Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effective radius of ground- and excited-state positronium in collisions
  with hard walls   We determine effective collisional radii of positronium (Ps) by considering
Ps states in hard-wall spherical cavities. $B$-spline basis sets of electron
and positron states inside the cavity are used to construct the states of Ps.
Accurate Ps energy eigenvalues are obtained by extrapolation with respect to
the numbers of partial waves and radial states included in the bases.
Comparison of the extrapolated energies with those of a pointlike particle
provides values of the effective radius $\rho_{nl}$ of Ps($nl$) in collisions
with a hard wall. We show that for $1s$, $2s$, and $2p$ states of Ps, the
effective radius decreases with the increasing Ps center-of-mass momentum, and
find $\rho_{1s}=1.65$ a.u., $\rho_{2s}=7.00$ a.u., and $\rho_{2p}=5.35$ a.u. in
the zero-momentum limit.

10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga
28
The categories of this paper are: alg-geom
31
The categories of this paper are: ao-sci