1. NLO QCD fits to polarized semi-inclusive DIS data
Rodolfo Sassot
Universidad de Buenos Aires
Primer pagina
JLAB MAY 5, 2005

2. 30 years studying the short distance structure of the proton:
from hints on point-like structure, to parton densities.
QCD + DIS high precision PDFs
predictions and tests of ‘new physics’
R. Sassot JLAB, May 5, 2005

3. why spin? why polarized DIS? why polarized SIDIS?
inessential complication?
indispensable tool for unveiling hadron structure,
search for the unexpected.
why polarized DIS?
best benchmark for hadron structure,
top cited spin crisis,
90’s experimental programs.
why polarized SIDIS?
flavor and quark-antiquark discriminatrion,
increasing statistics,
universality and precision of fragmentation functions (FF).
R. Sassot JLAB, May 5, 2005

4. Outline:
QCD improved parton model description of polarized DIS and SIDIS
global QCD fits to polarized data.
uncertainties in pPDFs
uncertainties in future/ongoing measurements
R. Sassot JLAB, May 5, 2005

5. Polarized DIS (pDIS) ‘structure function’ ‘parton distribution’ (pPDF)
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6. pDIS flavor decomposition
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7. QCD improved parton model: LO and NLO
‘naïve’
‘LO’
W R. Mertig, W. L. van Neerven, Z.Phys.C (1996)
W. Vogelsang, Phys.Rev.D (1996)
‘NLO’ ‘add a gluon’
R. Sassot JLAB, May 5, 2005

8. Polarized SIDIS (pSIDIS)
D. de Florian, C. Garcia Canal, R.S.
Nuc.Phys.B (1996)
‘fragmentation function’ (FF)
R. Sassot JLAB, May 5, 2005

9. Flavor decompositon in pSIDIS
R. Sassot JLAB, May 5, 2005

10. NLO combined analysis:
and non perturbative quantities to be measured,
QCD predicts Q -dependence, not boundary conditions 2
data obtained for different values of x and Q 2
1. make ansatz about the x-dependence at some scale
2. evolve from to and compute
3. compare with data
4. fit to minimize
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11. R. Sassot JLAB, May 5, 2005

12. borrowed from W. Vogelsang
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13. NLO combined analysis: parameterizations
pDIS can probe:
pSIDIS give access to:
20 parameters
positivity relative to MRST02:
A.D. Maritn et al. Eur.Phys.J.C28 (2002) 455
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14. NLO combined analysis: data
R. Sassot JLAB, May 5, 2005

15. Fragmentation functions input:
KRE: S. Phys.Rev.D (Kretzer 2000)
KKP: B. A. Kniehl, G. Kramer, B. Potter, Nucl.Phys.B (2000)
flavor separation:
R. Sassot JLAB, May 5, 2005

16. Results: Interplay between pDIS and pSIDIS 478-20=458 d.o.f 313 pDIS
R. Sassot JLAB, May 5, 2005

17. Uncertainties: J. Pumplin et al. Phys.Rev.D65 014011 (2002)
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18. R. Sassot JLAB, May 5, 2005

19. Future/ongoing measurements:
R. Sassot JLAB, May 5, 2005

20. Future/ongoing measurements:
R. Sassot JLAB, May 5, 2005

21. Conclusions: pPDFs have evolved dramatically:
successfull experimental programs
pPDFs have evolved dramatically:
tools for the analysis (NLO)
from ‘scenarios’ to ‘constraints’
pSIDIS opens a window to sea quarks and helps to constrain other densities
perfect consistency pDIS/pSIDIS
overall picture combined NLO global fits:
improved constraints on pPDFs
best fits favor SU(3) in the sea
dependence on FFs as a caveat & opportunity:
tackle both problems together?
PHENIX:
future prospects:
encouraging
COMPASS & CLAS, E and FFs
R. Sassot JLAB, May 5, 2005

22. Xiaodong Jiang, fruitfull collaboration,
Acknowledgments:
Xiaodong Jiang, fruitfull collaboration,
JLAB, hospitality and support.
R. Sassot JLAB, May 5, 2005

23. R. Sassot JLAB, May 5, 2005

24. Role of pDIS and pSIDIS in the extraction of pPDFs:
pDIS as the main source of information on pPDFs.
hadronic decays data & assumptions: flavor symmetry
e.m. interactions can not discriminate quarks from antiquarks:
large uncertainties in sea quark and gluon pPDFs
pSIDIS as a way out:
CERN: first steps; encouraging
DESY: from consistency checks to constraints
CERN: …..
JLAB: …..
R. Sassot JLAB, May 5, 2005

25. Uncertainties:
R. Sassot JLAB, May 5, 2005