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DOE OSTI2011

Coupling vector and pseudoscalar mesons to study baryon resonances

A study of meson-baryon systems with total strangeness -1 is made within a framework based on the chiral and hidden local symmetries. These systems consist of octet baryons, pseudoscalar and vector mesons. The pseudoscalar meson-baryon (PB) dynamics has been earlier found determinant for the existence of some strangeness -1 resonances, for example, {Lambda}(1405), {Lambda}(1670), etc. The motivation of the present work is to study the effect of coupling the closed vector meson-baryon (VB) channels to these resonances. To do this, we obtain the PB{yields}PB and VB{yields}VB amplitudes from the t-channel diagrams and the PB{r_reversible}VB amplitudes are calculated using the Kroll-Ruddermann term where, considering the vector meson dominance phenomena, the photon is replaced by a vector meson. The calculations done within this formalism reveal a very strong coupling of the VB channels to the {Lambda}(1405) and {Lambda}(1670). In the isospin 1 case, we find evidence for a double pole structure of the {Sigma}(1480) which, like the isospin 0 resonances, is also found to couple strongly to the VB channels. The strong coupling of these low-lying resonances to the VB channels can have important implications on certain reactions producing them.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Transverse-momentum and event-shape dependence of D-meson flow harmonics in Pb–Pb collisions at s NN = 5.02 TeV

The elliptic and triangular flow coefficients v 2 and v 3 of prompt D 0 , D + , and D * + mesons were measured at midrapidity ( | y | < 0.8 ) in Pb–Pb collisions at the centre-of-mass energy per nucleon pair of s NN = 5.02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decays in the transverse momentum interval 1 < p T < 36 GeV / c in central (0–10%) and semi-central (30–50%) collisions. Compared to pions, protons, and J / ψ mesons, the average D-meson v n harmonics are compatible within uncertainties with a mass hierarchy for p T ≲ 3 GeV / c , and are similar to those of charged pions for higher p T . The coupling of the charm quark to the light quarks in the underlying medium is further investigated with the application of the event-shape engineering (ESE) technique to the D-meson v 2 and p T -differential yields. The D-meson v 2 is correlated with average bulk elliptic flow in both central and semi-central collisions. Within the current precision, the ratios of per-event D-meson yields in the ESE-selected and unbiased samples are found to be compatible with unity. All the measurements are found to be reasonably well described by theoretical calculations including the effects of charm-quark transport and the recombination of charm quarks with light quarks in a hydrodynamically expanding medium.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Measurements of azimuthal anisotropy of nonprompt D 0 mesons in PbPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV

Measurements of the elliptic ($v$ 2 ) and triangular ($v$ 3 ) azimuthal anisotropy coefficients are presented for D 0 mesons produced in b hadron decays (nonprompt D 0 mesons) in lead-lead collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. The results are compared with previously published charm meson anisotropies measured using prompt D 0 mesons. The data were collected with the CMS detector in 2018 with an integrated luminosity of 0.58 nb –1 . Azimuthal anisotropy is sensitive to the interactions of quarks with the hot and dense medium created in heavy ion collisions. Comparing results for prompt and nonprompt D 0 mesons can assist in understanding the mass dependence of these interactions. The nonprompt results show lower magnitudes of $v$ 2 and $v$ 3 and weaker dependences on the meson transverse momentum and collision centrality than those found for prompt D 0 mesons. The results are in agreement with theoretical predictions that include a mass dependence in the interactions of quarks with the medium

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2013

Meson Spectroscopy at JLab@12 GeV

Meson, being the simplest hadronic bound system, is the ideal "laboratory" to study the interaction between quarks, to understand the role of the gluons inside hadrons and to investigate the origin of color confinement. To perform such studies it is important to measure the meson spectrum, with precise determination of resonance masses and properties, looking for rare qbar q states and for unconventional mesons with exotic quantum numbers (i.e. mesons with quantum numbers that are not compatible with a qbar q structure). With the imminent advent of the 12 GeV upgrade of Jefferson Lab a new generation of meson spectroscopy experiments will start: "Meson-Ex" in Hall B and "GLUEX" in Hall D. Both will use photo-production to explore the spectrum of mesons in the light-quark sector, in the energy range of few GeVs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

The hybrid mesons quest: the MesonEx experiment at Jefferson Laboratory

The meson spectroscopy plays nowadays a central role in the investigation of hadron structure thanks to the possible existence of exotic hybrid mesons, quark-antiquark-gluon bound states. Their explicit gluonic degrees of freedom which should clearly emerge from a Partial Wave Analysis (PWA) of the corresponding Dalitz plot of the exotic particle decay, may result in final JPC configurations not allowed in the constituent quark model. Besides this clear signature, hybrid mesons are also expected to have a large particle multiplicity decays, requiring for their search an experimental apparatus with high performances in terms of rate capability, resolution and almost a full acceptance to apply PWA methods. New-generation experiments are planned at Thomas Jefferson National Laboratory (VA, USA) for which an unprecedented statistics of large multiplicity decay events with fully reconstructed kinematics will be available. In particular for the MesonEx (CLAS12) experiment in Hall B, a wide scientific program that will start in 2016 has been deployed to study the meson spectrum at energies up to 11 GeV. A key role in such program is played by the Forward Tagger apparatus of the experiment, which will allow to extend the study of meson electro-production to very low Q2 values, in a quasi-real photo production kinematical region, where the production of hybrid mesons is expected to be favorite. Currently a new analysis framework for the search of the hybrid mesons is being set up by the HASPECT network, an international structure which gather people involved into theoretical and experimental hadronic physics all over the world. The goals of the network is to develop new analysis models and statistical techniques to unfold the signal and background distributions in high-statistics datasets. In this work are briefly presented the first preliminary results from the application of a statistical technique, namely the sPlot, to the data already acquired by the CLAS experiment for the decay f 1 (1285) --> (eta)pi+pi-.

Rizzo, Alessandro↗

DOE OSTI2017

Near-threshold J/ψ-meson photoproduction on nuclei

On the basis of the first-collision model that relies on the nuclear spectral function and which includes incoherent processes involving charmonium production in proton–nucleon collisions, the photoproduction of J/ψ mesons on nuclei is considered at energies close to the threshold for their production on a nucleon. The absorption of final J/ψ mesons, their formation length, and the binding and Fermi motion of target nucleons are taken into account in this model along with the effect of the nuclear potential on these processes. The A dependences of the absolute and relative charmonium yields are calculated together with absolute and relative excitation functions under various assumptions on the magnitude of the cross section for J/ψN absorption, the J/ψ-meson formation length, and their inmedium modification. It is shown that, at energies above the threshold, these features are virtually independent of the formation length and the change in the J/ψ-meson mass in nuclear matter but are rather highly sensitive to the cross section for J/ψN interaction. The calculations performed in the present study can be used to determine the unknown cross section for J/ψ-meson absorption in nuclei from a comparison of their results with data expected from experiments in the Hall C of the CEBAF (USA) facility upgraded to the energy of 12 GeV. It is also shown that the absolute and relative excitation functions for J/ψ mesons in photon–nucleus reactions at subthreshold energies are sensitive to the change in the meson mass and, hence, carry information about the properties of charmonium in nuclear matter.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2014

GlueX: Meson Spectroscopy in Photoproduction

The goal of the GlueX experiment \cite{gluex} is to provide crucial data to help understand the soft gluonic fields responsible for binding quarks in hadrons. Hybrid mesons, and in particular exotic hybrid mesons, provide the ideal laboratory for testing QCD in the confinement regime since these mesons explicitly manifest the gluonic degrees of freedom. Photoproduction is expected to be effective in producing exotic hybrids but there is little data on the photoproduction of light mesons. GlueX will use the new 12-GeV electron beam at Jefferson Lab to produce a 9-GeV beam of linearly polarized photons using the technique of coherent bremsstrahlung. A solenoid-based hermetic detector is under construction, which will be used to collect data on meson production and decays. These data will also be used to study the spectrum of conventional mesons, including the poorly understood excited vector mesons. This talk will give an update on the experiment as well as describe theoretical developments \cite{Dudek:2011bn} to help understand how these data can provide insights into the fundamental theory of strong interactions.

Salgado, Carlos↗

DOE OSTI2016

The meson spectroscopy program with CLAS12 at Jefferson Laboratory

The study of the hadronic spectrum is one of the most powerful tools to investigate the mechanism at the basis of quark confinement within hadrons. A precise determination of the spectrum allows not only to assess the properties of the hadrons in their fundamental and excited states, but also to investigate the existence of states resulting from alternative configurations of quarks and gluons, such as the glue-balls, hybrid hadrons and many-quarks configurations. The study of the mesonic part of the spectrum can play a central role in this investigation thanks to the strong signature that the hybrid mesons are expected to have: the presence of explicit gluonic degrees of freedom in such states may result in JPC configurations not allowed for the standard q ¯ q states. From the experimental side the expected high-multiplicity decays of the hybrid mesons require an apparatus with high performances in terms of rate-capability, resolution and acceptance. The CLAS12 experiment (formally MesonEx) is one of new-generation experiments at Thomas Jefferson National Laboratory (JLAB) for which an unprecedented statistics of events, with fully reconstructed kinematics for large particle multiplicity decays, will be available. A wide scientific program that will start in 2016 has been deployed for meson spectrum investigation with the CLAS12 apparatus in Hall B at energies up to 11 GeV. One of the main parts of the program is based on the use of the Forward Tagger apparatus, which will allow CLAS12 experiment to extend the study of meson electro-production to the quasi-real photo-production kinematical region (very low Q2), where the production of hybrid mesons is expected to be favoured. The data analysis which is required to extract the signal from hybrid states should go beyond the standard partial wave analysis techniques and a new analysis framework is being set up through the international network Haspect. The Haspect Network gathers people involved into theoretical and experimental hadronic physics all over the world, to investigate and propose new analysis models and new statistical techniques to unfold signal and background. The new analysis framework is being developed and tested using the existing CLAS data and results are projected to the CLAS12 performances, showing that the quest for hybrid exotic mesons is at reach.

Rizzo, Alessandro↗

DOE OSTI2011

Measurement and Interpretation of Moments of the Combined Hadronic Mass and Energy Spectrum in Inclusive Semileptonic B-Meson Decays

This thesis presents first measurements of moments of the hadronic n X 2 distribution measured in inclusive semileptonic decays of B mesons to final states containing a charm quark, B → X c ℓν. The variable n X 2 is a combination of the invariant mass of the charmed meson m X , its energy in the B-meson rest-frame E X;BRF , and a constant ~Λ = 0.65 GeV, n X 2 = m X 2 c 4 -2~ΛE X,BRF + ~Λ 2 . The moments <n X k > with k = 2,4,6 are measured as proposed by theory to constrain assumptions made in the theoretical description of inclusive observables in semileptonic B-meson decays. This description uses Heavy Quark Expansion (HQE), an effective QCD combined with an Operator Product Expansion. The measurement is based on a sample of 231.6 million e + e - → Υ(4S) {yields} B$\bar{B}$ events recorded with the BABAR experiment at the PEP-II e + e - -storage rings at SLAC. We reconstruct the semileptonic decay by identifying a charged lepton in events tagged by a fully reconstructed hadronic decay of the second B meson. Correction procedures are derived from Monte Carlo simulations to ensure an unbiased measurement of the moments of the n X 2 distribution. All moments are measured requiring minimum lepton momenta between 0.8 GeV/c and 1.9 GeV/c in the rest frame of the B meson. Performing a simultaneous fit to the measured moments <n X k > up to order k = 6 combined with other measurements of moments of the lepton-energy spectrum in decays B → X c ℓν and moments of the photon-energy spectrum in decays B → X s γ, we determine the quark-mixing parameter |V cb |, the bottom and charm quark masses, the semileptonic branching fraction β(B → X c ℓν), and four non-perturbative heavy quark parameters. Using HQE calculations in the kinetic scheme up to order 1/m b 3 we find |V cb | = (41.65 ± 0.43 ± 0.40 ± 0.58) • 10 -3 and m b = (4.570 ± 0.033 ± 0.043) GeV/c 2 , where the first uncertainty refers to experimental contributions, the second to uncertainties in the HQE, and the third to theoretical uncertainties in the calculations of the semileptonic decay rate Λ(B {yields} X c ℓν). All obtained results are consistent with previous determinations. The inclusion of the moments <n X 6 > decreases the uncertainty on the HQE parameters μ π 2 and ρ D 3 . Furthermore, the theoretical treatment of higher order corrections in the HQE used for the moments <m X k > has been verified with these new measurements.

43 PARTICLE ACCELERATORS↗

DOE OSTI2011

Semileptonic B and B{sub s} decays into orbitally excited charmed mesons

The BABAR Collaboration has recently reported products of branching fractions that include B meson semileptonic decays into final states with charged and neutral D{sub 1}(2420) and D{sub 2}*(2460), two narrow orbitally excited charmed mesons. We evaluate these branching fractions, together with those concerning D{sub 0}*(2400) and D{sub 1}{sup '}(2430) mesons, within the framework of a constituent quark model. The calculation is performed in two steps, one of which involves a semileptonic decay and the other is mediated by a strong process. Our results are in agreement with the experimental data. We also extend the study to semileptonic decays of B{sub s} into orbitally excited charmed-strange mesons, providing predictions to the possible measurements to be carried out at LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Mesons in strong magnetic fields: (I) General analyses

Here, we study properties of neutral and charged mesons in strong magnetic fields |eB| >> Λ 2 QCD with Λ QCD being the QCD renormalization scale. Assuming long-range interactions, we examine magnetic-field dependences of various quantities such as the constituent quark mass, chiral condensate, meson spectra, and meson wavefunctions by analyzing the Schwinger–Dyson and Bethe–Salpeter equations. Based on the density of states obtained from these analyses, we extend the hadron resonance gas (HRG) model to investigate thermodynamics at large B. As B increases the meson energy behaves as a slowly growing function of the meson's transverse momenta, and thus a large number of meson states is accommodated in the low energy domain; the density of states at low temperature is proportional to B 2 . This extended transverse phase space in the infrared regime significantly enhances the HRG pressure at finite temperature, so that the system reaches the percolation or chiral restoration regime at lower temperature compared to the case without a magnetic field; this simple picture would offer a gauge invariant and intuitive explanation of the inverse magnetic catalysis.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Nuclear modification factor of D 0 mesons in PbPb collisions at s NN = 5.02 TeV

The transverse momentum ( p T ) spectrum of prompt D 0 mesons and their antiparticles has been measured via the hadronic decay channels D 0 → K – π + and D - 0 → K + π – in p p and PbPb collisions at a centre-of-mass energy of 5.02 TeV per nucleon pair with the CMS detector at the LHC. The measurement is performed in the D 0 meson p T range of 2–100 GeV/ c and in the rapidity range of | y | < 1 . The p p (PbPb) dataset used for this analysis corresponds to an integrated luminosity of 27.4 pb –1 (530 μb –1 ). The measured D 0 meson p T spectrum in pp collisions is well described by perturbative QCD calculations. The nuclear modification factor, comparing D 0 meson yields in PbPb and p p collisions, was extracted for both minimum-bias and the 10% most central PbPb interactions. For central events, the D 0 meson yield in the PbPb collisions is suppressed by a factor of 5–6 compared to the p p reference in the p T range of 6–10 GeV/ c . For D 0 mesons in the high- p T range of 60–100 GeV/ c , a significantly smaller suppression is observed. The results are also compared to theoretical calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Helicity operators for mesons in flight on the lattice

Motivated by the desire to construct meson-meson operators of definite relative momentum in order to study resonances in lattice QCD, we present a set of single-meson interpolating fields at non-zero momentum that respect the reduced symmetry of a cubic lattice in a finite cubic volume. These operators follow from the subduction of operators of definite helicity into irreducible representations of the appropriate little groups. We show their effectiveness in explicit computations where we find that the spectrum of states interpolated by these operators is close to diagonal in helicity, admitting a description in terms of single-meson states of identified J PC . Lastly, the variationally determined optimal superpositions of the operators for each state give rapid relaxation in Euclidean time to that state, ideal for the construction of meson-meson operators and for the evaluation of matrix elements at finite momentum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2017

Monte Carlo Glauber wounded nucleon model with meson cloud

We study the effect of the nucleon meson cloud on predictions of the Monte Carlo Glauber wounded nucleon model for AA, pA, and pp collisions. From the analysis of the data on the charged multiplicity density in AA collisions we find that the meson–baryon Fock component reduces the required fraction of binary collisions by a factor of ~2 for Au + Au collisions at √s = 0.2 TeV and ~1.5 for Pb + Pb collisions at √s = 2.76 TeV. For central AA collisions, the meson cloud can increase the multiplicity density by ~16–18%. We give predictions for the midrapidity charged multiplicity density in Pb + Pb collisions at √s = 5.02 TeV for the future LHC run 2. We find that the meson cloud has a weak effect on the centrality dependence of the ellipticity ϵ{sub 2} in AA collisions. For collisions of the deformed uranium nuclei at √s = 0.2 TeV, we find that the meson cloud may improve somewhat agreement with the data on the dependence of the elliptic flow on the charged multiplicity for very small centralities defined via the ZDCs signals. We find that the meson cloud may lead to a noticeable reduction of ϵ{sub 2} and the size of the fireball in pA and pp collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2015

Mass spectrum of vector mesons and their leptonic-decay constants in the bilocal relativistic potential model

A phenomenological model is developed in terms of bilocal meson fields in order to describe a vector meson and its leptonic decays. A new Salpeter equation for this particle and the Schwinger-Dyson equation allowing for the presence of an arbitrary potential and for a modification associated with the renormalization of the quark (antiquark ) wave function within the meson are given. An expression for the constant of the leptonic decay of the charged rho meson is obtained from an analysis of the decay process τ → ρν via parametrizing in it the hadronization of intermediate charged weak W bosons into a bilocal vector meson. The potential is chosen in the form of the sum of harmonic-oscillator and Coulomb potentials, and the respective boundary-value problem is formulated. It is shown that the solutions to this problem describe both the mass spectrum of vector mesons and their leptonic-decay constants.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Light-Meson Spectroscopy at GlueX

GlueX at Jefferson Lab aims to study the light meson spectrum with an emphasis on the search for light hybrid mesons. To this end, a linearly-polarized 9 GeV photon beam impinges on a hydrogen target contained within a hermetic detector with near-complete neutral and charged particle coverage. In 2016, the experiment completed its commissioning and subsequently started to take data in its design configuration. With the size of the data set so far, GlueX already exceeds previous experiments for polarized photoproduction in this energy regime. A selection of early results will be presented, focusing on beam asymmetries for pseudo-scalar and vector mesons. The potential to make significant contributions to the field of light-meson spectroscopy is highlighted by the observation of several known meson resonances. As a result, the strategy to map the light meson spectrum with amplitude analysis tools will be outlined.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

Exclusive central diffractive production of scalar and pseudoscalar mesons; tensorial vs. vectorial pomeron

We discuss consequences of the models of “tensorial pomeron” and “vectorial pomeron” for exclusive diffractive production of scalar and pseudoscalar mesons in proton–proton collisions. Diffractive production of f{sub 0}(980), f{sub 0}(1370), f{sub 0}(1500), η, and η{sup ′}(958) mesons is discussed. Different pomeron–pomeron–meson tensorial coupling structures are possible in general. In most cases two lowest orbital angular momentum–spin couplings are necessary to describe experimental differential distributions. For f{sub 0}(980) and η production reggeon–pomeron, pomeron–reggeon, and reggeon–reggeon exchanges are included in addition, which seems to be necessary at relatively low energies. The theoretical results are compared with the WA102 experimental data. Correlations in azimuthal angle between outgoing protons, distributions in rapidities and transverse momenta of outgoing protons and mesons, in a special “glueball filter variable”, as well as some two-dimensional distributions are presented. We discuss differences between results of the vectorial and tensorial pomeron models. We show that high-energy central production, in particular of pseudoscalar mesons, could provide crucial information on the spin structure of the soft pomeron.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Measurement of beauty and charm production in pp collisions at $\sqrt{s}$ = 5.02 TeV via non-prompt and prompt D mesons

The pT-differential production cross sections of prompt and non-prompt (produced in beauty-hadron decays) D mesons were measured by the ALICE experiment at midrapidity (|y| < 0.5) in proton-proton collisions at s√ = 5.02 TeV. The data sample used in the analysis corresponds to an integrated luminosity of (19.3 ± 0.4) nb -1 . D mesons were reconstructed from their decays D 0 → K - π + , D + → K - π + π + , and D$^+_s$→ φπ + → K - K + π + and their charge conjugates. Compared to previous measurements in the same rapidity region, the cross sections of prompt D + and D$^+_s$ mesons have an extended pT coverage and total uncertainties reduced by a factor ranging from 1.05 to 1.6, depending on pT, allowing for a more precise determination of their pT-integrated cross sections. The results are well described by perturbative QCD calculations. The fragmentation fraction of heavy quarks to strange mesons divided by the one to non-strange mesons, f s /(f u + f d ), is compatible for charm and beauty quarks and with previous measurements at different centre-of-mass energies and collision systems. The $b\bar{b}$ production cross section per rapidity unit at midrapidity, estimated from non-prompt D-meson measurements, is d$σ_{b\bar{b}}$/d$y$| |y|<0.5 = $34.5 ± 2.4(stat)^{+4.7}_{-2.9}$(tot.syst) μb. It is compatible with previous measurements at the same centre-of-mass energy and with the cross section pre- dicted by perturbative QCD calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗