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We analyse Kepler/K2 lightcurve data of the AM CVn system HP Librae. Wedetect with confidence four photometric periodicities in the system: theorbital frequency, both positive and negative superhumps, and the positiveapsidal precession frequency of the accretion disc. This is only the secondtime that the apsidal precession frequency has ever been directly detected inthe photometry of a helium accreting system, after SDSS J135154.46-064309.0. Wepresent phase-folded lightcurves and sliding power spectra of each of the fourperiodicities. We measure rates of change of the positive superhump period of$10^{-7}$ days/day. We also redetect a QPO at 300 cyc/day, a feature that hasbeen stable over decades, and show that it is harmonically related to two otherQPOs, the lowest of which is centered on the superhump/orbital frequency. Thecontinuum power spectrum is consistent with a single power law with no evidenceof any breaks within our observed frequency range.

Periodicities in the K2 lightcurve of HP Librae