Studies of Proton Structure at HERA
13
Studies of Proton Structure at HERA I. Tsurin 12 th International QCD Conference on behalf of ZEUS and H1 Montpellier July 4- 9, 2005 • Neutral current (NC) • Charged current (CC) • Structure functions F 2 , xF 3 , F L • Parton distribution functions (PDF) • The strong coupling constant α S b b 2 c c 2 F , F • New results on
description
New results on. Studies of Proton Structure at HERA. I. Tsurin. on behalf of ZEUS and H1. Neutral current (NC) Charged current (CC) Structure functions F 2 , xF 3 , F L Parton distribution functions (PDF) The strong coupling constant α S. 12 th International QCD Conference. - PowerPoint PPT Presentation
Transcript of Studies of Proton Structure at HERA
Studies of ProtonStructure at HERA
I. Tsurin
12th International QCD Conference
on behalf of ZEUS and H1
Montpellier July 4-9, 2005
• Neutral current (NC)• Charged current (CC)• Structure functions F2, xF3 , FL
• Parton distribution functions (PDF)• The strong coupling constant αS
bb2
cc2 F,F• New results on
ep-Collider HERA
H1
ZEUS
• Liquid argon calorimeter (H1) and compensated uranium calorimeter (ZEUS)• Tracking and vertex detectors• Silicon micro-strip detectors• Muon barrels and endcaps
Detectors instrumentation:
p-energy: 920 GeVe-energy: 27.6 GeV
GeV931s
HERA II:longitudinal e± beam polarisation
Deeply Inelastic Scattering
;)'(
k
kkPy
222 )k'(kqQ
yx
s
Q2
high x, low Q2 NC event
CC eventhigh Q2 NC event
H1 ZEUS
low Q2 NC event
e p
e p
NC and CC Cross-sections
ChargedCurrent
Neutral Current
HERA I
NC cross-section (ץ*, Z0):
CC cross-section (W±):
NCsNC σ
Qx
πα
Qx
)(x,Qσ ~24
2
2
22
CCW
WCC σMQ
M
π
G
Qx
)(x,Qσ ~2 22
22
2
22
][ 32
22),(~ xFYFyFYQx LNC
][ 32
22),(~ xWYWyWYQx LCC
Reduced crosssections:
Neutral Current
322 )(~),(~ xFyfFQxNC
Z exchange increases electron proton cross section and reduces positron proton cross section at large Q2
e-
e+
115)( pbpeL
1110)( pbpeL
QPM (FL=0):
22~ ZZ
)(),( 222 qqexQxF q
)(2),( 23 qqaexQxxF qq
Z
HERA I:
Z0 Contribution at High Q2
Measurements of xF3 provide a constrainton u, d valence quark densities at large x
xduxFx vvZ 2~3
)]()(2[3
13 DDUUxxF Z
sdDcuU ;
;;;
;;;
ssddddd
ccuuuuu
seaseav
seaseav
peNC
peNCxF
~3
Proton Structure at Low x
Steep rise towardslow x driven by:
gqsgqqqs PgPgPFQ
F
)(~log
222
- sea quark densities- gluon densities
δF2/ δ(lnQ2) at low x
reflects the gluon mo-
mentum distributions.
at low x gluon density dominates !
Structure Function FL
)()()(~ 22
22
2 QFY
yQFQ LNC
Decreasing of the NCcross section at low x(high y) is due to FL
xcQF )( 22
Extrapolation:
Charged Current
DxyxU
xDyUx
CC
CC2
2
)1(~~
)1(~~
at high x:
CC processes provide flavor information
vCCvCC xuxd ~~;~~
measurements of uV and dV densities
e-
e+
CC with Polarised e± Beams
)0()1()(
ppp peCC
peCC
Linear dependence of CC cross section on the longitudinal polarisation of the electron and positron beams
)0()1()(
ppp peCC
peCC
HERA II
Electron Beam
Positron Beam
Parton Distribution Functions and αS
Determination of PDFs by H1 and ZEUSusing NC and CC events measurements only
Strong coupling constant αS as measured from jet rates and from jets and NLO QCD fits to structure functions.
Contribution from Heavy Quarks
New measurement: a c-quarklifetime tagging using the silicondetectors.
Classical method: reconstruct D*
75 pb-1
22 /FFf qqqq
The contribution ofc and b quarks up to30% and 3% respect.
The first measurement of bbF2
Outlook
H1 and ZEUS collect data withhigh luminosity and e± polarizedbeams.
Physics of HERA II has begun.
More statistics will lead to higherprecision in structure analyses.
Acknowledgments
• H1 Collaboration
• ZEUS Collaboration
• DESY directorate
