1
|
Abstract
The Lagrangian that defines quantum chromodynamics (QCD), the strong interaction piece of the Standard Model, appears very simple. Nevertheless, it is responsible for an astonishing array of high-level phenomena with enormous apparent complexity, e.g., the existence, number and structure of atomic nuclei. The source of all these things can be traced to emergent mass, which might itself be QCD’s self-stabilising mechanism. A background to this perspective is provided, presenting, inter alia, a discussion of the gluon mass and QCD’s process-independent effective charge and highlighting an array of observable expressions of emergent mass, ranging from its manifestations in pion parton distributions to those in nucleon electromagnetic form factors.
Collapse
|
2
|
Isupov EL, Chesnokov VV, Golovach EN, Golubenko AA, Ishkhanov BS, Klimenko VA. Electromagnetic form factors of nucleon resonances from CLAS. EPJ Web Conf 2019. [DOI: 10.1051/epjconf/201922202003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Exclusive single and double meson photo- and electroproduction reactions are the largest sources of information on the spectrum and structure of nucleon resonances. The excited states of the nucleon manifest as a complex interplay between the inner core of three dressed quarks and the external meson-baryon cloud. Various N* with distinctively different structure appear as unique laboratory where many features of strong QCD can be explored. With combination of nearly 4π acceptance of the CLAS detector and continuous electron beam (Jefferson Lab, USA) it is possible to obtain physics observables of the major reaction channels in the N* excitation region. The results on the electromagnetic transition form factors of N(1440)1/2+ and N(1520)3/2- are presented.
Collapse
|
3
|
Mokeev VI, Aznauryan IG, Burkert VD, Gothe RW. Recent results on the nucleon resonance spectrum and structure from the CLAS detector. EPJ Web of Conferences 2016. [DOI: 10.1051/epjconf/201611301013] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
|
4
|
Abstract
The composite nature of baryons manifests itself in the existence of a rich spectrum of excited states, in particular in the important mass region 1-2 GeV for the light-flavoured baryons. The properties of these resonances can be identified by systematic investigations using electromagnetic and strong probes, primarily with beams of electrons, photons, and pions. After decades of research, the fundamental degrees of freedom underlying the baryon excitation spectrum are still poorly understood. The search for hitherto undiscovered but predicted resonances continues at many laboratories around the world. Recent results from photo- and electroproduction experiments provide intriguing indications for new states and shed light on the structure of some of the known nucleon excitations. The continuing study of available data sets with consideration of new observables and improved analysis tools have also called into question some of the earlier findings in baryon spectroscopy. Other breakthrough measurements have been performed in the heavy-baryon sector, which has seen a fruitful period in recent years, in particular at the B factories and the Tevatron. First results from the large hadron collider indicate rapid progress in the field of bottom baryons. In this review, we discuss the recent experimental progress and give an overview of theoretical approaches.
Collapse
Affiliation(s)
- V Crede
- Florida State University, Department of Physics, Tallahassee, FL 32306, USA.
| | | |
Collapse
|
5
|
Krambrich D, Zehr F, Fix A, Roca L, Aguar P, Ahrens J, Annand JRM, Arends HJ, Beck R, Bekrenev V, Boillat B, Braghieri A, Branford D, Briscoe WJ, Brudvik J, Cherepnya S, Codling R, Downie EJ, Dexler P, Glazier DI, Grabmayr P, Gregor R, Heid E, Hornidge D, Jahn O, Kashevarov VL, Knezevic A, Kondratiev R, Korolija M, Kotulla M, Krusche B, Kulbardis A, Lang M, Lisin V, Livingston K, Lugert S, MacGregor IJD, Manley DM, Martinez M, McGeorge JC, Mekterovic D, Metag V, Nefkens BMK, Nikolaev A, Pedroni P, Pheron F, Polonski A, Prakhov SN, Price JW, Rosner G, Rost M, Rostomyan T, Schumann S, Sober D, Starostin A, Supek I, Tarbert CM, Thomas A, Unverzagt M, Walcher T, Watts DP. Beam-helicity asymmetries in double-pion photoproduction off the proton. Phys Rev Lett 2009; 103:052002. [PMID: 19792489 DOI: 10.1103/physrevlett.103.052002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2008] [Revised: 06/18/2009] [Indexed: 05/28/2023]
Abstract
Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels gamma[over -->]p-->pi(+)pi(0)n, gamma[over -->]p-->pi(0)pi(0)p, and gamma[over -->]p-->pi(+)pi(-)p. The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of pi(0) mesons were detected in a 4pi electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction dynamics.
Collapse
Affiliation(s)
- D Krambrich
- Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, Mainz, Germany
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
6
|
Abstract
We study the low-lying baryon spectrum (up to 2.2 GeV) provided by experiments and different quark models using statistical tools which allow us to postulate the existence of missing levels in spectra. We confirm that the experimental spectrum is compatible with random matrix theory, the paradigmatic model of quantum chaos, and we find that the quark models are more similar to a Poisson distribution, which is not compatible with what should be expected in a correlated spectrum. From our analysis it stems that the spectral fluctuation properties of quark-model spectra are incompatible with experimental data. This result can be used to enlighten the problem of missing resonances.
Collapse
Affiliation(s)
- C Fernández-Ramírez
- Instituto de Estructura de la Materia, CSIC, Serrano 123, E-28006 Madrid, Spain
| | | |
Collapse
|
7
|
Ablikim M, Bai JZ, Ban Y, Bian JG, Cai X, Chang JF, Chen HF, Chen HS, Chen HX, Chen JC, Chen J, Chen J, Chen ML, Chen YB, Chi SP, Chu YP, Cui XZ, Dai HL, Dai YS, Deng ZY, Dong LY, Du SX, Du ZZ, Fang J, Fang SS, Fu CD, Fu HY, Gao CS, Gao YN, Gong MY, Gong WX, Gu SD, Guo YN, Guo YQ, Guo ZJ, Harris FA, He KL, He M, He X, Heng YK, Hu HM, Hu T, Huang GS, Huang L, Huang XP, Ji XB, Jia QY, Jiang CH, Jiang XS, Jin DP, Jin S, Jin Y, Lai YF, Li F, Li G, Li HB, Li HH, Li J, Li JC, Li QJ, Li RB, Li RY, Li SM, Li WG, Li XL, Li XQ, Li XS, Liang YF, Liao HB, Liu CX, Liu F, Liu F, Liu HM, Liu JB, Liu JP, Liu RG, Liu ZA, Liu ZX, Lu F, Lu GR, Lu JG, Luo CL, Luo XL, Ma FC, Ma JM, Ma LL, Ma QM, Ma XY, Mao ZP, Mo XH, Nie J, Nie ZD, Olsen SL, Peng HP, Qi ND, Qian CD, Qin H, Qiu JF, Ren ZY, Rong G, Shan LY, Shang L, Shen DL, Shen XY, Sheng HY, Shi F, Shi X, Sun HS, Sun SS, Sun YZ, Sun ZJ, Tang X, Tao N, Tian YR, Tong GL, Varner GS, Wang DY, Wang JX, Wang JZ, Wang K, Wang L, Wang LS, Wang M, Wang P, Wang PL, Wang SZ, Wang WF, Wang YF, Wang Z, Wang Z, Wang Z, Wang ZY, Wei CL, Wei DH, Wu N, Wu YM, Xia XM, Xie XX, Xin B, Xu GF, Xu H, Xu Y, Xue ST, Yan ML, Yang F, Yang HX, Yang J, Yang SD, Yang YX, Ye M, Ye MH, Ye YX, Yi LH, Yi ZY, Yu CS, Yu GW, Yuan CZ, Yuan JM, Yuan Y, Yue Q, Zang SL, Zeng Y, Zeng Y, Zhang BX, Zhang BY, Zhang CC, Zhang DH, Zhang HY, Zhang J, Zhang JY, Zhang JW, Zhang LS, Zhang QJ, Zhang SQ, Zhang XM, Zhang XY, Zhang YJ, Zhang YY, Zhang Y, Zhang ZP, Zhang ZQ, Zhao DX, Zhao JB, Zhao JW, Zhao MG, Zhao PP, Zhao WR, Zhao XJ, Zhao YB, Zhao ZG, Zheng HQ, Zheng JP, Zheng LS, Zheng ZP, Zhong XC, Zhou BQ, Zhou GM, Zhou L, Zhou NF, Zhu KJ, Zhu QM, Zhu YC, Zhu YS, Zhu Y, Zhu ZA, Zhuang BA, Zou BS. Observation of two new N* peaks in J/psi-->ppi-n and ppi+n decays. Phys Rev Lett 2006; 97:062001. [PMID: 17026161 DOI: 10.1103/physrevlett.97.062001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2004] [Indexed: 05/12/2023]
Abstract
The decay J/psi-->NNpi provides an effective isospin 1/2 filter for the piN system due to isospin conservation. Using 58x10(6) J/psi decays collected with the Beijing Electromagnetic Spectrometer at the Beijing Electron Positron Collider, more than 100 thousand J/psi-->ppi-n+c.c. events are obtained. Besides the two well-known N* peaks at around 1500 MeV/c2 and 1670 MeV/c2, there are two new, clear N* peaks in the ppi invariant mass spectrum around 1360 MeV/c2 and 2030 MeV/c2 with statistical significance of 11sigma and 13sigma, respectively. We identify these as the first direct observation of the N*(1440) peak and a long-sought missing N* peak above 2 GeV/c2 in the piN invariant mass spectrum.
Collapse
Affiliation(s)
- M Ablikim
- Institute of High Energy Physics, Beijing 100039, People's Republic of China
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
8
|
Strauch S, Berman BL, Adams G, Ambrozewicz P, Anghinolfi M, Asavapibhop B, Asryan G, Audit G, Avakian H, Bagdasaryan H, Baillie N, Ball JP, Baltzell NA, Barrow S, Batourine V, Battaglieri M, Beard K, Bedlinskiy I, Bektasoglu M, Bellis M, Benmouna N, Bennhold C, Biselli AS, Boiarinov S, Bouchigny S, Bradford R, Branford D, Briscoe WJ, Brooks WK, Bültmann S, Burkert VD, Butuceanu C, Calarco JR, Careccia SL, Carman DS, Carnahan B, Chen S, Cole PL, Coleman A, Coltharp P, Cords D, Corvisiero P, Crabb D, Crannell H, Cummings JP, Degtyarenko PV, Denizli H, Dennis L, De Sanctis E, Deur A, Devita R, Dharmawardane KV, Dhuga KS, Djalali C, Dodge GE, Donnelly J, Doughty D, Dragovitsch P, Dugger M, Dytman S, Dzyubak OP, Egiyan H, Egiyan KS, Elouadrhiri L, Empl A, Eugenio P, Fatemi R, Fedotov G, Feldman G, Feuerbach RJ, Fix A, Forest TA, Funsten H, Gavalian G, Gilfoyle GP, Giovanetti KL, Girod FX, Goetz JT, Gothe RW, Griffioen KA, Guidal M, Guler N, Guo L, Gyurjyan V, Hadjidakis C, Hakobyan RS, Hardie J, Heddle D, Hersman FW, Hicks K, Hleiqawi I, Holtrop M, Hu J, Huertas M, Hyde-Wright CE, Ilieva Y, Ireland DG, Ishkhanov BS, Ito MM, Jenkins D, Jo HS, Joo K, Juengst HG, Kellie JD, Khandaker M, Kim KY, Kim K, Kim W, Klein A, Klein FJ, Klimenko AV, Klusman M, Kossov M, Kramer LH, Kubarovsky V, Kuhn J, Kuhn SE, Lachniet J, Laget JM, Langheinrich J, Lawrence D, Lee T, Lima ACS, Livingston K, Lukashin K, Manak JJ, Marchand C, McAleer S, McKinnon B, McNabb JWC, Mecking BA, Mestayer MD, Meyer CA, Mibe T, Mikhailov K, Minehart R, Mirazita M, Miskimen R, Mokeev V, Morrow SA, Muccifora V, Mueller J, Mutchler GS, Nadel-Turonski P, Napolitano J, Nasseripour R, Niccolai S, Niculescu G, Niculescu I, Niczyporuk BB, Niyazov RA, Nozar M, O'rielly GV, Osipenko M, Ostrovidov AI, Park K, Pasyuk E, Paterson C, Philips SA, Pierce J, Pivnyuk N, Pocanic D, Pogorelko O, Polli E, Pozdniakov S, Preedom BM, Price JW, Prok Y, Protopopescu D, Qin LM, Raue BA, Riccardi G, Ricco G, Ripani M, Ritchie BG, Roberts W, Ronchetti F, Rosner G, Rossi P, Rowntree D, Rubin PD, Sabatié F, Salgado C, Santoro JP, Sapunenko V, Schumacher RA, Serov VS, Shafi A, Sharabian YG, Shaw J, Skabelin AV, Smith ES, Smith LC, Sober DI, Stavinsky A, Stepanyan SS, Stepanyan S, Stokes BE, Stoler P, Strakovsky II, Suleiman R, Taiuti M, Taylor S, Tedeschi DJ, Thoma U, Thompson R, Tkabladze A, Tkachenko S, Todor L, Tur C, Ungaro M, Vineyard MF, Vlassov AV, Wang K, Weinstein LB, Weygand DP, Williams M, Wolin E, Wood MH, Yegneswaran A, Yun J, Zana L, Zhang J. Beam-helicity asymmetries in double-charged-pion photoproduction on the proton. Phys Rev Lett 2005; 95:162003. [PMID: 16241787 DOI: 10.1103/physrevlett.95.162003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2005] [Indexed: 05/05/2023]
Abstract
Beam-helicity asymmetries for the two-pion-photoproduction reaction gammap-->ppi(+)pi(-) have been studied for the first time in the resonance region for center-of-mass energies between 1.35 and 2.30 GeV. The experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer using circularly polarized tagged photons incident on an unpolarized hydrogen target. Beam-helicity-dependent angular distributions of the final-state particles were measured. The large cross-section asymmetries exhibit strong sensitivity to the kinematics and dynamics of the reaction. The data are compared with the results of various phenomenological model calculations, and show that these models currently do not provide an adequate description for the behavior of this new observable.
Collapse
Affiliation(s)
- S Strauch
- The George Washington University, Washington, District of Columbia 20052, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|