Physics overview
on the BESIII experiment
Xiao-Rui Lyu

University of Chinese Academy of Sciences (UCAS)(On behalf of the BESIII collaboration)
Xiao-Rui LYU

Lomonosov Conference, 2021

Outline• Introduction to BEPCII/BESIII• Selected highlights of BESIII results– charmed hadron decays– charmonium- and strangenium-like states– light hadrons– form factors of baryons• Prospects for the future• SummaryDisclaimer: selective overview, not comprehensive;
More results will be covered in the following BESIII talks.
SESSION 22.08. A (Colliders: New Physics)
SESSION 23.08. C (Physics at Colliders)
SESSION 25.08. A (Charm Physics)

Xiao-Rui LYU

Lomonosov Conference, 2021

Frontiers of the Standard Model

non-perturbative QCD

Xiao-Rui LYU

Lomonosov Conference, 2021

Beijing Electron Positron Collider (BEPCII)
beam energy: 1.0 – 2.3(2.45) GeV

LINAC

e+

BESIII
detectore-

2020: energy upgrade to 2.45 GeV
2004: started BEPCII upgrade,
BESIII construction
2008: test run
2009 - now: BESIII physics run••

Xiao-Rui LYU

Lomonosov Conference, 2021

1989-2004 (BEPC):
Lpeak=1.0x1031 /cm2s
2009-now (BEPCII):
Lpeak= 1.0 x1033/cm2(4/5/2016)

The BESIII detector
NIM A614, 345 (2010)

The new BESIII detector is hermetic for neutral and charged particle
with excellent resolution, PID, and large coverage.
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Lomonosov Conference, 2021

BESIII Collaboration
Europe (17/115)

USA(4/8)

Germany (6): Bochum University,
GSI Darmstadt, Helmholtz Institute Mainz, Johannes
Gutenberg University of Mainz, Universitaet Giessen,Universityof Münster
Italy (3): Ferrara University, INFN, University of Torino
Netherlands (1):KVI/University of Groningen
Russia (2): Budker Institute of Nuclear Physics, Dubna JINR
Sweden (1):Uppsala University
Turkey (1):Turkish Accelerator Center Particle
Factory GroupUK (2): University of Manchester, University of Oxford

Poland (1)National Centre for Nuclear Research

Asia (6/10)
Pakistan (2): COMSATS Institute of Information
Technology
University of the Punjab, University of Lahore
Mongolia (1): Institute of Physics and Technology
Korea (1): Chung-Ang University
India (1): Indian Institute of Technology madras
Thailand (1): Suranaree University of Technology~500 members
from 76 institutions in 16 countries

Xiao-Rui LYU

Carnegie Mellon University
Indiana University
University of Hawaii
University of Minnesota

South America (1/1)
Chile: University of Tarapaca

China (48/367)
Institute of High Energy Physics (146), other units(221): Beijing Institute of Petrochemical Technology, Beihang University,
China Center of Advanced Science and Technology, Fudan University,
Guangxi Normal University, Guangxi University,
Hangzhou Normal University, Henan Normal University,
Henan University of Science and Technology,
Huazhong Normal University, Huangshan College, Hunan University,
Hunan Normal University, Henan University of Technology
Institute of modern physics, Jilin University, Lanzhou University, Liaoning
Normal University, Liaoning University, Nanjing Normal University, Nanjing
University, Nankai University, North China Electric Power University,
Peking University, Qufu normal university, Shanxi University,
Shanxi Normal University, Sichuan University, Shandong Normal University,
Shandong University, Shanghai Jiaotong Univeristy, Soochow University,
South China Normal University, Southeast University, Sun Yat-sen University,
Tsinghua University, University of Chinese Academy of Sciences, University of
Jinan, University of Science and Technology of China,
University of Science and Technology Liaoning,
University of South China, Wuhan University, Xinyang Normal University,
Zhejiang University, Zhengzhou University,YunNan University , China Universityof Geosciences

Lomonosov Conference, 2021

BESIII Data Samples
Totally about 32 fb-1
in 12 year running

400
PRL

350
300

PRL+Other308

Publications

250

270

200

172

150
110

100
50

Xiao-Rui LYU

0

4
2

209

134

77
56 65 68
47
44
36
32
24 30
15
5 10 13 18

20
10
20
11
20
12
20
13
20
14
20
15
20
16
20
17
20
18
20
19
20
20
20
21

2020：3.8 fb-1 scan 4.61-4.7 GeV
2021：2 fb-1 scan 4.74-4.946 GeV
2021: 3.35 fb-1 @𝜓(2S) 3.0 B

351

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7

Physics at tau-charm Energy Region

Xiao-Rui LYU

Lomonosov Conference, 2021

Unique data sets near thresholds
e+e- symmetric collision:energy scan data sets at open
charm thresholds$
3.773 GeV, 2.93 !b"# , 𝐷 𝐷$$
4.008 GeV, 0.48 !b"# , 𝐷$ 𝐷$$∗
4.18-4.23 GeV, 6.32 !b"# , 𝐷$ 𝐷$&
4.6-4.7 GeV, 4.4 !b"# , Λ & ΛDD̄

Ds+ DsØ Meson and Baryon pair-productions near thresholds:
form-factors in the time-like production, precision branching fractions, relative phase;Ø Quantum-entangled pair productions of charmed mesons
Ø Hyperon and charmed baryon spin polarization in quantum entangled productions;Xiao-Rui LYU

Lomonosov Conference, 2021

9

BESIII advantage: unique data near to
the thresholds
Known initial 4-momentum

Single tag

Known beam energy: pair productionse+

Excellent resolution
Beam-constraint Lc masse-

Decay with neutron & 𝛑0
Decay with invisibles: neutrinos

Σ! → 𝑝𝜋 "Events /0.010 (GeV)

Missing mass or missing energy

Missing mass

Neutrino reconstruction+⇤+
c ! ⇤e ⌫⌫

Umiss
(GeV)

Xiao-Rui LYU

Lomonosov Conference, 2021

10

Charm hadron decays

0.567/fb at 4.6 GeV

2.93/fb at !(3770)

Purely Leptonic

Xiao-Rui LYU

Semi Leptonic

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Hadronic

Precision measurement of CKM elements-- Test EW theory
CKM matrix elements are fundamental SM parameters that
describe the mixing of quark fields due to weak interaction.

æ VudVusVub öæ d ö
æ d 'öç÷ç ÷ç÷ç s ' ÷ = ç Vcd VcsVcb ÷ç s ÷çV V V÷ç b ÷
ç b' ÷
èø
è td ts tb øè ø
Three generations of quark?

CKM matrix
BESIII + B factories +LQCD

Unitary matrix?

Expected precision < 2% at BESIIIBESIII + B factories +LHCb + LQCD

• Precision measurement of CKM matrix elements• A precise test of SM model• New physics beyond SM?
Xiao-Rui LYU

Lomonosov Conference, 2021

Extraction of |𝑽𝒄" | and 𝒇𝑫!
Take fDLQCD as input：

Take |Vcd|CKMfitter as input：|Vcd|=(0.2210±0.0058±0.0047) (µ+n mode)

fD+=(203.2±5.3±1.8) MeV (µ+n mode)

PRL 123, 211802

PRL 123, 211802, tn

Most precise measurement
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Lomonosov Conference, 2021

Extraction of |𝑽𝒄𝒔 | and 𝒇𝑫"𝒔

• Input 𝒇𝑫"𝒔 = 𝟐𝟒𝟗. 𝟗 ± 𝟎. 𝟓 MeV
from LQCD calculations• Input 𝑽𝒄𝒔 = 𝟎. 𝟗𝟕𝟑𝟐𝟎 ± 𝟎. 𝟎𝟎𝟎𝟏𝟏
from CKM global fit

Most precise measurement
Xiao-Rui LYU

Lomonosov Conference, 2021

𝑫→𝒉Form factors 𝒇$

Precisions better than those of LQCD results

Xiao-Rui LYU

Lomonosov Conference, 2021

Quantum entangled 𝐷! 𝐷! Strong
phase measurements
𝟎n 𝑫 → 𝑲𝑺/𝑳 𝝅

𝟎(2.93 𝐟𝐛#𝟏 @𝑬𝒄𝒎 = 𝟑. 𝟕𝟕𝟑 𝐆𝐞𝐕
4𝒆! 𝒆# → 𝛙 𝟑𝟕𝟕𝟎 → 𝑫𝑫𝝅)

PRL 124 (2020)241802% 𝑲&

PRD102(2020)052008

n𝑫 → 𝑲𝑺/𝑳 𝑲

𝑲& 𝝅% 𝝅% 𝝅& 𝐚𝐧𝐝 𝑲& 𝝅% 𝝅𝟎
JHEP 2021 (5) (2021) 164

Constraint on g measurement ~ 1.30
Xiao-Rui LYU

n𝑫 →Constraint on gmeasurement ~ 0.90

Constraint on g measurement ~ 60
Lomonosov Conference, 2021

PRL116.052001(2016)"The 𝛬! decays
Hadronic decay

PRL115.221805(2015)

𝚲"𝐜 → 𝒑𝑲#𝝅" + 11 CF modes

PRL 116, 052001 (2016)+ + 𝜦"
𝒄 →pK K , pπ π

PRL 117, 232002 (2016)+𝜦"𝒄 →nKsπ

PRL 118, 12001 (2017)0𝜦"𝒄 →pη, pπ

PRD 95, 111102(R) (2017)# + + 0𝜦"𝒄→𝜮 π π π

PLB 772, 388 (2017)𝟎(∗) 𝑲"𝜦"𝒄 →𝜩

PLB783, 200 (2018)"𝜦"𝒄 → 𝚲𝜼𝝅

PRD99, 032010 (2019)""𝜦"𝒄 → 𝚺 𝜼, 𝚺 𝜼′

CPC43, 083002 (2019)𝜦"𝒄 → BP decay asymmetries

PRD100, 072004 (2019)𝜦"𝒄 → 𝑝K ) 𝜼

arXiv: 2012.11106

Semi-leptonic decay+𝜦"𝒄 →𝜦e 𝝂𝒆

PRL 115, 221805(2015)+𝜦"𝒄 →𝜦μ 𝝂𝝁

PLB 767, 42 (2017)

Inclusive decay
𝜦"
𝒄 →𝜦X

PRL121, 062003 (2018)"𝜦"𝒄 →𝒆 XPRL 121 251801(2018)𝟎𝜦"𝒄 →𝑲𝒔 XEPJC 80, 935 (2020)

Production#𝜦"𝒄 𝜦𝒄 cross section

Xiao-Rui LYU

Lomonosov Conference, 2021

PRL 120,132001(2018)

Impacts on 𝚲𝒄 decay data
CLEOc
dominants theDs Branching
Fractionmeasurements.
(Sys. Err.
Dominates CF
modes. Many
SCS&DCSmodes
observed.)

Xiao-Rui LYU

Lomonosov Conference, 2021

Hadron Landscape
Hadron-physics challenges:llUnderstanding of establishedstates: precision spectroscopy
Nature of exotic states:
search and spectroscopy of
unexpected states

BESIIIAt BESIII, two golden measures to study
hadron spectroscopy, esp., to search for exotics• Light hadrons: charmonium radiative decays (actas spin filter) ( 10 B J/𝜓 and 0.4 B 𝜓(2S) )• Heavy hadrons: direct production, radiative andhadronic transitions (data above 3.8 GeV)
Xiao-Rui LYU

Lomonosov Conference, 2021

XYZ studies: about 23 /fb
data above 3.8 GeV

More X(3872) decay information• Observation of X(3872) à𝜋0𝜒𝑐1• Transition of 𝑋 3872 → 𝛾J/ψ, 𝛾ψ(2S)
BESIII, PRL 124, 242001 (2020)

g J/y

g y(2S)
3.5σ

5.2s

BESIII, PRL122, 202001 (2019)

BF(: ;<=> →?y(>A))
R=<0.59 at 90% C.L. , agrees
BF(: ;<=> →?J/y)with Belle(<2.1), while challenges Babar(3.4±1.1)
and LHCb results (2.46± 0.70)
" ∗!
!! !

5.7!
3.1!
3.4!

• Observation of X(3872) ® wJ/y
BESIII, PRL 122, 232002 (2019)

" ∗!
!! !

7.4σ

? ∗*
• Observation of X(3872) à𝐷 * 𝐷
BESIII, PRL 124, 242001 (2020)

Xiao-Rui LYU

Lomonosov Conference, 2021

5.1!
6.9!

The Y states• While not seen yet in B decays• Improved knowledges from BESIIIBESIII, arxiv:2107.09210
BESIII, PRL118, 092001 (2017)

Xiao-Rui LYU

Lomonosov Conference, 2021

Y(4260) è Y(4220) and new Y’s
PRL118, 092001 (2017)

PRD 102, 031101(R) (2020)

𝜼𝑱/𝝍

PRL118, 092002 (2017)!("+"−→#+#−ℎ!)PRL122, 102002 (2019)𝑒 ! 𝑒 # → 𝜋 ! 𝐷 " 𝐷 ∗#PRD 99, 091103 (2019)

Xiao-Rui LYU

Lomonosov Conference, 2021

arxiv:2107.09210

The Zc Family at BESIII
Zc(3900)+
PRL 110, 252001 (2013)

Zc(3885)+
ST: PRL 112, 022001(2014)
DT: PRD92, 092006 (2015)

Zc(3900)0
PRL 115, 112003 (2015)

Zc(3885)0
PRL 115, 222002 (2015)

Zc(4020)+

Zc(4020)0

PRL 111, 242001(2013)

PRL113,212002 (2014)

Zc(4025)+

Zc(4025)0

PRL 112, 132001 (2014)

PRL115, 182002 (2015)& )#!! !" → ## (%∗ %Which is the nature of these states?
If exists, there should be SU(3)counter-part Zcs state with strangenessXiao-Rui LYU

Lomonosov Conference, 2021

& ∗ )#!! !" → ## (%∗ %Spin-parity determination of the 𝑍"# (3900)• Zc line shape parameterized with Flatte-like formula

PRL 119.072001 (2017)

4.23GeV

JP=1+

4.26GeV

JP is measured to be 1+ withsignificance larger than 7.6𝞼
Xiao-Rui LYU

Lomonosov Conference, 2021

Zcs: SU(3) partner of Zc state• Important to look for 𝒁𝒄𝒔 , the SU(3) partners of𝑿(𝟑𝟖𝟕𝟐)/ 𝒁𝒄 (𝟑𝟗𝟎𝟎)• It’s useful to distinguish different models– Less exchange particles expected the 𝑍CD molecule picture•••

BESIII analyzes 3.7fb-1 data at energies between 4.628 and 4.698GeVPRL 126, 102001 (2021)
Partial reconstruction of 𝑲* 𝐚𝐧𝐝 𝑫"𝒔
Signature in the recoil mass spectrum of 𝑲*𝑫"𝒔 to identify the process of𝑒 *𝑒 " → 𝐾 *(𝐷$"𝐷 ∗+ + 𝐷$∗"𝐷 + )𝑫∗𝟎𝑫𝟎
𝝅𝟎 (𝜸)

#
𝑍-.

#
𝑍()

𝑫∗"
𝒔

𝑫#
𝒔

𝑫"
𝒔
𝑲%

𝟎
𝒆%𝒆& → 𝑲%𝑫∗&𝒔 𝑫

Xiao-Rui LYU

𝑲"∗𝟎𝒆( 𝒆) → 𝑲( 𝑫)𝒔𝑫

Lomonosov Conference, 2021

Observation of the 𝒁𝒄𝒔 𝟑𝟗𝟖𝟓±

PRL 126, 102001 (2021)••

Data driven background description: wrong Sign (WS) combination of 𝐷,) and 𝐾 )Conventional charmed mesons can not describe the enhancement below 4.0 GeV/c2 at
4.681 GeV

• Assume the structure as a 𝐷$"𝐷 ∗+ /𝐷$∗"𝐷 +resonance, denoting it as the 𝑍&$ 3985 ".
• A fit of J ,=1* S-wave Breit-Wigner withmass dependent width returns:>
𝒎 = 3985.2%>.K&>.J ± 1.7 MeV/c
𝜞 = 13.8%<.K&L.> ± 4.9 MeV• Global significance: >5.3 𝝈First candidate of the hidden-charm tetraquark with strangenessXiao-Rui LYU

Lomonosov Conference, 2021

Discussions on the nature of 𝒁𝒄𝒔 𝟑𝟗𝟖𝟓 ±• Various interpretations are possible for the structure– Tetraquark state– Molecule∗– 𝐷,(2573)( 𝐷,∗) threshold kinematic effects– (Re-scattering , Reflection, Triangle singularity)––

Mixture of molecular and tetraquark…

PRL127, 082001 (2021)

𝒁𝒄𝒔 𝟑𝟗𝟖𝟓 from 𝒆*𝒆" annihilations and𝒁𝒄𝒔 𝟒𝟎𝟎𝟎 from B decays• their masses are close, but widths aredifferent• If they are same, why width so different?
• If they are not same, is there thecorresponding wide Zc(3900)?
• Looking for more channels will be useful
𝐵 * → 𝐽/𝜓𝐾 ( 𝜋 )PRL 122 (2019) 152002

Xiao-Rui LYU

Lomonosov Conference, 2021

PRL126, 102001 (2021)

Light hadrons(containing u/d/s quarks)

Xiao-Rui LYU

Lomonosov Conference, 2021

X(𝒑'𝒑)/X(1835) from J/ψ radiative decays• X(1835)• X(𝑝𝑝)̅
• First observed by BESII in– An anomalous strong 𝑝𝑝̅ threshold
J/ψ→γηʹπ+πenhancement structure which was first• BESIII confirmed its existence withobserved by BESII in J/ψ→γpHp
much higher significance– BESIII confirmed its existence with• Spin-parity is not known
2much higher significance and PWA• Mass = 1836.5 ± 3.0(0.1)-./ MeV/c2(with FSI considered) is performed• Width = 190 ± 9(23)21 MeV/c
PRL106, 072002• 0"*
2• Mass = 1836.5*#/*#0"- "#. ±19 MeV/c• Width < 76 MeV/c2 @ 90% C.L.

X(1835)X(2120) X(2370)

PRL108, 112003

Are they the same state? A 𝒑?
𝒑 bound state?
What’s the spin-parity of X(1835)?
Why their widths are so different?
Xiao-Rui LYU

Lomonosov Conference, 2021

X(𝒑'𝒑)/X(18??) from J/ψ radiative decays
J/ψàγKsKsη

1.31B

225M
J/ψàγη'π+πJ/ψàγωφJ/ψàγ!!
"

225M

225M

PRL117, 042002 (2016)

J/ψ→γ𝛈4 𝛑( 𝛑)J/y®g3(π+π-)

PRD97, 051101(R)(2018)

J/ψ→γγ𝝓J/ψàωηπ+π225M

225M

Are they the same state? It is crucial to understand their connections.
Xiao-Rui LYU

Lomonosov Conference, 2021

X(1835)

The X(2120) and X(2370)• Observed in J/ψ→γη1 π*π" at BESIII[PRL106, 072002 (2011)][PRL117, 042002(2016)]• Candidates of glueball states• Combined analysis of 𝐽/𝜓 → 𝛾𝐾 *𝐾 "𝜂′ and𝛾𝐾2 𝐾2 𝜂′• Search for X(2370) in 𝐽/𝜓 → 𝛾𝜂𝜂𝜂′

PRL106, 072002 (2011)

EPJC80,746(2020)

PRD103, 012009(2021)

1.3B?
• Observation of X(2370) → 𝐾 𝐾𝜂′
with stat. significance of 8.3𝜎?
• No evidence of X(2120) → 𝐾 𝐾𝜂′?
• No evidence of X(2370) → 𝐾 𝐾𝜂′
Xiao-Rui LYU

Lomonosov Conference, 2021

Studies on the 𝜙(2170)/Y(2175)• A strangenium(-like) state: Y-particle with strange quark

Xiao-Rui LYU

Lomonosov Conference, 2021

More results on the 𝜙(2170)/Y(2175)
PRD99, 032001(2019)

PRD100, 032009 (2019)arXiv:2105.13597

PRD102, 012008 (2020)
aXiv:2104.05549

PRL124, 112001 (2020)

𝝓(2170)/Y(2175) is still a mysteryXiao-Rui LYU

Lomonosov Conference, 2021

Strangenium and strange-mesons in
J/𝜓 → 𝐾 # 𝐾 $ 𝜋 ! and 𝜓(3686) → 𝐾 # 𝐾 $ 𝜂
PRD101, 032008 (2020)
PRD100, 032004 (2019)(448M 𝜓(3686) decays) *J/𝜓 → 𝐾 𝐾 𝜋
223.7M• First observations of 𝐾-∗ 1980 and
𝐾5∗ 2045 in 𝐽/𝜓 decays• Two broad 𝐾 ( 𝐾 ) 1)) structures areobserved: possible from 𝜔 1650 and𝜌 2150

Xiao-Rui LYU• Dip around 1.75 GeV requires another1)) resonance X(1750) to introduce
interference with 𝜙 1680 : could be𝜌(1700) or X(1750) (photoproduction
at FOCUS)• Broad 𝐾 ( 𝐾 ) structure around 2.2 GeV:
contributions from 𝜌 2150 and/or
𝜌2 2250 resonances

Lomonosov Conference, 2021

Form factors of baryons

In the time-like region, access to the Electromagnetic Form
Factors (EFF) of the baryons, which characterize the internal
structure of the baryon

Xiao-Rui LYU

Lomonosov Conference, 2021

Threshold production of the nucleon

BESIII 2020 energy scan: PRL124, 042001 (2020)
BESIII untagged ISR: PRD99, 092002 (2019)
BESIII 2015 energy scan: PRD91, 112004(2015)• BESIII provides best precisions: crosssection threshold enhancement established• Oscillating structures observed in the EFF
after subtracted the modified dipole
parameterization [PRL114, 232301 (2015)]•
Xiao-Rui LYU

confirming the observation at BaBar

Lomonosov Conference, 2021

Threshold production of 𝑒 T 𝑒 U → 𝑛𝑛+
arXiv: 2103.12486
Accepted by Nature Physics• Very challenging measurement due to pure neutron final states• BESIII takes three approaches and provide validations among each other• XS measured in a wide range with
unprecedented precision (~10%):
confirming threshold enhancement• EFF ratio Rem and GM determined for the
first time
• XS ratio between proton and neutron: do
not support the FENICE conjecture, but arewithin the theoretical predictions• Oscillation of EFF observed in neutron data:
simultaneous fit of proton and neutron data
gives shared frequency (5.55±0.28) GeV-1
with almost orthogonal phase difference of(125±12)O
Xiao-Rui LYU

Lomonosov Conference, 2021

Form factors of hyperons• Through the weak decay of hyperons, we could probe its polarization. Hence
more information of the EFF can be studied• Δ𝜙 is the phase angle difference of GE and GM: can be explored via angularanalysis of the spin-coherent hyperon-pair weak decays
PRD97, 032013 (2018)• First complete EFF measurementof the Λ at 2.396 GeV
PRL123,122003 (2019)

Threshold enhancement observed
Xiao-Rui LYU

Lomonosov Conference, 2021

Hyperons produced at 𝜓 peaks? → 𝑝𝑝𝜋𝑒 ( 𝑒 ) → 𝐽/𝜓 → ΛΛ̅ (𝜋)𝑒 ( 𝑒 ) → 𝜓 → Σ ( Σd ) → 𝑝𝑝𝜋̅ *𝜋*Nature Physics 15, 631 (2019)

PRL125, 052004(2020)

PRL125, 052004 (2020)

𝐽/𝜓𝜓(3686)

DF = 42.4! ± 0.6! ( sta) ± 0.5! ( sys.)• Very precise determination of hyperon
decay asymmetry: è CPV search• Correct a long-history underestimation ofΛ decay asymmetry
Xiao-Rui LYU

Lomonosov Conference, 2021

BESIII: arXiv:2105.11155

CPV in X- àLp- decay
Based on 1.3 B J/𝜓 events(13% of total J/𝜓 events)
9-dimentional fit:¯+
e e ! J/ ! ⌅ ⌅+~73200 event candidates
Negligible background
First measurement of baryon weakphase difference
We obtain the same precision for
𝜙 as HyperCP with three ordersof magnitude smaller data sample!
HyperCP: 𝝓𝚵,𝑯𝒚𝒑𝒆𝒓𝑪𝑷 = −𝟎. 𝟎𝟒𝟐 ± 𝟎. 𝟎𝟏𝟏 ± 𝟎. 𝟎𝟏𝟏
BESIII: <𝝓𝚵> =𝟎.𝟎𝟏𝟔±𝟎.𝟎𝟏𝟒±𝟎.𝟎𝟎𝟕
Xiao-Rui LYU

Lomonosov Conference, 2021

HyperCP: PRL 93(2004) 011802

single tag method•

Lc decay asymmetries

PRD100, 072004 (2019)4(6)-fold angular analysis of the cascade decays of
Λ+ → 𝑝𝐾, , Λ𝜋 -, Σ-𝜋 . and Σ.𝜋 - based on 567/pb data

sin Δ𝝓=−0.28 ± 0.13 ± 0.03••
Xiao-Rui LYUBest precisions on the hadronic weak decay asymmetries
The transverse polarization is firstly studied and found to be
non-zero with 2.1𝜎
Lomonosov Conference, 2021

Xiao-Rui LYU

Lomonosov Conference, 2021

BESIII Physics

Int. J. Mod. Phys. A 24, S1-794 (2009)[arXiv:0809.1869 [hep-ex]].

Xiao-Rui LYU

Chin. Phys. C 44, 040001 (2020)
doi:10.1088/1674-1137/44/4/040001[arXiv:1912.05983 [hep-ex]].

Lomonosov Conference, 2021

Planned future data set

Xiao-Rui LYU

Lomonosov Conference, 2021

10 billon J/𝝍 events on tape！
from Stephen Olsen

Xiao-Rui LYU

Lomonosov Conference, 2021

Plan of the BEPCII upgrade

σ(e+e-à𝜇( 𝜇) )R=σ(e+e-àhadron)/• optimized energy at 2.35 GeV with luminosity 3 times higher than thecurrent BEPCII.
• extend the maximum energy up to 5.6 GeV
Nearly blank at 5-7GeV

𝑱/𝝍

?𝒄
𝛀𝒄 𝛀

𝝍(𝟐𝑺)

BEPC3 vs BEPCII
3倍

Xiao-Rui LYU

4.95 ~ 5.6 GeV: new energy
coverage of BEPCII

Lomonosov Conference, 2021

Summary• BESIII is successfully operating since 2008, and willcontinue to run for 5–10 years– collected large data samples in the τ-charm mass region• Many exciting results have been published covering many
aspects:üüüüCharmed mesons and baryons
XYZ states and light hadron spectroscopy
Form factors of the nucleon and hyperons
Low-Q2 QCD studies: R value, multi-meson production,
fragmentation function, …
ü Rare decays and new physics searchü …

• Future goals:

50M D0, 50M D+, 15M Ds, 2M Lc , high-lumi. fine scan up to 5.6 GeV

Xiao-Rui LYU

Lomonosov Conference, 2021

Xiao-Rui LYU

Lomonosov Conference, 2021

D(S) Leptonic decays
Purely Leptonic:• Extract decay constant fD(s) incorporates the strong interaction effects (wavefunction at the origin)• To validate Lattice QCD calculation of fD(s) and provide constrain of CKMunitarity
arXiv:2102.11734

Xiao-Rui LYU

Lomonosov Conference, 2021

𝐷)! → 𝜇! 𝜈: 2198 ± 55
𝐷)! → 𝜏 ! (→ 𝜋 ! 𝜈)𝜈: 946!*,#*+

D(S) Semi-Leptonic decays: e-mode
Semi-leptonic: form factor (FF)• Measure |Vcx| x FF
• Charm physics:• CKM-unitarity Þ | Vcx|, extract FF, test LQCD
• Input LQCD FF to test CKM-unitarity

Xiao-Rui LYU

Lomonosov Conference, 2021

D(S) Semi-Leptonic decays: 𝝁-mode

Xiao-Rui LYU

Lomonosov Conference, 2021

𝑫→𝒉Form factors 𝒇$

Precisions better than those of LQCD results

Xiao-Rui LYU

Lomonosov Conference, 2021

Determiend properties of the 𝒁#
𝒄 (𝟑𝟗𝟎𝟎)• If Zc is parameterized with a Flatte-like formula

PRL 119.072001 (2017)

M pole = 3881.2 ± 4.2 ± 52.7 MeV, G pole = 51.8 ± 4.6 ± 36.0 MeV
g1 ' = 0.075 ± 0.006 ± 0.025GeV 2
g 2 '/ g1 ' = 27.1 ± 2.0 ± 1.9(consistent with the previous published results)• Born cross section for e + e - ® Z c+p - + c.c. ® p +p - J / y
21.8 ± 1.0 ± 4.4 pb at 4.23 GeV
11.0 ± 1.2 ± 5.4 pb at 4.26 GeV• Search for e + e- ® Z c+ (4020)p - + c.c. ® p +p - J / y gives
upper limits at 90% C.L.:<0.9 pb at 4.23 GeV; <1.4 pb at 4.26 GeVs (e + e- ® Z c+ (4020) p - + c.c ® p +p - J / y )then< 4% at 4.23 GeVs ( e + e- ® Z c+ (3900) p - + c.c ® p +p - J / y )<13% at 4.26 GeV

Further couple channel amplitude analysis is on-going on
more energy points.
Xiao-Rui LYU

Lomonosov Conference, 2021

The Zc Family at BESIII

Xiao-Rui LYU

Lomonosov Conference, 2021

Cross sections of the 𝒁𝒄𝒔 𝟑𝟗𝟖𝟓 ± production
PRL126, 102001 (2021)•

Simultaneous fit to the five energy points• Largest cross sections around4.681 GeV

Xiao-Rui LYU

Lomonosov Conference, 2021

Proton: Oscillating Structure in the
Effective Form Factor

Xiao-Rui LYU

Lomonosov Conference, 2021

Magnetic form factor of the neutron

Xiao-Rui LYU

Lomonosov Conference, 2021

Hyperon decay parameters @ BESIII' → 𝒑'𝒆T 𝒆U → 𝑱/𝝍 → 𝚲𝚲𝒑𝝅T 𝝅UG. Faldt and A. Kupsc
PLB,772, 16 (2017)
EPJA, 52, 141 (2016)
EPJA, 51, 74 (2015).

$
T0: angular distribution of Λ and Λ
T3, T4, transverse polarization

T1, T2, T5: spin correlation

Xiao-Rui LYU

Lomonosov Conference, 2021

' → 𝑝𝑝𝜋𝑒 T 𝑒 U → 𝐽/𝜓 → ΛΛ
̅ T 𝜋 U , 𝑝𝑛𝜋+ U𝜋\
1.3 billion J/y events

simultaneous fit to the two data samples
47,009 events selected
420,593 events selected𝒑?
𝒑𝝅( 𝝅)𝒑?
𝒏𝝅𝟎 𝝅(Nature Physics (2019)

DF = 42.4! ± 0.6! ( sta) ± 0.5! ( sys.)
Xiao-Rui LYU

Lomonosov Conference, 2021

Fitting results and 𝚲 decay asymmetries
Nature Physics (2019)

Xiao-Rui LYU

Lomonosov Conference, 2021

1957
Phys. Rev. 108 1645 (1957)
From Hao-Kai Sun=

p|S|2 |P |2=|S|2 + |P |2↵2 cos ⌅1tan ⌅ =

Sandip PAKVASA

X.G. HeJohn Donoghue

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