One of the open challenges in subnuclear physics is to understand the
non-perturbative regime of Quantum Chromodynamics, including the world
of the nucleon and its excitations. One of the key issues is to identify
the relevant degrees-of-freedom and the effective forces between them.
A necessary step towards this aim is undoubtedly a
precise knowledge of the experimental spectrum and the...
With new data of unprecedented accuracy from ELSA, JLab, MAMI, and other facilities the reliable extraction of the the spectrum of excited baryons becomes into reach. Besides experimental advances, the phenomenological analysis of the data has made much progress in the last years. Different partial-wave analysis efforts start to converge although, especially at high energies, the...
The status of the Bonn-Gatchina analysis of the meson and photo-induced reactions is reported. A number of new results obtained from the analysis of the new data on the meson photoproduction are presented and the property of the observed baryon states are discussed.
We present a new version of the $\eta$MAID model for $\eta$ and $\eta'$
photoproduction on proton and neutron.
The model includes 23 nucleon resonances parameterized with Breit-Wigner shapes.
The background is described by vector and axial-vector meson exchanges in the
$t$ channel using the Regge cut phenomenology.
Parameters of the resonances were obtained from a fit to the new experimental...
Belle experiment performed a study of several multibody decays
of $B$ and $\Upsilon$-mesons with multidimensional phase-space
analysis of the final states. Such analysis allows to separate
contributions
of different intermediate states and determine their quantum numbers.
We present some recent results on $\bar{B}^0 \to D^{*+} \omega \pi^-$, $\bar{B}^0 \to
J/\psi K^-\pi^+$, $e^+e^-...
We compare the methods of amplitude reconstruction, for a complete
experiment and a truncated partial wave analysis, applied to the
photoproduction of pseudo-scalar mesons~[1]. A complete experiment
analysis (CEA) determines 4 complex amplitudes up to an overall
phase $\phi_0(E,\theta)$ at any given energy and angle and requires
a minimum set of 8 observables that must include beam-, target-...
For quite some time it is well known that single-channel physical observables are invariant with respect to a general energy and angle dependent phase rotation. This invariance is called continuum ambiguity. We show that, contrary to well-behaved energy dependent invariance, angle dependent phase rotation mixes multipoles, and changes their analytic structure. A direct consequence is that...
PHASE - the Panel on Hadronic Amplitudes - is a proposal to form a joint panel of theorists and experimentalists, who are engaged in the investigation of the structure of hadronic amplitudes. This panel will curate the collaborative infrastructure needed to develop consistent data analysis techniques across experiments and enable joint analyses of multiple data sets. Such global analyses will...
We perform partial wave analysis of the eta photo production data. In an iterative procedure, fixed-t amplitude analysis (FT AA) and conventional single energy partial wave analysis (SE PWA) are coupled in such a way that output from one analysis is used as an constraint in another. The fixed-t analyticity in the fixed-t amplitude analysis is imposed by using Pietarinen's expansion...
Within the framework of dispersion theory we analyze the decays $\bar B_{d,s}^0 \to J/\psi M_1 M_2$ with $M_1 M_2$ being an scalar isoscalar or isovector pair of pseudoscalars, $\pi\pi$, $\bar K K$ or $\pi\eta$. In a fit of the $\bar B_{d,s}^0 \to J/\psi\pi\pi$ spectrum to data we fix several parameters, whose number is reduced significantly compared to a phenomenological analysis. Using these...
The decay channel $\eta^\prime\to\eta\pi\pi$ offers several features of interest: due to
final-state interactions it can be used to constrain $\eta\pi$ scattering. It is also an essential
input for a study of inelastic effects in the decay $\eta^\prime\to3\pi$. In the past, extensions
of chiral perturbation theory have been employed to describe this decay.
In this talk, I will present a...
Fundamentals of the new, robust, pole extraction method based on representing the regular part of Laurent expansion of partial wave amplitude with quickly converging Pietarinen series are repeated. An overview of all recent applications of this method with summary of obtained results is made. Preliminary results in extracting baryon transition form factors at the pole and analysis of lowest...
An overview of the most effective methods used for parameterization of meson-meson amplitudes below 2 GeV will be presented. Theoretical constraints imposed on the amplitudes and requirements for amplitudes will be discussed.
The most widely discussed will be the pion-pion amplitudes in all important partial waves (S, P, D and F). All these methods, constraints and new results
can greatly...
The most recent $\gamma p \to p \pi^{0}$ [1,2,3] and $\gamma p \to n \pi^{+}$ data have been used
for multipole amplitude extraction at the $\Delta^{+}(1232)$ resonance.
The data have been analysed in a novel way, utilizing the Athens Model Independent Analysis Scheme (AMIAS),
yielding precise results with little, if any, model error. The benchmark quantity in nucleon deformation,
$EMR =...
We present some results on the analysis of $\eta\pi$ resonances from peripheral scattering of pions off of nuclear targets. This analysis is motivated by the recent results by the COMPASS collaboration. The theoretical models emphasize final state interactions which satisfy $S$-matrix principles. We show how the model fits to COMPASS results, and obtain the resonance content for the $\eta\pi$...
Results of the latest BnGa PWA analysis of the photoproduction data on neutron is pesented. New CLAS data on hyperon photoproduction are included in the analysis. We also present the analysis of latest MAMI data.
We discuss production of vector $K^∗$ and $D^∗$ mesons in $\pi^− p$ interaction
with their subsequent decay into pseudoscalar $K + \pi$ and $D + \pi$ mesons,
respectively. Our consideration is based on modified quark-gluon string model
which includes spin variables and allows to determine decay distributions
of the outgoing pseudoscalars. These distributions are sensitive to the vector
meson...
As it is well-known for a long time now, the observables in a single-channel scattering problem remain invariant once the amplitude is multiplied by an overall phase. This phase is generally allowed to depend on a full set of independent kinematic variables for the considered process. For a 2-body reaction, this means that the phase can depend on energy and angle.
For partial wave analysis...
It took more than 40 years until Lattice QCD tools have become evolved far
enough to address excited hadrons in a reliable way. Still, we are confined to
the low lying resonances with a few coupled two-hadron channels, mostly in the
meson-meson sector. Phase shifts at a few energy values for simple system have
been determined in this first principles approach. Meson-nucleon results are
scarce....
Large data sets in light meson spectroscopy from fixed target experiments are challeng-ing standard analysis methods in meson spectroscopy. On the one hand, they allow for innovative methodology but at the same time require a more profound and exact under-standing of underlying hadronic physics. Partial wave analysis now is a standard tool used across all experiments including heavy meson...
We introduce a near-threshold parameterization that is more general than the effective-range expansion
up to and including the effective-range because it can also handle with a near-threhold zero in the
$D^0\bar{D}^{*0}$ S-wave. In terms of it we analyze the CDF data on inclusive $p\bar{p}$ scattering to $J/\psi \pi^+\pi^-$, and the Belle and BaBar data on charged B decays to $K\, J/\psi...
Latest results of experiments at the VEPP-2000 e+e- collider with the SND and CMD-3 detectors are presented. In particular, the accuracies of several decays of the vector mesons rho(770), omega(783), phi(1020) are improved. New hadronic final states a0(980)rho, a0(980)omega in e+e- annihilation are observed.
GlueX at Jefferson Lab aims to study the meson spectrum with an emphasis on 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 spring of 2016, the experiment completed its commissioning and took its first substantial data in the design...
The measurement of the excitation spectrum of light-quark hadrons often requires to apply partial-wave analysis methods. The building blocks of the physical models used in such analyses are the partial waves, which describe the quantum numbers and the decay paths of the resonances. In diffractive reactions, in principle, infinitely many of these waves can contribute. However, for finite data...
I will give an overview of the analysis methods that are used by the LHCb collaboration
to investigate (exotic) hadron states in the heavy-quark sector. Emphasis will be placed on
amplitude analysis techniques that are employed to extract parameters of the exotic hadrons,
using the recently discovered pentaquark and X -> JpsiPhi tetraquark candidates as examples.
Properly constructed effective field theories (EFTs) hold the promise of model independence and order-by-order convergence of observable calculations.
EFTs have free parameters, the so-called low-energy constants (LECs), that often must be fixed using low-energy data relative to the breakdown scale of the EFT. We have developed a Bayesian framework for EFT parameter estimation that uses priors...
The t-channel reggeon exchange is the dominant mechanism of the high energy photoproduction of di-meson resonances on nucleons. The resulting amplitude naturally factorizes into initial production of meson pairs and subsequent final state interaction, which can be described in terms of binary amplitudes satisfying the constraints of unitarity and analyticity. However, for the final states...
The combination of leptonic production and selection rules imposed by the weak hadronic current make the experimental study of hadronic final states in tau decay particularly clean. In this presentation we describe studies carried out nearly 20 years ago at CLEO-II of the a1(1260) meson in tau decays to neutrino plus three pions. Notable results include identification of significant...
Recent results in studies of exotic states at LHCb are presented in this talk. The results include observation of pentaquark states in Lambda_b decays, studies of B -> psi' K pi and B -> jpsi phi K channels with contributions of tetraquark candidates, search for X(5568) in Bs pi channel, and the most recent constraints on the quantum numbers of molecular candidate Lambda_c(2940) from Lambda_b...
The decay $D^{0} \rightarrow \pi^{+}\pi^{-}\pi^{+}\pi^{-}$, with $D^{0} \rightarrow a_1(1260)^{+} \pi^{-}$ being the dominant intermediate state, provides an excellent environment to study the properties of the $a_1(1260)$ meson. We present new measurements of the $a_1(1260)$’s mass and width using data collected with the CLEO-c detector. The $a_1(1260)$ contribution is disentangled from the...
The mass-dependent analysis of $ \pi^- \pi^- \pi^+ $ COMPASS data on the proton target is discussed. The analysis is based on the currently worlds largest data set of 46 000 000 events, which allows us to divide the data into 100 mass bins and 11 intervals of momentum transfer squared $ t'$. The fit model includes Breit-Wigner amplitudes which are describing resonant contributions while...
Finding evidence for the existence of exotic states is one of the most exciting aspects of modern hadron physics. In the meson sector, it is possible to have a `smoking gun' signature of a genuine exotic nature provided by certain charge-mass combinations and $J^{PC}$-configurations that cannot be explained by a quark-antiquark pair. Observations of several candidates were claimed by...
A model for exclusive diffractive resonance production in proton-proton
collisions at the LHC is presented. Cross sections are calculated by folding
the Pomeron-Pomeron total cross section ($^{*}$) with the Donnachie-Landshoff
parameterisation of the Pomeron flux in the proton($^{**}$). The single differential
cross section dsigma/dM as well as the double differential cross section...
We study the $P_c(4450)$ structure in $J/\psi$ photoproduction, and discuss the feasibility of observing it in the CLAS12 experiment at the Jefferson Lab. This resonance-like structure has recently been observed in the $J/\psi~p$ spectrum by the LHCb collaboration.
Our study presents a first estimate of the upper limit for the branching ratio of the $P_c(4450)$ to the $J/\psi~p$ channel. We...
This talk will summarize the Partial Wave Analysis (PWA) activities carried
out at Ruhr-Universitaet Bochum. The key objective is to realize a powerful,
user-friendly and highly modular PWA software package with the ability to
provide amplitudes in different formalisms and to support single and coupled
channel analyses with data obtained from different hadron spectroscopy...
Progress in heavy-flavor hadron spectroscopy since the previous PWA/ATHOS meeting will be reviewed. Majority of the new results are concerned with candidates for exotic hadrons with the quark content matching tetraquark and pentaquark states. Clarifying the nature of these candidates often relies heavily on amplitude analyses, making this meeting particularly relevant for such studies. The...
This slot is open for issues to be discussed in greater detail. Discussion topics should be prepared on 1-2 slides or introduced orally.
"The majority of excited hadrons are seen as resonances in the scattering of lighter stable hadrons like pions and kaons. Many resonances decay into multiple final states necessitating coupled-channel analyses, and recently it has become possible to obtain coupled-channel scattering amplitudes from lattice QCD. I will describe one of these calculations, beginning with the computation of the...
Recent progress in the determination of the heavy meson spectrum from lattice QCD are reviewed with a focus on exotic states. I interpret the term "exotic" widely, using it to refer to hadrons with masses and/or properties not expected from calculations in simple potential models. Among these, I will highlight some recent calculations for XYZ charmonium-like states. Furthermore a lattice QCD...
We present our recent results on hadron-hadorn scattering from lattice
QCD. This includes pion-pion scattering in different isospin channels,
in particular I=0, and kaon-kaon with I=0. Eventually we discuss our
current attemts to investigate pion-nucleon scattering with the pion
mass at its physical value.
We consider some issues in the estimation of systematic errors as commonly performed by particle physicists. This is important in an era when large data samples reduce statistical errors to very small values,so that systematic uncertainties dominate. We highlight inconsistencies in the definitions and techniques currently used by some analysts, and offer guidelines for a more rigorous...
We discuss perspectives of future spectroscopic studies
using existing and planned electron-positron and proton-proton
colliders. While for mesons of light quarks prospects are
mostly related to VEPP-2000 in Novosibirsk and BEPC2 in Beijing,
heavier mesons as well as baryons will be readily produced at
the Super-tau-charm factory in Novosibirsk or China, KEKB at KEK,
LHC and future...
Recent activities of the PDG are reviewed together with
plans for further improvements. Topics include the criteria
for including new results and changes in the presentation of
particle properties.
"On the definition of branching ratios for overlapping hadron resonances",
Hadron resonances are wide and may overlap. This fact renders the definition
of a branching ratio difficult. In a simulation, different definitions of
the branching ratio are compared. Branching ratios can also be defined at
the pole position. Applications of this definition for baryons and mesons
are presented.
"On...
The meson team is responsible for all aspects concerning unstable (with respect to the strong
interaction) mesons within the Particle Data Group. This includes a literature scan, encoding of data into
the data base as well as the preparation of additional materials in tailor-made reviews. In the
presentation I briefly describe the current activities of the PDG meson team.
Despite of numerous experimentally observed signals of XYZ states, and impressive progress in the interpretation from the theory side, the quest for understanding the overall pattern is still on. In particular one of the questions for the present and the near-term future is, which particular new, yet-unobserved states with which quantum numbers would give us more information, if XYZ states are...
The study of electromagnetic transitions opens a window into the very nature of the strong interaction. And, indeed, such a study of how a ground-state nucleon transitions to an excited state, over a broad range of $q^2$, will provide keen insight into the evolution of how dynamically-generated masses emerge from the asymptotically-free, nearly massless quarks of perturbative QCD as well as...
We will provide the connection between hadron production in ultra-relativistic nuclear collisions and the hadron mass spectrum. In particular, we will demonstrate that all hadron resonances are important up to a mass of about 2.5 GeV, but details (quantum numbers, widths, etc) of resonances above a mass of 2 GeV are not so important because of Boltzmann suppression. We will also discuss the...
Their unique sensitivity to phases makes PWA / amplitude analyses a powerful tool for precision CP violation measurements in beauty and charm decays. The role and limitations of amplitude models in these measurements are discussed. Methods overcoming limitations of existing amplitude models through model independent approaches are presented, and how high quality amplitude models are still...
The non-conservation of lepton flavour number has only been observed so far in neutrino oscillations. The observation of this phenomena in the charged lepton sector would provide clean evidence of new dynamics beyond the Standard Model.
I plan to discuss the physics of lepton flavour violating tau decays in semileptonic modes with particular attention on the determination of the...
Analyticity provides constraints on the imaginary part of the amplitudes. The so-called finite energy sum rules. By relating the resonance region to the high-energy one, they can provide information useful to reduce the ambuigties in extracting baryons and mesons properties.
In this talk I will review their status in modern applications.
I shall give a brief introduction to triangle singularities (TS), with a new pedagogical way to face them. Then I will report on the interpretation of the $f_1(1420)$ as a decay mode of the $f_1(1285)$ into $\pi a_0(980)$ through a TS, and $K^* \bar{K}$. Then I briefly report on the $f_2(1810)$ and make predictions for the decay $\bar{B} \to \bar{K} \pi D_{s0}^*(2317)$, which shows a peak due...
The COMPASS experiment has collected a very large data set of 50 million
diffractively produced $\pi^-\pi^+\pi^-$ events using a $190\,$GeV$/c$
negatively charged hadron beam. In addition to the results of an
extensive Partial-Wave Analysis (PWA) of this data, we recently
published first results of a so-called freed-isobar PWA. In this
approach, fixed parametrizations of intermediate...
A precise determination of pion-kaon scattering amplitudes is very relevant for our understanding of both light meson physics as well as input for analysis of other hadronic decays. In this talk we first present our analysis of the fulfillment of Forward Dispersion Relations by the existing data up to 1.75 GeV, and by imposing these relations as constraints on the fits, we provide a set of...
The microscopic nature of the XYZ states remains an unsettled topic. We show how a thorough amplitude analysis of the data can help constraining models of these states.
Specifically, we consider the case of the Zc(3900) peak and discuss possible scenarios of a QCD state, virtual state, or a kinematical enhancement. We conclude that
current data are not precise enough to distinguish between...
High-energy peripheral reactions provide an excellent opportunity to study the excitation spectrum of hadrons. The COMPASS experiment at CERN has collected $5\times10^6$ events of the diffractive scattering of pions to the 3-pion final state.
Partial wave analysis techniques have been employed to obtain an expansion of the
reaction cross section in terms of partial waves with quantum numbers...
In recent years various near-threshold narrow
peaks were observed in heavy quarknoium mass regions, such as $X(3872)$, $Z_c(3900)$, $Z_c(4020)$, $Z_b(10610)$ and $Z_b(10650)$, which are located close to the $D\bar D^*$, $D\bar D^*$, $D^*\bar D^*$, $B\bar B^*$ and $B^*\bar B^*$
thresholds in an $S$ wave, respectively. Once there is a strongly coupled $S$-wave threshold nearby, the...
We are developing a software framework for Partial Wave and Amplitude Analysis called PyPWA. The PyPWA project aims to develop modular and flexible software that links to existing codes and Python libraries. The software also provides direct access to the JLab computing resources. The software contains a general-shell where amplitude's parameters (or any parametric model) can be estimated...
The considerable amount of data on three-body decays of mesons which has
become available in recent years has revived interest in the dispersive
formalism of Khuri and Treiman as a powerful analysis tool. We consider here
the isospin breaking eta -> 3 pi amplitude which is specific in that both the
low-energy chiral expansion and dispersion relation techiques can be
applied. We reconsider an...
A precise understanding of low-energy pion-nucleon interactions is central for many areas in nuclear and hadronic physics, ranging from the scalar couplings of the nucleon to the long-range part of two-pion-exchange potentials and three-nucleon forces in Chiral Effective Field Theory. We present a calculation that combines the general principles of analyticity, unitarity, and crossing symmetry...
The D*0(2400) is the known lightest non-strange scalar meson. In this talk, we study the D-pi, D-eta, and Ds Kbar scattering amplitudes in the context of unitarized Heavy Meson Chiral Perturbation Theory. We show that there are actually two poles in this energy region. Having fixed the value of the free parameters from previous works, we make a prediction of the energy levels of the system...
Fundamental interactions of components of matter are not yet fully understood. Some basic
questions such as: how do the quarks, light constituents of the proton and neutron sum up
to provide the visible mass of nucleons? Why the mediator of the strong interaction does not
show up in the spectrum of hadrons? Are the three quarks and quark-antiquarks configurations the only
possible? The...
Pseudoscalar-meson photoproduction on the nucleon is of current interest for hadron reaction studies. At low energies it provides information about the nucleon spectrum, while at high energies it reveals details of the residual hadron interactions due to cross-channel particle (Reggeon) exchanges. These two regimes are analytically connected, a feature that can be used to relate properties of...
Transition form factors are uniquely suited to trace the evolution of baryon degrees of freedom by measuring exclusive single-meson and double-pion electroproduction cross sections off the free proton. Recent efforts try to access their isospin dependence by analyzing the cross sections off the quasi-free neutron and proton in Deuterium. In the near future, these exclusive measurements will be...
Large data sets in light meson spectroscopy from fixed target experiments are challeng-ing standard analysis methods in meson spectroscopy. On the one hand, they allow for innovative methodology but at the same time require a more profound and exact under-standing of underlying hadronic physics. Partial wave analysis now is a standard tool used across all experiments including heavy meson...
