• Energy Research

A search is presented for new physics in events with two low-momentum, oppositely charged leptons (electrons or muons) and missing transverse momentum in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data collected using the CMS detector at the LHC correspond to an integrated luminosity of 35.9. The observed event yields are consistent with the expectations from the standard model. The results are interpreted in terms of pair production of charginos and neutralinos (X1 and X2) with nearly degenerate masses, as expected in natural supersymmetry models with light higgsinos, as well as in terms of the pair production of top squarks (t), when the lightest neutralino and the top squark have similar masses. At 95% confidence level, wino-like X1/X2 masses are excluded up to 230 GeV for a mass difference of 20 GeV relative to the lightest neutralino. In the higgsino-like model, masses are excluded up to 168 GeV for the same mass difference. For pair production, top squark masses up to 450 GeV are excluded for a mass difference of 40 GeV relative to the lightest neutralino. Physics Letters B, 782 ISSN:0370-2693 ISSN:0031-9163 ISSN:1873-2445

The transverse momentum spectra of $D^0$ mesons from b hadron decays are measured at midrapidity ($|y|<1$) in pp and PbPb collisions at a nucleon--nucleon center of mass energy of 5.02 TeV with the CMS detector at the LHC. The $D^0$ mesons from b hadron decays are distinguished from prompt $D^0$ mesons by their decay topologies. In PbPb collisions, the $B \to D^{0}$ yield is found to be suppressed in the measured $p_T$ range from 2 to 100 GeV/$c$ as compared to pp collisions. The suppression is weaker than that of prompt $D^0$ mesons and charged hadrons for $p_T$ around 10 GeV/$c$. While theoretical calculations incorporating partonic energy loss in the quark-gluon plasma can successfully describe the measured $B \to D^{0}$ suppression at higher $p_T$, the data show an indication of larger suppression than the model predictions in the range of $2 Physical review letters 123, 022001 (2019). doi:10.1103/PhysRevLett.123.022001 Published by APS, College Park, Md.