Analysis of the Radiative Decay of Eta in CLAS

Torri Jeske Moskov Amaryan Georgie Mbianda Njencheu Ilya Larin

APS April Meeting, 2019

Old Dominion UniversityOn behalf of the CLAS Collaboration

Light Meson Decay Program at CLAS

• Access to multiple light meson decays via

where

!2

γ + p → p + X

X = π0, η, ω, ρ, η′�, and ϕ

π0, η, η′� → e+e−γ

η, η′� → π+π−γ

η, η′� → π+π−π0

η′� → π+π−η

Dalitz decays Transition form factor

Radiative decays Box anomalies, FSI

Hadronic decays Dalitz plot analysis, quark mass ratio,

π0, η, η′� → e+e−γ

η, η′� → π+π−γ

η, η′� → π+π−π0

η′ � → π+π−η

Eta Meson Properties

!3

τ = 5 ⋅ 10−19sMη = 547.862 ± 0.017MeV

Γ = 1.31 ± 0.05keV

Decay Branching Ratio

η → π+π−π0 (22.92 ± 0.34) %

η → π+π−γ (4.22 ± 0.08) %

η → e+e−γ

η → μ+μ−γ

(6.9 ± 0.4) × 10−3

(3.1 ± 0.4) × 10−4

Triangle and Box anomalies

• At the chiral limit, all decays are determined by Wess-Zumino-Witten Lagrangian

• Amplitude is sensitive to box anomaly and predicts decay width of 35.7 eV(1)

!4

Aη→π+π−γ ∝e

4 3π2F3π ( Fπ

F8cos θ − 2

Fπ

F0sin θ)

ηπ+

π−

γ

η

γ

γ

+

The Box Anomaly

• Must properly include momentum dependence to describe experimental data

• Modify amplitude by reaction specific polynomial and pion vector form factor(4)

• Want to measure alpha parameter for decay:

!5

η → π+π−γ

Aη→π+π−γ × [FPV(sππ) ⋅ (1 + αsππ)]

Γexpt(η → π+π−γ) = 55.3 ± 2.4eV

Previous measurements of alpha parameter

!6

Gormley, et. al. α = 1.8 ± 0.04

The g11 experiment with CLAS at JLAB

•May 17, 2004 - July 29, 2004

•Beam energy: 4 GeV •Photon beam energy: 1.5-3.5 GeV

•Liquid H2 target •21 TB of raw data collected

!7

Event Selection and Particle ID

Trigger required two charged tracks in different sectors

Required events with three charged tracks corresponding to

Required events to have at least one photon

Time of Flight (TOF) was used for particle identification

Detect all final state particles!8

Talk Title Here

Data Cuts

!9

0 0.5 1 1.5 2 2.50200400600800

10001200140016001800

310× Momentum [GeV]γ

0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20

500

1000

1500

2000

2500

3000(me_PPipPim-Pgam) [GeV]

Data Cuts

!10

0.001− 0.0005− 0 0.0005 0.0010

100

200

300

400

500

]2mx2_PPipPimGam [GeV

0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26

]2) [GeV-π+πS(

10000

20000

30000

40000

50000

60000

70000

80000

Analysis

!11

Notacceptancecorrected

Simulations

1. Simulate IM( ) from 0.30 GeV to 0.50 GeV

2. GSIM: generated events were passed through GEANT software in CLAS

3. GPP: GSIM Post Processor is used for smearing due to detector response

4. RECIS: Reconstruction program to analyze GSIM output in same manner as raw data

!12

⇡+⇡�

h_PpEntries 64597Mean 1.07Std Dev 0.3452

0 0.5 1 1.5 2 2.5 3 3.500.0020.0040.0060.008

0.010.0120.0140.0160.0180.02

0.022 h_PpEntries 64597Mean 1.07Std Dev 0.3452

h_PpipEntries 64597Mean 0.513Std Dev 0.2787

0 0.5 1 1.5 2 2.500.0020.0040.0060.008

0.010.0120.0140.0160.0180.02

0.0220.024

h_PpipEntries 64597Mean 0.513Std Dev 0.2787

h_PpimEntries 64597Mean 0.6351Std Dev 0.3188

0 0.5 1 1.5 2 2.500.0020.0040.0060.008

0.010.0120.0140.0160.018

h_PpimEntries 64597Mean 0.6351Std Dev 0.3188

h_PgamEntries 64597Mean 0.2948Std Dev 0.1329

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.0050.01

0.015

0.020.025

0.030.035

h_PgamEntries 64597Mean 0.2948Std Dev 0.1329

MC and Data Comparison

!13

Pp [GeV ] Pπ+ [GeV ]

Pπ− [GeV ] Pγ [GeV ]

DatarecMC

h_th_PEntries 11898Mean 42.62Std Dev 9.742

0 10 20 30 40 50 600

0.0020.0040.0060.008

0.010.0120.014

h_th_PEntries 11898Mean 42.62Std Dev 9.742

h_th_PipEntries 11898Mean 35.91Std Dev 19.99

0 20 40 60 80 100 120 1400

0.005

0.01

0.015

0.02

h_th_PipEntries 11898Mean 35.91Std Dev 19.99

h_th_PimEntries 11898Mean 41.92Std Dev 17.65

0 20 40 60 80 100 120 1400

0.005

0.01

0.015

0.02

0.025 h_th_PimEntries 11898Mean 41.92Std Dev 17.65

h_th_GEntries 11898Mean 28.06Std Dev 9.552

0 10 20 30 40 50 600

0.002

0.004

0.006

0.008

0.01

0.012

0.014h_th_G

Entries 11898Mean 28.06Std Dev 9.552

MC + Data Comparison II

!14

θP [deg]

θπ+ [deg]

θπ− [GeV ]

θγ [deg]

θπ+ [deg]

θγ [deg]

DatarecMC

h_phi_PEntries 11898Mean 3.128− Std Dev 104.5

150− 100− 50− 0 50 100 1500

0.002

0.004

0.006

0.008

h_phi_PEntries 11898Mean 3.128− Std Dev 104.5

h_phi_PipEntries 11898Mean 3.708− Std Dev 104.4

150− 100− 50− 0 50 100 1500

0.002

0.004

0.006

0.008

0.01h_phi_Pip

Entries 11898Mean 3.708− Std Dev 104.4

h_phi_PimEntries 11898Mean 3.389− Std Dev 105.6

150− 100− 50− 0 50 100 1500

0.002

0.004

0.006

0.008

0.01

h_phi_PimEntries 11898Mean 3.389− Std Dev 105.6

h_phi_GEntries 11898Mean 2.793Std Dev 105

150− 100− 50− 0 50 100 1500

0.002

0.004

0.006

0.008

0.01

0.012h_phi_G

Entries 11898Mean 2.793Std Dev 105

MC + Data Comparison III

!15

ϕP [deg] ϕπ+ [deg]

ϕπ− [deg] ϕγ [deg]

DatarecMC

Summary and Future Work

Wednesday, October 25, 2017

Torri C. Jeske

roark@jlab.org

• Box anomaly is important to describe experimental distributions

• Alpha parameter has been measured previously but measurements are not consistent with theoretical descriptions

• Acceptance and systematic error calculations in progress

η → π+π−π0

References

1. B.R. Holstein, Phys. Scripta, T99:55-67, 2002

2. PDG, Chin. Phys, 090001, 2014

3. WASA-at-COSY Phys. Letter. B707, 243-249, 2012

4. F. Stollenwerk et al., Phys. Lett. B707, 184-190, 2012

5. KLOE Phys. Letter. B718, 910-914, 2013

!17