Jet multiplicity distributions in top quark pair (Formula: see text) events are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC using a data set ...corresponding to an integrated luminosity of 19.7Formula: see text. The measurement is performed in the dilepton decay channels (Formula: see text, Formula: see text, and Formula: see text). The absolute and normalized differential cross sections for Formula: see text production are measured as a function of the jet multiplicity in the event for different jet transverse momentum thresholds and the kinematic properties of the leading additional jets. The differential Formula: see text and Formula: see text cross sections are presented for the first time as a function of the kinematic properties of the leading additional Formula: see text jets. Furthermore, the fraction of events without additional jets above a threshold is measured as a function of the transverse momenta of the leading additional jets and the scalar sum of the transverse momenta of all additional jets. The data are compared and found to be consistent with predictions from several perturbative quantum chromodynamics event generators and a next-to-leading order calculation.
Inclusive jet production in pPb collisions at a nucleon-nucleon (NN) center-of-mass energy of Formula: see text is studied with the CMS detector at the LHC. A data sample corresponding to an ...integrated luminosity of 30.1 nbFormula: see text is analyzed. The jet transverse momentum spectra are studied in seven pseudorapidity intervals covering the range Formula: see text in the NN center-of-mass frame. The jet production yields at forward and backward pseudorapidity are compared and no significant asymmetry about Formula: see text is observed in the measured kinematic range. The measurements in the pPb system are compared to reference jet spectra obtained by extrapolation from previous measurements in pp collisions at Formula: see text. In all pseudorapidity ranges, nuclear modifications in inclusive jet production are found to be small, as predicted by next-to-leading order perturbative QCD calculations that incorporate nuclear effects in the parton distribution functions.
Context. Wide-range spectral coverage of blazar-type active galactic nuclei is of paramount importance for understanding the particle acceleration mechanisms assumed to take place in their jets. The ...Major Atmospheric Gamma Imaging Cerenkov (MAGIC) telescope participated in three multiwavelength (MWL) campaigns, observing the blazar Markarian (Mkn) 421 during the nights of April 28 and 29, 2006, and June 14, 2006. Aims. We analyzed the corresponding MAGIC very-high energy observations during 9 nights from April 22 to 30, 2006 and on June 14, 2006. We inferred light curves with sub-day resolution and night-by-night energy spectra. Methods. MAGIC detects γ-rays by observing extended air showers in the atmosphere. The obtained air-shower images were analyzed using the standard MAGIC analysis chain. Results. A strong γ-ray signal was detected from Mkn 421 on all observation nights. The flux (E > 250 GeV) varied on night-by-night basis between (0.92±0.11) × 10-10 cm-2 s-1 (0.57 Crab units) and (3.21±0.15) × 10-10 cm-2 s-1 (2.0 Crab units) in April 2006. There is a clear indication for intra-night variability with a doubling time of 36±$10_{\rm stat}$ min on the night of April 29, 2006, establishing once more rapid flux variability for this object. For all individual nights γ-ray spectra could be inferred, with power-law indices ranging from 1.66 to 2.47. We did not find statistically significant correlations between the spectral index and the flux state for individual nights. During the June 2006 campaign, a flux substantially lower than the one measured by the Whipple 10-m telescope four days later was found. Using a log-parabolic power law fit we deduced for some data sets the location of the spectral peak in the very-high energy regime. Our results confirm the indications of rising peak energy with increasing flux, as expected in leptonic acceleration models.
The flat-spectrum radio quasar 3C 454.3 is well known to be a highly active and variable source with outbursts occurring across the whole electromagnetic spectrum over the last decades. In ...spring 2005, 3C 454.3 has been reported to exhibit a strong optical outburst which subsequently triggered multi-frequency observations of the source covering the radio up to γ-ray bands. Here, we present first results of our near-IR/optical (V, R, I, H band) photometry performed between May 11 and August 5, 2005 with the Rapid Eye Mount (REM) at La Silla in Chile and the Automatic Imaging Telescope (AIT) of the Perugia University Observatory. 3C 454.3 was observed during an exceptional and historical high state with a subsequent decrease in brightness over our 86 days observing period. The continuum spectral behaviour during the flaring and declining phase suggests a synchrotron peak below the near-IR band as well as a geometrical origin of the variations e.g. due to changes in the direction of forward beaming.
A measurement of the forward-backward asymmetry Formula: see text of oppositely charged lepton pairs (Formula: see text and Formula: see text) produced via Formula: see text boson exchange in pp ...collisions at Formula: see text Formula: see text is presented. The data sample corresponds to an integrated luminosity of 19.7Formula: see text collected with the CMS detector at the LHC. The measurement of Formula: see text is performed for dilepton masses between 40Formula: see text and 2Formula: see text and for dilepton rapidity up to 5. The Formula: see text measurements as a function of dilepton mass and rapidity are compared with the standard model predictions.
A search for narrow resonances decaying to an electron and a muon is presented. The Formula: see text Formula: see text mass spectrum is also investigated for non-resonant contributions from the ...production of quantum black holes (QBHs). The analysis is performed using data corresponding to an integrated luminosity of 19.7Formula: see text collected in proton-proton collisions at a centre-of-mass energy of 8Formula: see text with the CMS detector at the LHC. With no evidence for physics beyond the standard model in the invariant mass spectrum of selected Formula: see text pairs, upper limits are set at 95 Formula: see text confidence level on the product of cross section and branching fraction for signals arising in theories with charged lepton flavour violation. In the search for narrow resonances, the resonant production of a Formula: see text sneutrino in R-parity violating supersymmetry is considered. The Formula: see text sneutrino is excluded for masses below 1.28Formula: see text for couplings Formula: see text, and below 2.30Formula: see text for Formula: see text and Formula: see text. These are the most stringent limits to date from direct searches at high-energy colliders. In addition, the resonance searches are interpreted in terms of a model with heavy partners of the Formula: see text boson and the photon. In a framework of TeV-scale quantum gravity based on a renormalization of Newton's constant, the search for non-resonant contributions to the Formula: see text Formula: see text mass spectrum excludes QBH production below a threshold mass Formula: see text of 1.99Formula: see text. In models that invoke extra dimensions, the bounds range from 2.36Formula: see text for one extra dimension to 3.63Formula: see text for six extra dimensions. This is the first search for QBHs decaying into the Formula: see text Formula: see text final state.
A search for a massive resonance Formula: see textdecaying into a W and a Higgs boson in the Formula: see text (Formula: see text, Formula: see text) final state is presented. Results are based on ...data corresponding to an integrated luminosity of 19.7Formula: see text of proton-proton collisions at Formula: see text Formula: see text, collected using the CMS detector at the LHC. For a high-mass (Formula: see text1Formula: see text) resonance, the two bottom quarks coming from the Higgs boson decay are reconstructed as a single jet, which can be tagged by placing requirements on its substructure and flavour. Exclusion limits at 95 % confidence level are set on the production cross section of a narrow resonance decaying into WH, as a function of its mass. In the context of a little Higgs model, a lower limit on the Formula: see text mass of 1.4Formula: see text is set. In a heavy vector triplet model that mimics the properties of composite Higgs models, a lower limit on the Formula: see text mass of 1.5Formula: see text is set. In the context of this model, the results are combined with related searches to obtain a lower limit on the Formula: see text mass of 1.8Formula: see text, the most restrictive to date for decays to a pair of standard model bosons.
Aims. We present the second AGILE-GRID Catalog (2AGL) of {\gamma}-ray sources in the 100 MeV-10 GeV energy range. Methods. With respect to previous AGILE-GRID catalogs, the current 2AGL Catalog is ...based on the first 2.3 years of science data from the AGILE mission (the so called 'pointing mode') and incorporates more data and several analysis improvements, including better calibrations at the event reconstruction level, an updated model for the Galactic diffuse gamma-ray emission, a refined procedure for point-like source detection, and the inclusion of a search for extended {\gamma}-ray sources. Results. The 2AGL Catalog includes 175 high-confidence sources (above 4{\sigma} significance) with their location regions and spectral properties, and a variability analysis with 4-day light curves for the most significant ones. Relying on the error region of each source position, including systematic uncertainties, 121 sources are considered as positionally associated with known couterparts at different wavelengths or detected by other {\gamma}-ray instruments. Among the identified or associated sources, 62 are Active Galactic Nuclei (AGNs) of the blazar class. Pulsars represent the largest Galactic source class, with 40 associated pulsars, 7 of them with detected pulsation; 8 Supernova Remnants and 4 high-mass X-ray binaries have also been identified. A substantial number of 2AGL sources are unidentified: for 54 sources no known counterpart is found at different wavelengths. Among these sources, we discuss a sub-class of 29 AGILE-GRID-only {\gamma}-ray sources that are not present in 1FGL, 2FGL or 3FGL catalogs; the remaining sources are unidentified in both 2AGL and 3FGL Catalogs. We also present an extension of the analysis of 2AGL sources detected in the 50-100 MeV energy range.
We compute the non-thermal emissions produced by relativistic particles accelerated by the AGN-driven shocks in NGC 1068, and we compare the model predictions with the observed gamma-ray and radio ...spectra . The former is contributed by pion decay, inverse Compton scattering, and bremsstrahlung, while the latter is produced by synchrotron radiation. We derive the gamma-ray and radio emissions by assuming the standard acceleration theory, and we discuss how our results compare with those corresponding to other commonly assumed sources of gamma-ray and radio emissions, like Supernova remnants (SNR) or AGN jets. We find that the AGN-driven shocks observed in the circumnuclear molecular disk of such a galaxy provide a contribution to the gamma-ray emission comparable to that provided by the starburst activity when standard particle acceleration efficiencies are assumed, while they can yield the whole gamma-ray emission only when the parameters describing the acceleration efficiency and the proton coupling with the molecular gas are tuned to values larger than those assumed in standard, SNR-driven shocks. We discuss the range of acceleration efficiencies (for protons and electrons) and of proton calorimetric fractions required to account for the observed gamma-ray emission in the AGN outflow model. We further compare the neutrino flux expected in our model with constraints from current experiments, and we provide predictions for the detections by the upcoming KM3NeT neutrino telescope. This analysis strongly motivates observations of NGC 1068 at >TeV energies with current and future Cherenkov telescopes in order to gain insight into the nature of the gamma-rays source.
The Level-1 Trigger plays a major role in the CMS experiment allowing the reduction of the raw event rate at the Large Hadron Collider. Its decision is based on information from the electromagnetic ...and hadronic calorimeters as well as the muon detectors. The electronics of the electromagnetic calorimeter generate and deliver basic quantities called "Trigger Primitives" which correspond to local energy deposits created by electromagnetic showers. In order to ensure the correct generation of the trigger primitives by the electronics, a special software called an emulator has been implemented. It is able to reproduce the ECAL trigger functionalities at the bit level using the same inputs and identical output format. It is configured in exactly the same way as the hardware.
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