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Published byClemence Ferguson Modified over 6 years ago
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Azimuthal asymmetries of di-hadron in e+e- annihilation at BESIII
Guan Yinghui(管颖慧)1, Li Haibo(李海波)1, Lu Xiao-Rui(吕晓睿)2 1. IHEP 2. UCAS
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Outline Introduction Methods to probe Collins effect on experiments(e+e- annihilation) Implement the azimuthal asymmetries analysis at BESIII Useful information about TMD evolution Difficulties: absence of high thrust two-jet events; backgrounds MC Test Summary and discussion PRD
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Introduction(1)—Single spin asymmetries
PRD 78, Introduction(1)—Single spin asymmetries H: describes the relation between the transverse spin of the fragmenting quark and the azimuthal distribution of final-state hadrons around the quark momentum z: fractional energy of hadron Ph: transverse momentum of hadron Single Spin Asymmetries
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Introduction(2) --two methods to probe DCA
PRD 78, Introduction(2) --two methods to probe DCA Double Collins Asymmetries(DCA) Method 12 Method 0
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Introduction(2)– two methods to probe DCA
Define the ratio: R Method0, Method12 The distribution expected with azimuthal asymmetries Backgrounds need to be understood well 2
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Introduction(3)– Double Ratio
Unlike: Like: Charged: Define Double ratio To cancel asymmetries produced by detector acceptance and radiative effects
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Introduction(4)--event shape and thrust axis
backgrounds Thrust value is used to suppress backgrounds at Belle/BaBar The thrust axis is used as a approximation of the q-qbar axis The thrust axis is the key issue: to separate h1 and h2 is the reference axis in Method12
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Data sample Sample: Event Selection MC@4.2GeV
event generator: KKMC/Pythia Event Selection Good charged tracks: Ncharged>=3 Identify p Evisible>2.5GeV Thrust>0.8 (All good charged and neutral tracks are used to reconstruct the thrust axis) z>0.2
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Thrust value—comparison with BABAR
BESIII @4.2GeV BABAR @10.6GeV arXiv: Select high thrust two-jet events
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Thrust axis--comparison with BABAR
BESIII @4.2GeV BABAR @10.6GeV The thrust axis is not a good approximation of the q-qbar axis at low energy
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MC Test --Method12 qqbar sample Black line: MC sample
MC Truth Using Truth axis Using Thrust axis Black line: MC sample Red line: weighted MC sample with asymmetry=10%
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MC Test--Method0 qqbar sample Black line: MC sample
MC Truth Using Truth axis Using Thrust axis Black line: MC sample Red line: weighted MC sample with asymmetry=10%
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MC Test –Double Ratio To cancel detector effects MC Truth MC Truth
accepted by detector Double Ratio
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MC Test — Double Ratio (Method0)
MC Truth Double Ratio Miss-combinations(h1,h1) may contribute
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MC Test– Method0’ High z means large angle between h1 and h2
They probably came from different quark cut: z1>0.5 && z2>0.5
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MC Test –Double Ratio(Method0’)
require z1>0.5&&z2>0.5 Without assigning them to hemisphere
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谢谢! Summary/Discussion Lesson from Belle and BABAR At BESIII Ideas: …
Suppress backgrounds Double ratio to cancel instrumental effects At BESIII Difficulties: isotropic event topology; backgrounds Ideas: Using Method0 Selecting sufficiently high z Other energy point (~3.6GeV) Others: Does factorization hold at BEPCII energy region? … 谢谢!
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BACKUP
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Multiplicity
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Thrust data vs MC
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Fractional energy z High z
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How many hadron-pairs we have?
Nominal cuts Further cuts with z1>0.5&&z2>0.5 ~10k p-pair survive
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Results from BABAR the asymmetry appears to grow with z
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Z vs
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Thrust vs
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Thrust axis at Belle
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MC Test-- Double Ratio(Method12)
Using Truth axis Using Thrust axis
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Method0’ cut: z1>0.2 && z2>0.2 cut: z1>0.5 && z2>0.5
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Double Ratio - -Method0 Method0’
cut: z1>0.2 && z2>0.2 belong1*belong2<0 cut: z1>0.5 && z2>0.5
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Double ratio- - backgrounds(M’)
hadrons DD ISR ditau gXYZ DDpi
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MC Test—background level
cut: z1>0.2 && z2>0.2 cut: z1>0.5 && z2>0.5
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Other variables could be used to suppress backgrounds
Also related to event shape Not good 4GeV R2=H2/H0
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R value
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