heavy flavor production at hera

1X. DongFeb. 17th, 2011 RNC Group Meeting

Heavy Flavor Production at HERA

Xin Dong

- Chapter 6 in arXiv: 0805.3334

Introduction Measurements of HF production at HERA

Production cross sections Structure functions

HF production at hadron collider Summary

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Heavy Production in ep and pp

LO direct production

c

c

p

p

Heavy flavors are sensitive probes to the initial gluon distributions!

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Production Cross Section

ep

pp

QCD, MQ, Q2 pT

MQ >>QCD in principle, amenable to pQCD calculations.

Q2>>MQ2 heavy quarks are massless

Treatment of heavy quarks in pQCD calculations:

Q2 ~ MQ2 heavy quarks are massive

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Kinematics

Ee, Ee’ : incident positron and scattered positron energye’ : polar angle of scattered positron

x: Bjorken x of photonxg: longitudinal momentum fraction of gluon in proton

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Charm Reconstruction at HERA

STAR 2009 p+p 200 GeVD*

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D* Production Cross Section in DIS

ZM-VFNS: massless charmNot appropriate at low Q2

HVQDIS: massive charmNot correct at high Q2

CASCADE: kt factorization

Insteresting:HVQDIS agrees with data better at high Q2!

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D*-jet-jet production

Angular correlation

Generally agree with NLO QCD- some room to improve in theory

-Hint of high order corrections

D*-jet-jet cross section

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Photon-gluon fusion processes

= 180o

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Charm Structure Function

epeccX

*gcc*cc

probe gluon/charm PDFs

NLO QCD -Extracted from the PDF based on the NLO QCD fit to F2

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HF in Photoproduction

x1, direct processx<1, resolved process

Quasi real photon (Q2~0)Expect pQCD to be applied over the full phase space

D* - jet angular correlation

A good pQCD test - check whether need for higher order terms.

Data/theory comparison indicates some inadequacies of the theory.

x

xg

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HF Production with Vertex Detector

Pointing resolution (H1 vertex detector)

Significance of signed 2D impact parameter (normalized by the resolution)

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Charm and Bottom Structure Functions

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HF Production in Hadron Collisions

At RHIC (mid-rapidity), dominated by the gluon-gluon fusionx range ~ 0.005 - 0.1

LO NLO

gluon splitting

flavor excitation

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Predictive Power for Total Cross Section

10-2 10-110-3 10-2 10-110-3

Important scales in calculating the total charm cross section:mc,

CTEQ6M

=2mc

=mc

=0.5mc

Drastic change of the gluon density function at low Q2

Strong dependence on s

Large uncertainty in predicted total charm cross section (at RHIC)

R. Vogt, LBL SeminarPDFs extracted from inclusive DIS and inclusive jet data.

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Fixed-Order-Next-to-Leading-Logarithm - FONLL

Treat the charm quark as light quarks; should be reliable at pT>>mc

STAR p+p 200 GeV CDF p+p 1.96 TeV

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Summary

Heavy flavors are sensitive probes to gluon distributions in nucleon/nucleus.

Measurements at HERA generally agree with NLO QCD calculations. However larger (x,Q2) region need to be explored and with high precision to constrain the gluon (spin-dependent) density distributions.

More complicated for HF production in hadron collisions. Precision measurements are needed for pQCD test.