Narrow Results

We present a measurement of W/Z boson + jets production and Z p_T measurement in the collisions at the Tevatron Collider at . The CDF II measures W+jets production based on 320 pb^-1 and the DØ Run II measures Z+jets with 950 pb^-1 data. The measurement of Z p_T is performed with DØ Run II data corresponding to an integrated luminosity of 960 pb^-1. The measurement of W + jets is compared to the Leading Order Alpgen + Pythia prediction and the Z+jets is compared to Sherpa and Pythia Monte Carlo. The Z p_T measurement is also compared to Resbos+Photos predictions.

At the Tevatron collider the production of prompt photons with high transverse momenta has been studied in collisions at by the CDF and DØ collaborations. In this report cross-sections for the production of isolated photons, isolated photons in connection with heavy flavor jets and two isolated photons is presented. The experimental data are compared to predictions of several QCD models.

Four studies are presented performed by the DELPHI collaboration investigating soft QCD effects in e⁺e^- collisions at the LEP accelerator.

1) A surplus of neutral leading systems in gluon jets compared to quark jets resp. MC simulations is observed, which is concentrated at low invariant masses (≲ 2.5 GeV) and might be explained by the existence of Colour Octet annihilation.

2) Colour reconnection studies in e⁺e^- → WW → 4 jets have been performed in the framework of the SK-I model.

3) The dependence of the excess of soft photons deep inside jets has been investigated revealing a prominant distinction of the anomalous soft photon signal from the bremsstrahlung-like behaviour with respect to the jet neutral multiplicity, but not with respect to charged multiplicity. Thus the anomalous photons might couple to quark constituents of hadrons.

4) The observed photon rate in Z → μ⁺μ^-nγ is in agreement with predictions from QED for the muon inner bremsstrahlung thus restricting soft photon anomaly to reactions of multiple hadron production.

A study of "underlying event" in Run 2 at CDF is presented. Several PYTHIA 6.2 tunes (with multiple parton interactions) are examined and compared with HERWIG (without multiple parton interactions) and with the ATLAS PYTHIA tune (with multiple parton interactions) and they are extrapolated to the LHC.

Latest results on inclusive jet production from Tevatron are presented in this conference note. Results are based on samples with collected luminosity of about 1 fb^-1. Measured cross sections are in good agreement with NLO QCD predictions in wide range of jet transverse momenta and rapidities.

A peculiar prediction of perturbative QCD, with the assumption of Local Parton Hadron Duality, is that the difference in mean hadron multiplicity between heavy and light quark initiated events in e⁺e^- annihilation, δ_Qℓ, is energy independent. In the Modified Leading Logarithmic Approximation (MLLA), the numerical value of the constant is derived in terms of a few experimentally measurable quantities. While the energy independence of δ_Qℓ has been succesfully verified experimentally for b-quarks up to the highest LEP2 energy, the numerical prediction originally published in 1992, , clearly overestimates the experimental results. In this work, done in collaboration with Yuri L. Dokshitzer, Valery A. Khoze and Wolfgang Ochs, we show that the original MLLA prediction needs a revision, in the light of new experimental results and the improvement in the understanding of the experimental data. We now find , in better agreement with experiment, and we show that the remaining difference can be attributed largely to next-to-MLLA contributions, an important subset of which are identified and evaluated. The situation for charmed quarks is also reviewed.

The physics potential of the Circular Electron Positron Collider (CEPC) can be significantly strengthened by two detectors with complementary designs. A promising detector approach based on the Silicon Detector (SiD) designed for the International Linear Collider (ILC) is presented. Several simplifications of this detector for the lower energies expected at the CEPC are proposed. A number of cost optimizations of this detector are illustrated using full detector simulations. We show that the proposed changes will enable one to reach the physics goals at the CEPC.

The Event Horizon Telescope promises to construct an image of the supermassive black hole in the Galaxy center. Since the black hole event horizon is visible only when illuminated appropriately, its direct detectability depends on the structures and radiative properties of the plasma in the nearest vicinity of the black hole. General relativistic magnetohydrodynamics simulations and corresponding radiative transfer models allow us to predict the appearance of magnetized plasma near a supermassive, rotating black hole accurately. Here, we present the details of the three-dimensional models of accreting black hole scaled to the Galactic center object. We present expected appearance of these models at the Event Horizon Telescope observing wavelengths as a function of black hole’s angular velocity and thermodynamical properties of the plasma around it. In the near future, similar models will be used to interpret the Event Horizon Telescope observations. The observations will constrain the supermassive black hole spin value and orientation and will reveal the nature of the compact synchrotron emission produced nearby the black hole.

The location of the main emitting region responsible for the bulk of the Blazar emission is a puzzling issue in our understanding of jetted Active Galactic Nuclei. Fast flares and a high Compton dominance are more easily explained if the gamma-ray zone is well inside the Broad Line Region (BLR), while the absence of γ-γ absorption features in the Fermi-LAT spectra as well as the detection at Very High Energies (VHE) of some FSRQ put the blazar zone at much larger distances along the jet, beyond the BLR. The latter seems now to be the most typical behavior in FSRQ, questioning SED models based on the external Compton process on BLR photons.

The Event Horizon Telescope promises to construct an image of the supermassive black hole in the Galaxy center. Since the black hole event horizon is visible only when illuminated appropriately, its direct detectability depends on the structures and radiative properties of the plasma in the nearest vicinity of the black hole. General relativistic magnetohydrodynamics simulations and corresponding radiative transfer models allow us to predict the appearance of magnetized plasma near a supermassive, rotating black hole accurately. Here, we present the details of the three-dimensional models of accreting black hole scaled to the Galactic center object. We present expected appearance of these models at the Event Horizon Telescope observing wavelengths as a function of black hole’s angular velocity and thermodynamical properties of the plasma around it. In the near future, similar models will be used to interpret the Event Horizon Telescope observations. The observations will constrain the supermassive black hole spin value and orientation and will reveal the nature of the compact synchrotron emission produced nearby the black hole.

I discuss the calculation of QCD jet rates in e⁺e^- annihilation as a testing ground for parton shower simulations and jet finding algorithms.

The 1-30 GHz light curves of the microquasars GRS1915+105, Cyg X-3, and SS433 were measured in the intensive daily monitoring programs with the RATAN-600 (SAO RAS) radio telescope during 2002-2009. A lot of the powerful flaring events were detected, being alerts of the VLBI or e-VLBI mapping. We detected clear correlations between radio emission (RATAN), soft (ASM XTE) and hard (ASM Swift/BAT) X-ray emission for Cyg X-3 and GRS 1915+105. The repeatedly similar pre-flaring evolution of the radio and X-ray emission of Cyg X-3 allow us to predict the strong flares (> 3 Jy) as in the case of the flare in December 2008. We used it in the high-energy emission (MAGIC, AGILE) search of the X-ray binary. The super-critical black hole accretor SS433 was mapping with the European e-VLBI during its unusual radio activity in November 2008. Possible microquasar, X-ray binary and luminous star LSI+61d303 was monitored during May-October 2009 and six periodically flaring events were detected. But we found that the most accurate ephemerids (Gregory, 2002) of radio flares according to super-orbital period (P2= 1664days) were not coincident with the mean (for six flares) light curves. That could be explained by or slightly the shorter P2, near 1600 days, or the variability of this super-orbital period on timescale of 10 years.

Jet-based trigger triggers allow the ATLAS experiment to perform an important first selection of physics events for use in studies of Standard Model processes and in searches for new physics at the LHC. The ATLAS jet trigger system has evolved substantially over the past few years of LHC operations, as experience accumulated with triggering in a high luminosity and high event pileup environment. In particular, the localised “region-of interest” (ROI) reconstruction strategy has been replaced by a full detector calorimeter reconstruction (“full scan”) at the third trigger level, and by a full scan of the level-1 trigger input at level-2 for some specific trigger chains. Hadronic calibration and cleaning techniques are applied in order to provide improved performance and increased stability in high luminosity data taking conditions. In this presentation we describe the structure and performance of the ATLAS jet trigger during 2011 and 2012 data taking.

The ATLAS and CMS collaborations have performed a wide range of studies of QCD phenomena, from the production of soft particles to hard photons and jets. Differential measurements of inclusive and dijet production by both ATLAS and CMS provide stringent tests of high-order QCD predictions, as well as input for the determination of parton density functions. Measurements of isolated and inclusive photon cross sections for high-p_T photons also test QCD predictions and further constrain PDFs. A survey of these QCD measurements is presented here.

Recent measurements of proton structure, jet production cross sections, the strong coupling constant value, prompt photon production cross sections, charmed hadron production cross sections and the charm and beauty quark mass values, performed by the H1 and ZEUS collaborations at the e^±p collider HERA, are presented.