​Department of Physics “G. Occhialini”

CERN-LHC. A measurement of the double-differential inclusive jet cross section as a function of jet transverse momentum pT and absolute jet rapidity |y| is presented. The analysis is based on proton-proton collisions collected by the CMS experiment at the LHC at a centre-of-mass energy of 13 TeV. The data samples correspond to integrated luminosities of 71 and 44 inverse-picobarns for |y|< 3 and 3.2 < |y| < 4.7, respectively. Jets are reconstructed with the anti-kt clustering algorithm for two jet sizes, R, of 0.7 and 0.4, in a phase space region covering jet pT up to 2 TeV and jet rapidity up to |y| = 4.7. Predictions of perturbative quantum chromodynamics at next-to-leading order precision, complemented with electroweak and nonperturbative corrections, are used to compute the absolute scale and the shape of the inclusive jet cross section. The cross section difference in R, when going to a smaller jet size of 0.4, is best described by Monte Carlo event generators with next-to-leading order predictions matched to parton showering, hadronisation, and multiparton interactions. In the phase space accessible with the new data, this measurement provides a first indication that jet physics is as well understood at sqrt(s) = 13 TeV as at smaller centre-of-mass energies.

CERN-LHC. CMS. A search for supersymmetry is presented based on events with at least one photon, jets, and large missing transverse momentum produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 35.9 $fb^{-1}$ and were recorded at the LHC with the CMS detector in 2016. The analysis characterizes signal-like events by categorizing the data into various signal regions based on the number of jets, the number of b-tagged jets, and the missing transverse momentum. No significant excess of events is observed with respect to the expectations from standard model processes. Limits are placed on the gluino and top squark pair production cross sections using several simplified models of supersymmetric particle production with gauge-mediated supersymmetry breaking. Depending on the model and the mass of the next-to-lightest supersymmetric particle, the production of gluinos with masses as large as 2120 GeV and the production of top squarks with masses as large as 1230 GeV are excluded at 95% confidence level.

CERN-LHC. A measurement of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta is presented for seven regions of leading jet transverse momentum up to 2.2 TeV. The analysis is based on the proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb^{-1}. The dijet azimuthal decorrelation is caused by the radiation of additional jets and probes the dynamics of multijet production. The results are compared to fixed-order predictions of perturbative quantum chromodynamics (QCD), and to simulations using Monte Carlo event generators that include parton showers, hadronization, and multiparton interactions. Event generators with only two outgoing high transverse momentum partons fail to describe the measurement, even when supplemented with next-to-leading-order QCD corrections and parton showers. Much better agreement is achieved when at least three outgoing partons are complemented through either next-to-leading-order predictions or parton showers. This observation emphasizes the need to improve predictions for multijet production.

A search is presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track. A disappearing track is an isolated track with missing hits in the outer layers of the silicon tracker, little or no energy in associated calorimeter deposits, and no associated hits in the muon detectors. This search uses data collected with the CMS detector in 2015 and 2016 from proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC, corresponding to an integrated luminosity of 38.4 $\mathrm{fb}^{-1}$. The results of the search are interpreted in the context of the anomaly-mediated supersymmetry breaking model. The data are consistent with the background-only hypothesis. Limits are set on the product of the cross section for direct production of charginos and their branching fraction to a neutralino and a pion, as a function of the chargino mass and lifetime. At 95% confidence level, charginos with masses below 715 (695) GeV are excluded for a lifetime of 3 (7) ns, as are charginos with lifetimes from 0.5 to 60 ns for a mass of 505 GeV. These are the most stringent limits using a disappearing track signature on this signal model for chargino lifetimes above $\approx$0.7 ns.

CERN-PS. Measurement of the double-differential cross sections for the production of charged pions in proton-tantalum collisions emitted at large angles from the incoming beam direction. The data were taken in 2002 in the T9 beam line with a target thickness of 5pct nuclear interaction length.. The errors given in the table are the combined statistics and systematics (excluding the overall 2 PCT normalisation uncertainty) and are the diagonal elements of the fitted covariance matrix.

Measurements are presented of the triple-differential cross section for inclusive isolated-photon+jet events in pp collisions at $\sqrt{s}$ = 8 TeV as a function of photon transverse momentum (${p_{T}^{\gamma}}$), photon pseudorapidity ($|{\eta^{\gamma}}|$), and jet pseudorapidity ($\eta^{jet}$). The data correspond to an integrated luminosity of 19.7 $fb^{−1}$ that probe a broad range of the available phase space, for $|{\eta^{\gamma}}|$ < 1.44 and 1.57 < $|{\eta^{\gamma}}|$ < 2.50, |${\eta^{\textrm{jet}}}$| < 2.5, 40 < ${p_{T}^{\gamma}}$ < 1000 GeV, and jet transverse momentum, ${p_{T}^{jet}}$, > 25 GeV.

CERN-LHC. The angular distributions and the differential branching fraction of the decay ${\rm B}^0 \to {\rm K^*(892)}^0 \mu^+ \mu^-$ are studied using data corresponding to an integrated luminosity of 20.5 fb$^{-1}$ collected with the CMS detector at the LHC in pp collisions at $\sqrt{s} = 8$ TeV. From 1430 signal decays, the forward-backward asymmetry of the muons, the ${\rm K^*(892)}^0$ longitudinal polarization fraction, and the differential branching fraction are determined as a function of the dimuon invariant mass squared. UPDATE (16 MAY 2017): changed 0.64 to 0.63 for FL in first bin of Table 2 on request of Mauro Dinardo (CMS).

Measurements are presented of the single-diffractive dijet cross section and the diffractive cross section as a function of the proton fractional momentum loss $\xi$ and the four-momentum transfer squared $t$. Both processes $\mathrm{pp} \to \mathrm{pX}$ and $\mathrm{pp} \to \mathrm{Xp}$, i.e. with the proton scattering to either side of the interaction point, are measured, where $\mathrm{X}$ includes at least two jets; the results of the two processes are averaged. The analyses are based on data collected simultaneously with the CMS and TOTEM detectors at the LHC in proton-proton collisions at $\sqrt{s} = 8\,\mathrm{TeV}$ during a dedicated run with $\beta^{\ast} = 90\,\mathrm{m}$ at low instantaneous luminosity and correspond to an integrated luminosity of $37.5\,\mathrm{nb}^{-1}$. The single-diffractive dijet cross section $\sigma^{\mathrm{pX}}_{\mathrm{jj}}$, in the kinematic region $\xi < 0.1$, $0.03 < \lvert t \rvert < 1\,\mathrm{GeV}^2$, with at least two jets with transverse momentum $p_{\mathrm{T}} > 40\,\mathrm{GeV}$, and pseudorapidity $\lvert \eta \rvert < 4.4$, is $21.7 \pm 0.9\,\text{(stat)} \,^{+3.0}_{-3.3}\,\text{(syst)} \pm 0.9\,\text{(lumi)} \,\mathrm{nb}$. The ratio of the single-diffractive to inclusive dijet yields, normalised per unit of $\xi$, is presented as a function of $x$, the longitudinal momentum fraction of the proton carried by the struck parton. The ratio in the kinematic region defined above, for $x$ values in the range $-2.9 \leq \log_{10} x \leq -1.6$, is $R = (\sigma^{\mathrm{pX}}_{\mathrm{jj}}/\Delta\xi)/\sigma_{\mathrm{jj}} = 0.025 \pm 0.001\,\text{(stat)} \pm 0.003\,\text{(syst)}$, where $\sigma^{\mathrm{pX}}_{\mathrm{jj}}$ and $\sigma_{\mathrm{jj}}$ are the single-diffractive and inclusive dijet cross sections, respectively. The results are compared with predictions from models of diffractive and nondiffractive interactions. Monte Carlo predictions based on the HERA diffractive parton distribution functions agree well with the data when corrected for the effect of soft rescattering between the spectator partons.

CERN-PS. Measurement of the double-differential cross sections for the production of charged pions in proton-Be,AL and PB collisions emitted at large angles from the incoming beam direction. The data were taken in the T9 beam line with a target thickness of 5pct nuclear interaction length.. The errors given in the table are the combined statistics and systematics (excluding the overall normalisation uncertainty) and are the diagonal elements of the fitted covariance matrix.

CERN-LHC. Dijet angular distributions are measured in proton-proton collisions at sqrt(s)=13 TeV based on a data set corresponding to an integrated luminosity of 35.9/fb collected by the CMS detector at the CERN LHC.