Results on two-particle angular correlations for charged particles emitted in proton-proton collisions at center-of-mass energies of 0.9, 2.36, and 7TeV are presented, using data collected with the CMS detector over a broad range of pseudorapidity (eta) and azimuthal angle (phi). Short-range correlations in Delta(eta), which are studied in minimum bias events, are characterized using a simple "independent cluster" parametrization in order to quantify their strength (cluster size) and their extent in eta (cluster decay width). Long-range azimuthal correlations are studied differentially as a function of charged particle multiplicity and particle transverse momentum using a 980 nb(-1) data set at 7TeV. In high multiplicity events, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate p(T) of 1-3 GeV/c, 2.0

A search for narrow resonances in the dijet mass spectrum is performed using data corresponding to an integrated luminosity of 2.9 pb⁻¹ collected by the CMS experiment at the Large Hadron Collider. Upper limits at the 95% confidence level are presented on the product of the resonance cross section, branching fraction into dijets, and acceptance, separately for decays into quark-quark, quark-gluon, or gluon-gluon pairs. The data exclude new particles predicted in the following models at the 95% confidence level: string resonances, with mass less than 2.50 TeV, excited quarks, with mass less than 1.58 TeV, and axigluons, colorons, and E6 diquarks, in specific mass intervals. This extends previously published limits on these models.

This Letter reports the results from a haloscope search for dark matter axions with masses between 2.66 and 2.81 μeV. The search excludes the range of axion-photon couplings predicted by plausible models of the invisible axion. This unprecedented sensitivity is achieved by operating a large-volume haloscope at subkelvin temperatures, thereby reducing thermal noise as well as the excess noise from the ultralow-noise superconducting quantum interference device amplifier used for the signal power readout. Ongoing searches will provide nearly definitive tests of the invisible axion model over a wide range of axion masses. DOI: 10.1103/PhysRevLett.120.151301 Axions are particles predicted to exist as a consequence of the Peccei-Quinn solution to the strong-CP problem [1][2][3] and could account for all of the dark matter in our Universe [4][5][6]. While there exist a number of mechanisms to produce axions in the early Universe [4,[7][8][9] that allow for a wide range of dark matter axion masses, current numerical and analytical studies of QCD typically suggest a preferred mass range of 1-100 μeV for axions produced after cosmic inflation in numbers that saturate the Lambda-CDM (cold dark matter) density [10][11][12][13][14]. The predicted coupling between axions and photons is model dependent; in general, axions with dominant hadronic couplings as in the Kim-Shifman-Vainshtein-Zakharov (KSVZ) model [15,16] are predicted to have an axion-photon coupling roughly 2.7 times larger than that of the Dine-FischlerSrednicki-Zhitnitsky (DFSZ) model [17,18]. Because the axion-photon coupling is expected to be very small, Oð10 −17 -10 −12 GeV −1 Þ over the expected axion mass range, these predicted particles are dubbed invisible axions [4].The most promising technique to search for dark matter axions in the favored mass range is the axion haloscope [19] consisting of a cold microwave resonator immersed in a strong static magnetic field. In the presence of this magnetic field, the ambient dark matter axion field produces a volume-filling current density oscillating at frequency f ¼ E=h, where E is the total energy consisting mostly of the axion rest mass with a small kinetic energy addition. When the resonator is tuned to match this frequency, the current source delivers power to the resonator in the form of microwave photons which can be detected with a low-noise microwave receiver. To date, a number of axion haloscopes have been implemented. All had noise levels too high to detect the QCD axion signal [20][21][22][23][24][25][26][27][28][29][30] in an experimentally realizable time. Previous versions of the Axion Dark Matter eXperiment (ADMX) [24][25][26][27][28][29] achieved sensitivity to the stronger KSVZ couplings in the ð1.91-3.69Þ-μeV mass range. ADMX has since been improved to utilize a dilution refrigerator to obtain a significantly lower system noise temperature, drastically increasing its sensitivity. We present here results from the first axion experiment to have sensitivity to the more weakly coupled DFSZ axion ...

Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the Compact Muon Solenoid (CMS) detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7 μb −1 . Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cutoff used in this study (jet p T = 120 GeV/c) up to the statistical limit of the available data sample (jet p T ≈ 210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet.

The first LHC pp collisions at centre-of-mass energies of 0.9 and 2.36 TeV were recorded by the CMS detector in December 2009. The trajectories of charged particles produced in the collisions were reconstructed using the all-silicon Tracker and their momenta were measured in the 3.8 T axial magnetic field. Results from the Tracker commissioning are presented including studies of timing, efficiency, signal-to-noise, resolution, and ionization energy. Reconstructed tracks are used to benchmark the performance in terms of track and vertex resolutions, reconstruction of decays, estimation of ionization energy loss, as well as identification of photon conversions, nuclear interactions, and heavy-flavour decays.