Recent New Physics Search Results
at BESIII
Dayong Wang

dayong.wang@pku.edu.cn“The 20th Lomonosov Conference on Elementary Particle Physics ”
Moscow State University, Aug 22 2021

BESIII experiment@BEPCII
p peak lumi of 1x1033 cm-2s-1 at
1.89GeV reached in April 2016
p 2019-2021: top-up injection，
c.m.s. E=>4.94GeV

Ref:
NIM A614,345 (2010)

BESIII Detector Perfor

2024: Inner tracker upgrade

MDC

MDC

EMC

Spatialresolution

dE/dx
resolution

Energyresolution

CLEO-c110 µm

5%2.2-2.4 %BaBar125 µm

7%2.67 %

CBelle130 µm

5.6%2.2 %B

115 µm<5%(Bhabha)

Exps.

Clean environment, highluminosity, large acceptance andhigh efficiency at BESIII are helpful
for indirect probe of new physics
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BESIIIEB
2.4%

MUC: Efficiency ~ 96%
2
BGWanglevel: < 0.04 Hz/cm2(B-MUC), < 0.1 Hz/cm
DayongBESIII New Physics Program

SymmetryRare

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ExoticMore details, r.f.

ü New Physics Searches at the BESIII
Experiment! Shenjian Chen and Stephen
Olsen!NSR, arXiv:2102.13290
ü New Physics Program of BES, Dayong
Wang, in "30 Years of BES Physics#

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Features for NP search@BESIIIp Event is very cleanp High tagging efficiency
p Many systematic uncertainties can be cancelled
p Could measure absolute BFs

J/ψ !"#$%&

2019/2/11

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Charged LFV in 𝑱/𝝍 decays•

New physics models predicting BR J/𝜓 → 𝑒𝜇 to 10!"# ~10!$,
BR J/𝜓 → 𝑒𝜏(𝜇𝜏 ) to 10!"% ~10!& .
• model-independent prediction [1, 2]• rotating mass matrix [3]• unparticle physics [4]• effective Lagrangian [5]• MSSM with gauged baryon and lepton number [6]• …
•Experimental results
𝑱/𝝍 number𝐽/𝜓 → 𝑒𝜇

𝐽/𝜓 → 𝑒𝜏𝐽/𝜓 → 𝜇𝜏BES

58 million< 1.1×10!" [7]< 8.3×10!" [8]< 2.0×10!" [8]BESIII

225 million< 1.6×10!# [9]--[1] X. M. Zhang et al, Phys. Rev. D 63, 016003 (2000).
[7] BES Collaboration, Phys. Lett. B 561, 112007 (2003).
[2] T. Gutche et al, Phys. Rev. D 83, 115015 (2011).
[8] BES Collaboration, Phys. Lett. B 598, 172 (2004).
[3] J. Bordes and H. M. Chan, Phys. Rev. D 63, 016006 (2000).
[9] BESIII Collaboration, Phys. Rev. D 87, 112007 (2013).
[4] K. S. Sun et al, Mod. Phys. Lett. A 27, 1250172 (2012).
[5] D. E. Hazard and A. A. Petrov, Phys. Rev. D 94, 074023 (2016).
[6] X. X. Dong et al, Phys. Rev. D 97, 056027 (2018).
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Search for 𝐽/𝜓 → 𝑒 ± 𝜏 ∓Phys. Rev. D 103, 112007 (2021)• Based on 10 billion 𝐽/𝜓 data set:•1310.6M collected @2009+2012 (sample I), 8774.01M collected @2017-2019(sample II).
𝐽/𝜓 → 𝑒𝜏, τ → 𝜋𝜋 3𝜈.

• Select one electron and one charged pion.
• At least two photon showers and one 𝜋 % .
• Two-body-decay:
20

data
inclusive MCsignal MC

Events /( 3 MeV/c2)

Events /( 3 MeV/c)

20
15
10
50
0.95

11.05

Pe (GeV/c)

1.1

data
inclusive MCsignal MC

15
10
50
1.7

1.75

1.8

1.85
2

Me_recoil (GeV/c )• One undetected neutrino with missing energy 𝐸'()) > 0.43𝐺𝑒𝑉.

• Blind analysis to avoid possible bias.
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𝐒𝐞𝐚𝐫𝐜𝐡 𝐟𝐨𝐫 𝐜𝐋𝐅V: 𝑱/𝝍 → 𝒆±𝝉∓• No excess of events is observed over the background.

data
backgroundsignal MC

6420-0.2

00.2

Umiss (GeV)

15

data
backgroundsignal MC

1050-0.20• Determination of upper limit at 90% confidence level(C.L.) with Bayesian method. Combined result:• 𝐵𝑅(𝐽/𝜓 → 𝑒𝜏) < 7.5×10!" @ 90% C.L.
• This result improves the previous published limits by
two orders of magnitude and comparable with thetheoretical predictions.
• The 1st submitted paper based on full 10 billion 𝐽/𝜓data of BESIII

1Phys. Rev. D 103, 112007 (2021)

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0.2Umiss (GeV)

L/Lmax

8𝑈$%&& = 𝐸$%&& −𝑐|𝑃$%&& |Events /( 10 MeV)

Events /( 10 MeV)

100.5

00

Dayong Wang

0.05

0.1

0.15

×10<60.2

B(J/s A eo)
7

J/ψ weak decays

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Search for 𝑱⁄𝝍 → 𝑫-𝒆+𝝂𝒆 ,𝑫-→ 𝑲+𝝅-𝝅nnn

A search based on 10B Jpsi sample
𝑼𝒎𝒊𝒔𝒔 = 𝑬𝒎𝒊𝒔𝒔 − 𝒄|𝒑𝒎𝒊𝒔𝒔|a fit on 𝑼𝒎𝒊𝒔𝒔 distribution to extract the signal.
Two main backgrounds:
Gamma conversion with 𝒆 misid: 𝑱⁄𝝍 → 𝝆𝝅 → 𝜸𝜸𝝅𝝅 → 𝜸𝒆𝒆𝝅𝝅;
𝟎u 𝝅⁄𝑲 misid : 𝑱⁄𝝍 → 𝜸𝜼(𝟏𝟒𝟎𝟓) → 𝜸𝑲𝑲 𝝅 → 𝜸𝝅𝝅𝝅𝑲u

JHEP 06 (2021) 157
𝑱⁄𝝍 → 𝑫−𝒆+𝝂𝒆 + 𝒄. 𝒄. < 7.1×10-8 @ 90% CL
ü the most sensitive searchü improves the limit by a factor of 170.
ü stringent constraint for NP models
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9Search for 𝜮! → 𝒑𝒆! 𝒆! 𝐚𝐧𝐝 𝜮! → 𝜮" 𝑿•

Two down-type ( 𝒅 𝐨𝐫 𝒔 ) quarks convert into twoup-quarks[1-2], similar to 𝟎𝝂𝜷𝜷𝒍!

%
𝝂=𝝂𝒍!

𝑩!
𝑩𝟎• Blind analysis
𝟏• Double tag (DT)B 𝟏𝟑𝟖𝟓 *𝜮! + 𝒄. 𝒄., 𝜮B 𝟏𝟑𝟖𝟓 * → 𝝅*𝚲
B (→ 𝒑B𝝅*),ü ST events: 𝑱/𝝍 → 𝜮
B 𝟏𝟑𝟖𝟓 * candidates; fit the recoil mass of 𝜮
B 𝟏𝟑𝟖𝟓 *.
save all 𝜮

𝑩$𝟐

𝑵𝐒𝐓 = 𝟏𝟒𝟕𝟕𝟒𝟑 ± 𝟓𝟔𝟑𝐬𝐭𝐚𝐭.
B 𝟏𝟑𝟖𝟓 *𝜮!
𝑩 𝑱/𝝍 → 𝜮= 𝟑. 𝟐𝟏 ± 𝟎. 𝟎𝟕𝐬𝐭𝐚𝐭. ×𝟏𝟎!𝟒
PRD 103 (2021) 052011[1] C. Barbero, G. Lopez Castro, and A. Mariano, Phys. Lett. B 556, 98 (2003).
[2] C. Barbero, L. F. Li, G. Lopez Castro, and A. Mariano, Phys. Rev. D 76, 116008 (2007); Phys. Rev. D 87, 036010 (2013).

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Results: 𝜮! → 𝒑𝒆! 𝒆! 𝐚𝐧𝐝 𝜮! → 𝜮" 𝑿
ü DT events:
ü in the recoil side of the selected ST eventsü 𝜮! → 𝒑𝒆!𝒆!; 𝜮! → 𝜮*(→ 𝒑𝝅𝟎 )𝑿;ü ULs @90 CL： Frequentist method with unbounded profile
likelihood treatment of systematic uncertainties.

PRD 103 (2021) 052011

𝑩(𝜮!→ 𝒑𝒆!𝒆!) < 𝟔. 𝟕 ×𝟏𝟎!𝟓2021/8/22

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𝑩(𝜮!→ 𝜮*𝑿) < 𝟏. 𝟐 ×𝟏𝟎!𝟒Dayong Wang11

< 𝒐𝒔𝒄𝒊𝒍𝒍𝒂𝒕𝒊𝒐𝒏
Search 𝒇𝒐𝒓 Λ − Λ• Oscillation event (charge conjugation implied)!D𝐽/𝜓 → 𝑝𝐾 Λ'&(%))*+%,-

!

𝑝𝐾 Λ

DB=2 process• Time integrated oscillation rate

Most of the systematic uncertainties cancelled.
• The oscillation parameter
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< 𝐨𝐬𝐜𝐢𝐥𝐥𝐚𝐭𝐢𝐨𝐧
𝐏𝐫𝐞𝐥𝐢𝐦𝐢𝐧𝐚𝐫𝐲 ： 𝜦 − 𝜦• Result based on 1.3 billion 𝐽/𝜓 events.

WS• Total systematic uncertainty (~1%).
• Upper limit is obtained by utilizing afrequentist method.
RS• Upper limit on oscillation rate (90% C.L.)𝑃 Λ < 4.4×10!#• Oscillation parameter (90% C.L.)
𝛿𝑚445 < 3.8×10!"6 MeV

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Data: the dot with error bar
MC: the pink filled histogram, normalized arbitrarily
RS:
Data: the dots with error bars
Signal shape: MC shape ⨂ Gaussian
Background shape: inclusive MC sample after
excluding RS events
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Summary
BESIII performed wide range study of exotic decays andnew physics, with many first search or best limitn The latest searching results are reported
nPhys. Rev. D 103, 112007 (2021)
Charged LFV decay 𝑱/𝝍 → 𝒆±𝝉∓- +JHEP 06 (2021) 157
u Charmonium weak decay: 𝑱⁄𝝍 → 𝑫 𝒆 𝝂𝒆
HH HHI
PRD 103 (2021) 052011
u LNV and BNV : 𝜮 → 𝒑𝒆 𝒆 𝐚𝐧𝐝 𝜮 → 𝜮 𝑿> 𝐨𝐬𝐜𝐢𝐥𝐥𝐚𝐭𝐢𝐨𝐧 Preliminaryu DB=2 process：𝚲 − 𝚲un

BESIII has great potential with unique datasets andanalysis techniques…More to come!
Future Physics Programme of BESIII
Chinese Phys. C 44, 040001 (2020).

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Thanks!

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