Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: S-wave elastic scattering of ${\it o}$-Ps from $\text{H}_2$ at low
  energy   The confined variational method is applied to investigate the low-energy
elastic scattering of ortho-positronium from $\text{H}_2$ by first-principles
quantum mechanics. Describing the correlation effect with explicitly correlated
Gaussians, we obtain accurate $S$-wave phase shifts and pick-off annihilation
parameters for different incident momenta. By a least-squares fit of the data
to the effective-range theory, we determine the $S$-wave scattering length,
$A_s=2.06a_0$, and the zero-energy value of the pick-off annihilation
parameter, $^1\!\text{Z}_\text{eff}=0.1858$. The obtained
$^1\!\text{Z}_\text{eff}$ agrees well with the precise experimental value of
$0.186(1)$ (J.\ Phys.\ B \textbf{16}, 4065 (1983)) and the obtained $A_s$
agrees well with the value of $2.1(2)a_0$ estimated from the average
experimental momentum-transfer cross section for Ps energy below 0.3 eV (J.\
Phys.\ B \textbf{36}, 4191 (2003)).

30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ