Narrow Results

In this talk, focusing on groomed jet and quarkonium production and decay processes, we discuss the factorization and resummation of large logarithms at the level of cross section involving TMDs. For groomed jets we analyze the measurement of hadronic transverse momentum with respect to the groomed-jet-axis and show that this observable can be used for probing the non-perturbative part of the TMD (rapidity) evolution kernel. For the case of quarkonium we present a new framework for factorization of quarkonium production and decay TMD related processes. In this new approach the factorization theorems are written in terms of the new TMD quarkonium shape functions. We work in the framework of effective field theories and particularly soft collinear effective theory and non-relativistic quantum chromodynamics.

Weeks V and VI of the INT program 2018 were dedicated to physics opportunities at a future Electron-Ion Collider. Discussions were wide ranging and included topics such as short-range correlation, jets physics in deep inelastic scattering, nuclear PDFs, TMDs, and GPDs as well as small-x helicity distributions, non-linear small-x evolution equations, diffraction and particle production and correlations.

Week VII of the INT program 2018 “Probing Nucleons and Nuclei in High Energy Collisions” was dedicated to topics at the interface of the electron-ion collider (EIC), heavy ion and proton-nucleus collisions. The EIC will provide complementary tools to investigate and constrain the initial state in HIC collisions, as well as transport properties of QCD matter which can be extracted from observables that are sensitive to final states interactions such as pt-broadening and energy loss. The contributed talks and discussions covered a variety of physics topics from saturation physics and the origin of multi-particle correlations in HIC to jet quenching and the strong coupling regime of high energy scattering.

The Marcel Grossmann triennial meetings are focused on reviewing developments in gravitation and general relativity, aimed at understanding and testing Einstein’s theory of gravitation. The 15^th meeting (Rome, 2018) celebrated the 50^th anniversary of the first neutron star discovery (1967), and the birth of relativistic astrophysics. Another discovery of the same caliber is the detection of the binary neutron star GW170817 in 2017 — almost as if to celebrate the same jubilee — marking the beginning of multi-messenger gravitational wave astronomy. We present work in progress to craft open-sourced numerical tools that will enable the calculation of electromagnetic counterparts to gravita- tional waveforms: the GiRaFFE (General Relativistic Force-Free Electrodynamics) code. GiRaFFE numerically solves the general relativistic magnetohydrodynamics system of equations in the force-free limit, to model the magnetospheres surrounding compact binaries, in order (1) to characterize the nonlinear interaction between the source and its surrounding magnetosphere, and (2) to evaluate the electromagnetic counterparts of gravitational waves, including the production of collimated jets. We apply this code to various configurations of spinning black holes immersed in an external magnetic field, in order both to test our implementation and to explore the effects of (1) strong gravitational field, (2) high spins, and (3) tilt between the magnetic field lines and black hole spin, all on the amplification and collimation of Poynting jets. We will extend our work to collisions of black holes immersed in external magnetic field, which are prime candidates for coincident detection in both gravitational and electromagnetic spectra.

Black hole surroundings and relativistic jets host magnetically dominated regions and fast magnetic reconnection are likely to play an important role concerning astrophysical phenomena associated with such regions. In this contribution, we highlight the works related to turbulence-driven reconnection processes. These processes have been studied by us using analytical as well as numerical methods which showed that fast reconnection processes are powerful ways to giving rise to relativistic particles and associated non-thermal emissions around stellar-mass and supermassive black holes. The power released from the reconnection can even compete with those of extraction from black hole spin.

Gamma-ray bursts (GRBs) are bright extragalactic flashes of gamma-ray radiation and briefly the most energetic explosions in the Universe. Their catastrophic origin —the merger of compact objects or the collapse of massive stars— drives the formation of a newborn compact remnant (black hole or magnetar) that powers two highly relativistic jets. As these jets continue to travel outwards, they collide with the external material surrounding the dying star, producing a long-lasting afterglow that can be seen across the entire electromagnetic spectrum, from the most energetic gamma-ray emission to radio wavelengths. But how can such material be accelerated and focused into narrow beams? The internal shock model proposes that repeated collisions between material blasted out during the explosion can produce the gamma-ray flash. The competing magnetic model credits primordial large-scale ordered magnetic fields that collimate and accelerate the relativistic outflows. To distinguish between these models and ultimately determine the power source for these energetic explosions, our team studies the polarization of the light during the first minutes after the explosion (using novel instruments on fully autonomous telescopes around the globe) to directly probe the magnetic field properties in these extragalactic jets. This technology allowed the detection of highly polarized optical light in GRB 120308A and confirmed the presence of mildly magnetized jets with large-scale primordial magnetic fields in a reduced sample of GRBs (e.g. GRB 090102, GRB 110205A, GRB 101112A, GRB 160625B). Here we discuss the observations of the most energetic and first GRB detected at very high TeV energies, GRB 190114C, which opens a new frontier in GRB magnetic field studies suggesting that some jets can be launched highly magnetized and that the collapse and destruction of these magnetic fields at very early times may have powered the explosion itself. Additionally, our most recent polarimetric observations of the jet of GRB 141220A indicate that, when the jetted ejected material is decelerated by the surrounding environment, the magnetic field amplification mechanisms at the front shock —needed to generate the observed synchrotron emission— produce small magnetic domains. These measurements validate theoretical expectations and contrast with previous observations that suggest large magnetic domains in collisionless shocks (i.e. GRB 091208B).

We present a complete description of all fiber product preserving gauge bundle functors F on the category of affine bundles with m-dimensional bases and affine bundle maps with local diffeomorphisms as base maps.

The inclusive jet cross section measurements at LHC are presented. A discussion on the theoretical and experimental uncertainties focusing especially on the jet energy measurement is given.

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

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.