  The abundance patterns observed in the Sun and in metal-poor stars show a
clear odd-even effect. An important question is whether the odd-even effect in
solar-metallicity stars is similar to the Sun, or if there are variations that
can tell us about different chemical enrichment histories. In this work, we
report for the first time observational evidence of a differential odd-even
effect in the solar twin HIP 11915, relative to the solar odd-even abundance
pattern. The spectra of this star were obtained with high resolving power (140
000) and signal-to-noise ratio ($\sim$420) using the ESPRESSO spectrograph and
the VLT telescope. Thanks to the high spectral quality, we obtained extremely
precise stellar parameters ($\sigma(T_{\rm eff})$ = 2 K, $\sigma(\rm{[Fe/H]})$
= 0.003 dex, and $\sigma(\log g)$ = 0.008 dex). We determine the chemical
abundance of 20 elements ($Z\leq39$) with high precision ($\sim$0.01 dex),
which shows a strong pattern of the odd-even effect even after performing
Galactic Chemical Evolution corrections. The odd-even effect is reasonably
well-reproduced by a core-collapse supernova of 13 $\rm{M_{\odot}}$ and
metallicity Z = 0.001 diluted into a metal-poor gas of 1 $\rm{M_{\odot}}$. Our
results indicate that HIP 11915 has an odd-even effect slightly different than
the Sun, thus confirming a different supernova enrichment history.
