Measurement of proton electromagnetic form factors in the time-like region using initial state radiation at BESIII

M Ablikim,R Baldini Ferroli,Z Wang,J.L Liu,M Lellmann,D Bettoni,B Kopf,M Rolo,L Xia,S Janchiv,G Cibinetto,Y Jin,V Prasad,H.J Wang,A Gilman,J Libby,H Leithoff,W.D Li,Meng Wang,X Pan,J Tang,B Wang,W.H Wang,L.K Li,W Gradl,M Fritsch,X.L Wang,F Yan,Q Zhao,Fang Liu,S Nisar,P Weidenkaff,L Gong,B.J Liu,M Irshad,H Zhang,S.B Liu,J.Q Zhang,P Larin,Feng Liu,A Pathak,M Greco,S Marcello,L Koch,J Dong,A Yuncu,V Rodin,M Wang,Y Ding,Ziyi Wang,J.J Zhang,L Wollenberg,Huihui Liu,Y.B Chen,S Zhang,N Cao,C.H Li,K Wang,S Malde,Y Liu,Y.D Wang,Y Hu,T Johansson,H Cai,I Denysenko,M Rump,M Shao,A Denig,J.Q Li,Shuai Liu,A.Q Zhang,C Schnier,D Liu,C Dong,K Ravindran,J Fang,Xu Yan,F De Mori,G Chen,T Hussain,F Cossio,L Sun,Lei Li,X Zeng,L Yang,C Li,M Destefanis,O Bakina,M Albrecht,J.B Liu,F Feldbauer,W Xu,Y Pan,X Cai,K.Y Liu,Q An,S Spataro,Ling Zhao,A Rivetti,Y Ban,N Berger,L Yan,I Balossino,W Ikegami Andersson,T Liu,H Muramatsu,P Adlarson,H.P Wang,Y Zhang,Y.F Wang,H Liang,M Bertani,X.R Chen,Shulei Zhang,K Schoenning,W.G Li,J.Y Zhang,Cheng Li,Z.Y Li,M Himmelreich,P Kiese,C.X Liu,M Kuessner,Y Zheng,M Maggiora,T Yu,V Thoren,A Guskov,J.L Zhang,Y Fang,M Wolke,Q Zhou,Z.Y Wang,K Liu,J.S Li,R Kappert,Jianyu Zhang,K Peters,S Jin,F Weidner,A Mangoni,G Mezzadri,G Rong,Y.Y Wang,T Held,S Pacetti,S Gu,J Bloms,D.Y Wang,G Felici,K Zhu,Lei Zhang,B Zhong,Z Qian,F.C Ma,Y Nefedov,Q Ouyang,T Holtmann,W Imoehl,S.J Chen,A Sarantsev,F Nerling,Z Ning,B.X Zhang,F.H Liu,A Calcaterra,H.H Zhang,C.W Wang,Z Wu,H.M Liu,R Kliemt,H.Y Zhang,M Kuemmel,Y Lu,S Ahmed,Z.Q Liu,X Shi,M.H Liu,Y Yuan,J Zhao,L Fava,M Ye,C Geng,H.J Li,J.Y Liu,W Shan,Y.B Liu,H Li,Jiawei Zhang,P.R Li,S Sosio,M.Z Wang,D.M Li,T Hu,Z Huang,M Qi,S Nakhoul,I Garzia,A Lavania,U Wiedner,Guangyi Zhang,Zongyuan Wang,Y Wang,A Zhemchugov,Y.Q Wang,J Pettersson,M Pelizaeus,Y.T Zhang,W Wang,S Jaeger,Y Zeng,M Scodeggio,J.W Zhang,T Luo,G Zhao,T Sun,R Kiuchi,L.L Ma,Z.H Zhang,Z.A Liu,A Khoukaz,Q Liu,Y Schelhaas,J.L Li,Yifan Yang,M.L Chen,W Kühn,R Aliberti,X Wang,L Liu,S Lusso,H.B Li,A Dbeyssi,R Farinelli,X.D Zhang,G Li,H Xiao,Z.J Chen,Huanhuan Liu,K Goetzen,W.P Wang,M Kavatsyuk,Z.Y Zhang,X.Y Zhang,N Hüsken,M.H Ye,K Begzsuren,L Lavezzi,I Uman,X Dong,T Lenz,Z Jiao,G Yu,Y Bai,A Bortone,Yao Zhang,Y Gao,F Li,Y.H Zhang,S.F Zhang,X Liu,Q Ji,Yi Zhang,Ch Rosner,G Wilkinson,S.Y Li,P.L Liu,L.Q Zhang,C Herold,Yan Zhang,B Zheng,S Maldaner,F Bianchi,X Wu,H.B Liu,R Poling,H.S Chen,D.Y Chen,W.M Liu,X.L Li,A Amoroso,Xinxin Ma ,Xiaoyan Ma ,S Q Qu ,F X Lu ,R Q Ma ,J P Zheng ,G F Xu ,G S Huang ,C L Luo ,Y Y Ji ,Y P Guo ,M Y Dong ,R S Shi ,J L Ping ,N Kalantar‐Nayestanaki ,P W Luo ,W Y Han ,X P Qin ,C X Yu ,S Y Xiao ,T J Min ,R G Ping ,C J Tang ,Z H Qin ,J D Lu ,S L Olsen ,X S Kang ,L Z Liao ,R E De Boer ,A N Zhu ,W H Tian ,I B Nikolaev ,Qin Liu ,Y Mao ,X R Zhou ,X Y Shen ,S L Yang ,W S Cheng ,X S Jiang ,X Q Yuan ,G Y Tang ,C D Fu ,Y J Sun ,Q P Ji ,C X Yue ,H M Hu ,L M Gu ,T J Zhu ,X K Zhou ,Tao Han ,X L Ji ,Y T Gu ,Ké Li ,E Gersabeck ,S J Qian ,S J Zhao ,T Y Qi ,W Y Sun ,Y X Tan ,N Yu Muchnoi ,J G Lu ,C P Shen ,L Q Huang ,F H Heinsius ,K H Qi ,L B Guo ,Liang-Liang Wang ,Y Sun ,D C Shan ,W C Yan ,Y J Mo ,Xiongfei Wang ,X C Dai ,Y C Xu ,R E Mitchell ,H F Shen ,G R Liao ,K J Zhu ,J X Teng ,X B Ji ,S A Çetin ,Y Zhu ,F E Maas ,H R Qi ,S S Fang ,Z Zhao ,D H Wei ,P X Shen ,H S Sang ,Jian Wu ,X H Sun ,Y Xie ,X Y Shan ,X R Lyu ,C F Qiao ,Y Z Sun ,J Lange ,M X Luo ,Miao Ma ,X L Luo ,X L Lu ,Q J Xu ,L H Wu ,D J White ,G A Chelkov ,J F Shangguan ,P Patterí ,H Lu ,J F Sun ,J W Zhao ,T Y Xing ,Z Meng ,M G Kurth ,B C Ke ,Z P Mao ,M H Gu ,М Н Ачасов ,F A Harris ,Y H Tan ,Xiaoyü Li ,W Qian ,H C Shi ,G X Sun ,Hailong Ma ,C Z Yuan ,S H Zhu ,Dong Liu ,W M Song ,Z Y Deng ,F F Sui ,J H Feng ,J J Song ,Zhong Chen ,A Q Guo ,Z Y Yuan ,G Y Hou ,G F Cao ,X H Mo ,Y X Song ,J J Lane ,S P Wen ,O B Kolcu ,Y F Liang ,H X Yang ,X H Xie ,H L Dai ,Y K Heng ,S X Du ,Zhao Liu ,D X Lin ,X P Xu ,Z Y You ,Z H Lei ,I K Keshk ,D V Dedovich ,C Heinz ,J F Qiu ,W J Zhu ,Z A Zhu ,Y Huang ,X H Li ,J G Messchendorp ,X F Cui ,K H Rashid ,X S Qin ,K L He ,Q M Ma ,R A Briere ,M G Zhao ,Z T Sun ,A Kupść ,B X Yu ,M Q Jing ,C F Redmer ,Y L Fan ,Zhou Li ,C Q Feng ,J B Jiao ,J F Hu ,X H Bai ,Ye Zhao ,P Ge ,S S Sun ,Y B Zhao ,C Y Guan ,C X Lin ,X Lou ,M R An ,R P Guo ,Y S Gao ,J F Chang ,Jing Zhu ,Yuan Li ,Z Yang ,H K Sun ,Y R Hou ,Y P Lu ,H B Jiang ,X T Huang ,B S Zou ,Z J Xiao ,J H Yin ,Y T Liang ,I R Boyko ,Q A Malik ,A A Zafar ,W B Yan ,J S Yu ,L J Wu ,H Peng ,X Q Hao ,W L Chang ,Z L Hou ,K X Su ,W X Gong ,P P Su ,H J Yang ,J H Zou

doi:10.1016/j.physletb.2021.136328

Abstract

The electromagnetic process e+e−→pp¯ is studied with the initial-state-radiation technique using 7.5 fb−1 of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/c2 using the pp¯ invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.

Highlights

The investigation of nucleon structure through electromagnetic probes plays a central role in the understanding of strong interactions
A total integra√ted luminosity of experiment at s between 3.773 and 4.600 GeV, the ratio of the proton electromagnetic form factors (FFs) absolute values, the Born cross section for the process e+e− → p pand the effective FF of the proton are measured from the p pthreshold to 3.0 GeV/c2 through the ISR process e+e− → p pγ
This measurement confirms an enhancement of the ratio of FFs in the M ppregion below 2.2 GeV/c2 previously observed by BABAR and BESIII

Summary

Introduction

The investigation of nucleon structure through electromagnetic probes plays a central role in the understanding of strong interactions. The ISR technique with an undetected photon has been used in our previous study [25] of the process e+e− → p pγ to measure the TL proton FFs. In that analysis, events were selected where the ISR photon was emitted at small polar angles (SA-ISR), and the threshold region below 2 GeV/c was not accessible due to the limited angular acceptance of the BESIII tracking system. Letter we extend our previous study to the case where the ISR photon is emitted at large polar angles (LA-ISR) and is detected This allows access to the threshold region and provides measurements of the proton helicity angle θp in the full M pprange, in contrast to the analysis of the SA-ISR events. In the study of the e+e− → p pγ process, the cross section for the process e+e− → p pand the ratio of the proton FFs ca√n be measured over the full M pprange from the p pthreshold to s

BESIII experiment and data sets

Background estimation

Ratio of proton form factors

Findings

Summary