Higher Twist Effect in Fragmentation Sector And Its Experimental Extraction.

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Higher Twist Effect in Fragmentation Sector And
Its Experimental Extraction.
Ed. Hungerford, Larry Pinsky, Guanghua Xu,
University of Houston, TX.

• Introduction
• Duality phenomenon in ep ? eX and its
  explanation
• ep?ehX and Jlab E00-108
• Duality in parton fragmentation sector.
• ee- ? hX
• ep?ehX
• Summary

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Introduction

• Duality phenomenon in ep ? eX and its
  explanation

The discussion about duality in inclusive e-p
scatterings can be explained by higher twist
effect in parton structure sector.
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ep?ehX and Jlab E00-108

• Jlab E00-108 experiment tried to detect duality
  in semi-inclusive reaction ep?epX.
  Semi-inclusive reaction contains information from
  both structure and fragmentation sector.

• Questions
• Q1 Does duality exist in parton fragmentation
  sector?
• Q2 How can one isolate the information of
  fragmentation sector from ep?epX?
• Q3 Appealing to factorization, could the
  scale relating to the parton structure sector
  have different value from the scale relating to
  the parton fragmentation sector in ep?epX?

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Duality in parton Fragmentation Sector
We will mainly study ee- ? hX and e-p ? hX in
the following. We will, first, carry out twist
expansion for the processes and, then, discuss
their experimental extractions.

The main difference between semi-inclusive and
inclusive reaction is
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• Step 1

• Step 2 Use of the fact that

• Step 3 Changing

to
A gauge invariant
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• Step 4

and light-cone expansion.
Twist expansion

• Step 5 Light-cone gauge

• Step 6 The definition of the twist of an
  invariant matrix element of a light-cone bilocal
  operator.

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Answer 1

• The fragmentation functions can also be expanded
  in terms of contributions of operators of
  various twists.

• The phenomenon of duality can appear if the
  signs of the coefficients of the higher twist
  contributions are not positive definite.

• Such experiments are straightforward in ee-
  collisions, where one can compare the cross
  sections of hadron, h, production at fixed z for
  various

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Comparing to ee- Similarity
Difference contain information of both parton
structure and parton fragmentation sectors.
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Answer 2

• Choose large

and compare measurement of various
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Answer 3

• In e-p

• In e-p

• In ee-

• Universality of P

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• At Jlab beam energies,

effect is significant.
Working in the lab frame
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• The small cross-section at

can be avoided by lowering the beam energy.
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Summary
cross-section

• The contributions to

can be expanded as contributions of operators
with various twists. Experimental extraction of
higher twist contributions can be carried out by
comparing measurements of cross-sections vs. z at
various .

• A way to extract higher twist effect in
  fragmentation sector through

with various
is to choose large
at the same z.

• We have not attempted to study the evolution of
  the ratio,

as a function of z. However, we suggest
that this ratio contains information of the
higher twist effects in the fragmentation sector
and should be studied in the future.
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My Contact Information

• Guanghua Xu
• Physics Department
• University of Houston
• 4800 Calhoun Road
• Houston, TX 77204
• Ph. [phone] or [phone]
• gxu_at_uh.edu or guahxu_at_cognifast.com