DIS 23/04/2003 Benjamin Portheault

Strange sea asymmetry

from global QCD fits

Benjamin Portheaulton behalf of

V. Barone, C. Pascaud, F. Zomer

Update of the global QCD FitResults on the strange sea asymmetry

Impact on the NuTeV measurement

2sin W

DIS 23/04/2003 Benjamin Portheault

New global QCD fit

Based on HERA I (H1,Zeus) data + NMC, BCDMS

DIS cross section data from BEBC, new CCFR, CDHSW, Drell Yan data from E605, E772 and new from E866

,pp pd NLO QCD Fixed Flavour Scheme

, , , ,v vg u d u d d u ,s sand

,s s is not constrained to have the same shape as u ds salso is allowed with the constraint

1

0( ) d 0s s x

phenomenological meson-baryon fluctuation of the protonIntrinsic strange sea :

previously :hep-ph/9907512

DIS 23/04/2003 Benjamin Portheault

fit results

s s is slightly favoured with respect to (8 units for 2

more paramaters)

s s

2 6463 6520 34 9Ndata Npar Nconst

DIS 23/04/2003 Benjamin Portheault

Constraints on ,s s

Comes from high x cross section measurment (isoscalar target)2 2

22 2

d d1 (1 ) ( )

d d d d

N N

v vxs y xu xdxx Q x Q

s

dimuon data (x<0.5) are not a direct constraint in this region

no significant statistics, large background

x=0.65 E=110 GeV

CDHSW neutrino data higher than CCFR

agreement forantineutrino data

Both CCFR and CDHSW provide high x data

DIS 23/04/2003 Benjamin Portheault

Results on the strange sea

asymmetry without CCFR, same asymmetry

as in previous studies

1 4

0( ) d 1.8 3.8 10xs xs x

using all data sets, the asymmetryis strongly reduced

1 3

0( ) d 1.8 0.5 10xs xs x

momentum asymmetry is compatible with zero

all data

no CCFR

DIS 23/04/2003 Benjamin Portheault

How favoured is the strange

asymmetry ?

CDHSW neutrino data decrease by 8 unitsCCFR E770 neutrino data increase by 6 units

(E774 neutrino data decrease by 3 units)

BUT :

Dominant systematic uncertainty(flux normalisation) on CCFR neutrino

data is fitted to –5.2 (data is scaled up by 4%)

with and without the strange asymmetryKown problem in the y shape of the

CDHSW data at low x (< 0.1)

Solution in global analysis is to take both by default

Impact on the partial allowing s s2

DIS 23/04/2003 Benjamin Portheault

NuTeV use a quantity related to(exact for an isoscalar target)

The NuTeV

2sin W

21sin

2NC NC

WCC CC

R

NuTeVLEP

EWWG

2

2

sin 0.22 0.0016

sin 0.22

77

27 0.00037

W

W

a 3.1 discrepancy

Must be corrected for a target with a fractionnal neutron excess and if s sN

DIS 23/04/2003 Benjamin Portheault

Corrections to R-

2 2 2( ) 41 7 1

s 1 s s2 3 9)

(

2( (

)

)

v v sW W W

v v v v

x u d dxR N

x

x s

u d dx x u d dx

s dx

neutron excessstrange asymmetry

NLO correction(NuTeV : LO)reduction

21s

2 WR R

Compute these corrections using our pdfsand properly propagate the errors

Kulagin hep-ph/0301045 :

DIS 23/04/2003 Benjamin Portheault

no discrepancy

Without CCFR (with the significant strange asymmetry )

0.0080 0.00005R

0.0135 0.0008R 2sin 0.2222 0.0018W

All data included :

0.0107 0.0005R 2sin 0.22 0.001749W 1.35 discrepancy

reduction is due to neutron excess correction

(with CTEQ5 pdfs )0.0117R

NuTeV reports :

DIS 23/04/2003 Benjamin Portheault

Conclusion

New global fit including the up-to-date DIS and Drell Yan data

The strange sea asymmetry is found to bereduced by the recently analysed CCFR

dataImpact on the measurement : the

neutron excess and the strange sea asymmetry reduce the NuTeV

discrepancy but the effect of the latter is small

but no access to NuTev detector effect

2sin W