Test Of QCD Research Articles

Study of the strong coupling constants, α<sub>s</sub> (q<sup>2</sup> ) of π- and K<sup>0</sup> mesons from π<sup>-</sup>+p and π<sup>-</sup>+C interactions at 40 GeV/c

This paper is devoted to the production of π-and K0 mesons from π-+p→π-+X and π-+C→π-,K0+X interactions at 40 GeV/c as a function of the square of four momentum transfer. The cut parameter of the strong coupling constant is taken as Λac2=ma2+mc2. Values of the strong coupling constant are then compared to leading-order and next-to-leading-order perturbative QCD calculations for the first time. Agreement between the experimental data and theory is good, thus providing a precision test of QCD at large momentum transfers (q). The strong coupling constant αs is extracted as a function of q, showing a good agreement with the renormalisation group equation and with previous analyses. As the momentum transfers increases, the running coupling constant decreases. For each high-energy interaction, a quantity called the cut parameter is chosen differently depending on the secondary particles produced by the reaction. For each high-energy interaction, a quantity called the cut parameter is chosen differently depending on the secondary particles produced by the reaction.

Precision measurements of jet and photon production at the ATLAS experiment

The production of jets and prompt isolated photons at hadron colliders provides stringent tests of perturbative QCD. We present the latest measurements of photon+jets and diphoton production using proton-proton collision data collected by the ATLAS experiment at the LHC. The measurements are compared to state-of-the-art NLO and NNLO predictions.

Double-gluon charmonium hybrid states with various exotic quantum numbers

We study the double-gluon charmonium hybrid states with various quantum numbers, each of which is composed of one valence charm quark and one valence charm antiquark as well as two valence gluons. We concentrate on the exotic quantum numbers JPC=0−−/0+−/1−+/2+−/3−+ that the conventional q¯q mesons cannot reach. We apply the QCD sum rule method to calculate their masses to be 7.28−0.43+0.38, 5.19−0.46+0.36, 5.46−0.62+0.41, 4.48−0.31+0.25, and 5.54−0.43+0.35 GeV, respectively. We study their possible decay patterns and propose to search for the JPC=2+−/3−+ states in the D*D¯(*)/Ds*D¯s(*)/Σc*Σ¯c(*)/Ξc*Ξ¯c(′,*) channels. Experimental investigations on these states and decay channels can be useful in classifying the nature of the hybrid state, thus serving as a direct test of QCD in the low energy sector. Published by the American Physical Society 2024

Determination of the strong coupling constant from transverse energy-energy correlations in multijet events at sqrt{s} = 13 TeV with the ATLAS detector

Measurements of transverse energy-energy correlations and their associated azimuthal asymmetries in multijet events are presented. The analysis is performed using a data sample corresponding to 139 fb−1 of proton-proton collisions at a centre-of-mass energy of sqrt{s} = 13 TeV, collected with the ATLAS detector at the Large Hadron Collider. The measurements are presented in bins of the scalar sum of the transverse momenta of the two leading jets and unfolded to particle level. They are then compared to next-to-next-to-leading-order perturbative QCD calculations for the first time, which feature a significant reduction in the theoretical uncertainties estimated using variations of the renormalisation and factorisation scales. The agreement between data and theory is good, thus providing a precision test of QCD at large momentum transfers Q. The strong coupling constant αs is extracted as a function of Q, showing a good agreement with the renormalisation group equation and with previous analyses. A simultaneous fit to all transverse energy-energy correlation distributions across different kinematic regions yields a value of {alpha}_{textrm{s}}left({m}_Zright)=0.1175pm 0.0006{left(exp .right)}_{-0.0017}^{+0.0034}left(textrm{theo}.right) , while the global fit to the asymmetry distributions yields {alpha}_{textrm{s}}left({m}_Zright)=0.1185pm 0.0009{left(exp .right)}_{-0.0012}^{+0.0025}left(textrm{theo}.right) .

The heavy tetra-quark states after the discovery of tetra-charm states.

This paper is devoted to the study of exclusive charm and bottom bound states which are suitable, at least partially, for a non-relativistic description. Starting from a simple choice of quarkonia and tetra-quark wave functions we study their production cross sections, total widths and more interesting decay properties. In particular, we compute the production cross sections of the ground state scalar quarkonia getting results compatible with the values appearing in the literature. We also compute the production cross sections of the lower energy states of the charm and bottom tetra-quarks, their decay widths and the decay rates in two mu bar{mu } pairs and in the q{bar{q}}mu bar{mu } channel. Our results on the tetra-charm are consistent with the data published by the LHCb Collaboration and those on the tetra-bottom show a reasonable agreement with the indications published by the CMS Collaboration. Our cross section analyses are based on interpolations based on the gluon–gluon luminosity grids published by the NNPDF and CTEQ Collaborations. The hard amplitude calculations are based on QCD in the tree approximation. We think that a careful improvement of our method and a refinement of the experimental data after the foreseen luminosity increase at the LHC will make possible valuable tests of QCD at the intermediate energies.

Initial performance of the GlueX DIRC detector

The GlueX experiment at Jefferson Laboratory aims to perform quantitative tests of non-perturbative QCD by studying the spectrum of light-quark mesons and baryons. A Detector of Internally Reflected Cherenkov light (DIRC) was installed to enhance the particle identification (PID) capability of the GlueX experiment by providing clean π/K separation up to 3.7 GeV/c momentum in the forward region (θ < 11°), which will allow the study of hybrid mesons decaying into kaon final states with significantly higher efficiency and purity. The new PID system is constructed with radiators from the decommissioned BaBar DIRC counter, combined with new compact photon cameras based on the SuperB FDIRC concept. The full system was successfully installed and commissioned with beam during 2019/2020. The initial PID performance of the system was evaluated and compared to one from Geant4 simulation.

Measurements of W and Z boson production in ATLAS

Precision measurements of the production cross-sections of W and Z boson at LHC provide important tests of perturbative QCD and information about the parton distribution functions for quarks within the proton. We present measurements of cross sections for inclusive W^+W+, W^{-}W− and Z boson production using data collected by the ATLAS experiment at a center-of-mass energy of \sqrt{s}s=2.76 TeV. Measurement of the transverse momentum distribution of Z boson at \sqrt{s}s=13 TeV is also presented. The measurements are corrected for detector effects and compared with state-of-the-art theoretical calculations.

Prospects of CKM elements |V_{cs}| and decay constant f_{D_{s}^+} in D_s^+rightarrow mu ^+nu _mu decay at STCF

We report a feasibility study of pure leptonic decay D_s^+rightarrow mu ^+nu _mu by using a fast simulation software package at STCF. With an expected luminosity of 1~mathrm {ab}^{-1} collected at STCF at a center-of-mass energy of 4.009 GeV, the statistical sensitivity of the branching fraction is determined to be 0.3%. Combining this result with the c rightarrow s quark mixing matrix element |V_{cs}| determined from the current global Standard Model fit, the statistical sensitivity of D_s^+ decay constant, f_{D_s^+}, is estimated to be 0.2%. Alternatively, combining the current results of f_{D_s^+} calculated by lattice QCD, the statistical sensitivity of |V_{cs}| is determined to be 0.2%, which helps probe possible new physics beyond Standard Model. The unprecedented precision to be achieved at STCF will provide a precise calibration of QCD and rigorous test of Standard Model.

New hadron configuration: The double-gluon hybrid state

This is the first study on the double-gluon hybrid, which consists of one valence quark and one valence antiquark together with two valence gluons. We concentrate on the one with the exotic quantum number $J^{PC} = 2^{+-}$ that conventional $\bar q q$ mesons can not reach. We apply QCD sum rule method to evaluate its mass to be $2.26^{+0.20}_{-0.25}$ GeV, and study its possible decay patterns. Especially, its three-meson decay patterns are generally not suppressed severely compared to two-meson decay patterns, so the $S$-wave three-meson decay channels $f_1\omega\pi/f_1\rho\pi$ can be useful in identifying its nature, which is of particular importance to the direct test of QCD in the low energy sector.

Bottomonium precision tests from full lattice QCD: Hyperfine splitting, ϒ leptonic width, and b quark contribution to e+e−→hadrons

We calculate the mass difference between the $\mathrm{\ensuremath{\Upsilon}}$ and ${\ensuremath{\eta}}_{b}$ and the $\mathrm{\ensuremath{\Upsilon}}$ leptonic width from lattice QCD using the highly improved staggered quark formalism for the $b$ quark and including $u$, $d$, $s$ and $c$ quarks in the sea. We have results for lattices with lattice spacing as low as 0.03 fm and multiple heavy quark masses, enabling us to map out the heavy quark mass dependence and determine values at the $b$ quark mass. Our results are ${M}_{\mathrm{\ensuremath{\Upsilon}}}\ensuremath{-}{M}_{{\ensuremath{\eta}}_{b}}=57.5(2.3)(1.0)\text{ }\text{ }\mathrm{MeV}$ (where the second uncertainty comes from neglect of quark-line disconnected correlation functions) and decay constants, ${f}_{{\ensuremath{\eta}}_{b}}=724(12)\text{ }\text{ }\mathrm{MeV}$ and ${f}_{\mathrm{\ensuremath{\Upsilon}}}=677.2(9.7)\text{ }\text{ }\mathrm{MeV}$, giving $\mathrm{\ensuremath{\Gamma}}(\mathrm{\ensuremath{\Upsilon}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}})=1.292(37)(3)\text{ }\text{ }\mathrm{keV}$. The hyperfine splitting and leptonic width are both in good agreement with experiment, and provide the most accurate lattice QCD results to date for these quantities by some margin. At the same time results for the time moments of the vector-vector correlation function can be compared to values for the $b$ quark contribution to $\ensuremath{\sigma}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\text{hadrons})$ determined from experiment. Moments 4--10 provide a 2% test of QCD and yield a $b$ quark contribution to the anomalous magnetic moment of the muon of $0.300(15)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$. Our results, covering a range of heavy quark masses, may also be useful to constrain QCD-like composite theories for beyond the Standard Model physics.

Simulation of neutron-tagged deep inelastic scattering at EicC * *Supported by the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34030301)

Measuring the pionic structure function is of high interest, as it provides a new area for understanding the strong interaction among quarks and testing QCD predictions. To this end, we investigate the feasibility and expected impact of a possible experiment at EicC (Electron-ion collider in China). We show the simulation results on the statistical precision of an EicC measurement, based on the model of leading neutron tagged DIS process and the parton distribution functions of the pion from JAM18 global analysis. The simulation shows that at EicC, the kinematics cover the range from 0.01 to 1, and the range from 1 to 50 GeV , within the acceptable statistical uncertainty. Assuming an integrated luminosity of 50 fb , in the low- region ( GeV ), the Monte Carlo data show that the suggested measurement in the whole range reaches very high precision ( %). To perform such an experiment, only the addition of a far-forward neutron calorimeter is needed.

An experimental review of open heavy flavor and quarkonium production at RHIC

Open heavy flavor and quarkonium are unique probes of the hot-dense medium produced in heavy-ion collisions. Their production in p+p collisions also provide important test of QCD. In this paper, we review the selected results on open heavy flavor and quarkonium in p+p and heavy-ion collisions achieved at RHIC. Physics implications are also discussed.

Global baryon number conservation encoded in net-proton fluctuations measured in Pb–Pb collisions at [formula omitted] TeV

Experimental results are presented on event-by-event net-proton fluctuation measurements in Pb–Pb collisions at sNN=2.76 TeV, recorded by the ALICE detector at the CERN LHC. These measurements have as their ultimate goal an experimental test of Lattice QCD (LQCD) predictions on second and higher order cumulants of net-baryon distributions to search for critical behavior near the QCD phase boundary. Before confronting them with LQCD predictions, account has to be taken of correlations stemming from baryon number conservation as well as fluctuations of participating nucleons. Both effects influence the experimental measurements and are usually not considered in theoretical calculations. For the first time, it is shown that event-by-event baryon number conservation leads to subtle long-range correlations arising from very early interactions in the collisions.

Measurement of photon production at ATLAS

The production of isolated prompt photons at hadron colliders provides stringent tests of perturbative QCD and can be used to evaluate probability distribution functions of partons in the proton. At the LHC, the ATLAS Collaboration has performed precise measurements of the inclusive production of isolated-prompt photons in proton-proton collisions at a centre-of-mass energy of 13 TeV. The ratio of the cross sections for inclusive isolated-photon production at centre-of-mass energies of 13 and 8 TeV has been measured as a function of the photon transverse energy in different regions of the photon pseudorapidity. The measurements are compared with state-of-the art theory predictions at next-to-leading as well as next-to-next-to-leading order in perturbative QCD in the case of the measurement of inclusive production of isolated-prompt photons.

Recent Tests of QCD with the ATLAS Detector

Recent Tests of QCD with the ATLAS Detector

Quarkonium Production Measurements with the ALICE Detector at the LHC

In (ultra-)relativistic heavy-ion collisions, the strongly interactingmatter is predicted to undergo a phase transition into a plasma of deconfinedquarks and gluons (QGP) and quarkonia probe different aspects of this medium.However, the medium modification of quarkonium production includes also the contribution of cold nuclear matter effects (CNM), such as shadowing or nuclear break-up in addition to QGP effects. Proton--nucleus collisions, where no QGP is expected, are used to measure cold nuclear matter effects on quarkonium production. Vacuum production of quarkonia is modelled in proton--proton (pp) collisions, which are used as reference for both heavy-ion and proton--nucleus collisions. Besides serving as reference, results in pp collisions represent a benchmark test of QCD based models in both perturbative and non-perturbative regimes. The ALICE detector has unique capabilities at the LHC for measuring quarkonia down to zero transverse momentum. Measurements are carried out at both central and forward rapidity, in the dielectron and dimuon decay channel, respectively. In this contribution the latest quarkonium measurements for various energies and colliding systems, performed by the ALICE Collaboration during the LHC Run-2 period, will be discussed.

Quarkonium tomography of heavy ion collisions at the LHC

Quarkonium production in high-energy hadronic collisions provides a fundamental test of QCD. Its modification in a nuclear medium is a sensitive probe of the space-time temperature profile and transport properties of the QGP, yielding constraints complementary to the ones obtained from the quenching of light hadrons and jets, and open heavy flavor. In these proceedings, we report new results for the suppression of high transverse momentum charmonium [J/ψ, ψ(2S)] and bottomonium [ϒ(1S), ϒ(2S), ϒ(3S)] states in Pb+Pb collisions at the Large Hadron Collider. Our theoretical formalism combines the collisional dissociation of quarkonia, as they propagate in the quark-gluon plasma, with the thermal wavefunction effects due to the screening of the QQ‾ attractive potential in the medium. We find that a good description of the relative suppression of the ground and higher excited quarkonium states, transverse momentum and centrality distributions is achieved, when comparison to measurements at a center-of-mass energy of 2.76 TeV is performed. Theoretical predictions for the highest Pb+Pb center-of-mass energy of 5.02 TeV at the LHC, where new experimental results are being finalized are presented. Preliminary calculations for smaller systems, such as Xe+Xe are also shown. Last but not least, the potential of jet substructure to shed light in the mechanisms of heavy flavor production is discussed.

Direct photon production in pp, p-Pb and Pb-Pb collisions: results from ALICE

Direct photon measurements provide a tool for testing QCD predictions in pp collisions and valuable information about properties of the quarkgluon matter created in nucleus-nucleus collisions. Comparing direct photon production in pp, p-Pb and Pb-Pb collisions, one can check the scaling with the number of binary collisions expected at high transverse momentum and get insight into the hot and cold hadronic matter properties with soft photons. The elliptic flow of direct photons is another unique possibility to trace the collective flow formation and space-time evolution of the fireball. We present the latest measurements of direct photon production in pp, p-Pb and Pb-Pb collisions and of the elliptic flow in Pb-Pb collisions at the LHC energies. Comparison to recent theory predictions will be also discussed.

Hadron Form Factors at BESIII

Form factors of hadron provide fundamental information about its structure and dynamics. They constitute a rigorous test of non-perturbative QCD as well as of phenomenological models. Based on data samples collected with BESIII detector at BEPCII collider, born cross section of [Formula: see text] and proton effective form factors are measured at 12 center-of-mass energies between 2.2324 and 3.671 GeV. The ratio [Formula: see text]s are extracted by fitting polar angle distribution of proton for data samples with large statistics. For data between 3.773 and 4.6 GeV, we use initial state radiation (ISR) method to study [Formula: see text] by tagged or un-tagged ISR photon, where the pair cross section, effective form factors and [Formula: see text]s are obtained from proton pair threshold to about 3 GeV. For [Formula: see text] and [Formula: see text], the pair cross section and [Formula: see text] form factors are measured near threshold. With data scanned in 2015 from 2-3.08 GeV, charged Kaon pair cross section and form factors are measured at 21 center-of-mass energies.

Measurement of photon production cross sections also in association with jets with the ATLAS detector

The production of prompt isolated photons at hadron colliders provides a stringent test of perturbative QCD and can be used to probe the proton structure. The production of prompt photons in association with jets provides an additional testing ground for perturbative QCD with a hard colourless probe less affected by hadronisation effects than jet production. At the LHC, the ATLAS collaboration has performed precise measurements of the inclusive production of isolated prompt photons at a centre-of-mass energy of 13 TeV. The dynamics of isolated-photon plus jet production in pp collisions at a centre-of-mass energy of 8 TeV have also been measured. In addition, the integrated and differential cross sections for isolated photon pairs at a centre-of-mass energy of 8 TeV have been measured. The results are compared with state-of-the art theory predictions at next-to-leading order in perturbative QCD.