Extracting Charged and Neutral Current Structure Functions

Fred Olness, Southern Methodist University
 

F2: Comparing Charged and Neutral Current Structure Functions

Deep inelastic lepton-nucleon scattering experiments have been used to determine the quark distributions in the nucleon.  However, the structure functions determined from Neutral Current (NC) muon experiments and Charged Current (CC) neutrino experiments were found to be different at small values of Bjorken x.

The figure below (from  Seligman, et al.)  compares Neutral Current (NC) muon data from NMC and E665 experiments with Charged Current (CC) neutrino data from CCFR.  Note that for the smallest x values (x=0.0125), the Charged Current (CC) data (filled squares) are above the Neutral Current (NC) data (open symbols).

 

A new analysis (by Yang et al.)  performed the extraction of the structure functions in a physics model independent (PMI) manner. The extracted PMI values for Charged Current F2 neutrino are then compared with Neutral Current F2 muon/electron within the framework of NLO models for massive charm production; these are found to be in general agreement, thus resolving the long-standing discrepancy between the two sets of data.

The figure above (from Yang et al.) shows F2 neutrino physics model independent (PMI) data divided by the predictions of TR-VFS (MRST99) with target mass and higher twist corrections; (right) The ratio of the previous F2 neutrino physics model dependent (PMD) data and the predictions of MRSR2.  Also shown are the ratios of the F2 muon (NMC, BCDMS) and F2 electron (SLAC) to the theoretical predictions.

(Note: a comparison of F2 from neutrino DIS to that from charged lepton DIS shows good agreement above x=0.0125, but shows differences at smaller x. This low x discrepancy can be explained by the different behavior of F2 from neutrino DIS to that from muon/electron DIS as Q goes to zero. Cf., Fleming et al., for details.)

The first measurements of Delta-xF3 are systematically higher than current theoretical predictions.   Kretzer et al.,   investigates the sensitivity of these theoretical predictions upon a variety of factors including: renormalization scheme and scale, quark mass effects, higher twist, isospin violation, and PDF uncertainties.  However, the conclusion is that it is difficult to shift the theoretical precisions in the small Q region by the amount needed to bring the theory in line with the central values of the data.
 

Delta-xF3: Comparing Charged Current Data with NLO Theory

The figure below (from Kretzer et al., based on Yang et al.) shows a collection of theoretical predictions as compared with the Delta-xF3.data.  The theoretical predictions for Delta-xF3  systematically undershoot the fixed target data at the 1-sigma-level at low x and Q.


 

As the situation stands now, this Delta-xF3 puzzle poses an important challenge to our understanding of QCD and the related nuclear processes in an important kinematic region. The resolution of this puzzle is important for future data analysis, and the solution is sure to be enlightening, and allow us to expand the applicable regime of the QCD theory.

Structure Function Measurements from HERA:

For a recent update of the structure function measurements from HERA, see ZEUS and H1 results.



Comments on this entry are welcome, and may be sent to Fred Olness.


Some References:

This list is not intended to be comprehensive, and only  serve as a starting point.  (See the Standard Disclaimer.)

SOME RECENT EXPERIMENTAL MEASUREMENTS FROM HERA.

Measurement of Neutral and Charged Current Cross Sections in Electron-Proton Collisions at High Q^2
H1 Collaboration, C.Adloff, et al.

Measurement of the Proton Structure Function F_2 at Very Low Q^2 at HERA
       ZEUS Collaboration; J. Breitweg et al.
      DESY 00-071 (May 2000)
      Physics Letters B 487 (2000) 1-2, 53-73
 

SOME EXPERIMENTAL MEASUREMENTS OF F2.

MEASUREMENT OF THE PROTON AND DEUTERON STRUCTURE FUNCTIONS, F2(P) AND F2(D), AND OF THE RATIO SIGMA-L / SIGMA-T.
By New Muon Collaboration (M. Arneodo et al.). Oct 1996. 22pp.
Published in Nucl.Phys.B483:3-43,1997
e-Print Archive: hep-ph/9610231

IMPROVED DETERMINATION OF ALPHA(S) FROM NEUTRINO NUCLEON SCATTERING.
By W.G. Seligman, et al.
Phys.Rev.Lett.79:1213-1216,1997
 

RECENT RE-ANALYSIS AND COMPARISON WITH THEORY

MEASUREMENTS OF F(2) AND X F**NEUTRINO(3) - X F**ANTI-NEUTRINO(3) FROM CCFR MUON NEUTRINO-FE AND MUON ANTI-NEUTRINO-FE DATA IN A PHYSICS MODEL INDEPENDENT WAY.
By CCFR/NuTeV Collaboration (U.K. Yang et al.). e-Print Archive: hep-ex/0009041.  Phys.Rev.Lett.86:2742-2745,2001

RECENT STRUCTURE FUNCTION RESULTS FROM NEUTRINO SCATTERING AT FERMILAB.
By CCFR / NuTeV Collaboration (U.K. Yang et al.). e-Print Archive: hep-ex/0010001

A FIRST MEASUREMENT OF LOW X LOW Q**2 STRUCTURE FUNCTIONS IN NEUTRINO SCATTERING.
By CCFR Collaboration and NuTeV Collaboration (B.T. Fleming et al.). Nov 2000. 5pp.
e-Print Archive: hep-ex/0011094. Submitted to Phys.Rev.Lett.

PREDICTIONS FOR NEUTRINO STRUCTURE FUNCTIONS.
By S. Kretzer, F.I. Olness, R.J. Scalise, R.S. Thorne, U.K. Yang.
e-Print Archive: hep-ph/0101088