Level truncation analysis of a simple tachyon vacuum solution in cubic   superstring field theory
  We evaluate the vacuum energy of a simple tachyon vacuum solution using the level truncation scheme in cubic superstring field theory. By truncating the standard Virasoro $L_0$ level expansion of the solution, we obtain a value of the vacuum energy in agreement with Sen's first conjecture. 
E. Aldo Arroyo
hep-th