Higher Twist Effect in Fragmentation Sector

And Its Experimental

Extraction.

Introduction Duality phenomenon in ep → e’X and its explanation ep→e’hX and Jlab E00-108

Duality in parton fragmentation sector. e+e- → h+X ep→e’hX

Summary

Ed. Hungerford, Larry Pinsky, Guanghua Xu, University of Houston, TX.

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Introduction Duality phenomenon in ep → e’X 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→e’hX and Jlab E00-108

Jlab E00-108 experiment tried to detect duality in semi-inclusive reaction ep→e’pX. 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→e’pX? 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→e’pX?

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Duality in parton Fragmentation Sector

We will mainly study e+e- → h+X and e-p → h+X 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:

Step 5: Light-cone gauge

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

and light-cone expansion.

Twist

expansion

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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 e+e- collisions, where one can compare the cross sections of hadron, h, production at fixed z for various

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Comparing to e+e- 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

Universality of P:

In e+e-

In e-p:

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At Jlab beam energies,

Working in the lab frame

effect is significant.

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The small cross-section at

can be avoided by lowering the beam energy.

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Experimentally measurable quantities:

The angles and

play roles in determining at Jlab beam energies. Therefore, it is important to measure these quantities.

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SummaryThe contributions to cross-section 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 .

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

A way to extract higher twist effect in fragmentation sector through is to choose large with various

at the same z.

that this ratio contains information of the higher twist effects in the fragmentation sector and should be studied in the future.

as a function of z. However, we suggest

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My Contact Information

Guanghua XuPhysics Department

University of Houston4800 Calhoun RoadHouston, TX 77204

Ph.: (713)743-3723 or (281)324-9398gxu@uh.edu or guahxu@cognifast.com