Study of →𝛾𝐷 at BESIIIΒ Β· Study of + βˆ’β†’π›Ύπ· 𝑠 +𝐷 𝑠 βˆ’ at BESIII Wenjing...

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Study of 𝑒+π‘’βˆ’ β†’ 𝛾𝐷𝑠+𝐷𝑠

βˆ’ at BESIII

Wenjing Zhu1, XiaoLong Wang1,ChangZheng Yuan2

Fudan University1

IHEP2

2019.10.9

2019/10/9 1

Outline

β€’ Motivation and introduction

β€’ BESIII data samples

β€’ General selections

β€’ Signals and background study

β€’ Summary and plan

2019/10/9 2

Motivations β€’ Z(3930) was discovered by Belle in 𝛾𝛾 β†’ D𝐷 process is asigned to be πœ’π‘2(2P).

β€’ M=(3929 Β± 5 Β± 2)MeV/𝑐2 and Ξ“=(29Β±10 Β± 2)MeV

β€’ π‘‹βˆ—(3860) was discovered by Belle in 𝑒+π‘’βˆ’ β†’ 𝐽 πœ“ + 𝐷𝐷 , which agrees with πœ’π‘0 2P . β€’ M = (3862

+26 + 40βˆ’32 βˆ’ 13

) MeV/𝑐2 and Ξ“=(201+154 + 88βˆ’67 βˆ’ 82

) MeV

β€’ The highest charmoniumlike vector Y(4660) state was discovered in 𝑓0(980)πœ“β€² final states, where 𝑓0(980) could contain ssbar components.

β€’ How about replacing 𝐷𝐷 with 𝐷𝑠+𝐷𝑠

βˆ’ ?

β€’ The radiative decay Y(4660)β†’ 𝛾𝐷𝑠+𝐷𝑠

βˆ’ should be allowed, and a πœ’π‘π½(nP)–like state may exist in 𝐷𝑠

+π·π‘ βˆ’, since there should ssbar in 𝐷𝑠+π·π‘ βˆ’ system.

β€’ BESIII is taking data on Y(4660), which allows the search.

β€’ We have Y(4360) data right now, which can be used for preliminary study.

2019/10/9 3

[Phys.Rev.Lett.96,082003] [PhysRevD.95.112003]

Z(3930)β†’ D𝐷 π‘‹βˆ—(3860) β†’ D𝐷 Y(4660) Y(4360)

BESIII data/MC samples and MC simulation I

β€’ XYZ Data(Boss 703) at Ecms=4.36GeV β€’ Signal MC:

β€’ 0.1 M events at √s=4.36GeV and √s=4.66GeV β€’ The channel: β€’ 𝑒+π‘’βˆ’ β†’ 𝛾X(3.94),(via PHSP) X(3.94)β†’ 𝐷𝑠+π·π‘ βˆ’(via PHSP) β€’ 𝐷𝑠+ β†’ 𝐾+πΎβˆ’πœ‹+, (via D_DALITZ)

β€’ π·π‘ βˆ’ β†’ 𝐾+πΎβˆ’πœ‹βˆ’, (via D_DALITZ)

β€’ Inclusive MC: MC-703(hadron) at √s=4.36GeV β€’ Bkg MC:

β€’ 0.1 M events at√s=4.36GeV β€’ The channel:

β€’ 𝑒+π‘’βˆ’ β†’ π‘Œ β†’ π·π‘ βˆ—βˆ’π·π‘ 

+ (via HELAMP 1.0 0.0 0.0 0.0 -1.0 0.0)

Case1:

β€’ π·π‘ βˆ—βˆ’ β†’ π›Ύπ·π‘ βˆ’(93.5Β±0.7) % (via VSP_PWAVE), π·π‘ βˆ—βˆ’ β†’ πœ‹0π·π‘ βˆ’(5.8Β±0.7)%(via VSS), π·π‘ βˆ—βˆ’ β†’

𝑒+π‘’βˆ’π·π‘ βˆ’(6.7Β±1.6)Γ— 10βˆ’3(via PHSP), π·π‘ βˆ’ β†’anything

β€’ 𝐷𝑠+ β†’ 𝐾+πΎβˆ’πœ‹+ (via D_DALITZ)

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BESIII data/MC samples and MC simulation II

β€’ Case2:

π·π‘ βˆ—βˆ’ β†’ π›Ύπ·π‘ βˆ’(93.5Β±0.7) % (via VSP_PWAVE), π·π‘ βˆ—βˆ’ β†’ πœ‹0π·π‘ βˆ’(5.8Β±0.7)%(via VSS),

π·π‘ βˆ—βˆ’ β†’ 𝑒+π‘’βˆ’π·π‘ βˆ’(6.7Β±1.6)Γ— 10βˆ’3(via PHSP), π·π‘ βˆ’ β†’ 𝐾+πΎβˆ’πœ‹βˆ’(via D_DLITZ)

𝐷𝑠+ β†’anything

β€’ 0.1 M events at√s=4.36GeV

β€’ The channel:

𝑒+π‘’βˆ’ β†’ π‘Œ β†’ π·π‘ βˆ—+π·π‘ βˆ—βˆ’(via PHSP), π·π‘ βˆ—+ β†’ 𝛾𝐷𝑠+(via VSP_PWAVE), π·π‘ βˆ—βˆ’ β†’ π›Ύπ·π‘ βˆ’(via VSP_PWAVE), 𝐷𝑠+ β†’ 𝐾+πΎβˆ’πœ‹+(via D_DLITZ)

β€’ 0.1 M events at 𝑠= 4.36GeV

β€’ The channel :

𝑒+π‘’βˆ’ β†’ π‘Œ β†’ 𝛾𝐼𝑆𝑅𝐷𝑠+π·π‘ βˆ’(via VSS), 𝐷𝑠+ β†’ 𝐾+πΎβˆ’πœ‹+(via D_DLITZ)

2019/10/9 5

Selection criteria I β€’ Reconstruction:

β€’ 𝑒+π‘’βˆ’ β†’ 𝛾𝐷𝑠+π·π‘ βˆ’, 𝐷𝑠+ β†’ 𝐾+πΎβˆ’πœ‹+/πœ™πœ‹+, πœ™ β†’ 𝐾+πΎβˆ’

β€’ Charged tracks: β€’ N(trk)β‰₯ 3

β€’ 𝑉π‘₯𝑦= 𝑉π‘₯2 + 𝑉𝑦2<1 cm and 𝑉𝑧 < 10π‘π‘š

β€’ π‘π‘œπ‘ πœƒ < 0.93, in the active region of MDC

β€’ Photon(s): β€’ E_barrel > 25 MeV or E_endcap > 50 MeV β€’ N(𝛾)β‰₯ 1 β€’ >5∘ away from any good charged track β€’ t < 700ns after T0 of one event

2019/10/9 6

Selection criteria II

β€’ PID: β€’ Prob(K)>Prob(πœ‹) and Prob(K)>0.001 for Kaon β€’ Otherwise, it is a pion.

β€’ Kinematic constrain β€’ 4C kinematic fit

β€’ π‘€π‘Ÿπ‘’π‘(𝛾𝐷𝑠) constraint to Ds nominal mass

β€’ Mass windows: β€’ 𝑀 𝐾+πΎβˆ’πœ‹+ βˆ’π‘š(𝐷𝑠) < 15 MeV for Ds signal β€’ π‘€π‘Ÿπ‘’π‘ 𝛾𝐷𝑠 βˆ’π‘š(𝐷𝑠) <15 MeV for another Ds

β€’ π‘«π’”βˆ— veto: 𝑀 𝛾𝐷𝑠 βˆ’π‘š(π·π‘ βˆ—) > 15MeV and π‘€π‘Ÿπ‘’π‘ 𝐾+πΎβˆ’πœ‹+ βˆ’π‘š(𝐷𝑠 βˆ—) >

15MeV

β€’ Efficiencies： β€’ 𝑒+π‘’βˆ’ β†’ 𝛾𝐷𝑠+π·π‘ βˆ’, 𝐷𝑠+ β†’ 𝐾+πΎβˆ’πœ‹+: πœ€ = 32.28% at Ecms=4.36 GeV

β€’ 𝑒+π‘’βˆ’ β†’ 𝛾𝐷𝑠+π·π‘ βˆ’, 𝐷𝑠+ β†’ 𝐾+πΎβˆ’πœ‹+: πœ€ = 19.61% at Ecms=4.66 GeV

2019/10/9 7

Ds signals in M(𝐾+πΎβˆ’πœ‹+)

2019/10/9 8

M = (1968.6Β±0.2) MeV /𝑐2 𝜎 = 4.2 Β± 0.2 MeV/𝑐2

M = (1967.8Β±0.1) MeV /𝑐2 𝜎 = 4.4 Β± 0.1 MeV/𝑐2

PDF: Gaussian + second-order polynomial

Signal MC

Data

M = (1968.6Β±0.3) MeV /𝑐2 𝜎 = 4.1 Β± 0.3 MeV/𝑐2

Signal MC

𝑠=4.36GeV 𝑠=4.66GeV

𝜎 β‰ˆ 4 MeV/𝑐2 Signal region: 𝑀 𝐾+πΎβˆ’πœ‹+ βˆ’π‘š(𝐷𝑠) < 15 MeV

Ds in M(𝐾+πΎβˆ’πœ‹+) from bkgs

2019/10/9 9

Case1 π·π‘ βˆ—π·π‘ βˆ— MC

Inclusive MC M = (1968.8Β±0.3) MeV /𝑐2 𝜎 = 4.4 Β± 0.3 MeV/𝑐2

The mass resolution is similar to the one from signal MC simulation

PDF：Gaussian + second-order polynomial

Case2

M = (1968.7Β±0.2) MeV /𝑐2 𝜎 = 4.7 Β± 0.2 MeV/𝑐2

M = (1968.7Β±0.1) MeV /𝑐2 𝜎 = 4.6 Β± 0.1 MeV/𝑐2

𝛾𝐼𝑆𝑅𝐷𝑠+π·π‘ βˆ’

M = (1968.3Β±0.2) MeV /𝑐2 𝜎 = 4.7 Β± 0.2 MeV/𝑐2

Resolutions of π‘€π‘Ÿπ‘’π‘(𝛾𝐷𝑠+)

2019/10/9 10

PDF: Gaussian/Crystal_ball + second-order polynomial/Agus

M = (1963.8Β±0.2) MeV /𝑐2 𝜎 = 9.6 Β± 0.3 MeV/𝑐2

M = (1974.8Β±0.6) MeV /𝑐2 𝜎 = 9.7 Β± 0.7 MeV/𝑐2

Signal MC

Data

𝑠=4.36GeV

M = (1976.1Β±0.3) MeV /𝑐2 𝜎 = 14.5 Β± 0.5 MeV/𝑐2

𝑠=4.36GeV

Signal MC Signal MC

𝑠=4.66GeV

π‘€π‘Ÿπ‘’π‘ 𝛾𝐷𝑠 = 𝑀 𝐷𝑠 for signal Mass resolution increases from Ecms=4.36 GeV to 4.66 GeV, becoming

worse Mass window for another Ds:

π‘€π‘Ÿπ‘’π‘ 𝛾𝐾+πΎβˆ’πœ‹+ βˆ’ 1.968 < 30 MeV, 4.36 GeV data used currently

π‘€π‘Ÿπ‘’π‘(𝛾𝐷𝑠+) from bkgs in MC samples

2019/10/9 11

PDF: Crystal ball + Agus

Case2

M = (1964.6Β±0.9) MeV /𝑐2 𝜎 = 8.7 Β± 0.9 MeV/𝑐2

Only bkgs from π·π‘ βˆ—π·π‘  have clear Ds singal in π‘€π‘Ÿπ‘’π‘(𝛾𝐷𝑠+)

π·π‘ βˆ—π·π‘ βˆ— MC Inclusive MC

Case1

M = (1964.3Β±0.4) MeV /𝑐2 𝜎 = 8.5 Β± 0.7 MeV/𝑐2

Distributions of M(𝛾𝐷𝑠+)

2019/10/9 12

PDF: Gaussian + second-order polynomial

π·π‘ βˆ—π·π‘  MC Data

The data show clear Ds* component from e+e- -> Ds*Ds, which can be simulated.

Ds* veto: 𝑀 𝛾𝐾+πΎβˆ’πœ‹+ βˆ’π‘š(π·π‘ βˆ—) > 15 MeV

π·π‘ βˆ—π·π‘ βˆ— MC Inclusive MC

M = (2111.6Β±0.4)MeV/𝑐2 𝜎 = 3.7 Β± 0.4 MeV/𝑐2

Case1 Case2

M = (2111.5Β±0.1)MeV/𝑐2 𝜎 = 3.9 Β± 0.1 MeV/𝑐2

Data

M = (2112.8Β±0.5)MeV/𝑐2 𝜎 = 3.8 Β± 0.5 MeV/𝑐2

𝛾𝐼𝑆𝑅𝐷𝑠+π·π‘ βˆ’ MC

2019/10/9 13

Ds* in π‘€π‘Ÿπ‘’π‘(𝐾+πΎβˆ’πœ‹+)

PDF: Gaussian + second-order polynomial

Case1 Data

Second Ds* veto: 𝑀 𝐾+πΎβˆ’πœ‹+ βˆ’π‘š(π·π‘ βˆ—) > 15 MeV

π·π‘ βˆ—π·π‘ βˆ— MC Inclusive MC

Case1

M=(2112.6Β±0.6)MeV/𝑐2 𝜎 = 4.9 Β± 0.4 MeV/𝑐2

Case2

M=(2112.9Β±0.1)MeV/𝑐2 𝜎 = 5.6 Β± 0.2 MeV/𝑐2

Data M=(2115.1Β±0.4)MeV/𝑐2 𝜎 = 4.7 Β± 0.4 MeV/𝑐2

𝛾𝐼𝑆𝑅𝐷𝑠+π·π‘ βˆ’ MC

Energy and angle of 𝛾

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π‘π‘œπ‘ π›Ύπœƒ π‘π‘œπ‘ π›Ύπœƒ π‘π‘œπ‘ π›Ύπœƒ

E(𝛾

)

E(𝛾

)

E(𝛾

) 𝑠=4.36 GeV 𝑠=4.66 GeV

Signal MC Signal MC

Data

Signal MC

𝑠=4.36 GeV

Signal MC

𝑠=4.66 GeV

E(𝛾) is related to the mass of X and 𝑠 in signal MC

Signal in π‘€π‘Ÿπ‘’π‘(𝛾) in MC simulation

2019/10/9 15

π‘€π‘Ÿπ‘’π‘(𝛾) = M(DsDs) MC simulation shows very good resolution of M(DsDs) in π‘€π‘Ÿπ‘’π‘(𝛾) : 𝜎 = 4.2 βˆ’ 4.3 MeV/𝑐2 !!!

Signal MC

𝑠=4.36 GeV 𝑠=4.66 GeV

Signal MC

M = (3939.5Β±0.3)MeV/𝑐2 𝜎 = 4.2 Β± 0.3 MeV/𝑐2

M = (3939.3Β±0.5)MeV/𝑐2 𝜎 = 4.3 Β± 0.4 MeV/𝑐2

Distributions of E(𝛾) and π‘€π‘Ÿπ‘’π‘(𝛾)

2019/10/9 16

Inclusive MC describes most of the events observed in data. Besides bkgs from inclusive MC, π·π‘ βˆ—π·π‘†, π·π‘ βˆ—π·π‘ βˆ—and 𝛾𝐼𝑆𝑅𝐷𝑆𝐷𝑠,

there are still room from other contributions in data. Are they events of e+e- ->𝛾+DsDs directly?

Data Inclusive MC Case1 Case2 π·π‘ βˆ—π·π‘ βˆ— MC 𝛾𝐼𝑆𝑅𝐷𝑠𝐷𝑠 MC

Data Inclusive MC Case1 Case2 π·π‘ βˆ—π·π‘ βˆ— MC 𝛾𝐼𝑆𝑅𝐷𝑠𝐷𝑠 MC

Data sum

Data sum

sum=inclusive MC+Case1+Case2+π·π‘ βˆ—π·π‘ βˆ— MC+𝛾𝐼𝑆𝑅𝐷𝑠𝐷𝑠

Summary and plan

β€’ Summary

β€’ We have studied the signal MC at √s=4.36GeV and √s=4.66GeV

β€’ We have researched for Data at √s=4.36GeV and have estimated backgrounds by inclusvie MC , 𝐷𝑠𝐷𝑠

βˆ— , π·π‘ βˆ—π·π‘ βˆ— and 𝛾𝐼𝑆𝑅𝐷𝑠𝐷𝑠 .

β€’ Plan β€’ To optimize general selections β€’ To study more data and MC samples in different energy points.

2019/10/9 17

Back up

2019/10/9 18

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