First massive level of a chiral RNS sector ($N_{\mathrm{NS}}=3/2,N_R=1,M^2=4/{\alpha }^{\prime }$)

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.

At the first massive chiral level, 128 NS bosons and 128 R fermions furnish a massive multiplet with 16 real supercharges and no central charge. Its rest-frame supersymmetry algebra has eight fermionic creation operators, producing $2^8=256$ states. The massive little-group representations are $44+84$ for the bosons and a 128-dimensional vector-spinor for the fermions.

At R level one, the families are ${\alpha }_{-1}^i|s⟩$ and $d_{-1}^i|s^{\prime }⟩$, each of dimension $8\cdot 8$. The zero-mode spinors have opposite chirality because the one fermionic oscillator reverses the oscillator contribution to the GSO projection. The resulting 128 states form a gamma-traceless Spin(9) vector-spinor, of dimension $9\cdot 16-16$.

At NS level $3/2$, the light-cone families are $b_{-3/2}^i|0⟩$, ${\alpha }_{-1}^i{b}_{-1/2}^j|0⟩$, and three distinct $b_{-1/2}$ oscillators. Their dimensions are $8+64+\left(\genfrac{}{}{0ex}{}{8}{3}\right)=128$. All have odd fermion-excitation parity. They assemble into the massive Spin group representations $44+84$, a symmetric traceless tensor and a three-form of Spin(9).