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The pairing of composite fermions (CFs), electron-flux quasi-particles, iscommonly proposed to explain the even-denominator fractional quantum Hall stateobserved at $\nu=5/2$ in the first excited ($N=1$) Landau level (LL) of atwo-dimensional electron system (2DES). While well-established to exist in thelowest ($N=0$) LL, much is unknown about CFs in the $N=1$ LL. Here we carry outgeometric resonance measurements to detect CFs at $\nu=5/2$ by subjecting the2DES to a one-dimensional density modulation. Our data, taken at a temperatureof 0.3 K, reveal no geometric resonances for CFs in the $N=1$ LL. In starkcontrast, we observe clear signatures of such resonances when $\nu=5/2$ isplaced in the $N=0$ LL of the anti-symmetric subband by varying the 2DES width.This finding implies that the CFs' mean-free-path is significantly smaller inthe $N=1$ LL compared to the $N=0$ LL. Our additional data as a function ofin-plane magnetic field highlight the role of subband index and establish thatCFs at $\nu=5/2$ in the $N=0$ LL are more anisotropic in the symmetric subbandthan in the anti-symmetric subband.

Search for Composite Fermions at Filling Factor 5/2: Role of Landau Level and Subband Index