 First massive level of a chiral RNS sector

After the GSO projection, the first positive shifted level is one: $N_{\mathrm{NS}}=3/2$ and $N_R=1$. In a closed-string mass convention it corresponds to $M^2=4/{\alpha }^{\prime }$. The transverse oscillator basis has 128 NS states and 128 R states. They form the bosonic and fermionic pieces of a massive supersymmetry multiplet.