Study of 𝐽/𝜓->𝛾𝜋0𝜋0𝜋0

Qiao Zhou, Beijiang Liu, Xiaoyan Shen

IHEP

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Outline

Motivation

Dataset

Event selection

Background study

PWA I/O check

Summary and next to do

Motivation

• 𝜂(1405) as a candidate of pseudoscalar glueball. However this state is not favored by lattice QCD prediction, which predict a glueball above 2 GeV.

• The peak at 1440MeV has a more complex structure. Since 𝜂(1405) and𝑓1(1420) are close in mass, peak at 1440MeV could be due to𝜂(1405), 𝑓1(1420) or both.

• The existence of the 𝜂(1295) is a controversial issue. DM2 and BaBar have observed 𝜂(1295). However it is not seen in some experiments and theobservations of the 𝜂(1295) are always in conjunction with the 𝑓1(1285)

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Motivation

• 1. BESIII studied the 𝐽/𝜓->𝛾𝜋+𝜋−𝜋0 and 𝐽/𝜓->𝛾𝜋0𝜋0𝜋0. The 𝑓1(1285) was observed with signal significance of 3.7𝜎and 1.2𝜎 for charged and neutral channels respectively.

2. The ratio of Br(𝜂(1440)−>𝑓0(980) 𝜋0->𝜋+𝜋−𝜋0) to Br(𝜂(1440)−>𝑎0(980) 𝜋0->𝜂𝜋0𝜋0) is 17.8%, which is much more than 𝑓0(980) - 𝑎0(980) mixing intensity(<1%).

3. The measured width of 𝑓0(980) is 4.6±5.1 MeV, which isanomalously narrower than the world average.

• We will study 𝐽/𝜓->𝛾𝜋0𝜋0𝜋0 with a PWA to understand the component of peak around at 1.4GeV in M(𝜋0𝜋0𝜋0) and measure 𝐽𝑃𝐶 as it has less backgroundthan 𝐽/𝜓->𝛾𝜋+𝜋−𝜋0

Phys. Rev. Lett. 108, 182001 (2012)

𝐽/𝜓->𝛾𝜋0𝜋0𝜋0

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225 M J/𝜓(2009)

225 M J/𝜓(2009)

Data sets

• Data:224M + 1087M 𝐽/𝜓 data (2009+2012)

• Inclusive MC:225M + 1000M 𝐽/𝜓 data (2009+2012)

• Signal MC:0.3M 𝐽/𝜓->𝛾𝜋0𝜋0𝜋0 (PHSP)

• Boss versionV7.0.1

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Event Selection for 𝐽/𝜓->𝛾𝜋0𝜋0𝜋0, 𝜋0->𝛾𝛾

Good charged tracks:• |cos(θ)| < 0.93• |𝑅𝑥𝑦|<1cm, |𝑅𝑍|<10cm

• 𝑁good = 0

Good photon• |Δ𝑡|<500ns• Barrel: E ≥ 25MeV, |cos(θ)| <0.8 • Endcap: E ≥ 50MeV, 0.86 < |cos(θ)| < 0.92• 7 ≤ 𝑁𝛾 ≤20

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1C kinematic fit

• 𝜒1𝑐2 < 10 , 𝑁𝜋0 ≥ 3

7C kinematic fit and 4C kinematic fit

• 𝜒7𝑐2 < 40

• To veto background with different number of photons𝜒4𝑐2 (7𝛾) < 𝜒4𝑐

2 (8𝛾) ; 𝜒4𝑐2 (7𝛾) < 𝜒4𝑐

2 (9𝛾)

Veto 𝝎

• 𝜔 come from 𝐽/𝜓->𝜔𝜋0𝜋0

• 𝑀𝛾6𝜋0 −𝑚𝜔 > 60MeV to veto it

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Invariant mass of 𝜸𝟔𝝅𝟎

𝛾6 is radiative photon

Veto 𝝅𝟎:

• 𝜋0 peak come from wrong combination between 𝜋0s or with radiative photon

• |𝑀𝛾6𝛾 − 𝑚𝜋0|> 20MeV to veto it. 𝛾6 is radiative photon, others is photon from 𝜋08

Invariant mass of 𝜸𝟔𝜸

After these above requirement, the 𝑀(𝜋0𝜋0𝜋0) are shown in below

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Zoom in to 1-3 GeV

In the left figure, there are three peak which are 𝜂, 𝜂′, 𝜂(1405) respectively.

𝜂 𝜂′ 𝜂(1405)

𝒇𝟎(980) mass window

• |M(𝜋10 𝜋20)-M(𝑓0(980)|<0.05GeV

Suppress the wrong combination of 𝛑𝟎

• |M(𝜋20 𝜋30)-0.99|>0.07&& |M(𝜋1

0 𝜋30)-0.99|>0.07GeV

• Scatter plot of M(𝜋0𝜋0𝜋0) vs M(𝜋10 𝜋20)

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After above criteria, Dalitz plot of 𝑀2 𝜋10𝜋20 vs. 𝑀2(𝜋1

0𝜋30) , Dalitz plot of 𝑀2(𝜋0𝑓0) vs.

𝑀2(𝛾𝑓0) and M(𝜋0𝜋0𝜋0) are shown in below.

𝜂(1405) and 𝑓1(1285)/𝜂(1295) for PWA11

𝑃(𝜋10)>𝑃(𝜋2

0)>𝑃(𝜋30)

Ratio of wrong combination of photon or 𝝅𝟏𝟎𝝅𝟐𝟎

Match:

At least 𝑘=0𝑛 (𝑝𝑥

𝑘(𝑔𝑒𝑛) − 𝑝𝑥𝑘′(𝑟𝑒𝑐))2+ (𝑝𝑦

𝑘(𝑔𝑒𝑛) − 𝑝𝑦𝑘′(𝑟𝑒𝑐))2+(𝑝𝑧

𝑘(𝑔𝑒𝑛) −

𝑝𝑧𝑘′(𝑟𝑒𝑐))2+ (𝐸𝑘 𝑔𝑒𝑛 − 𝐸𝑘

′(𝑟𝑒𝑐))2

PHSP MC sample 𝐽/𝜓′->𝛾𝜂(1405)->𝛾𝑓0(980)𝜋0 MC sample

Total event 300000 Total event 100000

After event selection 28835 After event selection 6528

Wrong combination of 𝛾 210 (0.7%) Wrong combination of 𝜋0 63 (1%)

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Background study

Inclusive MC sample

• After the selection, the distribution of 𝑀𝜋0𝜋0𝜋0 and 𝑀𝜋0𝜋0 are shown. There is no peaking background observed.

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• Channel of inclusive mc with selection

Number of 𝛾 Final state Number of event

7 𝛾𝜋0𝜋0𝜋0 𝜋0𝜋0𝜔 24

Non 𝜔 1

𝛾𝛾𝛾𝜋0𝜋0 16

8 𝜋0𝜋0𝜋0𝜋0 2

9 𝛾𝜋0𝜋0𝜋0𝜋0/𝛾𝛾𝛾𝜋0𝜋0𝜋0 3

6 𝜋0𝜋0𝜋0𝐾𝐿 2

5 𝛾𝜋0𝜋0 2

Total background 50

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Partial Wave Analysis

𝐵𝑊(𝑠) = 1

𝑀2−𝑠−𝑖𝑀Γ

ln 𝐿 =

𝑖=1

𝑁

ln(𝑑𝜎

𝑑Φ) − 𝑁𝑙𝑛𝜎

PWA is performed using unbinned maximum likelihood fit. In practice, 𝑆 = − ln 𝐿 is minimized.

Amplitudes constructed using convariant tensor formalism.

The intermediate state decay is described with a relativistic constant width Breit-Wigner

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PWA I/O check

We generated two MC sample to do the input/output check

Sample 1: taking 𝜂 1405 , 𝑓0 980 and PHSP

Component

𝜂(1405)−> 𝑓0980 𝜋0

𝜂(1405)-> 𝜋0𝜋0𝜋0

𝐽/𝜓->(direct)𝛾𝑓0980 𝜋0

𝐽/𝜓->(direct)𝛾𝜋0𝜋0𝜋0

Sample 2: on the basis of sample 1, add 10% 𝑓1(1420)->𝑓0 980 𝜋0

Component

𝜂(1405)−> 𝑓0980 𝜋0

𝜂(1405)-> 𝜋0𝜋0𝜋0

𝐽/𝜓->(direct)𝛾𝑓0980 𝜋0

𝐽/𝜓->(direct)𝛾𝜋0𝜋0𝜋0

𝑓1(1420)->𝑓

0980 𝜋0

PWA I/O check

Sample 1

The projection of mass spectra of global fit

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Component input output

𝜂(1405)−> 𝑓0 980 𝜋0 2711.1 2725.6 ± 29.9 (+0.5𝜎)

𝜂(1405)-> 𝜋0𝜋0𝜋0 1951.8 1974.7± 78.3 (+0.3𝜎)

𝐽/𝜓->(direct)𝛾𝑓0 980 𝜋0 3334.1 3260.8± 117.4 (+0.6𝜎)

𝐽/𝜓->(direct)𝛾𝜋0𝜋0𝜋0 4800.1 4801.5 ± 112.8 (+0.01𝜎)

The angular distributions of global fit

Check for number of events for component

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PWA I/O check

Sample 2:

The projection of mass spectra of global fit

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Component input output

𝜂(1405)−> 𝑓0 980 𝜋0

1710.3 1839.9±66.5 (+1.9𝜎)

𝜂(1405)-> 𝜋0𝜋0𝜋0 697.9 696.1±40.3 (-0.04𝜎)

𝐽/𝜓->(direct)𝛾𝑓0 980 𝜋0

427.5 454.4±34.8 (+0.8𝜎)

𝐽/𝜓->(direct)𝛾𝜋0𝜋0𝜋0 847.7 834.6±40.3 (-0.3𝜎)

𝑓1(1420)->𝑓0 980 𝜋0

173.5 163.3±36.6 (-0.3𝜎)

The angular distributions of global fit

Check for number of events for component

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component significance

𝜂(1405)−> 𝑓0 980 𝜋0 17.8𝜎

𝜂(1405)-> 𝜋0𝜋0𝜋0 18.8𝜎

𝐽/𝜓->(direct)𝛾𝑓0 980 𝜋0 8𝜎

𝐽/𝜓->(direct)𝛾𝜋0𝜋0𝜋0 >>5𝜎

𝑓1(1420)->𝑓0 980 𝜋0 11.7𝜎

Check for significance of each component

Check for 𝐽𝑃𝐶 of 𝜂(1405) and 𝑓1(1420)

𝟎− + 𝟏+ + 𝟐− +

𝜂(1405) -2533.95 -2313.95 -2365.23

𝑓1(1420) -2423.59 -2533.95 -2425.52

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Summary • In the channel of 𝐽/𝜓->𝛾𝜋0𝜋0𝜋0, 𝜂 1405 and 𝑓0(980) signal are

observed.• The ratio of wrong combinations of gamma or photon is less than 1%• I/O check for PWA are consistent within statistic error.

Next to do• PWA with the real data is ongoing• The resolution of M(pi pi) will be included in PWA fit• Working with theorist to import triangle singularity model

in PWA fit

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Back up

The difference between our’s event selection and Phys. Rev. Lett. 108, 182001 • Good charged track

Vr < 2 cm ,|Vz| < 20 cm (Vr < 1 cm ,|Vz| < 10 cm with |cos(θ)| < 0.93)𝑁𝑔𝑜𝑜𝑑=0

• Good photonBarrel: E ≥ 25MeV, |cos(θ)| <0.8 ;Endcap: E ≥ 50MeV, 0.86 < |cos(θ)| < 0.927 ≤ 𝑁𝛾 ≤ 9 (7 ≤ 𝑁𝛾 ≤ 20 )

• Candidates are reconstructed from pairs of photon candidates0.075GeV < 𝑀 𝛾𝛾 < 0.175GeV and 𝜒1𝑐

2 <25; |cos(θ)| < 0.95 (only 𝜒1𝑐2 <10)

𝑁𝜋0 ≥ 3

• 7C fit is been performed by three 𝜋0 and single photon.𝜒7𝑐2 < 60 (𝜒7𝑐

2 < 40 ; 𝜒4𝑐2 (7𝛾) < 𝜒4𝑐

2 (8𝛾)， 𝜒4𝑐2 (7𝛾) < 𝜒4𝑐

2 (8𝛾) )

• 𝑀𝛾7𝜋0 −𝑚𝜛 > 50MeV( 𝑀𝛾7𝜋0 −𝑚𝜛 > 60MeV)

• |𝑀𝛾6𝛾 − 𝑚𝜋0|> 20MeV