Observation of e e → η' ϕ

Observation of e+e- → η' ϕ

(R-Scan Data: √s=2.0GeV~3.08GeV)

Yankun Sun Zhihong Wang

(BESIII-USTC Group)

2017/2/19 1

Observation of e+e- → η' ϕ

(R-Scan Data: √s=2.0GeV~3.08GeV)

2017/2/19 2

Outline

1. Introduction.

2. Data samples and MC simulation.

3. Event selection.

4. Cross section measurement.

5. Systematic error estimation.

6. Summary.

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Introduction(Cross section Line shape)

From 232fb-1 of BABAR data, signal of e+e- →γISR ϕ(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'ϕ(1020).

Possible decay mode of Y(2175) → η' ϕ(1020) with study of cross section line shape.

Data sets and MC simulation

1. BOSS665p01.

2. R-scan data sets: ( 2015)

3. 100K Signal MC by “ConExc” at each energy point.

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√s (GeV) Lum. (pb-1)

3.080 126.185

3.020 17.290

3.000 15.881

2.981 16.071

2.950 15.942

2.900 105.253

√s (GeV) Lum. (pb-1)

2.800 1.008

2.700 1.034

2.6464 34.003

2.6444 33.722

2.500 1.098

2.396 66.869

√s (GeV) Lum. (pb-1)

2.3864 22.549

2.3094 21.089

2.2324 11.856

2.200 13.699

2.175 10.625

2.150 2.841

√s (GeV) Lum. (pb-1)

2.125 108.49

2.100 12.167

2.050 3.343

2.000 10.074

(1) e+ e-→η'ϕ(1020) (2) e+ e-→K+K-ρ0 (3) e+ e-→K+K-π+π-

(4) e+ e-→ϕπ+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;

Kaon: prob_K>prob_p && prob_K>prob_π;

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): χ21C(K+K-K±γ) < 20;

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@2125MeV: L=108.49pb-1

After ϕ selection(1) χ2

1C(K+K-π+π-γ) < 20;

@2125MeV: L=108.49pb-1

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@2125MeV: L=108.49pb-1

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@2125MeV: L=108.49pb-1

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(1) χ21C(K+K-π+π-γ) < 20;

(2)|M(K+K-)-Mϕ|<0.02GeV/c2;

(3)η' Fitting : Signal: MC shape ⊗Gaussian;Background: 3rd Poly;N=255.6 ± 23.4

Factor = 0.36

1M Inclusive MC @2125MeV

112017/2/19 /besfs/groups/tauqcd/gaoxl/Omegaeta/SigBkgMC/qqbarMC/2125/MC

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Comparison MC and RealData

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Comparison MC and RealData

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Comparison MC and RealData

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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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Parameters of Gaussian

Minimizer is LinearChi2 = 8.7NDf = 10p0 = 1.8 +/- 0.3

Minimizer is LinearChi2 = 12.3NDf = 10p0 = -1.2 +/- 0.2

Results (I)

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Results (II)

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Due to their low statistic, theseenergy points are fitted withfixed parameters from nearenergy points with largerstatistic.

σ(e+e-→ ϕ(1020)η'): with η'→π+π-γ

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Systematic uncertainty(2125MeV)

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Source Method Value (%)

Luminosity Bhabha events 1.0

Tracking* Control sample: e+e-→ K+K-π+π- 3.0

PID Control sample: e+e-→ K+K-π+π- 3.0

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

Fitting range [0.85,1.05] [0.80,1.10] 1.8

MC Statistic of MC 0.5

Branching ratio 2014 PDG 2.0

Others Trigger, Start time, FSR 1.0

Total -- 7.8

Systematic uncertainty

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Fit of cross section line shape

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Assuming a single resonance around 2.2GeV.

Signal: a phase-space modified Breit-Wigner function:

2 2

( ' ) ( )( )

( )

tote e

tot

B PS sBW s

s M iM PS M

Background: phase-space contribution: ( )PS s

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' ϕ 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

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Backup

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@2125MeV: Topolgy

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(1) χ21C(K+K-π+π-γ) < 20;

(2)M(K+K-) : [0.48, 0.50] GeV/c2;

@2125MeV: L=107.73pb-1

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(1) χ21C(K+K-π+π-γ) < 20;

@2125MeV: L=107.73pb-1

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Background Analysis

Momentum(γ)≤0.05GeV

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Background Analysis

χ21C(K+K-π+π-γ) < 20;

|M(K+K-)-Mϕ|<0.015GeV/c2;|M(π+π-γ)-Mη’|<0.015GeV/c2;

χ21C(K+K-π+π-γ) < 20;

|M(K+K-)-Mϕ|<0.015GeV/c2;Momentum(γ) ≤ 0.005GeV/c;

χ21C(K+K-π+π-γ) < 20;

|M(K+K-)-Mϕ|<0.015GeV/c2;Momentum(γ) >0.005GeV/c;

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Generator : CONEXC

Decay J/psi1.000 phi eta' DIY_PhiEtap;Enddecay

Decay phi1.00 K+ K- AngSam 1 -1;Enddecay

Decay eta'1.000 pi+ pi- gamma DIY_rho2 0;Enddecay

End

BesEvtGen-00-03-18

Amplitude including ω、 ρ、 ρ’(1450)

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Cuts of mass windows

(1) χ21C(K+K-π+π-γ) < 20;

(2)|M(K+K-)-Mϕ|<0.015GeV/c2;

(3)|M(π+π-γ)-Mη’|<0.015GeV/c2;

χ21C(K+K-π+π-γ) < 20 χ2

1C(K+K-π+π-γ) < 20|M(K+K-)-Mϕ|<0.015GeV/c2

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Comparison (1)

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Comparison (2)

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Comparison (3)

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Comparison (4)

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Comparison (5)

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Amplitude(η'→π+π-γ)

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Amplitude(η'→π+π-γ)

Cross Check of 1C and 4C: η'→π+π-γ

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Cross Check of 1C and 4C: η'→π+π-γ

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Cross Check : η'→π+π-η

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Cross Check : η'→π+π-η

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Cross Check : Miss η'

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