reaction cross section measurements for the positive antihydrogen ion production in the gbar...
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Reaction cross section measurements for the positive antihydrogen ion
production in the GBAR experiment
L. LiszkayIRFU CEA Saclay, France
GBAR collaboration
L. Liszkay, P. Comini*, P. Debu, P. Pérez, J.M. Rey, Y. Sacquin, B. Vallage, D. P. van der Werf**IRFU CEA Saclay (France)A. Maia-Leite, Liam Dodd (PhD students)* present address: ETHZ (Switzerland)** permanent address: Univ. Swansea (UK)
François Nez, Pierre CladéLKB (Laboratoire Kastler-Brossel, Paris)
David LunneyAudric Husson (PhD student)CSNSM (Centre de Sciences Nucléaires et de Sciences de la Matière, Orsay)
Paul-Antoine Hervieux, Giovanni ManfrediIPCMS (Institut de Physique et Chimie des Matériaux de Strasbourg)
Participants (France, ANTION project)
The GBAR collaboration
Outline
• Introduction - the GBAR project• Antihydrogen ion creation for GBAR• Reaction cross section - past experiments• Reaction cross sections - theoretical results• Preparations for new cross section measurements
– Reaction zone– Detection– Positron pulse– Laser– Proton source– Antiproton beamline
• Summary and outlook
The GBAR experiment at CERN
• Direct observation of the gravitational free fall of antihydrogen (two experiments: AEGIS and GBAR)
• Requires very cold antihydrogen (10 µK)
• Distinctive idea: cool down posively charged antihydrogen ion, then photodetach the extra positron
• Antiprotons from CERN AD + ELENA (100 keV)
• Positrons from a linac-based source + high field trap (5T) (GBAR was accepted by CERN
research Board in 2012)
Scheme of GBAR at CERN
Positron source at CEA Saclay Laszlo Liszkay, SLOPOS-13, 19 Sept.2013 6
ELENA Decelerator
Linac W target Moderator Buncher e+ trap
100 keV
𝑝 𝑝
1 keV
e-
9 MeVe+
~1 MeVe+
eV
e+
keV
Posi
tron
ium
ta
rget
clo
ud
e+
keV
AD𝑝
5.3 MeV
Cooling
Lase
r
Experimental chamber with detectors
Lase
r
𝐻+¿1 keV
𝐻+¿20 µK
- e+𝐻
20 µKLa
ser
sCapture
1eV𝐻+¿
Positronium target cloud for the GBAR experiment
eHPsH
eHPspReactions in the cloud
Target cavity
107/pulse(~110 s)~3 keV
Positron-positronium converter (mesoporous SiO2)
eHPsH
eHPsp
eHPsH
eHPsp
Cross section measurements: aims
Measurement of the cross section of the following reactions of positronium (Ps, positron-electron bound system):
1. Hydrogen and negative hydrogen ion production
2. Antihydrogen and antihydrogen ion production
With positronium (Ps) is in the fundamental, 3D or 2P stateProton and antiproton in the 1-10 keV kinetic energy range
Earlier measurement
eHPsp
Merrison et al,, Phys. Rev. Lett. 78, 2828(1997)
Method: positron detection
• 10-16 keV proton energy
• Ground state Ps only
New theoretical calculations: proton reaction
P. Comini and P. –A. Hervieux, N. J. of Phys. 15, 095022 (2013)
eHPsp• Theoretical calculations by one of the partners (IPCMS)
• 2p & 3d states are good candidates
• Optimal energy depends on the state
New theoretical calculations: second reaction
P. Comini and P. –A. Hervieux, N. J. of Phys. 15, 095022 (2013)
eHPsH• Calculation for ground state H
• 4-body problem, quantitative results may be unreliable
• Cross section is much lower at excited state of H
• Max. at lowest energy (above threshold)
• 1s, 2p, 3d states OK
New theoretical calculations: two reactions in the Ps cloud
P. Comini and P. –A. Hervieux, N. J. of Phys. 15, 095022 (2013)
eHPsH
eHPsp
• Advantage of excited Ps state is not clear
• Measurements are needed to optimize the energy & ps state
• H* relaxation to ground state is important
New theoretical calculations: comparison with experiment
P. Comini and P. –A. Hervieux, N. J. of Phys. 15, 095022 (2013) Merrison et al,, Phys. Rev. Lett. 78, 2828(1997)
eHPsp
• Calculation agrees well with measurement for the proton reaction
• No test yet for the four-body reaction
Cross section meas.: target chamber and detector
(anti)proton beam (anti)atoms
protons
(anti)ions
grid
MCP
Positron pulse
Electricquadrupole
CCDcamera
Fast phosphor screen
Viewport
Faraday cup
Ion detection
• Camera: fast shutter (1µs)• MCP: switched (~400 ns)
Positronium target cloud
Detection of keV atoms with an MCP
Detection efficiency corresponds to the sensitive area of the MCP above ~1 keV (hydrogen)
• Gated MCP + fast phosphor screen• fast ( 1 µs) CCD camera
• Low background detection needed:• Suppress direct annihilation
gamma background• Suppress MCP noise• Suppress camera dark noise• Separate charged particles
Penning trap for e+ (RIKEN)
Slow e+ rate 3x106 s-1
e- linac(4.3 MeV)
e+/e- magnetic separator
W target+ W mesh moderator
The slow positron beam at Saclay (CEA/IRFU)
Slow positron drift tube (~10 eV)
Beam switch/user port (materials science)
Multiring trap: positron cooling by trapped electrons
5 T field
e+ beam
• Electron cooling• Switched entry (synchronized with linac pulses)• Bunched exit (short, intense pulse)
~10 mm diam.4-5 keV
1 x 10 mm ellipse
Positron optics after the trap
~100 Gauss (?)
• Electrostatic focussing• Exit from magnetic field with ~4 keV energy
Optical excitation of Ps
3D - 410 nm Doppler-free(in construction, GBAR)
2P - 243 nm frequency comb
Proton source
• Penning-discharge source with electrostatic focussing• The same source is used to develop the antiproton decelerator
Experiments at IRFU (Saclay) and CERN
• The positron beam intensity is sufficient only to measure the proton reaction
• Energy dependence will be measured• Reaction with Ps in 3D and 2P states will be measured
• The measurement will be continued at the stronger source at CERN
• When antiprotons are available, the antiproton and antihydrogen reaction will be performand
eHPsp
eHPsH
eHPsp
eHPsH
Cross section of the (anti)hydrogen-Ps reaction
• At the moment we have no tool to generate hydrogen atoms in the relevant energy range
• The cross section will be deduced from the quantity of ions generated in the two reactions in one Ps target cloud
• It is sufficient for GBAR but limits the precision of the cross section measurement
Second phase: measurements at CERN
• New positron source --> measurement of the double reaction (CEA source is too weak)
• Antiproton beam (AD+ELENA+GBAR decelerator) --> cross section of the reaction with antiproton and antihydrogen
Upgrade - GBAR at CERN
300 mm
4.3 MeV (magnetron)200 Hz, 2.5 µs pulse120 mA peak current70 µA average current
3x106 e+/s
9 MeV (Klystron)300 Hz 300 mA peak current200 µA average current
1x108 e+/s
~900 mmElectron target + moderator: same construction
Antiproton deceleration after ELENA
• Antiprotons at ~1-10 keV energy
• Switched decelerator
Summary
• Preparations for cross section measurements at IRFU• Continuation at CERN (ion creation, antiproton and
antihydrogen reaction)• Essential information for GBAR (optimal Ps state, proton
energy)
• See also talk of Sebastian Wolf (next talk)
The work is supported by the Agence National de la Recherche, project number ANR-14-CE33-0008-01
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