CP violation in charm has not yet been observed, although measurements of time-integrated CP asymmetries in D0→K+K− and D0→π+π− decays have reached a precision of O(10−3). The D0→K0SK0S decay is a promising discovery channel for CP violation in charm. A prediction based on the Standard Model gives an upper limit for the CP asymmetry of about 1% and further enhancements could result from contributions from physics beyond the Standard Model. A preliminary measurement of the time-integrated CP asymmetry in prompt D0→K0SK0S decays is presented, performed using data collected with the LHCb experiment in 2015 and 2016 at a 13 TeV pp center-of-mass energy (Run 2). The CP asymmetry is measured to be
ACP(D0→K0SK0S)=(0.042±0.034±0.010),
where the first uncertainty is statistical and the second is systematic. This result represents a significant improvement with respect to the previous LHCb Run 1 measurement.
