Study of (2170) at BESIII

Guangshun Huang (on behalf of the BESIII Collaboration) University of Science and Technology of (USTC)

40th International Conference on High Energy Physics Jul. 28-Aug.6, 2020, Prague, Czech (virtual ICHEP2020) Outline

 Strangenium states  BEPCII/BESIII  (2170) studies at BESIII . e+e-  K+K- . e+e-   K+K- / K+K-K+K- . e+e-  / 

. e+e-  K+K-00  Summary

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 2 The strange quarkonium

s퐬

 s퐬 analogue of c퐜 and b퐛 , poorly known;  XYZ particles with strange quark as well?  a bridge between light and heavy quark. Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 3 (2170)/Y(2175)

PRD74, 091103 (2006) PRL 100, 102003 (2008)

BESII

PRD80, 031101 (2009) Eur. Phys. J. C72, 2008 (2012)

Y(2175), strange partner as Y(4260)

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 4 The nature of (2170)

PDG2018  From experiments:  Limited decay modes  Diverged mass & width

 On theory side:  s퐬 g hybrid 3 3  2 D1 or 3 S1 s퐬  Tetraquark  Molecular state 횲횲

 f0(980) resonance w/ FSI  Three-body system KK  Conclusion? Not yet.

 Not fully understood.

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 5 Bird View of BEPCII /BESIII Linac Storage ring

Beijing electron positron collider BEPCII Beam energy 1.0-2.3 GeV Energy spread: ퟓ. ퟏퟔ × ퟏퟎ−ퟒ Design luminosity 1  1033/cm2/s @ (3770) BESIII Achieved Apr.5, 2016! detector BSRF

2004: start BEPCII construction 2008: test run of BEPCII IHEP， 2009-now: BECPII/BESIII data taking 6 BEPC II: Large Crossing Angle, Double-ring

RF RF Beam energy: 1-2.3 GeV Compton back-scattering Luminosity: for high precision beam 1×1033 cm-2s-1 energy measurement Optimum energy: 1.89 GeV 0.1cm Energy spread: 5.16 ×10-4 No. of bunches: 8ns 93 22 mrad 1.5cm 2.5m Bunch length: 1.5 cm Total current: 0.91 A BESIII is here SR mode: [email protected]

Jul.31, 2020, Cloud IP G.S. Huang: phi(2170) @BESIII 7 BESIII Detector MDC TOF BTOF: two layers ETOF: 48 for each

R inner: 63mm ; R outer: 810mm CsI(Tl) EMC Length: 2582 mm Layers: 43

RPC MUC

Crystals: 28 cm(15 X0)

Barrel: |cos|<0.83

BMUC: 9 layers – 72 modules Endcap: EMUC: 8 layers – 64 modules 0.85 < |cos| < 0.93 8 BESIII Detector

MDC MDC EMC Exps. Wire dE/dx Energy resolution resolution resolution

CLEO 110 m 5% 2.2-2.4 %

Babar 125 m 7% 2.67 % TOF Belle 130 m 5.6% 2.2 % Exps. time resolution BESIII <5% （XYZ 115 m 2.3% CDFII 100 ps (Bhabha) data） Belle 90 ps BESIII 68 ps (BTOF) • New ETOF (MRPC) (XYZ 100  65 ps • Cylindrical GEM/New Inner MDC Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII data) (ETOF) 9 Europe (16) Germany(6): Bochum University, GSI Darmstadt, Helmholtz Institute Mainz, Johannes Gutenberg University of Mainz, Universitaet Giessen,University of Münster Italy(3): Ferrara University, INFN, University of Turin Mongolia(1) Netherlands(1 ):KVI/University of Groningen Institute of Physics and Technology Russia(2): Budker Institute of Nuclear Physics, Dubna JINR Korea(1) Sweden(1):Uppsala University Seoul USA(5) Turkey (1):Turkish Accelerator Center Particle Factory Group Carnegie Mellon University UK(2): University of Manchester, University of Oxford Japan(1) Indiana University Pakistan(3) Tokyo University University of Hawaii COMSATS Institute of Information Technology Thailand(1) University of Minnesota University of the Punjab, Suranaree University of Technology University of Rochester University of Lahore India(1) Indian Institute of Technology madras China (45) Beijing Institute of Petro-chemical Technology, , China Center of Advanced Science and Technology, , Normal University, , Hangzhou Normal University, Normal University, Henan University of Science and Technology, Huazhong Normal University, Huangshan College, University, Hunan Normal University, Institute of High Energy Physics, Institute of modern physics, University, , Normal University, , Nanjing Normal University, , , North China Electric Power University, , Qufu Normal University, University, Shanxi Normal University, University, Normal University, , Jiao Tong Univeristy, Soochow University, South China Normal University, , Sun Yat-sen University, , University of Chinese Academy of Sciences, University of http://bes3.ihep.ac.cn Jinan, University of Science and Technology of China, University of Science and Technology Liaoning, The Collaboration has ~500 members University of South China, , Xinyang Normal University, University, from 74 institutions in 15 countries. 10 Data used in this talk • 650 pb-1 in 2.0 – 3.08 GeV collected in 2015.

7 Apr. 2016, Mainz G.S. Huang: Timelike Form factors @BESIII 11 e+ e- → K+ K-  K+K- @ (2170)  Controversial in theory;  isoscalar: w*/*;  isovector: r*.  s(e+e-→ K+K- ) measured in [2.0-3.08] GeV: PRD99, 032001 (2019)

3 S1횲횲

PRD96, 074027 (2017)

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 12 e+ e- → K+ K-  (2170): resonance of KK

PRD79, 034018 (2009) 횲횲 threshold PRD100, 022009 (2019) s=3.08 GeV

 A hint for a resonance around 횲횲 threshold:  Mass = 22323.5MeV;  Width < 20 MeV  Three-body system KK: ?

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 13 e+ e- →2(K+ K-)

횲횲 threshold PRD100, 022009 (2019) PRD100, 022009 (2019)

e+ e- → 횲횲  Both K+K- and 2(K+K-) show similar enhancement around 2.2324 GeV;  횲횲 threshold effect?  Any other explanations?

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 14 e+ e- →  /    /  modes: isoscalar  * or w* (OZI suppressed)  Parameter info helpful  Tetraquark favors  and 

PLB669, 160 (2008)

--  1 s풔 g hybrid has larger G and smaller G

1-- s풔 g alt 2.2 GeV Standard IKP Ding PRD59, 034016 (1999) PLB650,390(2007)  2 19 11 3 1.2  0.01 2 0.1 0.02 0.4 Br()/Br() 200 9.5 110 150 3

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 15 e+ e- →   e+ e-→ with →K+K-, →g +- PRD102, 012008 (2020) s=2.125 GeV  

M=2177.54.819.5 MeV (2170) para. G = 149.015.68.9 MeV

(2170)   ?

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 16  and   e+e- →  and   BaBar  : 1.70.71.3 eV, [PRD77, 092002(2008)]  BESIII : 7.10.70.7 eV, [PRD102,012008(2020)] 퐵푟 [휙 2170 →휙휂]Γ 푒푒 =0.240.21 퐵푟 [휙 2170 →휙휂′]Γ푒푒  With e+e- →  prevailing, can (2170) still be an 1-- s풔 g ?

1-- s풔 g alt 2.2GeV standard IKP Ding PRD59, 034016 (1999) PLB650,390(2007)  2 19 11 3 1.2  0.01 2 0.1 0.02 0.4 Br()/Br() 200 9.5 110 150 3

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 17 - mixing

 SU(3) quark model, SU(3) singlet state 0 and octet state 8, ퟏ 휼 = (풖풖 + 풅풅 ) and 휼 = 풔풔 .  = -11.7. 풒 ퟐ 풔

 Resonance decay

PRD58, 114006 (1998) r: 0.810.08 < r: 1.930.23 (in 10-4)

 (2170) →  / , arXiv:2007.14893[hep-lat] Jul.29, 2020, 퐵푟 [휙 2170 →휙휂]Γ 푒푒 =0.230.100.18 퐵푟 [휙 2170 →휙휂′]Γ푒푒 Can be understood as either 3S s풔 or 1-- s풔 g along with mixing. Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 18 e+ e- → K K    e+e- → KK: important to distinguish (2170) theory models * * 3  K K : s퐬 g (unfavored), 3 S1 (favored)  KK1(1400): s퐬 g (favored) 3  KK(1460): s퐬 g (unfavored), 2 D1 (favored) * *  BaBar: K (892), K2 (1430), K1(1270) and K1(1400)  J/ → (2170) → K*K*  BESII: 58M J/, an upper limit

PLB685, 27 (2010) K1(1270) K*(892) BESII

K1(1400)

* K2 (1430) BaBar: PRD86, 012008 (2012)

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 19 e+ e- → K+ K- 0 0

s=2.125 GeV PhysRevLett.124, 112001 (2020)  PWA at multiple energies in [2.0, 2.644] GeV  No significant signal observed for e+e-→KK*(1410).  Born cross section measured for intermediate states as well.

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 20 e+ e- → K+ K- 0 0 PhysRevLett.124, 112001 (2020) KK1(1400) KK(1460)

K*(892)K*(892) KK1(1270)

(2170) para.

Fitting results  Dots: BESIII data  Black curves: fit results  Red long-dashed: (2170)  Green shot-dashed: 1/sn  Blue dash-dotted: interference (2170)  K K1(1400) / K K(1460)? Likely! Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 21 Results in a glance

• Hopefully help to know the (2170) better? Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 22 Summary

 Strangenium s퐬 is a terra incognita to be explored;  BESIII provides experimental data on (2170);  May help to resolve the property of (2170): 3  Pure 3 S1 s퐬 ? 3  Pure 2 D1 s퐬 ?  Molecular state 횲횲 ?  Three-body system KK ?  1-- s퐬 g hybrid ?  Tetraquark ?  Mixing state ?  More studies needed; some ongoing at BESIII;  Revisits/Inputs from theory are highly desired!

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 23 ~650 pb-1 total BESIII data in [2-3.08] GeV (this talk)

Access by initial state radiation

4230+4260 J/ 1.9 fb-1 10x109

4190-4300 3.5 fb-1

~16 fb-1 XYZ data 4fb-1 (2020)

Jul.31, 2020, Cloud 24 -- 3 1 3 S1 s풔

 Fraction Gi/G: weakly model & input parameters dependent  Dominant decay modes: KK*(1410) & K*K*  KK: sharp distinction ? Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 25 3 (2170) as pure 3 S1 s퐬

3 Decay modes 3 S1 s퐬

3  Reduction to Absurdity P0 model Lanzhou  33S s퐬 : G > G KK 0 35.8 1 K*K* KK1(1400)  Exp. (2170) @ KK (1400) K*K* 102 45.7 1  Exp. no (2170) @ K*K* KK(1460) 29 30.9  Exp. similar e * eff KK (1410) 93 49.3 3  (2170) as pure 3 S1 s퐬 ??? KK (1270) 58 7.1 1  Similar check for several modes KK (1400) 26 41.4 1  KK*(1410): No (2170) * 25.2 KK2 (1430) 9.0  KK(1460): Yes (2170)  21 0.3 3  (2170) as pure 3 S1 s퐬 : ??? ’ 11 0.8

Jul.31, 2020, Cloud G.S. Huang: phi(2170) @BESIII 26