πΎπ0π0π0indico.ihep.ac.cn/event/6543/session/5/...Β Β· motivation β’ 1. besiii studied...
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Study of π½/π->πΎπ0π0π0
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
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Motivation
β’ π(1405) as a candidate of pseudoscalar glueball. However this state is not favored by lattice QCD prediction, which predict a glueball above 2 GeV.
β’ The peak at 1440MeV has a more complex structure. Since π(1405) andπ1(1420) are close in mass, peak at 1440MeV could be due toπ(1405), π1(1420) or both.
β’ The existence of the π(1295) is a controversial issue. DM2 and BaBar have observed π(1295). However it is not seen in some experiments and theobservations of the π(1295) are always in conjunction with the π1(1285)
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Motivation
β’ 1. BESIII studied the π½/π->πΎπ+πβπ0 and π½/π->πΎπ0π0π0. The π1(1285) was observed with signal significance of 3.7πand 1.2π for charged and neutral channels respectively.
2. The ratio of Br(π(1440)β>π0(980) π0->π+πβπ0) to Br(π(1440)β>π0(980) π0->ππ0π0) is 17.8%, which is much more than π0(980) - π0(980) mixing intensity(<1%).
3. The measured width of π0(980) is 4.6Β±5.1 MeV, which isanomalously narrower than the world average.
β’ We will study π½/π->πΎπ0π0π0 with a PWA to understand the component of peak around at 1.4GeV in M(π0π0π0) and measure π½ππΆ as it has less backgroundthan π½/π->πΎπ+πβπ0
Phys. Rev. Lett. 108, 182001 (2012)
π½/π->πΎπ0π0π0
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225 M J/π(2009)
225 M J/π(2009)
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Data sets
β’ Data:224M + 1087M π½/π data (2009+2012)
β’ Inclusive MC:225M + 1000M π½/π data (2009+2012)
β’ Signal MC:0.3M π½/π->πΎπ0π0π0 (PHSP)
β’ Boss versionV7.0.1
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Event Selection for π½/π->πΎπ0π0π0, π0->πΎπΎ
Good charged tracks:β’ |cos(ΞΈ)| < 0.93β’ |π π₯π¦|<1cm, |π π|<10cm
β’ πgood = 0
Good photonβ’ |Ξπ‘|<500nsβ’ Barrel: E β₯ 25MeV, |cos(ΞΈ)| <0.8 β’ Endcap: E β₯ 50MeV, 0.86 < |cos(ΞΈ)| < 0.92β’ 7 β€ ππΎ β€20
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1C kinematic fit
β’ π1π2 < 10 , ππ0 β₯ 3
7C kinematic fit and 4C kinematic fit
β’ π7π2 < 40
β’ To veto background with different number of photonsπ4π2 (7πΎ) < π4π
2 (8πΎ) ; π4π2 (7πΎ) < π4π
2 (9πΎ)
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Veto π
β’ π come from π½/π->ππ0π0
β’ ππΎ6π0 βππ > 60MeV to veto it
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Invariant mass of πΈππ π
πΎ6 is radiative photon
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Veto π π:
β’ π0 peak come from wrong combination between π0s or with radiative photon
β’ |ππΎ6πΎ β ππ0|> 20MeV to veto it. πΎ6 is radiative photon, others is photon from π08
Invariant mass of πΈππΈ
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After these above requirement, the π(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 π, πβ², π(1405) respectively.
π πβ² π(1405)
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ππ(980) mass window
β’ |M(π10 π20)-M(π0(980)|<0.05GeV
Suppress the wrong combination of ππ
β’ |M(π20 π30)-0.99|>0.07&& |M(π1
0 π30)-0.99|>0.07GeV
β’ Scatter plot of M(π0π0π0) vs M(π10 π20)
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After above criteria, Dalitz plot of π2 π10π20 vs. π2(π1
0π30) , Dalitz plot of π2(π0π0) vs.
π2(πΎπ0) and M(π0π0π0) are shown in below.
π(1405) and π1(1285)/π(1295) for PWA11
π(π10)>π(π2
0)>π(π30)
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Ratio of wrong combination of photon or π πππ ππ
Match:
At least π=0π (ππ₯
π(πππ) β ππ₯πβ²(πππ))2+ (ππ¦
π(πππ) β ππ¦πβ²(πππ))2+(ππ§
π(πππ) β
ππ§πβ²(πππ))2+ (πΈπ πππ β πΈπ
β²(πππ))2
PHSP MC sample π½/πβ²->πΎπ(1405)->πΎπ0(980)π0 MC sample
Total event 300000 Total event 100000
After event selection 28835 After event selection 6528
Wrong combination of πΎ 210 (0.7%) Wrong combination of π0 63 (1%)
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Background study
Inclusive MC sample
β’ After the selection, the distribution of ππ0π0π0 and ππ0π0 are shown. There is no peaking background observed.
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β’ Channel of inclusive mc with selection
Number of πΎ Final state Number of event
7 πΎπ0π0π0 π0π0π 24
Non π 1
πΎπΎπΎπ0π0 16
8 π0π0π0π0 2
9 πΎπ0π0π0π0/πΎπΎπΎπ0π0π0 3
6 π0π0π0πΎπΏ 2
5 πΎπ0π0 2
Total background 50
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Partial Wave Analysis
π΅π(π ) = 1
π2βπ βππΞ
ln πΏ =
π=1
π
ln(ππ
πΞ¦) β ππππ
PWA is performed using unbinned maximum likelihood fit. In practice, π = β ln πΏ 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 π 1405 , π0 980 and PHSP
Component
π(1405)β> π0980 π0
π(1405)-> π0π0π0
π½/π->(direct)πΎπ0980 π0
π½/π->(direct)πΎπ0π0π0
Sample 2: on the basis of sample 1, add 10% π1(1420)->π0 980 π0
Component
π(1405)β> π0980 π0
π(1405)-> π0π0π0
π½/π->(direct)πΎπ0980 π0
π½/π->(direct)πΎπ0π0π0
π1(1420)->π
0980 π0
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PWA I/O check
Sample 1
The projection of mass spectra of global fit
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Component input output
π(1405)β> π0 980 π0 2711.1 2725.6 Β± 29.9 (+0.5π)
π(1405)-> π0π0π0 1951.8 1974.7Β± 78.3 (+0.3π)
π½/π->(direct)πΎπ0 980 π0 3334.1 3260.8Β± 117.4 (+0.6π)
π½/π->(direct)πΎπ0π0π0 4800.1 4801.5 Β± 112.8 (+0.01π)
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
π(1405)β> π0 980 π0
1710.3 1839.9Β±66.5 (+1.9π)
π(1405)-> π0π0π0 697.9 696.1Β±40.3 (-0.04π)
π½/π->(direct)πΎπ0 980 π0
427.5 454.4Β±34.8 (+0.8π)
π½/π->(direct)πΎπ0π0π0 847.7 834.6Β±40.3 (-0.3π)
π1(1420)->π0 980 π0
173.5 163.3Β±36.6 (-0.3π)
The angular distributions of global fit
Check for number of events for component
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component significance
π(1405)β> π0 980 π0 17.8π
π(1405)-> π0π0π0 18.8π
π½/π->(direct)πΎπ0 980 π0 8π
π½/π->(direct)πΎπ0π0π0 >>5π
π1(1420)->π0 980 π0 11.7π
Check for significance of each component
Check for π½ππΆ of π(1405) and π1(1420)
πβ + π+ + πβ +
π(1405) -2533.95 -2313.95 -2365.23
π1(1420) -2423.59 -2533.95 -2425.52
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Summary β’ In the channel of π½/π->πΎπ0π0π0, π 1405 and π0(980) signal are
observed.β’ The ratio of wrong combinations of gamma or photon is less than 1%β’ I/O check for PWA are consistent within statistic error.
Next to doβ’ PWA with the real data is ongoingβ’ The resolution of M(pi pi) will be included in PWA fitβ’ Working with theorist to import triangle singularity model
in PWA fit
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Back up
The difference between ourβs event selection and Phys. Rev. Lett. 108, 182001 β’ Good charged track
Vr < 2 cm ,|Vz| < 20 cm (Vr < 1 cm ,|Vz| < 10 cm with |cos(ΞΈ)| < 0.93)πππππ=0
β’ Good photonBarrel: E β₯ 25MeV, |cos(ΞΈ)| <0.8 ;Endcap: E β₯ 50MeV, 0.86 < |cos(ΞΈ)| < 0.927 β€ ππΎ β€ 9 (7 β€ ππΎ β€ 20 )
β’ Candidates are reconstructed from pairs of photon candidates0.075GeV < π πΎπΎ < 0.175GeV and π1π
2 <25; |cos(ΞΈ)| < 0.95 (only π1π2 <10)
ππ0 β₯ 3
β’ 7C fit is been performed by three π0 and single photon.π7π2 < 60 (π7π
2 < 40 ; π4π2 (7πΎ) < π4π
2 (8πΎ)οΌ π4π2 (7πΎ) < π4π
2 (8πΎ) )
β’ ππΎ7π0 βππ > 50MeV( ππΎ7π0 βππ > 60MeV)
β’ |ππΎ6πΎ β ππ0|> 20MeV