Photon detection with the CMS ECAL in the present and at the HL-LHC and its impact on Higgs-Boson measurement

The CMS experiment at the LHC features a high-resolution and homogeneouselectromagnetic calorimeter (ECAL). The excellent performance of ECAL in thereconstruction of high-energy photons played a key role in the discovery of theHiggs boson and the measurement of its properties. The High-Luminosity LHC (HL-LHC) is expected to deliver an integrated luminosity 20 times larger than theLHC, allowing for the study of rare processes such as Higgs-boson pairproduction and self-coupling. During HL-LHC operations, up to 200 concurrentinteractions per bunch collision are expected. In order to maintain its currentperformance in the harsher environment of the HL-LHC, an upgrade of the ECAL isplanned. This contribution describes the ECAL performance in photonreconstruction and its impact on the measurement of the Higgs boson propertiesduring the LHC Run II. Prospects for Higgs-boson measurements at the HL-LHC arepresented as well.