Waterflooding Macroscopic Effficiency Relations Compatibility Mode
DD Shape · Tag e ciency ( i) for each mode is determined from MC simulation via i = Nfound i =N...
Transcript of DD Shape · Tag e ciency ( i) for each mode is determined from MC simulation via i = Nfound i =N...
DD̄ Shape
Speaker: Yi FANGfor BESIII Collaboration
The 7th International Workshop on Charm PhysicsMay 18-22, 2015
Detroit, Michigan
Y. Fang (IHEP) DD̄ Shape Charm 2015 1 / 16
Outline
1 Introduction
2 Analysis
3 Summary
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Introduction
Introduction
Since the discovery of ψ(3770), it is a long-standing puzzle in understandingof ψ(3770) production and decays
(MeV)(3770)ψM3760 3770 3780 3790
BES-II
Belle
BABAR
KEDR
PDG’2014
hadrons→ -e+e
hadrons→ -e+e
+K0D0 D→B
DDγ → -e+e
KD D→B
hadrons→ -e+e
PLB 652, 238 (2007)
PLB 660, 315 (2008)
PRL 100, 092001 (2008)
PRD 76, 11105(R) (2007)
PRD 77, 011102 (2008)
PLB 711, 292 (2012)
0.3±0.4±3772.4
1.9±3772.0
4.0±5.0±3776.0
0.9±1.9±3778.8
0.5±2.4±3775.5
-1.7-0.7-0.3+1.8+0.5+0.33779.2
0.33±3773.15
Includes interference between resonant
productionDand nonresonat D
(MeV)(3770)ψM3760 3770 3780 3790
Discrepant results of ψ(3770) parameters are observedModel? Interference?
Analyze DD̄ shape around ψ(3770) at BESIII with higher statistic
Y. Fang (IHEP) DD̄ Shape Charm 2015 3 / 16
Introduction
BESIII Experiment
BEPCII Collider
symmetric e+e− collider, double-rings, 2.0 GeV < ECM < 4.6 GeV
BESIII Detector
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Introduction
Data Sets
ψ(3770) Scan Data
∼ 70 pb−1, 3.74 < ECM < 3.89 GeVLuminosity (L) is determined using large-angle Bhabha scattering events
(GeV)CME3.75 3.8 3.85
)-1
L (p
b
0
2
4
6
8
Monte Carlo Simulation
1 ψ(3770)→ D0D̄0,D+D−
2 e+e− → qq̄, τ+τ−,γISRJ/ψ,γISRψ(2S)
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Analysis
Reconstruction of D Mesons
The cross sections for e+e− → DD̄ are measured usingsingle tag method
Tag modes (charge conjunction is implied):
D0 → K−π+ D+ → K−π+π+ D+ → K 0Sπ
+π0
D0 → K−π+π0 D+ → K−π+π+π0 D+ → K 0Sπ
+
D0 → K−π+π+π− D+ → K+K−π+ D+ → K 0Sπ
+π+π−
Define variables:∆E = Etag − Ebeam
mBC =√
E 2beam − |~ptag|2
Select D candidate with ∆E closest to 0 for each mode
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Analysis
Extraction of Signal Yields
Signal yield (Ntag) is extracted from a maximum-likelihood fit to the
2D distribution in ∆E vs. mBC
Signal and background PDFs are formed from MC simulation
Float normalization of signal and background
• Data
— Signal
- - Background
— Fit
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Analysis
Changes in mBC Shapes due to ISR Effect
Two peaks seen in higher beam energy mBC distribution
• Data
— Signal
- - Background
— Fit
Left Peak — Events from Born Level contribution
Right Peak — Events from ISR contribution
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Analysis
Cross Section
Reconstruction Efficiency
Tag efficiency (εi ) for each mode is determined from MC simulation via
εi = N foundi /Ngenerated
i and then weighted by the branching fraction ofmode i (Bi ) to obtain the average efficiency
ε =∑i
εiBi
ε0tag = (11.3± 0.2)%, ε+tag = (9.8± 0.1)%
(the branching fractions of sub-resonance decays are included)
Calculation of Cross Section
σRCDD̄
(Ei ) =Ntag(Ei )
2εtagL(Ei )
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Analysis
Fits to Cross Sections
Fit the measured D0D̄0 and D+D− cross sections simultaneously using the theoret-ical cross sections
σRCDD̄
(W ) =
∫zDD̄(W
√1 − x)σDD̄(W
√1 − x)F(x ,W 2)dx
zDD̄ Factor describing Coulomb interaction
F(x , s) Probability to lose a fraction of s in initial state radiation
σDD̄(W ) =π2α
3W 2β3
D |FD(W )|2, FD(W ) = FRD (W )e iφR + FNR
D (W )
Use Breit-Wigner formula for resonant component
FRD (W ) =
6W√(Γee/α2)(ΓDD̄(W )/β3
D)
M2 −W 2 − iMΓ(W ), ΓDD̄(W ) = Γ(W )× (1 −BnDD̄)
Analyze two models for non-resonant component
Exponential Model - FNRD (W ) = FNR exp(−q2
D/α2NR)
Vector Dominance Model (VDM) - FNRD (W ) = F
ψ(2S)D (W ) + F0
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Analysis
Fits to Cross SectionsSingle Breit-Wigner Shape
Single Breit-Wigner formula is unable to describe data
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Analysis
Fits to Cross SectionsExponential Model
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Analysis
Fits to Cross SectionsVector Dominance Model
VDM provides more physically based resultsY. Fang (IHEP) DD̄ Shape Charm 2015 13 / 16
Analysis
Preliminary Results and Comparisons
Use Γψ(3770)→DD̄ee = Γ
ψ(3770)ee ×B(ψ(3770)→ DD̄)
Remains constant from fit independent of branching fraction
Preliminary results of ψ(3770) parameters (errors are only statistical)
Preliminary results of ψ(3770) parameters are consistent with those
measured at KEDR
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Analysis
Systematics
Expect statistics-limited result due to scan data size
Systematics evaluation still in progress
Current main sources (ranked by contribution to total)
1 Meson radii used for ψ(2S) and ψ(3770)
2 Charged tracking
3 Neutral tracking
4 Luminosity
Negligible effect seen when altering B(ψ(3770)→ DD̄)
All parameters remain constant except Γψ(3770)ee
Scales inversely to input branching fraction
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Summary
Summary
Cross sections for e+e− → DD̄ in the vicinity of the ψ(3770) are
studied at BESIII
Able to well fit the DD̄ line shape near ψ(3770) with interference based
models
Both exponential model and vector dominance model provide quality
description of data
Upcoming aspects
1 Finalize estimation of systematic uncertainty
2 Compare to alternate models
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