Energy-dependent Ps-He momentum-transfer cross section at low energies

Abstract

Positronium ͑Ps͒-He scattering presents one of the few opportunities for both theory and experiment to tackle the fundamental interactions of Ps with ordinary matter. Below the dissociation energy of 6.8 eV, experimental and theoretical work has struggled to find agreement on the strength of this interaction as measured by the momentum-transfer cross section ͑ m ͒. Here, we present work utilizing the Doppler broadening technique with an age-momentum correlation apparatus. This work demonstrates a strong energy dependence for this cross section at energies below 1 eV and is consistent with previous experimental results.

Calculations of positronium-atom scattering using a spherical cavity

“…The measurement by Nagashima et al [57] is in perfect agreement with our frozen-target calculation, and owing to the large error bars, is compatible with the van der Waals cross sections. Our calculations do not agree with the measurements of Skalsey et al [60] or Engbrecht et al [61], though we note that the results of Engbrecht et al [61] disagree with the other low-energy measurements. [51]; filled yellow square, Rytsola et al [52]; open navy circle, Coleman et al [53]; filled red circle, Skalsey et al [60]; open black triangle, Nagashima et al [57]; dash-double-dotted black line, Engbrecht et al [61].…”

Detailed investigation of low-energy positronium-hydrogen scattering

“…Positronium (Ps) scattering from atoms and molecules is an area of current experimental and theoretical interest. The development of energy-tunable ortho-Ps beams [1][2][3][4][5] has enabled measurements to be made of Ps scattering from the inert gases He, Ne, Ar, Kr, and Xe [4][5][6][7][8][9][10][11] and the molecules H 2 , N 2 , O 2 , CO 2 , H 2 O, and SF 6 [4,6,8,9,[11][12][13]. Cross sections for Ps scattering from H have not been measured due to the difficulty of creating an atomic H beam, although the binding energy of positronium hydride (PsH) has been measured in the reaction of a positron with methane, e + + CH 4 → CH + 3 + PsH [14].…”

Monte Carlo simulation of positronium thermalization in gases

“…Stoga, energijski opseg u kojem je rađena simulacija iznosi od nula do otprilike 8 eV u zavisnosti od početne energijske raspodele. Zato je neke preseke, kao na primer one date u [5], bilo neophodno ekstrapolirati za više energije. Pristup koji smo usvojili pri ekstrapolaciji preseka jeste da linearno ekstrapoliramo preseke do energije od 2 eV, nakon čega se presek drži konstantnim na vrednosti 6×10 -16 cm 2 (slika 1).…”

“…Odskora su dostupni eksperimentalno određeni preseci za prenos impulsa u interakciji Ps-He na niskim energijama. Engbrecht i saradnici [5] merili su Doppler--ovo širenje zračenja nastalog anihilacijom pozitronijuma i određivali profil termalizacije (relaksacija energije roja čestica u vremenu) Ps u helijumu. Iz termalizacionog profila, na osnovu teorije koju su dali Nagashima i saradnici [6] Ps-He i ranije dostupne teorijski određene preseke za helijum, i testirali koliko parametri kao što je presek i početna energijska raspodela utiču na oblik profila termalizacije.…”