A first determination of the strong coupling $\alpha_s$ in
next-to-next-to leading order (NNLO) from inclusive jet and dijet
production in deep-inelastic scattering at HERA is presented.
The strong coupling is determined in a fit of jet data collected by the H1
experiment in the range of momentum transfer $5.5 < Q^2< 15000$ GeV${}^2$
and jet transverse momenta $p_T>5$ GeV. The running of the...
According to recent measurements, the mass of jets created in LHC energy pp collisions has broad fluctuation. Typically, the mean mass of a jet with transverse momentum 200-600 GeV/c is around 40-100 GeV/c^2, so the ratio (jet mass)/(jet energy) is of order 0.2. As this value is not negligibly small, as required for factorisation to be applicable, the virtualitis of partons created in the hard...
The pion electromagnetic form factor, $F_\pi$, is a fundamentally important topic for our understanding of the hadron structure and the transition from perturbative to nonperturbative QCD. JLAB’s experiment E12-06-101 proposes to extend the high quality $F_\pi$ data to $Q^2=6.0$ GeV$^2$ as a part of JLAB’s $12$ GeV upgrade. Being motivated by this, we present a lattice QCD calculation of...
The nucleon form factors have been evaluated in light of the improved precision of the experimental measurements and enormous theoretical progress to understand the dynamical behavior of nucleons emerging from the theory of strong interactions between quarks. We have analysed the vector and axial-vector nucleon form factors ($G^{p,n}_{E,M}(Q^2)$ and $G^{p,n}_{A}(Q^2)$) using the spin...
Threshold resummation is often used to improve the theoretical accuracy of inclusive cross sections at hadron colliders. However, when differential distributions are considered, we acquire sensitivity to more energy scales which triggers the appearance of different types of logarithms. In these situations a joint resummation formalism becomes relevant. The general framework for joint threshold...
The production of vector bosons (W, Z, gamma) in association with jets is a stringent test of perturbative QCD and is a background process in searches for new physics. Total and differential cross-section measurements of vector bosons produced in association with jets and heavy flavour quarks in proton-proton collisions performed by the CMS collaboration at the LHC are presented. The...
I will be discussing the production of a single Z or W boson in association with jets at the LHC. I will be presenting results obtained by matching NLO QCD predictions with the Herwig 7 and Pythia 8 parton showers, and by merging all of the underlying matrix elements with up to two light partons at the Born level. These will be compared to several measurements by the ATLAS and CMS collaborations.
A detailed comparison between four- and five- flavour scheme predictions for $b$-associated production for $Z$ and Higgs bosons is presented. Results obtained for $Z$ production at 7 TeV are then compared to LHC data. The comparison is then used
to validate results for $b$-associated Higgs boson production at the 13 TeV Run II.
The production of jets in association with vector bosons is an important process to study QCD in a multi-scale environment. The ATLAS collaboration has performed measurements of vector boson+jets cross sections, differential in several kinematic variables, in proton-proton collision data taken at center-of-mass energies of 8TeV and 13TeV. The measurements are compared to state-of-the art...
Latest tests of double parton scattering, underlying event tunes, minimum bias, and diffraction made by comparing CMS Run I and Run II data to the state-of-the-art theoretical predictions interfaced with up-to-date parton shower codes are presented. Studies to derive and to test the new CMS event tune obtained through jet kinematics in top quark pair events and global event variables are described.
We present angular correlations in multi-jet events at highest center-of-mass energies and compare the measurements to theoretical predictions including higher order parton radiation and coherence effects.
ATLAS measurements of angular correlations between particle pairs at large pseudorapidity separation in pp and pPb collisions are presented. The data were collected using a combination of the minimum-bias and high track-multiplicity triggers. A detailed study of the dependence of two-particle correlations on the charged particle multiplicity, transverse momentum of the pair constituents and...
The transverse momentum spectra, $d^2\sigma/(d\eta dp_T^2)$, of charged hadrons produced in various high energy interactions (pp, $\gamma$p, $\gamma \gamma$, heavy-ion collisions) and measured in different experiments from ISR to LHC are considered simultaneously within several phenomenological models. As a result, the recently introduced "two component model" is shown to provide a much better...
Photons and weak bosons do not interact strongly with the dense and hot medium formed in the nuclear collisions, thus should be sensitive to the nuclear modification of parton distribution functions (nPDFs). The in-medium modification of heavy quarkonium states plays an important role in studying the hot and dense medium formed in the larger collision systems. The ATLAS detector, optimized for...
The production of prompt photons in association with jets in proton–proton collisions provides a testing ground for perturbative QCD (pQCD) with a hard colourless probe less affected by hadronisation effects than jet production. The measurements of the angular correlations between the photon and the jets can be used to probe the dynamics of the hard-scattering process. We present here a...
Isolated photons with high transverse energy have been studied in $ep$ scattering with the ZEUS detector at HERA, using and integrated luminosity of 326 pb$^{-1}$. The kinematic region includes photon virtualities $10 < Q^2 < 350$ GeV$^2$. Photons with transverse energy $4< E_T^\gamma< 15$ GeV and pseudorapidity $-0.7 <\eta^\gamma< 0.9$ were measured with accompanying jets having transverse...
The OLYMPUS collaboration has recently published a precise
measurement of the positron-proton to electron-proton elastic
scattering cross section ratio, $R_{2\gamma}$, over a wide range of
the virtual photon polarization, $0.456<\epsilon<0.978$. This
provides a direct measure of hard two-photon exchange in elastic
lepton-proton scattering widely thought to explain the discrepancy
...
I am going to present results of application of recently formulated Transversal Momentum Dependent Factorisation (ITMD) to provide predictions for spectra of produced at LHC di-jets in p-Pb collisions. Furthermore I am going to compare the results to results obtained within High Energy Factorization (HEF). The results show that while the ITMD predicts significant enhancement of the cross...
Jet quenching has been considered an important probe of the properties of the quark-gluon plasma (QGP) formed in the heavy ion collisions at RHIC and LHC. However, since d+Au collisions also show significant suppression of jet production, a thorough understanding cannot be achieved without the determination of other non-QGP nuclear medium effects. One of the competing factors involved, parton...
K+->pi+nunu is one of the theoretically cleanest meson decay where to look for indirect effects of new physics complementary to LHC searches. The NA62 experiment at CERN SPS is designed to measure the branching ratio of this decay with 10% precision. NA62 took data in pilot runs in 2014 and 2015 reaching the final designed beam intensity. The quality of data acquired in view of the final...
We report the status of R measurement in 2-4.6 GeV at BESIII, and some new results from QCD studies, including: proton form factor with ISR, pi+pi- cross section and pion form factor with ISR, new measurement of J/psi parameters, e+ e- -> K+ K- cross sections in 2-3.08 GeV.
The NA48/2 experiment at CERN collected a very large sample of charged kaon decays into multiple final states. From this data sample we have reconstructed about 1500 events of the very rare decay K+- —>mu+- nu e+ e- over almost negligible background in the region with m(e+e-) above 140 MeV, which is of great interest in Chiral Perturbation Theory. We present the m_ee spectrum and a...
Hadron spectroscopy is one of the most important physics goals of BESIII. Since 2009, BESIII has collected 1.3 10^8 J/psi and 0.410^8 of psi', which are the world's largest data samples of J/psi and psi' from e+e- collision. These data are being used to make a variety of interesting and unique studies of QCD exotics (e.g. gluonic excitations and multiquarks) and light meson decay dynamics....
The NA48/2 experiment presents a final result of the charged kaon semileptonic decays form
factors measurement based on 4.28 million $K^\pm_{e3}$ and 2.91 million $K^\pm_{\mu 3}$ selected
decays collected in 2004. The result is competetive with other measurements in $K^\pm_{\mu 3}$
mode and has a smallest uncertainty for $K^\pm_{e3}$, that leads to the most precise
combined $K^\pm_{l3}$...
At short distance between partons, double parton scattering overlaps with loop contributions to standard single hard scattering. Responsible for this is the splitting of one parton into two, and different choices for the partitioning of these contributions between single and double scattering give rise to different cross section formulae and to different evolution equations for the double...
Double parton scattering (DPS) describes two colliding hadrons having interactions in the form of two hard processes, each initated by a separate set of partons. Just as for single parton scattering, the resummation of soft gluons gives rise to a soft function, which is a necessary ingredient for obtaining rapidity evolution equations. For various regions of phase space, I derive the rapidity...
The BABAR Collaboration has an intensive program studying hadronic cross sections in low-energy e+e- annihilations, accessible via initial-state radiation.
Our measurements allow significant improvements in the precision of the
predicted value of the muon anomalous magnetic moment.
These improvements are necessary for shedding light on the current ~3 sigma
difference between the predicted...
We present the effective weak angle measurements from the CDF and D0¬ experiments at Fermilab. We combine the most precise published results based on the forward-backward asymmetry of $p\bar{p}\rightarrow Z/\gamma^{*} \rightarrow e^+ e^-/\mu^+\mu^- + X$ events in the full Run II data set corresponding to up to $10 fb^{-1}$ of luminosity. We use the extracted values of...
A precise measurement of the mass of the W boson mass represents an important milestone to test the overall consistency of the Standard Model. Since the discovery of a Higgs Boson, the the W boson mass is predicted to 7 MeV precision, while the world average of all measurements is 15 MeV, making the improved measurement an important goal.
The ATLAS experiment at the LHC represents an ideal...
We attempt to estimate the top-quark mass extraction uncertainty due to Monte Carlo modeling of top-pair production and its leptonic decay. Using three different NLO+PS generators based on the POWHEG method implementing an increasingly precise treatment of $t\bar{t}$ production and decay, including hvq and bb4l, and two different PS implementations we obtain predictions for various kinematic...
We review the recent developments of the Loop-Tree Duality method, focussing our discussion on the first numerical implementation and its use in the direct numerical computation of multi-leg Feynman integrals. Non-trivial examples are presented.
The investigation of pair production processes of the electroweak gauge bosons is of great importance at the Large Hadron Collider. They represent an irreducible background to precision studies of the Higgs boson and are important signal processes for new physics searches. In this talk, the next-to-leading order electroweak corrections to the off-shell production of WW, WZ and ZZ pairs...
We present the latest results from CMS measurements in final states with two or more vector bosons (V = W, Z or gamma).
Measurements of the cross sections of the production of pairs of electroweak gauge bosons at the LHC constitute stringent tests of the electroweak sector of the Standard Model and provide a model-independent means to search for new physics at the TeV scale.
The ATLAS collaboration has performed detailed measurements of integrated and differential cross sections of the production of heavy...
Vector-boson scattering is a key process to investigate the mechanism of electroweak symmetry breaking at the LHC.
For the first time full NLO electroweak corrections to off-shell vector-boson scattering are presented.
The computation features the complete matrix elements, including all non-resonant and off-shell contributions, to the electroweak process pp → μ + ν μ e + ν e jj.
It is fully...
Measurements of the cross sections of the production of three electroweak gauge bosons and of vector-boson scattering processes at the LHC constitute stringent tests of the electroweak sector of the Standard Model and provide a model-independent means to search for new physics at the TeV scale. The ATLAS collaboration searched for the production of three W bosons or of a W boson and a photon...
The most recent results on the production of single W and Z bosons with two jets at high invariant mass at centre-of-mass energies of 7, 8 and 13 TeV are presented. Integrated and differential cross sections are measured in many different phase space regions with varying degree of sensitivity to the electroweak production in vector boson fusion. The cross section for the electroweak W boson...
We propose a new mechanism for prompt simultaneous production of $J/\psi$ and $\Upsilon$ mesons in high energy hadronic collisions. The process is considered as a perturbative production of $B_c^{(*)}$ mesons $g{+}g\to B_c^{(*)}{+}\bar{B_c}^{(*)}$ followed by a long-distance final state interaction that rearranges the quarks to form $J/\psi$ and $\Upsilon$ mesons. Passing from $B_c^{(*)} +...
We present results on measurements of characteristics of events with jets, from jet-charge over investigations of shapes to jet mass distributions. The measurements are compared to theoretical prediction including those matched to parton shower and hadronization.
Besides a rich polarized-target program, the HERMES experiment at HERA took a wealth of deep-inelastic scattering (DIS) data on light and heavy nuclear gas targets. Together with an excellent hadron identification, this allowed the study of medium-induced flavor conversion in semi-inclusive DIS. A
predicted high sensitivity of the nuclear modification factor for $K^-$ in semi-inclusive DIS in...
We present a model for vacuum and in-medium hadronization of the leading quark, based on Berger model. In this model, after a length $L_p$, the outgoing quark
hadronized into a pre-hadron (dipole). This dipole can be absorbed by the medium,
leading to nuclear suppression. Our results are compared with EG2 and HERMES
data for the multiplicity ratio and $p_t$-broadening. Induced energy loss has...