HELAC-Onia: An automatic matrix element generator for heavy quarkonium physics

Section: Jhep08(2017)120supporting

confidence: 75%

Feasibility of measuring the magnetic dipole moments of the charm baryons at the LHC using bent crystals

Fomin

Korchin

Stocchi

et al. 2017

“…The position along the p T axis of each of the data points shown in these figures is adjusted to reflect the average value of the transverse momentum, p J/ψ T or p χ c T , for the χ c candidates within that p T bin, after all acceptance and efficiency corrections have been applied. The measurements are compared with the predictions of next-to-leading-order (NLO) non-relativistic QCD (NRQCD) [19,34,35], the k T factorisation approach [36,37] and leading-order (LO) colour-singlet model (CSM) [38] calculations. The NRQCD factorisation approach separates the perturbative production of a heavy quark pair (in a colour-singlet or -octet state) from the non-perturbative evolution of a heavy quark pair into a quarkonium state [1].…”

Section: Differential Cross-sectionsmentioning

confidence: 99%

Measurement of χ c1 and χ c2 production with s $$ \sqrt{s} $$ = 7 TeV pp collisions at ATLAS

Agustoni¹,

Beck²,

Albert³

et al. 2014

Abstract:The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at √ s = 7 TeV with the ATLAS detector at the LHC using 4.5 fb −1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c → J/ψγ (with J/ψ → µ + µ − ) where photons are reconstructed from γ → e + e − conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured. The ATLAS collaboration 36 Keywords: Hadron-Hadron Scattering IntroductionThe study of heavy quarkonium production in hadronic collisions offers a unique insight into the dynamics of the strong interaction. Understanding the hadronic production of quarkonium states within quantum chromodynamics (QCD) has been a long-standing challenge, complicated by the presence of several important energy scales [1]. While the production -1 - JHEP07(2014)154of a heavy quark pair is generally a high-energy process that can be well described perturbatively, the energy scale associated with the evolution of a heavy quark pair into a physical bound state introduces large uncertainties to theoretical predictions. Understanding the hadronic production of the charmonium states is particularly challenging as the mass of the charm quark is such that the modelling of the bound state as a simple non-relativistic system is less well motivated than for the heavier bottomonium system. Several theoretical approaches have been developed to describe hadronic charmonium production, though the wealth of production and polarisation measurements that now exist are not comprehensively described by any single theoretical approach [2]. However, progress is being made in the calculation of colour-singlet (CS) and colour-octet (CO) production processes at higher perturbative orders and recent calculations provide a good description of the world data on prompt J/ψ production cross-sections [3].The χ cJ (1P ) states (with J = 0, 1, 2) are the only triplet of P -wave states below the open-charm threshold. The spectroscopy of these states is characterised by small hyperfine mass splittings and the branching fractions for the decays χ cJ → J/ψ γ are large for the J = 1, 2 states (34.4% and 19.5%, respectively), while the corresponding branching fraction for the J = 0 state is significantly lower (1.3%) [4]. The χ cJ states may be produced directly in hadronic collisions or through the decay of higher-mass quarkonium states; these production modes are referred to as prompt. In addition to prompt production, the decay chains of b-hadrons can also produce χ cJ states; these production modes are referred to as non-prompt.The large cross-section for inclusive charmonium production and extensive data ...

“…The NRQCD predictions presented here are derived using HELAC-ONIA [48][49][50][51], an automatic matrix-element generator for the calculation of the heavy quarkonium helicity amplitudes in the framework of NRQCD factorisation. Uncertainties in the predictions come from the uncertainties due to the choice of scale, charm quark mass and long-distance matrix elements (LDME) as discussed in ref.…”

Section: Jhep09(2014)079mentioning

confidence: 99%

Measurement of the production cross-section of ψ(2S) → J/ψ(→μ + μ − )π + π − in pp collisions at s $$ \sqrt{s} $$ = 7 TeV at ATLAS

Aad¹,

Abbott²,

Abdallah³

et al. 2014

Measurement of the production cross-section of ψ(2S) → J/ψ(→ µ + µ − )π + π − in pp collisions at √ s = 7 TeV at ATLASThe ATLAS collaboration E-mail: atlas.publications@cern.ch Abstract:The prompt and non-prompt production cross-sections for ψ(2S) mesons are measured using 2.1 fb −1 of pp collision data at a centre-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. The measurement exploits the ψ(2S) → J/ψ(→ µ + µ − )π + π − decay mode, and probes ψ(2S) mesons with transverse momenta in the range 10 ≤ p T < 100 GeV and rapidity |y| < 2.0. The results are compared to other measurements of ψ(2S) production at the LHC and to various theoretical models for prompt and non-prompt quarkonium production. Keywords: Hadron-Hadron ScatteringArXiv ePrint: 1407.5532Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP 3 .doi:10.1007/JHEP09(2014)079 JHEP09(2014)079 A Acceptance correction factors 28The ATLAS collaboration 33 IntroductionThe production of quarkonium states in hadronic collisions has been the subject of intense theoretical and experimental study for many decades, especially since measurements of prompt J/ψ and Υ production at the Tevatron [1-7] exposed order-of-magnitude differences between data and theoretical expectations [8]. Despite these being among the most studied heavy-quark bound states, there is still no satisfactory understanding of the mechanisms of their formation. Quarkonium production acts as a unique and important testing ground for quantum chromodynamics (QCD) in its own right. While the production of a heavy quark pair occurs at a hard scale and is generally well-described by QCD, its subsequent evolution into a bound state includes many non-perturbative effects at much softer scales that pose a challenge to current theoretical methods. With the data obtained from the Large Hadron Collider (LHC), it is possible to perform stringent tests of theoretical models across a large range of momentum transfer. Studies of heavy quarkonia were conducted previously by ATLAS in the J/ψ → µ + µ − [9] and Υ(nS) → µ + µ − [10, 11] decay modes. The measurements described here are based on an analysis of 2.1 fb −1 of pp collision data at √ s = 7 TeV, and study the prompt and non-prompt production of the ψ(2S) meson through its decay to J/ψ(→µ + µ − )π + π − . The prompt production arises from direct QCD production mechanisms and the nonprompt production arises from weak decays of b-hadrons. The J/ψ(→µstate offers improvements in ψ(2S) mass resolution and background discrimination over exclusive dilepton channels. Unlike prompt J/ψ production, which can occur through either direct QCD production of J/ψ or the production of excited states that subsequently decay into J/ψ + X final states, no appreciable prompt production of excited states decaying into ψ(2S) has been established in hadron collisions. In this respect the ψ(2S) is a unique state with no significant feed-down from higher quarkonium resonances, which decay predominantly to DD pairs.The measu...