Overview of Parton Distribution Functions (with a decided high-x BJ bias) Jorge G. Morfín Fermilab DNP04 - Chicago, IL

Outline  Quick review of everything but valence quarks  The valence quarks  Look at high-x: t Recent indications of more and less quarks at high-x? t d/u  How to cleanly measure valence quarks at high-x (and individual sea-quark distributions at all x)

PDFs from Global Fits Formalism LO, NLO, NNLO DGLAP MSbar factorization Q 0 2 functional Q 0 2 sea quark (a)symmetry etc. Who? Alekhin, CTEQ, MRST, Botje, H1, ZEUS, GRV, …. Data DIS (SLAC, BCDMS, NMC, E665, CCFR, H1, ZEUS, … ) Drell-Yan (E605, E772, E866, …) High E T jets (CDF, D0) W rapidity asymmetry (CDF) N dimuon (CCFR, NuTeV) etc. f i (x,Q 2 )   f i (x,Q 2 ) J. Stirling - Hix2004

MRST Parton Distributions in the Proton Martin, Roberts, Stirling, Thorne

Comparison of three modern PDF global fits Djouadi & Ferrag, hep-ph/ small MRST and CTEQ differences largely understood, see hep-ph/ J. Stirling; Hix2004

How has our picture of the PDF’s evolved over the years. With thanks to Wu-Ki Tung - MSU Gluon

Does the gluon go negative at small x and low Q? (MRST )

Uncertainty in the Gluon Distribution Normalized to CTEQ6M Dashed - CTEQ5HJ Dotted - MRST01 Solid - CTEQ5M

The non-strange sea quarks DY Asymmetry exerts its Influence - NA51 and E866

Experimental input: (low statistics) data on Dimuon (charm) production in Neutrino-Nucleus scattering.

A better determination of  should emerge from current full NLO analyses of the CCFR-NuTeV dimuon data. 

Is the strangeness sector charge symmetric? Still no experimental data to decide, one way or the other.

New CCFR-NuTeV dimuon data that can, in principle, determine s(x) and sbar(x) separately!

The Valence u Quark: progression of improvements

NLO fits to more fixed-target DIS data sets

HERA exerts its influence

All in the details now, at least for lower x

It looks like we know the d and u quark fairly well…right?

Indication that the valence quarks not quite right at high-x?? E866 Preliminary Results (R. Towell - Hix2004) x beam distribution measures 4u + d as x--> 1. Both MRST and CTEQ overestimate valence distributions as x --> 1 by 15-20%. Possibly related to d/u ratio as x --> 1, but requires full PDF-style fit. Radiative corrections have recently been calculated. (Not yet fully applied) x target x beam OOPS!

Relative Concentration of Valence Quarks in the Nucleon d/u

Latest look at d/u… What’s going on at high-x?

CTEQ uncertainties in u and d quark fits Theory uncertainties NOT included

CTEQ High-x Working Group With C. Keppel - Jefferson Lab

Extraction of d/u using deuterium targets involves nuclear D 2 corrections

What happens when we include (preliminary) E866? PRELIMINARY

Compare 6.1 with E866 to CTEQ5 with deuteron correction (F-S) - time to revisit deuteron corrections… PRELIMINARY

Wally Melnitchouk: This line is what CTEQ used for “Large-x paper” Range of Deuteron Corrections in the Literature (a few somewhat dated)

Implement full FS instead of approximate line and compare with MST correction PRELIMINARY

E866 discrepancy can be reduced/removed with deuteron corrections, change in d/u ratio looks similar to CTEQ6.1 + E866 fit. Extracting d/u will continue to be a problem as long as we must invoke deuteron corrections Need final data with radiative corrections, but feeling a bit better about E866… Preliminary Impressions of CTEQ High-x Study

NuTeV Compared to CCFR (currently in PDF fits) at High-x Indicates Effect Opposite to E866 V. Radescu - DIS04 nuclear effects? OOPS!

How do we Resolve the High-x Quark Dilemma? The cleanest, most straightforward way to study high x quarks, including the d/u ratio is with  / - proton scattering

Neutrino - Proton Scattering No messy nuclear corrections! At high x F 2 p - xF 3 p = 4xu F 2 p - xF 3 p = 4xd F 2 p + xF 3 p = 4xu

Similar Expressions for Neutrino-Nucleon Scattering - What Can We Learn With All Six Neutrino Structure Functions? Combining measured values in a given x-Q 2 bin, for example Using Leading order expressions (for isoscalar target):

How do we measure Neutrino-Proton Scattering? The MINER A Experiment in the NuMI Beam at Fermilab Approved in April C, Fe and Pb Nuclear targets Main Physics Topics with Expected Produced Statistics  Quasi-elastic 300 K events off 3 tons CH  Resonance Production 600 K total, 450 K 1   Coherent Pion Production25 K CC / 12.5 K NC  Nuclear Effects C:0.6M, Fe: 1M and Pb: 1 M  Pert/nonPert and Structure Functions 2.8 M total /1.2 M DIS event  Strange and Charm Particle Production > 60 K fully reconstructed events  Generalized Parton Distributions (few K events?)

Both HEP and NP collaborators D. Drakoulakos, P. Stamoulis, G. Tzanakos, M. Zois University of Athens, Athens, Greece D. Casper University of California, Irvine, California E. Paschos University of Dortmund, Dortmund, Germany D. Boehnlein, D. A. Harris, M. Kostin, J.G. Morfin, P. Shanahan, P. Spentzouris Fermi National Accelerator Laboratory, Batavia, Illinois M.E. Christy, W. Hinton, C.E.Keppel Hampton University, Hampton, Virginia R. Burnstein, A. Chakravorty, O. Kamaev, N. Solomey Illinois Institute of Technology, Chicago, Illinois S.Kulagin Institute for Nuclear Research, Moscow, Russia I. Niculescu. G..Niculescu James Madison University, Harrisonburg, Virginia G. Blazey, M.A.C. Cummings, V. Rykalin Northern Illinois University, DeKalb, Illinois W.K. Brooks, A. Bruell, R. Ent, D. Gaskell,, W. Melnitchouk, S. Wood Jefferson Lab, Newport News, Virginia S. Boyd, D. Naples, V. Paolone University of Pittsburgh, Pittsburgh, Pennsylvania A. Bodek, H. Budd, J. Chvojka, P. de Babaro, S. Manly, K. McFarland, I.C. Park, W. Sakumoto, R. Teng University of Rochester, Rochester, New York R. Gilman, C. Glasshausser, X. Jiang, G. Kumbartzki, K. McCormick, R. Ransome Rutgers University, New Brunswick, New Jersey H. Gallagher, T. Kafka, W.A. Mann, W. Oliver Tufts University, Medford, Massachusetts J. Nelson William and Mary College, Williamsburg, Virginia Red = HEP, Blue = NP, Green = Theorist

After initial (parasitic to MINOS) run - would add a Liquid H 2 /D 2 (/O/Ar) Target NOT YET APPROVED FOR THIS H_2/D_2 MINOS Near Fid. vol: r = 80 cm. l = 150 cm. 350 K CC events in LH K CC events in LD 2 2.5x10 20 POT he- beam. Technically easy/inexpensive to build and operate. Meeting safety specifications the major effort. Planes of C, Fe, Pb For part of run ≈ Statistical Errors for.7 / 2 year of he-  x Bj CHLH 2 LD %2.2%1.5%

Summary  Aside from low x gluon, PDFs fairly well established for x <  For x > 0.3, uncertainty of the gluon grows dramatically.  (d - u) / (d+u) reasonably constrained by E866 out to x ≈ 0.4.   = (s + s) / (u + d) seems to be increasing with x (NuTeV input).  (s - s) / (s + s) and heavy quarks need further clarification (NuTeV).  The valence u-quark is reasonable out to x = 0.5, while the d-quark uncertainty blows up around x = 0.3. Whoops…E866 & NuTeV!!  d/u at high-x still uncertain due to spread in deuteron correction.  BoNuS experiment at Jlab, particularly with upgrade, will help  THE CLEANEST WAY TO MEASURE d/u: + p SCATTERING  The MINER A Experiment at Fermilab, an NP + HEP collaboration, could make a high-statistics measurement of + p scattering.