global analysis of qcd and parton distribution functions · 2005-05-13 · and parton distribution...
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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.
May 2005 CTEQ Summer School 2
“QCD is our most perfect physical theory.”
-- Frank Wilczek
F. Wilczek, Nuclear Physics A663&664 (2000) 3c-20c.
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.
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.
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.
May 2005 CTEQ Summer School 6
The parton model and global analysis of QCD ---inclusive scattering processes
May 2005 CTEQ Summer School 7
Outline1/ Introduction2/ Experiments3/ Methods of Analysis4/ Results
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, …
May 2005 CTEQ Summer School 9
2/Experiments
May 2005 CTEQ Summer School 10
The HERA e±p collider
May 2005 CTEQ Summer School 11
Theory of deep-inelastic electron scattering
( )[ ]{ }),(),( 2222
24
2
2
2
112
QxFyQxFyQxdQdx
dL−−+= πασ
scorrection same ),(
scorrection ),(),(
)(
)(
+=
+=∑2
1
2222
2 QxFx
QxqxeQxF
em
iii
em
+ corrections
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
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
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?
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 .
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?
May 2005 CTEQ Summer School 17
Theory of deep-inelastic neutrino scattering
[ ]{[ ] } ),()(
),(),()(
yxxFy
yxFyyxFysG
dydxd
LF
32
22
222
11
114
−−±
−−+=π
σ
[ ][ ] scorrection ),(),(),(
scorrection ),(),(),(
+−=
++=
∑
∑
iii
iii
QxqQxqxQxFx
QxqQxqxQxF
2223
2222
2
2
May 2005 CTEQ Summer School 18
Experiment E605
For CTEQ6 : 119 data points
The Drell-Yan process
May 2005 CTEQ Summer School 19
The Drell-Yan process — lepton pair production in hadroncollisions
( )2221
22
212
1
01
FXab
FbFaba
X
Qxx
xfxfdxdx
µσ
µµσ
/,,ˆ
),(),(,
→×
=∑∫
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?
Xp
Xp
+→++→+
−+
−+
µµµµ
deuterium hydrogen
… using 800 GeV protons from the Tevatron
The NuSea Collaboration
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?
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 +→+
May 2005 CTEQ Summer School 23
D0 Collaboration, Inclusive jet production in ppbar collisions, PRL 86, 1707 (2001).
May 2005 CTEQ Summer School 24
D0 Collaboration, Inclusive jet production in ppbar collisions, PRL 86, 1707 (2001).
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?
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).