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A measurement of the underlying activity in scattering processes with a hard scale in the several GeV region is performed in proton-proton collisions at sqrt(s) = 0.9 and 7 TeV, using data collected by the CMS experiment at the LHC. The production of charged particles with pseudorapidity |eta| < 2 and transverse momentum pT > 0.5 GeV/c is studied in the azimuthal region transverse to that of the leading set of charged particles forming a track-jet. A significant growth of the average multiplicity and scalar-pT sum of the particles in the transverse region is observed with increasing pT of the leading track-jet, followed by a much slower rise above a few GeV/c. For track-jet pT larger than a few GeV/c, the activity in the transverse region is approximately doubled with a centre-of-mass energy increase from 0.9 to 7 TeV. Predictions of several QCD-inspired models as implemented in PYTHIA are compared to the data. Journal of high energy physics 2011(9), 109(2011). doi:10.1007/JHEP09(2011)109 Published by Springer, Berlin

Abstract A search has been made for events containing an energetic jet and an imbalance in transverse momentum using a data sample of pp collisions at a center-of-mass energy of 7 TeV. This signature is common to both dark matter and extra dimensions models. The data were collected by the CMS detector at the LHC and correspond to an integrated luminosity of 5.0 fb−1. The number of observed events is consistent with the standard model expectation. Constraints on the dark matter-nucleon scattering cross sections are determined for both spin-independent and spin-dependent interaction models. For the spin-independent model, these are the most constraining limits for a dark matter particle with mass below 3.5 GeV/c 2, a region unexplored by direct detection experiments. For the spin-dependent model, these are the most stringent constraints over the 0.1–200 GeV/c 2 mass range. The constraints on the Arkani-Hamed, Dimopoulos, and Dvali model parameter M D determined as a function of the number of extra dimensions are also an improvement over the previous results.

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.