Title: Parton distributions and Physical Measurements
1Parton distributions and Physical Measurements
- Hung-Liang Lai
- Taipei Municipal University of Education, TAIWAN
In collaboration with J. Huston, S. Mrenna, P.
Nadolsky, J. Pumplin, D. Stump , W.K. Tung, C.-P.
Yuan
_at_QCD08, July 7, 2008
2Outline
- An overview of latest CTEQ PDFs
- Impact on LHC predictions
- Analysis of Correlations due to PDFs
- PDFs for LO Monte Carto Generators (Preliminary)
3CTEQ 6.6 series (arXiv0802.0007 hep-ph)
- Full implementation of the General-mass (GM) QCD
formalism - Factorization scheme (Collins)
- PDFs and their evolution
- Mass-dependence of hard cross section (SACOT)
- Final States, on-shell kinematics
- Rescaling (ACOTc), Phase space,
- Free strange PDFs, i.e. independent shape
parameters from (ubar dbar) - ? CTEQ6.6M 44 uncertainty sets
- Exploration of PDFs with intrinsic charm ?
CTEQ6.6C - Alternative sets for variousaS(MZ)0.112.125?
CTEQ6.6A
4Suppression of charm contribution to F2 in the GM
scheme results in larger light quark distribution
at small x ? CTEQ6.1(dashed) u d are below
CTEQ6.6 by 2-5 at x 10-3
5Very different strange distribution (fixed vs.
free strange shape)
6Impact of new CTEQ PDFs on LHC Predictions
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9W Z production at LHC x 10-3
-10-2 Difference of 3 in quark distributions
results in 6 q-qbar luminosity and W Z cross
sections
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13Analysis of correlations due to PDFs
14For 2N PDF uncertainty eigensets, the uncertainty
for an observable X due to PDF is given by
Correlation cosine for observables X and Y
15Role of the correlation angle
(0) measurement of X imposes tight (loose)
constraints on Y
16Cosf0.956
Cosf-0.80
17Z vs. PDFs
W vs. PDFs
Z,W are strongly correlated with g,b,c at
x0.005, and anti-correlated at x0.1 due to
momentum conservation of gluon.
18Higgs vs. PDFs
t-tbar vs. PDFs
19PDFs for LO Monte Carlo Generators (preliminary)
- Problem in consistency of using LO matrix
elements, parton showering, with usual LO/NLO
PDFs in Monte Carlo generators. - Prescriptions
- (a) relax momentum sum rule (Sherstnev Thorne)
- (b) adding selected pseudo-data sets in the
fits with free expt. normalizations
factorization scales
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23Summary
- Our knowledge of PDFs and its uncertainty is
crucial for hadron collider physics. - Heavy quark mass effects are noticeable, even at
high scale, and thus have impact on LHC study. - Analysis of correlations in PDF parameter space
is a powerful method to understand relations
among physical observables as well as PDFs. - Modified LO PDFs could be more suitable for LO
MC generators.