Hyperon Production Hyperon Production

in High Energy Processesin High Energy Processes

Bo-Qiang MaBo-Qiang Ma (Peking University)(Peking University)

OutlineOutline

• The MotivationThe Motivation

• Distribution and Fragmentation FunctionsDistribution and Fragmentation Functions

• Case Study: Case Study:

• Case Study:Case Study:

• Case Study: Ratio in Case Study: Ratio in

• Case Study: Production in l+A Process Case Study: Production in l+A Process

• ConclusionsConclusions

Xee

XNl

/ ' ( )l N l X

Our View of the ProtonOur View of the Proton with historywith history

• Point-Like Point-Like 19191919• Finite Size with RadiusFinite Size with Radius 1930s-1950s1930s-1950s• Quark ModelQuark Model 1960s1960s• QCD and GluonsQCD and Gluons 1970s1970s• Puzzles and AnomaliesPuzzles and Anomalies 1980s-present1980s-present

•Quark Sea of the NucleonQuark Sea of the Nucleon•Baryon-Meson Fluctuations Baryon-Meson Fluctuations •Statistical FeaturesStatistical Features• …… ……

Surprises & UnknownSurprises & Unknownabout the Quark Structure of Nucleon: about the Quark Structure of Nucleon: SeaSea

• Spin Structure:Spin Structure:

“puzzle”: where is the proton’s missing spin

• Strange ContentStrange Content

• Flavor AsymmetryFlavor Asymmetry

• Isospin Symmetry Breaking Isospin Symmetry Breaking

3.0 sdu

)()( 0 xsxss

du

npnp uddu

Brodsky & Ma, PLB381(96)317

Ma, PLB 274 (92) 111Boros, Londergan, Thomas, PRL81(98)4075

UnknownUnknown about theabout the nucleon:nucleon: valence valence xx→→11 behaviors of flavor and spinbehaviors of flavor and spin

• Flavor Flavor

• SpinSpin

Ratio of Ratio of Neutron/Proton Neutron/Proton

Structure Structure FunctionsFunctions

Flavor Content of the ProtonFlavor Content of the Proton with nuclear binding correctionwith nuclear binding correction

W.Melnitchouk & A.W. ThomasPLB 377(1996) 11

Flavor Content of the ProtonFlavor Content of the Proton from DIS neutrino data analysisfrom DIS neutrino data analysis

U.K. Yang & A. BodekPRL 82 (1999) 2467.

Quark Helicity Distributions of ProtonQuark Helicity Distributions of Proton

Measurements at JLAB and HERMESMeasurements at JLAB and HERMES

JLAb Hall A Collaborationnucl-ex/0308011, PRL

Present StatusPresent Status of the Flavor and Spin Contents of the Protonof the Flavor and Spin Contents of the Proton

• Flavor favors pQCDFlavor favors pQCD

• Spin favors diquark model Spin favors diquark model

Unclear & In Contradiction!Unclear & In Contradiction!

How to Test Various Theories?How to Test Various Theories?

SU(3) Symmetry together with Proton SU(3) Symmetry together with Proton Spin ProblemSpin Problem

The u,d sea of Lambda versus The u,d sea of Lambda versus s sea of Nucleons sea of Nucleon

Different flavor & spin structure in Different flavor & spin structure in different modelsdifferent models

Spin structure in two different modelsSpin structure in two different models

Flavor structure in two different modelsFlavor structure in two different models

An intuitive argumentAn intuitive argument

Significantly different predictionsSignificantly different predictions

Connections between structure functions Connections between structure functions and fragmentation functionsand fragmentation functions

Various ProcessesVarious Processes

Flavor separationFlavor separation

Extension to Sigma HyperonExtension to Sigma Hyperon

The advantage of using Sigma hyperonsThe advantage of using Sigma hyperons

New Domain for Theorists and ExperimeNew Domain for Theorists and Experimenlistsnlists

Spin structure of Lambda from Lambda Spin structure of Lambda from Lambda polarization in Zpolarization in Zº decayº decay

Diquark model and pQCD resultsDiquark model and pQCD results

Spin Transfer to Spin Transfer to ΛΛ in Semi-Inclusive DIS in Semi-Inclusive DIS

Different predictionsDifferent predictions

Ratio in DIS ProductionRatio in DIS Production

• A sensitive quantity that can provides iA sensitive quantity that can provides information about the flavor structure of nformation about the flavor structure of hyperon. hyperon.

/

B.-Q. Ma, I. Schmidt, J.-J. YangPhys. Lett. B 574 (2003) 35

The flavor structure of LambdaThe flavor structure of Lambda u/s ratio with x-dependenceu/s ratio with x-dependence

Different predictionsDifferent predictions

Anti-Lambda production as a probe of Anti-Lambda production as a probe of the nuclear sea structure?the nuclear sea structure?

•有三类原子核模型可以解释 EMC 效应 : 团簇模型 ,Pi 盈余模型 , 重新标度模型 .

•通过考察原子核与核子荷电轻子半单举过程中末态强子 anti-Lambda 的产率比对 x的依赖性，我们发现 anti-Lambda 能够区分定性描述原子核 EMC 效应的三类不同原子核结构模型 .

Different sea behaviors in nucleiDifferent sea behaviors in nuclei

Different predictions of anti-lambda productionDifferent predictions of anti-lambda production

High Energy Spin Physics ExperimentHigh Energy Spin Physics Experiment @ @ HERMES HERMES by China Groupby China Group

• Yajun Mao Yajun Mao @ @ PKUPKU

• Yunxiu Ye Yunxiu Ye @ @ USTCUSTC

• Bo-Qiang Ma Bo-Qiang Ma @@ PKUPKU

• & students & students

Conclusion 1: Lambda PhysicsConclusion 1: Lambda Physics

Conclusion 2: Anti-Lambda ProductionConclusion 2: Anti-Lambda Productionfor Nuclear Physicsfor Nuclear Physics

Anti-Lambda production charged lepton Anti-Lambda production charged lepton semi-inclusive deep inelastic scattering semi-inclusive deep inelastic scattering off nuclear target is ideal to figure out off nuclear target is ideal to figure out the nuclear sea content, which is the nuclear sea content, which is differently predicted by different models differently predicted by different models accounting for the nuclear EMC effect.accounting for the nuclear EMC effect.