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13 pages, 425 KiB

Open AccessArticle

Theoretical and Experimental Essentials on Baryon Form Factors

by Monica Bertani, Alessio Mangoni and Simone Pacetti

Symmetry 2022, 14(3), 439; https://doi.org/10.3390/sym14030439 - 23 Feb 2022

Cited by 2 | Viewed by 1382

Abstract

This brief review is a practical guide on the basic concepts, pivotal formulae, standard relations, and some unusual, often forgotten, but sometimes revealing features of baryons’ form factors. All available measured values of nucleon form factors in the space-like and time-like regions extracted [...] Read more.

This brief review is a practical guide on the basic concepts, pivotal formulae, standard relations, and some unusual, often forgotten, but sometimes revealing features of baryons’ form factors. All available measured values of nucleon form factors in the space-like and time-like regions extracted from scattering and annihilation cross-sections are also reported. Full article

(This article belongs to the Special Issue Baryon Structure: Form Factors and Polarization)

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12 pages, 4384 KiB

Open AccessArticle

Electromagnetic Structure of the Neutron from Annihilation Reactions

by Paul Larin, Xiaorong Zhou, Jifeng Hu, Frank Maas, Rinaldo Ferroli Baldini, Haiming Hu and Guangshun Huang

Symmetry 2022, 14(2), 298; https://doi.org/10.3390/sym14020298 - 1 Feb 2022

Cited by 3 | Viewed by 2137

Abstract

The investigation of the fundamental properties of the nucleon is one of the most important topics in the modern hadron physics. Its internal structure and dynamics can be studied through the measurement of electromagnetic form factors which represent the simplest structure observables and [...] Read more.

The investigation of the fundamental properties of the nucleon is one of the most important topics in the modern hadron physics. Its internal structure and dynamics can be studied through the measurement of electromagnetic form factors which represent the simplest structure observables and serve as a test ground for our understanding of the strong interaction. Since the first attempt to measure the time-like form factors of the neutron, only four experiments published results on its structure from annihilation reactions. Due to the lack of statistics and experimental challenges, no individual determination of the form factors of the neutron has been possible so far. Modern developments of electron-positron colliders and the associated detectors allow to measure the effective FF of the neutron with the process

e^{+} e^{-} \to n \bar{n}

with unprecedented precision at the BESIII experiment, which is based at the BEPCII collider in Beijing, China. In this report, we review the published results of the form factors on the neutron in the time-like regime, describe the experimental setup, and discuss their impact on our understanding of the strong interaction. Future works at BESIII will help to improve the precision of the neutron FFs and, combined with theoretical progress in this field, help to illuminate the properties of the neutron structure. Full article

(This article belongs to the Special Issue Baryon Structure: Form Factors and Polarization)

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10 pages, 345 KiB

Open AccessArticle

Experimental Review of

Λ \bar{Λ}

Production

by Xiaorong Zhou, Liang Yan, Rinaldo Baldini Ferroli and Guangshun Huang

Symmetry 2022, 14(1), 144; https://doi.org/10.3390/sym14010144 - 12 Jan 2022

Cited by 6 | Viewed by 1570

Abstract

Exclusive hyperon-antihyperon production provides a unique insight for understanding of the intrinsic dynamics when strangeness is involved. In this paper, we review the results of

Λ \bar{Λ}

production via different reactions from various experiments, e.g., via

\bar{p} p

annihilation from the [...] Read more.

Exclusive hyperon-antihyperon production provides a unique insight for understanding of the intrinsic dynamics when strangeness is involved. In this paper, we review the results of

Λ \bar{Λ}

production via different reactions from various experiments, e.g., via

\bar{p} p

annihilation from the LEAR experiment PS185, via electron-positron annihilation using the energy scan method at the CLEO-c and BESIII experiments and the initial-state-radiation approach utilized at the BaBar experiment. The production cross section of

Λ \bar{Λ}

near the threshold is sensitive to QCD based prediction. Experimental high precision data for

\bar{p} p \to \bar{Λ} Λ

close to the threshold region is obtained. The cross section of

e^{+} e^{-} \to Λ \bar{Λ}

is measured from its production threshold to high energy. A non-zero cross section for

e^{+} e^{-} \to Λ \bar{Λ}

near threshold is observed at BaBar and BESIII, which is in disagreement with the pQCD prediction. However, more precise data is needed to confirm this observation. Future experiments, utilizing

\bar{p} p

reaction such as PANDA experiment or electron-positron annihilation such as the BESIII and BelleII experiments, are needed to extend the experimental data and to understand the

Λ \bar{Λ}

production. Full article

(This article belongs to the Special Issue Baryon Structure: Form Factors and Polarization)

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10 pages, 364 KiB

Open AccessArticle

Electromagnetic Form Factors of Σ Hyperons

by Muzaffar Irshad, Dong Liu, Xiaorong Zhou and Guangshun Huang

Symmetry 2022, 14(1), 69; https://doi.org/10.3390/sym14010069 - 4 Jan 2022

Cited by 5 | Viewed by 1525

Abstract

Electromagnetic form factors (EMFFs) are fundamental observable of baryons that intimately related to their internal structure and dynamics, where the EMFFs of hyperons provide valuable insight into the behavior of the strangeness. The EMFFs of hyperons can also help to understand those of [...] Read more.

Electromagnetic form factors (EMFFs) are fundamental observable of baryons that intimately related to their internal structure and dynamics, where the EMFFs of hyperons provide valuable insight into the behavior of the strangeness. The EMFFs of hyperons can also help to understand those of nucleons as they are connected with the flavor SU(3) symmetry. The EMFFs of nucleons can be measured in both spacelike and timelike regions. However, it is difficult to probe the EMFFs of hyperons in spacelike region due to the unstable nature of hyperons. By means of electron-positron annihilation, the EMFFs of hyperons in timelike region is accessible via the production of hyperon-antihyperon pair. The timelike EMFFs of the isospin triplet

Σ

hyperons measured at Babar, CLEO-c and BESIII experiments are reviewed in this paper. Besides, the relevant theoretical discussion based on the experimental results are also presented. Full article

(This article belongs to the Special Issue Baryon Structure: Form Factors and Polarization)

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14 pages, 1993 KiB

Open AccessArticle

Electromagnetic Form Factor of Doubly-Strange Hyperon

by Xiongfei Wang and Guangshun Huang

Symmetry 2022, 14(1), 65; https://doi.org/10.3390/sym14010065 - 3 Jan 2022

Cited by 10 | Viewed by 1781

Abstract

The standard model of particle physics is a well-tested theoretical framework, but there are still some issues that deserve experimental and theoretical investigation. The

Ξ

resonances with strangeness

S = - 2

, the so-called doubly-strange hyperon, can provide important information to further [...] Read more.

The standard model of particle physics is a well-tested theoretical framework, but there are still some issues that deserve experimental and theoretical investigation. The

Ξ

resonances with strangeness

S = - 2

, the so-called doubly-strange hyperon, can provide important information to further test the standard model by studying their electromagnetic form factors, such as probing the limitation of the quark models and spotting unrevealed aspects of the QCD description of the structure of hadron resonances. In this work, we review some recent studies of the electromagnetic form factors on doubly-strange hyperons in pair production from positron–electron annihilation experiment. Full article

(This article belongs to the Special Issue Baryon Structure: Form Factors and Polarization)

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9 pages, 425 KiB

Open AccessArticle

Production Mechanism of the Charmed Baryon

Λ_{c}^{+}

by Weiping Wang, Xiaorong Zhou, Rinaldo Baldini Ferroli and Guangshun Huang

Symmetry 2022, 14(1), 5; https://doi.org/10.3390/sym14010005 - 21 Dec 2021

Cited by 2 | Viewed by 2551

Abstract

As the lightest charmed baryon, precision measurement of the pair production cross section of

Λ_{c}^{+}

provides unprecedented experimental information for the investigation of baryon production mechanism. In addition, the extraction of the polar angle distributions of the outgoing

Λ_{c}^{+}

[...] Read more.

As the lightest charmed baryon, precision measurement of the pair production cross section of

Λ_{c}^{+}

provides unprecedented experimental information for the investigation of baryon production mechanism. In addition, the extraction of the polar angle distributions of the outgoing

Λ_{c}^{+}

in the annihilation of the electron–positron help to determine its electromagnetic form factors, which is currently the unique key to access the internal structure of the baryons. In this article, the measurement of

e^{+} e^{-} \to Λ_{c}^{+} {\bar{Λ}}_{c}^{-}

process via the initial state radiation technique at Belle detector and direct electron–positron annihilation at BESIII with discrete center-of-mass energies near threshold are briefly reviewed. In addition, the electromagnetic form factor ratios of

Λ_{c}^{+}

measured by BESIII are also investigated. A few theoretical models that parameterize the center-of-mass energy dependence of the cross section and electromagnetic form factors of baryon are introduced and the contributions of

Λ_{c}^{+}

data to them are discussed. Full article

(This article belongs to the Special Issue Baryon Structure: Form Factors and Polarization)

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8 pages, 353 KiB

Open AccessArticle

Dynamical Properties of Baryons

by Egle Tomasi-Gustafsson, Andrea Bianconi and Simone Pacetti

Symmetry 2021, 13(8), 1480; https://doi.org/10.3390/sym13081480 - 12 Aug 2021

Cited by 2 | Viewed by 1489

Abstract

The internal structure of composite particles is conveniently described in terms of form factors (FFs)—these are experimentally accessible in annihilation and scattering of elementary reactions, and are theoretically calculable by all models that describe the properties of particles. FFs depend only on one [...] Read more.

The internal structure of composite particles is conveniently described in terms of form factors (FFs)—these are experimentally accessible in annihilation and scattering of elementary reactions, and are theoretically calculable by all models that describe the properties of particles. FFs depend only on one kinematical variable,

q^{2}

. This is the four-momentum transferred by the virtual photon that carries the interaction. Important developments in accelerator and detector techniques have brought impressive advances, both by extending the kinematical region and by reaching a higher precision. A critical review on the underlying methods and findings in polarized and unpolarized experiments is presented. The unique role played by polarization in determining the ratio of electric to magnetic form factors in the space-like region, and the extraction of individual form factors in the whole kinematical region, are described. Recent results at electron accelerators and electron–positron colliders confirm the existence of periodical structure in the annihilation cross section. We suggest a global framework which describes the dynamical structure of charge distribution in baryons, in order to build a coherent view of the creation and annihilation of baryonic matter. Full article

(This article belongs to the Special Issue Baryon Structure: Form Factors and Polarization)

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Review

Jump to: Research

20 pages, 11201 KiB

Open AccessReview

Proton Electromagnetic Form Factors in the Time-like Region through the Scan Technique

by Lei Xia, Christoph Rosner, Yadi Wang, Xiaorong Zhou, Frank E. Maas, Rinaldo Baldini Ferroli, Haiming Hu and Guangshun Huang

Symmetry 2022, 14(2), 231; https://doi.org/10.3390/sym14020231 - 25 Jan 2022

Cited by 14 | Viewed by 2730

Abstract

For over 100 y, scientists have investigated the properties of the proton, which is one of the most abundant components of visible matter in the universe. Nevertheless, researchers do not fully understand many details about its internal structure and dynamics. Time-like electromagnetic form [...] Read more.

For over 100 y, scientists have investigated the properties of the proton, which is one of the most abundant components of visible matter in the universe. Nevertheless, researchers do not fully understand many details about its internal structure and dynamics. Time-like electromagnetic form factors are some of the observable quantities that can help us achieve a deeper understanding. In this review article, we present an overview of the current experimental status in this field, consisting of measurements of the time-like reactions

e^{+} e^{-} \to p \bar{p}

and

p \bar{p} \to e^{+} e^{-}

and future measurements of

p \bar{p} \to μ^{+} μ^{-}

. The focus is put on recent high-precision results of the reaction

e^{+} e^{-} \to p \bar{p}

that have been obtained after analyzing 688.5 pb

^{- 1}

of data taken at the BESIII experiment. They are compared to and put into perspective with results from previous measurements in this channel. We discuss the channels

p \bar{p} \to e^{+} e^{-}

and

p \bar{p} \to μ^{+} μ^{-}

in terms of the few existing, as well as future measurements, which the PANDA experiment will perform. Finally, we review several new theoretical models and phenomenological approaches inspired by the BESIII high-precision results and then discuss their implications for a deeper understanding of the proton’s structure and inner dynamics. Full article

(This article belongs to the Special Issue Baryon Structure: Form Factors and Polarization)

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15 pages, 573 KiB

Open AccessEditor’s ChoiceReview

Time-like Proton Form Factors with Initial State Radiation Technique

by Dexu Lin, Alaa Dbeyssi and Frank Maas

Symmetry 2022, 14(1), 91; https://doi.org/10.3390/sym14010091 - 6 Jan 2022

Cited by 6 | Viewed by 2107

Abstract

Electromagnetic form factors are fundamental quantities describing the internal structure of hadrons. They can be measured with scattering processes in the space-like region and annihilation processes in the time-like region. The two regions are connected by crossing symmetry. The measurements of the proton [...] Read more.

Electromagnetic form factors are fundamental quantities describing the internal structure of hadrons. They can be measured with scattering processes in the space-like region and annihilation processes in the time-like region. The two regions are connected by crossing symmetry. The measurements of the proton electromagnetic form factors in the time-like region using the initial state radiation technique are reviewed. Recent experimental studies have shown that initial state radiation processes at high luminosity electron-positron colliders can be effectively used to probe the electromagnetic structure of hadrons. The BABAR experiment at the B-factory PEP-II in Stanford and the BESIII experiment at BEPCII (an electron positron collider in the

τ

-charm mass region) in Beijing have measured the time-like form factors of the proton using the initial state radiation process

e^{+} e^{-} \to p \bar{p} γ

. The two kinematical regions where the photon is emitted from the initial state at small and large polar angles have been investigated. In the first case, the photon is in the region not covered by the detector acceptance and is not detected. The Born cross section and the proton effective form factor have been measured over a wide and continuous range of the the momentum transfer squared

q^{2}

from the threshold up to 42 (GeV/c)

^{2}

. The ratio of electric and magnetic form factors of the proton has been also determined. In this report, the theoretical aspect and the experimental studies of the initial state radiation process

e^{+} e^{-} \to p \bar{p} γ

are described. The measurements of the Born cross section and the proton form factors obtained in these analyses near the threshold region and in the relatively large

q^{2}

region are examined. The experimental results are compared to the predictions from theory and models. Their impact on our understanding of the nucleon structure is discussed. Full article

(This article belongs to the Special Issue Baryon Structure: Form Factors and Polarization)

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