accelerate/decelerate antimatter by means of electric field gradients: Properties of Rydberg atoms: Binding energy Orbital radius Dipole moment Radiative lifetime Ionization electric field n-2 n2 n2 n3 n-4 Energy levels of H in an electric field Deceleration of H already demonstrated: H with v = 700 m/s stopped in 5 µs over 1.8 mm E. Vliegen, F. Merkt, J. Phys. B 39 (2006) L241
Antihydrogen fall and detection Moirè deflectometer: 2 gratings+1detector A force on the beam produce a fringes shift y M. K. Oberthaler et al., Phys Rev A 54 (1996) 3165 In the case of gravity: y = gτ 2 By measuring the antih time of flight τ and δ = y/a, g is obtained from a fit: Classical device, beam collimation not required. A fringes pattern is generated
Status of the AEgIS apparatus: hot antiprotons Anti-p catching from AD 3 107 p from AD, degraded through Al foil an HV trap captures p with energy < e(hv) up to 1.3 105 p captured per single AD shot Detected by scintillators around the 5 T region..d. Krasnicky et al., AIP Conf. Proc. 1521 (2013) 144
Status of the AEgIS apparatus: cold antiprotons Anti-p electron cooling: Anti-p storage time: Preloaded e- (>108) in the trap electron cooling of p to 7 K (e- cooled by radiation) Most p are cooled within 40 s after capture Lifetime of cold p 600 sec (end 2012) Improvements expected thanks to: better vacuum (a factor two) lower temperature in the region
Status of the AEgIS apparatus: positrons e+ source: 440 MBq Moderation+transport efficiency: 2.5 10-3 Trapping+dumping efficiency: 0.14 Accumulated e+ > 107 Lifetime > 100 s according to the base pressure Transport efficiency up to 0.9
Status of the AEgIS apparatus: positronium SiO2 Positron beam Ps Ps generation from e+ implanted into a nanoporous silica target: high Ps formation and emission in vacuum Ps S. Mariazzi et al., Phys. Rev. B 78 (2008) 085428 S. Mariazzi et al., Phys. Rev. B 81 (2010) 235418 Nanochannels size: Ps Ps Ps log(dn /de) [arbitrary units] tuning the nanochannel size to optimize Ps cooling Presence of a thermal fraction in the sample temperature range 150-300 K Si 7 KeV, T = 300 K 7 KeV, T = 200 K 7 KeV, T = 150 K T=305±10K T=1515±15K T=195±10K T=1425±25K T=145±10K #0 4 7 nm T=1260±15K #1 8 12 nm #2 8 14 nm #3 10 16 nm 0.0 0.1 0.2 0.3 #4 14 20 nm o-ps kinetic energy [ev] #5 80 120 nm
Status of the AEgIS apparatus: laser system Assembled and tested in Milano (2012) Transferred to CERN (2013) and ready to work
Status of the AEgIS apparatus: mini-moirè S. Aghion et al. Nature Comm 5 (2014) 1 p beam impinges onto the two gratings, poduces fringe patterns, shifted in the presence of a force, and detected with a spatially resolved emulsion Light fringes (undeflected) produced by LEDs onto the same gratings Silicon transmission gratings: Periodicity 40 µm Open fraction 30% Thickness 100 µm Additional grating in contact with the detector plane used as a reference for alignement (transit time zero, no force dependence)
Status of the AEgIS apparatus: mini-moirè 1) p annihilation signal extracted with 2 µm precision. 2) p and light fringes are compared, after alignement by overlaying the patterns obtained with the contact grating 3) Shift between pbar and light fringes: presence of a force (500 an, compatible with a 1 mt magnetic field normal to the p direction)
Status of the AEgIS apparatus: antih monitoring Need to monitor antih when formed. Constraints: operate at 4 K, in high vacuum inside 1 T power dissipation < 10 W. Optimized to reconstruct the annihilation position vertex on the beam axis (resolution 2 mm expected) Tests performed up to 4 K with cosmic rays: only slight degradation (10%) of the trigger rate vs. T Solution: a suitably designed Fast Annihilation Particle Tracking no mechanical damage of the fibres after many thermal cycles J. Storey et al., Nucl Instr. Meth A 732 (2013) 437
Status of the AEgIS apparatus: antih detection antih detection after moirè deflectometer. Requirements: spatial resolution time tagging Nuclear emulsions: up to 2 µm resolution. Solution: hybrid detector: Si strip+emulsion+scint fibres Important in order to decrease the number of detected events, for a given accuracy on g P. Scampoli et al., J Instr. 9 (2014) C01061
Short term plans Increased e+ production (new source and optimization of the transport system) Optimization of the Ps fraction formed Assembling of the moirè deflectometer (size 20 cm) and antih detector Improving p cooling (evaporative cooling) First antih generation (at a few K): 2015 antih beam, gravity measurements: 2015-2016
Conclusions Several antimatter experiments are running, commissioning or approved at CERN. Precision tests on fundamental physics are planned AEGIS; challenging experiment, aiming to test the WEP on antimatter (first phase) and antih spectroscopy (future plan). Current experiments limited by p statistics 2014 Outlook 2017: ELENA (Extra Low Energy Antiproton Ring) planned to start working p deceleration form 5.3 MeV to 0.1 MeV Increased p trapping efficiency (x100!) Up to 4 experiments running in parallel ELENA
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