1. Cittadella Universitaria di Monserrato, Cagliari, Italia
Latest Results and
Hardware Activities
from BESIII
Marco Destefanis Università degli Studi di Torino e INFN
on behalf of the BESIII Collaboration
IFAE2013 – XII Edizione
Cittadella Universitaria di Monserrato, Cagliari, Italia
April 03-05, 2013

2. S tuned depending on energy
The BESIII IHEP
BEijing Spectrometer III
e+e- collisions
S tuned depending on energy
Charmonium Physics
D-Physics
Light Hadron Spectroscopy
-Physics
...
Physics program
D.M. Asner et al, Physics at BES-III, arXiv: v1 [hep-ex] (2008)

3. BEPCII Storage Rings e+ e- Beijing Electron-Positron Collider II
Beam energy:
GeV
Design Luminosity:
1×1033 cm-2s-1
Achieved Luminosity:
 0.65×1033 cm-2s-1
Optimum energy:
1.89 GeV
Energy spread:
5.16 ×10-4
No. of bunches: 93
Bunch length:
1.5 cm
Total current:
0.91 A
Circumference:
237m
Beijing Electron-Positron Collider II e+ e-

4. BESIII Detector TOF: EMC: CsI crystals, 28 cm T = 80 ps Barrel
110 ps Endcap
EMC: CsI crystals, 28 cm
E/E = GeV
z = 0.6 cm/E
Magnet: 1T Superconducting
MDC: small cell & He gas
xy= 130 m
p/p =
dE/dx = 6%
Muon: 9 layer RPC
Trigger: Tracks & Showers
Pipelined; Latency = 2.4 ms
Data Acquisition:
Event rate = 3 kHz
Thruput ~ 50 MB/s
Zero Degree Detector (ISR)

5. BESIII Data Taking Il più grande set di J/ψ, ψ(2S) e ψ(3770) al mondo
• Luglio 2008: prime collisioni e+e- in BESIII
• Nov 2008: ~14M y(2S) eventi per calibrazione
• 2009: 106M ψ(2S) 4xCLEOc
225M J/ψ 4xBESII
• : 2.9 fb-1 ψ (3770) 3.5xCLEOc
• 2011: GeV (Ds, XYZ)
• 2012: 0.4B ψ(2S)
J/y: 1B eventi,
lineshape scan sottosoglia per misura della fase relativa ampiezze e.m e forte della J/ψ , richieste dalla collab. italiana, 14pb-1/pto, tot 5 punti R 2.4, 2.8, 3.4 GeV
• 2013: MeV
• Luminosità di picco raggiunta: 6.5x MeV
Il più grande set di
J/ψ, ψ(2S) e ψ(3770)
al mondo

6. Risultati Pubblicati χcJ decays and transitions
1)Measurements of ψ’ →pK+Σ0 and χ cj →pK+Λ. PRD87, (2013)
2)Search for hadronic transition χcJ→ηcπ+π− and observation of χcJ→KKπππ. PRD87, (2013)
3)Measurement of χcJ decaying into pnπ− and pnπ−π0. PRD86, (2012)
4)Observation of χcJ Decays to ΛΛ— π+π−. PRD86, (2012)
5)Two-photon widths of the χc0,2 states and helicity analysis for χc2 →γγ. PRD85, (2012)
6)Observation of χc1 decays into vector meson pairs ϕϕ, ωω, and ωϕ. PRL107, (2011)
7)Study of χcJ radiative decays into a vector meson. PRD83, (2011)
8)First Observation of the Decays χcJ→ π0π0π0π0. PRD83, (2011)
Studies of η, η’, η(1405), ηc and ηc’ mesons
9)Evidence for ηc (2S)  in ψ(3686)→γKSK±π∓π+π−. PRD87, (2013)
10)Search for η and η’→π+e-ν̅e+c.c. decays in J/ψ→ϕη and ϕη’. PRD87, (2013)
11)Measurements of Baryon pair decays of χcJ mesons. [ arXiv: ]
12)Observation of ηc decaying into Σ+Σ- and Ξ-Ξ+. [arXiv: ]
13)The analysis on hc exclusive decays into γηc. PRD86, (2012)
14)Search for η and η’ Invisible Decays in J/ψ→ϕη and ϕη’. [arXiv ]
15)Observation of e+e−→ηJ/ψ at center-of-mass energy s1/2=4.009 GeV. PRD86, (2012)
16)Evidence for ηc→γγ and Measurement of J/ψ→3γ. [arXiv ]
17)First observation of η(1405) decays into f 0(980)π0. PRL108, (2012)
18)Measurements of the mass and width of the ηc using ψ’→γηc. PRL108, (2012)
19)Search for ηc’ decays into vector meson pairs. PRD84, (2011)
20) ηπ+π− Resonant Structure around 1.8 GeV/c2 and η(1405) in J/ψ →ωηπ+π−. PRL107, (2011)
21)Search for CP and P violating pseudoscalar decays into ππ. PRD84, (2011)
22)Measurement of the Matrix Element for the Decay η’→ηπ+π−. PRD83, (2011)

7. Risultati Pubblicati Decays of cc mesons Scalar mesons and new states
23)Partial wave analysis of J/ψ→γηη. [arXiv: ]
24)PWA of J/ψ → γφω. [arXiv: ]
25)Measurement of ψ’ → γpKΛ. [arXiv: ] accepted by PRD
26)Measurement of branching fractions for J/ψ and ψ(3686) to ΛΛπ0 and ΛΛη. [arXiv: ]
27)Precision measurement of branching fractions of ψ’ → π0J/ψ and ηJ/ψ. PRD86, (2012)
28)Determination of the number of ψ(2S) events at BesIII. [arXiv: ]
29)Experimental study of ψ’ decays to K+K-π0 and K+K-η. PRD86, (2012)
30)First observation of the isospin violating decay J/ψ→ΛΣˉ0+c.c.. PRD86, (2012)
31)Determination of the number of J/ψ events with J/ψ→inclusive decays. [arXiv: ]
32)Observation of two new N* resonances in ψ (3686) → ppπ0 . [arXiv: ]
33)First observation of the M1 transition ψ(3686)→γηc(2S). PRL109, (2012)
34)Study of J/ψ→pp and J/ψ→nn [arXiv: ] PRD86 (5), (2012)
35)Evidence for the Direct Two-Photon Transition from ψ’ to J/ψ. [arXiv: ]
36)Precision measurement of the branching fractions of J/ψ → π+π−π0 and ψ’ →π+π−π0. PLB710, 594 (2012)
37)Spin-Parity Analysis of pp Mass Threshold Structure in J/ψ and ψ’ Radiative Decays. PRL (2012)
38)Higher-order multipole amplitude measurement in ψ(2S)→γχc2. PRD84, (2011)
39)Evidence for ψ’ decays into γπ0 and γη. PRL (2010)
Scalar mesons and new states
40)Observation of a charged charmoniumlike structure in e+e- -> π+π-J/ψ at sqrt(s) = 4.26 GeV. [arXiv ]
41)Search for a light Higgs-like boson A0 in J/ψ radiative decays. PRD (2012)
42)Study of a00(980)−f0(980) mixing. PRD83, (2011)
43)Confirmation of the X(1835) and observation of the resonances X(2120) and X(2370) in J/ψ→γπ+π−η’.
PRL106, (2011)

8. pp Near Threshold Enhancement: J/ψ -> γpp
PRL 108, (2012)
Unclear nature: normal
meson, ppbound state,
multiquark, glueball,…
PWA fit features:
●Mass structure can be
described by BW and FSI
corrections (PRD 71,
(2005))
● FSI corrections notably
improve description
● Different FSI → model
systematic
Fit components: X(pp), f2(1920), f0(2100), 0++ PHSP
Fit results:

9. ηc Resonance Parameters from ψ’ -> γηc
PRL 108, (2012)
Simultaneous fit of shown ηc decay modes.
● ηc line shape: interference with non-ηc decays
● phases for different modes are consistent
within 3σ, a common phase is used
Currently the most precise measurements!

10. First Observation of M1 Transition ψ’->γηc(2S)
Never before observed in charmonium transitions
PRL 109, (2012)
Combined fit of two channels:
● significance >10σ ●
● combined branching ratios
BaBar: PRD (2008)

11. Observation of a charmonium like structure: Zc(3900)±
BESIII: arXiv:
2013: MeV
e+e-  +-J/ψ
Dominant background e+e-+-+-
J/ signal: [3.08,3.12] GeV
J/ sideband: [3.0,3.06] GeV or [3.14,3.20] GeV
Structure seen: Zc(3900)± -> π± J/ψ

12. Dalitz Plots and 1D Projections
BESIII: arXiv:

13. The Zc(3900) signal Significance >8 Couples tocc
BESIII: arXiv:
Significance
>8
Couples tocc
Has electric charge
At least 4-quarks
What is its nature?
S-wave Breit-Wigner with efficiency correction
Mass = (3899.0±3.6±4.9) MeV
Width = (46±10±20) MeV
Fraction = (21.5±3.3±7.5)%

14. Confirmed by Belle Collaboration
The Zc(3900) signal
BESIII: arXiv:
Significance
>8
Couples tocc
Has electric charge
At least 4-quarks
What is its nature?
Confirmed by Belle Collaboration
arXiv: 1304,0121
S-wave Breit-Wigner with efficiency correction
Mass = (3899.0±3.6±4.9) MeV
Width = (46±10±20) MeV
Fraction = (21.5±3.3±7.5)%

15. GEM detector features
flexible geometry  arbitrary shape: rectangular, cylindrical …
ultra-light structure  very low material budget: <0.5% X0/chamber
gas multiplication separated from readout stage  arbitrary readout pattern: pad, strips (XY, UV), mixed …
high rate capability: > 50 MHz/cm2
high safe gains: > 104
high reliability: low discharge, Pd < per incoming particle
rad hard: up to 2.2 C/cm2 integrated over the whole active area without permanent damages (corresponding to 10 years of operation at LHCb1)
high spatial resolution: down to 50µm (COMPASS with analog readout Nucl.Phys.Proc.Suppl. 125 (2003) )
good time resolution: down to 3 ns (with CF4)
, Tsinghua U

17. Material Budget
KLOE2
BESIII

18. M. Maggiora

19. M. Maggiora

21. J/ψ Strong and Electromagnetic Decay Amplitudes
Strong → A3g
hadrons
Resonant contributions
ΓJ/ψ ~ 93KeV → pQCD
pQCD: all amplitudes almost real [1,2]
QCD -> Фp ~ 10° [1]
Electromagnetic → Aγ
hadrons
Non-resonant Continuum → AEM
Non-resonant continuum
pQCD regime
AEM 
hadrons
[1] J. Bolz and P. Kroll, WU B
[2] S.J. Brodsky, G.P. Lepage, S.F. Tuan, Phys. Rev. Lett. 59, 621 (1987).

22. J/ψ Strong and Electromagnetic Decay Amplitudes
If both real, they must interfere (Фp ~ 0°/180°)
On the contrary Фp ~ 90° → No interference
J/ψ → NN (½+½-) Фp = 89° ± 15° [1]; 89° ± 9°[2]
J/ψ → VP (1-0-) Фp = 106° ± 10° [3]
J/ψ → PP (0-0-) Фp = 89.6° ± 9.9° [4]
J/ψ → VV (1-1-) Фp = 138° ± 37° [4]
Results are model dependent
Model independent test:
interference with the non resonant continuum
[1] R. Baldini, C. Bini, E. Luppi, Phys. Lett. B404, 362 (1997); R. Baldini et al., Phys. Lett. B444, 111 (1998)
[2] J.M. Bian et al., J/ψ -> ppbar and J/ψ -> nnbar measurement by BESIII, to be published on PRD
[3] L. Kopke and N. Wermes, Phys. Rep. 174, 67 (1989); J. Jousset et al., Phys. Rev. D41,1389 (1990).
[4] M. Suzuki et al., Phys. Rev. D60, (1999).

23. Investigated Processes
Exclusive scenario: could see interference effects
e+e+ -> J/ψ -> pp, nn NN
BR ~ 2.17x10-3 σcont~ 11 pb
e+e- -> J/ψ -> ρπ VP
BR ~ 1.69% σcont~ 20 pb
e+e- -> J/ψ -> 2(π+π-)π0
BR ~ 5.5% σcont~ 500 pb

24. radiative corrections
Simulated Yields for e+e--> pp
Δφ = 0°
Δφ = 90°
Δφ = 180°
beam energy spread +
radiative corrections
(to be optimized)
continuum reference
σ ~ 11 pb
no corrections
beam energy spread
(0.93 MeV)

25. J/ψ Phase PRELIMINARY Energy requested [MeV] collected Lint [pb-1]
3050
3046
14.0
3060
3056
3083
3086
16.5
3090
3085
3093
3088
3097
79.6
PRELIMINARY

26. Summary Il più grande set di J/ψ, ψ(2S) e ψ(3770) al mondo
Più di 20 articoli pubblicati nell’ultimo anno
Zc(3900)± -> π± J/ψ
Studi sulla fase avanzati per diversi canali
ZDD: maggior σISR e unico luminometro online di BESIII
CGEM come opzione per il tracker centrale