Slide 1(R-Scan Data: √s=2.0GeV~3.08GeV)
Yankun Sun Zhihong Wang
(R-Scan Data: √s=2.0GeV~3.08GeV)
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3. Event selection.
Introduction (Cross section Line shape)
From 232fb-1 of BABAR data, signal of e+e- →γISR (1020) η' are observed.
Because of the low statistics, no further study is carried out.
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PRD 76, 092005 (2007)
With R-scan data (2.000~3.080GeV), we search for the production of e+e- → η'(1020).
Possible decay mode of Y(2175) → η' (1020) with study of cross section line shape.
Data sets and MC simulation
1. BOSS665p01.
3. 100K Signal MC by “ConExc” at each energy point.
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2.125 108.49
2.100 12.167
2.050 3.343
2.000 10.074
(1) e+ e-→η'(1020) (2) e+ e-→K+K-ρ0 (3) e+ e-→K+K-π+π-
(4) e+ e-→π+π- (5) e+ e-→K*K+π- (6) e+ e-→K*K-π+ 2017/2/19
Event selection (η'→π+π-γ)
• Good Charged Track: |Vz| < 10.0 && |Vr|< 1.0 && |cosθ|<0.93;
NGood ==3||4; (To improve statistics: Missing one Kaon.)
• PID with dE/dx and TOF: Pion: prob_π >prob_K && prob_π>prob_K;
N(π+)=N(π-) = 1;
At least one Kaon are indentified:
N(K+)=N(K-) = 1; or N(K+)=1 && N(K-) = 0; or N(K+)=0 && N(K-) = 1;
• Good Photon: Ebarrel>25MeV; Eendcap>50MeV; 0≤Time ≤ 14; Nγ ≥ 1.
• Vertex fit (π+π-K±).
• 1C kinematic fit (π+π-K±γ): χ2 1C(K+K-K±γ) < 20;
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1C(K+K-π+π-γ) < 20;
(2)|M(K+K-)-M|<0.02GeV/c2;
(3)η' Fitting : Signal: MC shape ⊗Gaussian; Background: 3rd Poly; N=255.6 ± 23.4
Factor = 0.36
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Independent Fit
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Independent Fit
There are 11 energy points, whose statistic are large than others.
We use same method to fit the distribution of energy points independently.
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Minimizer is Linear Chi2 = 8.7 NDf = 10 p0 = 1.8 +/- 0.3
Minimizer is Linear Chi2 = 12.3 NDf = 10 p0 = -1.2 +/- 0.2
Results (I)
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Due to their low statistic, these energy points are fitted with fixed parameters from near energy points with larger statistic.
σ(e+e-→ (1020)η'): with η'→π+π-γ
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1C Kinematic fit* Tracking Parameters Correction 2.7
ISR factor Difference between Iteration of line shape 0.6
Background shape 3nd poly 2rd poly 1.2
Signal shape MC shape ⊗ Gaussian(free) MC shape ⊗ Gaussian(fixed+1σ)
3.4
Others Trigger, Start time, FSR 1.0
Total -- 7.8
Systematic uncertainty
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2 2


2 2| ( ) | | ( ) ( ) |iA s PS s e BW s
With X(2200): χ2/ndf = 16.54/6
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Summary
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With R-scan data sets [2.0, 3.08]GeV, the process e+e- → η' is observed for the first time.
The cross sections are measured at 11 energy points.
Possible structure around 2.2GeV is observed in the cross section line shape.
We extract the mass and width of the structure: M= 2178.9±4.8MeV/c2
Γ= 129.2 ±14.8MeV/c2
(2)M(K+K-) : [0.48, 0.50] GeV/c2;
@2125MeV: L=107.73pb-1
@2125MeV: L=107.73pb-1
|M(K+K-)-M|<0.015GeV/c2; |M(π+π-γ)-Mη’|<0.015GeV/c2;
χ2 1C(K+K-π+π-γ) < 20;
|M(K+K-)-M|<0.015GeV/c2; Momentum(γ) ≤ 0.005GeV/c;
χ2 1C(K+K-π+π-γ) < 20;
|M(K+K-)-M|<0.015GeV/c2; Momentum(γ) >0.005GeV/c;
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Decay phi 1.00 K+ K- AngSam 1 -1; Enddecay
Decay eta' 1.000 pi+ pi- gamma DIY_rho2 0; Enddecay
End
BesEvtGen-00-03-18
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(2)|M(K+K-)-M|<0.015GeV/c2;
(3)|M(π+π-γ)-Mη’|<0.015GeV/c2;
1C(K+K-π+π-γ) < 20 |M(K+K-)-M|<0.015GeV/c2
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