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May 2005 CTEQ Summer School 1
Global Analysis of QCDand Parton Distribution Functions
Dan StumpDepartment of Physics and Astronomy
Michigan State University
Ref: Pumplin, Stump, Huston, Lai, Nadolsky, Tung,New generation of parton distributions with uncertainties from global QCD analysis, JHEP07 (2002) 012.
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May 2005 CTEQ Summer School 2
“QCD is our most perfect physical theory.”
-- Frank Wilczek
F. Wilczek, Nuclear Physics A663&664 (2000) 3c-20c.
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May 2005 CTEQ Summer School 3
High energy particles interact through their quark and gluon constituents – the partons.
Asymptotic freedom : the parton cross sections can be approximated by perturbation theory.
Factorization theorem : Parton distribution functions of the nucleon are the link between the PQCD theory and measurements on nucleons.
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May 2005 CTEQ Summer School 4
Motivations for global analysis of QCD
• the deep structure of the nucleon
• testing QCD – gluon radiation, higher order perturbation theory, the value of αS
• The PDF’s are needed to calculate cross sections for scattering processes at the LHC; the search for new physics.
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May 2005 CTEQ Summer School 5
The goals of QCD global analysis are
• to construct accurate PDF’s;
• to know the uncertainties of the PDF’s;
• to enable predictions, including uncertainties.
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May 2005 CTEQ Summer School 6
The parton model and global analysis of QCD ---inclusive scattering processes
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May 2005 CTEQ Summer School 7
Outline1/ Introduction2/ Experiments3/ Methods of Analysis4/ Results
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May 2005 CTEQ Summer School 8
PDF’s from Global Analysis
QCD TheoryLO, NLO, NNLOMS-bar factorizationDGLAP evolution
DataDIS (H1, ZEUS, BCDMS, NMC, CCFR)DY (E605, E866)High ET jets (CDF, D0)W asymmetry (CDF)
),(),( 22 QxfQxf ii δ±
αS(MZ)
PhenomenologyCTEQ, MRST, Alekhin, GGK, H1, ZEUS, …
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May 2005 CTEQ Summer School 9
2/Experiments
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May 2005 CTEQ Summer School 10
The HERA e±p collider
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May 2005 CTEQ Summer School 11
Theory of deep-inelastic electron scattering
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May 2005 CTEQ Summer School 12
H1 collaboration at HERA
Data used in the CTEQ6 analysis…DIS e± + p e± + X @ low-x 104 pointsDIS e± + p e± + X @ high-x 126 points… published 2000, 2001
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May 2005 CTEQ Summer School 13
ZEUS collaboration at HERA
Data used in the CTEQ6 analysis …DIS e± + p e± + X 229 points… published 2001
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May 2005 CTEQ Summer School 14
BCDMS collaboration
DIS µ+p µ+X 339 pointsDIS µ+d µ+X 251 points
Bologna - CERN - Dubna - Munich - SaclayNA4 muon scattering experiment at CERN
History: 1976 (C. Rubbia) to 1994
Homework Problem -- Why was µυον scattering used?Why is µd an interesting contrast to µp?
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May 2005 CTEQ Summer School 15
NMC collaboration at CERN
DIS µ+p µ+X 201 pointsDIS µ+d µ+X 123 points… published 1997
The kinematic range 0.0001 < x < 0.7 and 0.01< Q2 < 70 GeV2 is covered .
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May 2005 CTEQ Summer School 16
CCFR collaboration
• In the CTEQ6 analysis, number of data points = 156; from publications of 1997 and 2001
Chicago Columbia Fermilab Rochester
• The Lab E neutrino experiments at Fermilab (E744 in 1985; and E770 in 1987-88).
• Measurements of F2(x,Q2) and xF3(x,Q2) for ν and ν DIS
Homework Problem: What do we learn from neutrino/antineutrino scattering that we don’t know from electron scattering?
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May 2005 CTEQ Summer School 17
Theory of deep-inelastic neutrino scattering
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May 2005 CTEQ Summer School 18
Experiment E605
For CTEQ6 : 119 data points
The Drell-Yan process
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May 2005 CTEQ Summer School 19
The Drell-Yan process — lepton pair production in hadroncollisions
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May 2005 CTEQ Summer School 20
The Drell-Yan process
Experiment E866
Homework Question:E866 measured the asymmetry of down and up anti-quarks in the nucleon sea using Drell-Yan di-muons produced in 800 GeV proton interactions with hydrogen and deuterium targets. How does it work?
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… using 800 GeV protons from the Tevatron
The NuSea Collaboration
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May 2005 CTEQ Summer School 21
FNAL E866 – the NuSea Collaboration
Homework Problem: How does this experiment tell us about the light-quark flavor asymmetry in the nucleon sea?
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May 2005 CTEQ Summer School 22
Inclusive jet productionat the Tevatron collider
CDF collaboration: 33 data points at central rapidity (-0.7 < η < 0.7)
D0 collaboration: 90 data points in five rapidity bins (-3 < η < 3)
TeV ~at jet 2sXpp +→+
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May 2005 CTEQ Summer School 23
D0 Collaboration, Inclusive jet production in ppbar collisions, PRL 86, 1707 (2001).
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May 2005 CTEQ Summer School 24
D0 Collaboration, Inclusive jet production in ppbar collisions, PRL 86, 1707 (2001).
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May 2005 CTEQ Summer School 25
Lepton charge asymmetry from W+/W- production (CDF collaboration)
lyA versus)/()( −+−+ +−= σσσσHomework Problem: What can the asymmetry A tell us about the PDF’s?
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May 2005 CTEQ Summer School 26
CDF Collaboration, Measurement of the lepton charge asymmetry in W boson decays produced by ppbar collisions, PRL 81, 5754 (1998).