The cosmological parameters prefered by the cosmic microwave background ( CMB ) primary anisotropies predict many more galaxy clusters than those that have been detected via the thermal Sunyaev-Zeldovich ( tSZ ) effect .
This tension has attracted considerable attention since it could be evidence of physics beyond the simplest \Lambda CDM model .
However , an accurate and robust calibration of the mass-observable relation for clusters is necessary for the comparison , which has been proven difficult to obtain so far .
Here , we present new contraints on the mass-pressure relation by combining tSZ and CMB lensing measurements about optically-selected clusters .
Consequently , our galaxy cluster sample is independent from the data employed to derive cosmological constrains .
We estimate an average hydrostatic mass bias of b = 0.26 \pm 0.07 , with no significant mass nor redshift evolution .
This value greatly reduces the tension between the predictions of \Lambda CDM and the observed abundance of tSZ clusters while being in agreement with recent estimations from tSZ clustering .
On the other hand , our value for b is higher than the predictions from hydro-dynamical simulations .
This suggests the existence of mechanisms driving large departures from hydrostatic equilibrium and that are not included in state-of-the-art simulations , and/or unaccounted systematic errors such as biases in the cluster catalogue due to the optical selection .