Post on 21-Oct-2020
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 1
e p
Physics at HERA
Katsuo Tokushuku(KEK, ZEUS)
Contents•HERA and ZEUS•Electroweak results•Structure of the proton
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 2
DESY/HERA
ZEUSH1
HERA: (27.5GeV e vs 920GeV p)the world largest electron microscope
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 3
A view of the HERA ring tunnel
Proton ring
Electron ring
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 4
The corner stone(定礎)In 1984
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 5
H1
Experiments started in 1992
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 6
Year
Res
olve
d di
men
sion
[fm
]
10
1
0.1
0.01
1900 1950 2000
0.001
0.0001
Rutherford
Hofstadter
SLAC ep
CERN µ,ν N
HERA
THERA
partons10-16
10-19[m
]
proton
nuclei
QWavelengthResolutionh→-1~( )
Progress in accelerator enables us to investigate the smaller structure.
HERA: (27.5GeV electron vs
920GeV proton)
Q2max=s=4EeEp~10000GeV2
cf. in the rest frames=2EeMp
In order to obtain the same CMS energy as HERA in a fixed target experiment,it requires 54TeV electron beam.
No sub-parton structuredown to 0.85x10-18m
(HERA-I result)
( )22 fi qqQ −−≡
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 7
Proton 920GeV
quark920x GeV
Electron27.5GeV
Scattered quark(Jet)
HERA probes the quarks in the proton
Parton distribution in the protonsearch for quark structure
new interactions and new particles
HERA
①High Energy
High Resolution②Polarized experiment
Good sensitivity to the interaction type
Photon,Z
Neutral Current
neutrino
W
Charged Current
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 8
Introduction: Deep Inelastic Scattering
x = Q2/2p.q
Described by 2 kinematic variables
p
∑=f
f QxxqeF ),(22
2
:),( 2Qxq f quark distribution function
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 9x
Q2
(GeV
2 )
Kine
mat
ic lim
it y=
1
y=0.
004
ZEUS 1996-97
ZEUS 1998-99 (Preliminary)
ZEUS BPT 1997
ZEUS SVX 1995
NMC
BCDMS
CCFR
E665
10-1
1
10
10 2
10 3
10 4
10-6
10-5
10-4
10-3
10-2
10-1
1
Kinematical region for HERA structure function measurements
s=Q2xy
•2 order higher region in Q2,
•2 order lower region in x
•Wide (O(106)) span in Q2:Precise measurements
for Q2 evolution
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 1010 2
10 3
10 4
10 5
10−2
10−1
1x
Q2 (
Ge
V2)
y =
1
y =
0.1
y =
0.01
θe = 2.25 rad
y(1−
x)2 =
0.00
4
E′
ZEUS e−p 98−99
ZEUSe
eθ = 0.6
4 rad
= 1
0 G
eV
Statistics
x
Q2
(GeV
2 )
Kine
mat
ic lim
it y=
1
y=0.
004
ZEUS 1996-97
ZEUS 1998-99 (Preliminary)
ZEUS BPT 1997
ZEUS SVX 1995
NMC
BCDMS
CCFR
E665
10-1
1
10
10 2
10 3
10 4
10-6
10-5
10-4
10-3
10-2
10-1
1
High Q2 measurements: still limited by statistitics
HERA II
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 11
Neutral Current (NC) Charged Current (CC)
Positron Proton
Scattered positron
Jet Jet
Proton 920GeV
quark(u,d,s,c..)
positron27GeV
γ、Z
Scattered positron
Scattered quark(jet)
Proton 920GeV
d、s-quark
positron27GeV
W
Anti-neutrino
u、c-quark (jet)
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 12
At high Q2 (Q2~MWZ2),
σNC ~ σCC
αNC~αCCElectroweak unification
Good agreement with the SM
( )2222
2
ExchangeMQdQdσ
+
′∝
α
Measurements of NC/CC Cross sections
HERA-I Final Results
•NC(e+p) < NC(e-p)γZ interference
•CC(e+p)
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 13
“softer” scatteringIf the quark is not point-like
10-2
10-1
1
150 175 200 225 250 275 300 325 350 375 400
H1 CI
SCALAR LEPTOQUARKS WITH F=2 ( S 0, L )
M LQ (GeV)
λ
EXCL
UDED L3 indir. limit
Preliminary
ZEUS limit
H1 direct limit(e- p)
D0 limit
Q2 (GeV2)
N/N
CT
EQ
5D
Quark Radius Limits
ZEUSZEUS 94-00 e±pRq
2 = (0.85 ⋅10-16cm)2
Rq2 = -(1.06 ⋅10-16cm)2
1
10
103
104
0.8
0.9
1
1.1
1.2
103
104
Good agreement with the SM
Quark Radius<0.85×10-16cmNo signal for Leptoquarks
LQ
e
q
λ
e pLQ
LQ––
q
q–g
p p e e
Excess in 1994-1997 data (e+p)
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 14
{ } { }[ ]322242
2
2
)1(1)1(12 xFyFyxQdxdQ
d pe −−−+=±
mπασ
[ ][ ]∑
∑
−+−=
++++−=
qZeeffZeff
qZeeffZefff
QxqxQxxqPavavPaaeQxxF
QxqxQxxqPavavPvveeQxF
),(),(}42{),(
),(),(}))((2{),(
22223
2222222222
+
= 222
2 2sin1
Zwz MQ
QPθ
NC Cross section including Z
ZEUS
0
5
10
15
20
25
30
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9x
dσ/d
x (p
b)
ZEUS e−p 98−99 √s=318 GeVZEUS-S | γ + Z |2
ZEUS-S | γ |2
ZEUS e+p 94−97 √s=300 GeVZEUS-S | γ + Z |2
ZEUS-S | γ |2
Q2 > 10 000 GeV2
γZ interference effect
ZEUS
10-3
10-2
10-1
1
10
10 2
10 3
103
104
Q2 (GeV2)
σ∼
ZEUS e−p 98−99 √s=318 GeVZEUS e+p 96−97 √s=300 GeV
e−p ZEUS-S √s=318 GeVe+p ZEUS-S √s=300 GeV
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 15
HERA I II
Longitudinal polarization of lepton beam : Direct EW sensitivitySokolov-Ternov effectLepton beam has
transverse polarization+
Spin rotator before/after the H1/ZEUS/HERMES detectors.
Polarization build-up at HERA
Luminosity Upgrade :High-Q2 requires large luminosity
Final focusing magnets in the detector
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 16
0
20
40
60
80
100
120
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
ZEUS CC Cross Sections
e-p Data (Prelim. 16 pb-1)
e-p SM √s=320 GeV
e-p SM (MC)
√s=320 GeV (50 pb-1)
e+p Data (48 pb-1)
e+p SM √s=300 GeV
e+p SM (MC)
√s=300 GeV (50 pb-1)
P
σCC
TO
T (
Q2
> 20
0 G
eV2 )
(pb
)
Left handed Right handed
Cro
ss s
ectio
n
Expectation
Proton 820GeV
d、s-quark
Left handedelectron
W(left handed)
electron neutrino (left handed)
u、c-quark (Jet)
Proton 820GeV
d、s-quark
Right handedelectron
W(right handed)
Right handed electron neutrino
u、c-quark(Jet)
ΔMWL~80MeVMWR>400GeV
With ~ 200 pb-1 for each polarized beam,
CC Expectations
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 17
HERA delivered
0
25
50
75
100
125
150
175
200
0 200 400 600 800 1000 1200 1400days of running
Inte
gra
ted
Lu
min
osi
ty (
pb
-1)
Highest Luminosity :3.8 x 1031 cm-2s-1
HERA is back againAverage HERA polarisation
Pol
aris
atio
n [%
]
Oct 2003 Nov 2003 Dec 2003 Jan 2004
Day in month
Feb 2004
Pol
aris
atio
n [%
]
Mar 2004
Apr 2004 May 2004
Day in month
Jun 2004
Pol
aris
atio
n [%
]
Jul 2004
Day in month
Aug 2004
5 10 15 20 25 30-60
-40
-20
0
20
40
60
5 10 15 20 25 30 5 10 15 20 25 30 5 10 15 20 25 30-60
-40
-20
0
20
40
60
5 10 15 20 25 30-60
-40
-20
0
20
40
60
5 10 15 20 25 30 5 10 15 20 25 30 5 10 15 20 25 30-60
-40
-20
0
20
40
60
5 10 15 20 25 30-60
-40
-20
0
20
40
60
5 10 15 20 25 30 5 10 15 20 25 30-60
-40
-20
0
20
40
60
Average longitudinal PolarizationP=+32%P=-40%
(~50% in Feb 2005)
with polarized positron beam
Even better performance withe- p
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 18
0
10
20
30
40
50
60
70
80
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
ZEUS
ZEUS CC (prel.) 03-04 e+p (30.5 pb-1)
ZEUS CC 99-00 e+p (P=0)
SM (ZEUS-S)SM (ZEUS-S)
P
σCC (
Q2
> 20
0 G
eV2 )
(pb
)
PolarizationLeft handed Right handed
•The first measurement of Left/Right asymmetry in CC in this energy region.
•Consistent with the Standard Model
σR=3.6±3.5(pb)WR>116GeV(M. Kataoka (NaraWU) D-thesis
to be submitted on 12/Jan)
Polarized Charged Current Cross section Q2 > 200 GeV2
pblumisyststat
)(3.2.)(0.1.)(4.27.46
±±±=σ
pblumisyststat
)(1.1.)(5.0.)(6.15.22
±±±=σ
)1.14(%9.08.31 1−=±+= pbLP
)4.16(%1.12.40 1−=±−= pbLP
3.4 σ above the unpol. prediction
6.1 σ below the unpol. prediction
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 19
10-5
10-4
10-3
10-2
103
104
10-1
1
10
10 2
10 3
10-2
10-1
1
0
20
40
60
80
100
120
140
160
0 0.2 0.4 0.6 0.8
ZEUS
Q2 (GeV2)
dσ/d
Q2
(pb/
GeV
2 )
dσ/d
x (p
b)x
dσ/d
y (p
b)
y
ZEUS CC (prel.)03-04 e+p (14.1pb-1)
ZEUS CC (prel.)04 e+p (16.4pb-1)
SM (ZEUS-S) P = +32%SM (ZEUS-S) P = -40%
dσ/ dQ2dσ/ dxdσ/ dy
Polarization effects observed in overall, i.e. no phase space bias.Agrees with the SM prediction of : overall normalization change
by (1+P) factor.
CC Single Differential Cross-Sections [ZEUS]
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 20
0
10
20
30
40
50
60
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
HERA II
H1 (prel.)H1ZEUS (prel.)ZEUSSM (MRST)
Q2 > 400 GeV2
y < 0.9
P
σCC (
pb)
e+p → ν_X
pbsyststatPCC .)(7.2.)(4.27.3)1( ±±−=−=σH1 preliminary result on σRCC Cross-Sections [H1/ZEUS]
H1 cross sections are slightly lower but the two results are consistent.
σCC (RH)=0
Q2 > 400 GeV2y< 0.9
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 21Q2 (GeV 2)
e-L
e-R
e+L
e+Ra)
0
0.5
1
1.5
2
2.5
3
10 102
103
104
105
(d2 σ
/dxd
Q2 )
/ (
d2σ
em /d
xdQ
2 )ZEUS
0.5
1
1.5
103
104
P=
+3
2%
/ P
=0
Q2 (GeV2)
0.5
1
1.5
103
104
03-04 P=+32% (prel.) / 99-00 P=0
0.5
1
1.5
103
104
P=
-40
% /
P=
0Q2 (GeV2)
dσ
/dQ
2 ra
tio0.5
1
1.5
103
104
04 P=-40% (prel.) / 99-00 P=0
0.5
1
1.5
103
104
P=
+3
2%
/ P
=-4
0%
Q2 (GeV2)
0.5
1
1.5
103
104
SM (ZEUS-S)
03-04 P=+32% (prel.) / 04 P=-40% (prel.)
Polarized Neutral Current Cross section
•Very subtle effect from γ-Z interference•Larger effect in e-p
(The experiment has started in Nov 2004)
Pol=70%
χ2 = 1.69(w/ Pol.)χ2 = 2.29(w/o Pol.)
at Q2>1000 GeV2
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 22x
Q2
(GeV
2 )
Kine
mat
ic lim
it y=
1
y=0.
004
ZEUS 1996-97
ZEUS 1998-99 (Preliminary)
ZEUS BPT 1997
ZEUS SVX 1995
NMC
BCDMS
CCFR
E665
10-1
1
10
10 2
10 3
10 4
10-6
10-5
10-4
10-3
10-2
10-1
1
Kinematical region for HERA structure function measurements
s=Q2xy
•2 order higher region in Q2,
•2 order lower region in x
•Wide (O(106)) span in Q2:Precise measurements
for Q2 evolution
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 23
HERA
Kine
matic
Limit
0
1
“pQCD” : parton evolution
“Hadronic”: Regge theorybehavior of γp total cross section
Predictions of F2
Donnachie & Landshoff
Gluck, Reyaand Vogt
Fixedtarget data
Early ZEUS data showed rapid increase of F2 at low x.
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 24
Scaling violation
DGLAP evolution (Dokshitzer, Gribov, Lipatov, Altarelli, Parisi)
( ) ( ) ( ) ( )[ ]∫∑ ⋅+⋅=∝1
222
22
2 ,,2
)(ln x
qgqqs
qq QygyxPQyqyxPy
dyQeQd
dFπ
α
splitting function (known from pQCD)( )yxPqq
( )yxPqg
y
x
(y-x)
y
x
(y-x)
Q2→larger:high-x q and g are split into
low x q and g.
x
xq
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 25
• Strong rise of F2 as xdecreases– Soft ‘sea’ of quarks in the proton
• Slope of rise gets steeper as Q2 ↑
softer parton smaller resol.
dynamics of quarks and gluons
• Good agreement with fixed-target experiments at middle -high x– Sea + valence quarks
HERA F2
0
1
2 Q2=2.7 GeV2 3.5 GeV2 4.5 GeV2 6.5 GeV2
0
1
2 8.5 GeV2 10 GeV2 12 GeV2 15 GeV2
0
1
2 18 GeV2
F2 em
22 GeV2 27 GeV2 35 GeV2
0
1
2 45 GeV2 60 GeV2
10-3
1
70 GeV2
10-3
1
90 GeV2
0
1
2
10-3
1
120 GeV2
10-3
1
150 GeV2
x
ZEUS NLO QCD fit
tot. error
H1 96/97ZEUS 96/97
BCDMSE665NMC
Results of F2 Structure Function
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 26
F2 for fixed x, as a function of Q2
• At low x, strong scaling violationis seen.Large gluon density + splitting
→ F2 increases
• At x ~ 0.1, approximate scaling.• At higher x, F2 decreases as Q2 ↑.
Quark radiates off gluon: q→qg
• Line = result of QCD fit– All data points well described.
g→qq
HERA F2
0
1
2
3
4
5
1 10 102
103
104
105
F2 em
-lo
g 10(
x)
Q2(GeV2)
ZEUS NLO QCD fit
tot. error
H1 94-00 prelim.
H1 96/97
ZEUS 96/97
BCDMS
E665
NMC
x=6.32E-5x=0.000102x=0.000161
x=0.000253
x=0.0004x=0.0005
x=0.000632x=0.0008
x=0.0013
x=0.0021
x=0.0032
x=0.005
x=0.008
x=0.013
x=0.021
x=0.032
x=0.05
x=0.08
x=0.13
x=0.18
x=0.25
x=0.4
x=0.65
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 27
x=0.65
x=0.40
x=0.25
x=0.18
x=0.13
x=0.08
x=0.05
x=0.032
x=0.02
x=0.013
x=0.008
x=0.005
x=0.0032
x=0.002
x=0.0013
x=0.0008
x=0.0005
x=0.00032
x=0.0002
x=0.00013
x=0.00008
x=0.00005
x=0.000032
x=0.00002
(i=1)
(i=10)
(i=20)
(i=24)
Q2 /GeV2
Fp 2+
c i(x
)
NMC BCDMS SLAC H1
H1 96 Preliminary(ISR)
H1 97 Preliminary(low Q2)
H1 94-97 Preliminary(high Q2)
NLO QCD FitH1 Preliminary
ci(x)= 0.6 • (i(x)-0.4)
0
2
4
6
8
10
12
14
16
1 10 102
103
104
105
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 28
PDF parameterization
• xf(x) = p1xp2(1-x)p3(1+p5x) at Q02=7GeV2– p1: normalization– p2(p3): x→0 (x→1) bahavior– p5: high-x shape
• Some assumptions– For xuv and xdv, fix p2=0 (not sensitive to low-x valence)– For xg, fix p5=0 (not sensitive to high-x gluon shape)– xSea=(xubar+xdbar+xStrange+xCharm), xStrange=0.2*xSea (CCFR)– Use MRST form for x(ubar-dbar) shape (only fit p1)
• Sum-rule constraints (number and momentum)– ∫uv(x)dx=2, ∫dv(x)dx=1, ∫x∑f(x)dx=1
• Total: 11 free parameters, 1263 data points
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 29
•As seen in the F2 rise at low-x, many sea quarks.
•Gluons are dominant at low-x
• Similar conclusion from ZEUS andthe PDF fitters (Durham, CTEQ)
How about H1 results?
PDFs obtained from the fits
ZEUS
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
10-3
10-2
10-1
1
ZEUS NLO QCD fit
αs(MZ2) = 0.118
tot. error
CTEQ 6M
MRST2001
Q2=10 GeV2
xuv
xdv
xg(× 0.05)
xS(× 0.05)
x
xf
HERA: PDF determination
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
10-3
10-2
10-1
1
H1 2002 PDF Fit (prel.)αs(MZ
2) = 0.1185 fixeddata set: H1 (94/00) + BCDMS
ZEUS NLO QCD fitαs(MZ
2) = 0.1180 fixeddata set: ZEUS (96/97) + BCDMS, NMC, E665, CCFR
experimental errors only
Q2=1000 GeV2
xuv
xdv
xS( 0.05)
x
xf
Note the scale factor.Gluon dominant at low-x
H1/ZEUS comparison:The main difference comes from
•Initial Parameter •Selection of low energy experiments
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 30
Simultaneous extraction of αs and PDFth. uncert.
exp. uncert.
World average (S. Bethke, hep-ex/0407021)
Dijet cross sections in NC DIS ZEUS (Phys Lett B 507 (2001) 70)
Inclusive jet cross sections in NC DIS ZEUS (Phys Lett B 547 (2002) 164)
NLO QCD fit ZEUS (Phys Rev D 67 (2003) 012007)
NLO QCD fit ZEUS prel. (contributed paper to ICHEP04)
Subjet multiplicity in NC DIS ZEUS (Phys Lett B 558 (2003) 41)
Subjet multiplicity in CC DIS ZEUS (Eur Phys Jour C 31 (2003) 149)
Inclusive jet cross sections in γp ZEUS (Phys Lett B 560 (2003) 7)
Multi-jets in NC DIS ZEUS prel. (contributed paper to ICHEP04)
Jet shapes in NC DIS ZEUS (DESY 04-072 - hep-ex/0405065)
0.1 0.12 0.14αs(MZ)
HERA F2
0
1
2
3
4
5
1 10 102
103
104
105
F2 em
-lo
g 10(
x)
Q2(GeV2)
ZEUS NLO QCD fit
tot. error
H1 94-00 prelim.
H1 96/97
ZEUS 96/97
BCDMS
E665
NMC
x=6.32E-5x=0.000102x=0.000161
x=0.000253
x=0.0004x=0.0005
x=0.000632x=0.0008
x=0.0013
x=0.0021
x=0.0032
x=0.005
x=0.008
x=0.013
x=0.021
x=0.032
x=0.05
x=0.08
x=0.13
x=0.18
x=0.25
x=0.4
x=0.65
• Scaling violation: ∂F2/∂lnQ2 ~ αs•xg(x,Q2)
Data at low x allow disentangling correlation of αs and xg
• αs-free fit gives:
H1:(additionally ±0.0005 from renormalization scale)
ZEUS:(additionally ±0.0004 from renormalization scale)
Difference in exp. error mainly from the treatment ofsystematic error and normalization of data pointsin the fitting procedure and error propagation.
)model((exp)0017.01150.0 0009.0 0005.0+−±=sα
)model(0018.0(exp)0049.01166.0 ±±=sα
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 31
What if there were no HERA data?
• HERA data determine the low-x gluon and sea-quark PDF.
• HERA revealed: F2 is very steep.
ZEUS
0
1
2 Q2=2.7 GeV2 3.5 GeV2 4.5 GeV2 6.5 GeV2
0
1
2 8.5 GeV2 10 GeV2 12 GeV2 15 GeV2
0
1
2 18 GeV2
F2 em
22 GeV2 27 GeV2 35 GeV2
0
1
2 45 GeV2 60 GeV2
10-3
1
70 GeV2
10-3
1
90 GeV2
0
1
2
10-3
1
120 GeV2
10-3
1
150 GeV2
x
ZEUSNLO-QCD fit
tot. error
WITHOUT-ZEUS fittot. error
ZEUS 96/97BCDMSE665NMC
ZEUS
0
10
20 Q2=1 GeV2
ZEUS NLO QCD fit
tot. error
2.5 GeV2
WITHOUT-ZEUS fit
tot. error
0
10
20
xg
7 GeV2 20 GeV2
0
10
20
10-4
10-3
10-2
10-1
1
200 GeV2
10-4
10-3
10-2
10-1
1x
2000 GeV2
HERA F2
0
1
2 Q2=2.7 GeV2 3.5 GeV2 4.5 GeV2 6.5 GeV2
0
1
2 8.5 GeV2 10 GeV2 12 GeV2 15 GeV2
0
1
2 18 GeV2
F2 em
22 GeV2 27 GeV2 35 GeV2
0
1
2 45 GeV2 60 GeV2
10-3
1
70 GeV2
10-3
1
90 GeV2
0
1
2
10-3
1
120 GeV2
10-3
1
150 GeV2
x
ZEUS NLO QCD fit
tot. error
H1 96/97ZEUS 96/97
BCDMSE665NMC
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 32
Low-Q2 sea and gluon distributions• At Q2 ~ 1GeV2, gluon becomes valence-like
(and even tends to be negative)• Sea quark is still rising
ZEUS
-2
0
2
4
6 Q2=1 GeV2
ZEUS NLO QCD fit
xg
xS
2.5 GeV2
xS
xg
0
10
207 GeV2
tot. error(αs free)
xS
xg
xf
20 GeV2
tot. error(αs fixed)
uncorr. error(αs fixed)
xS
xg
0
10
20
30
10-4
10-3
10-2
10-1
1
200 GeV2
xS
xg
10-4
10-3
10-2
10-1
1
2000 GeV2
x
xS
xg
ZEUS
0
5
10
15
20
1 10 102
103
104
xg
Q2(GeV2)
(a)
ZEUS NLO QCD fit
tot. error ( αs-free)
tot. error ( αs-fixed)
x=0.0001
x=0.001
x=0.01
x=0.1
Q02
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 33
S.F.measurements with 1 fb-1
• Expected precision in F2 and gluon determination
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 34
Flavor-specific measurements
• Complete ‘mapping’ of the proton…– d/u at high x: charged current– Strange: charm in CC and/or leading φ particle– Charm and bottom: improved tagging with micro-vertex
Charm 500 pb-1 Bottom/charm 500 pb-1
3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 35
Summary• HERA and ZEUS/H1 experiments
– Collider = x100 extended region in Q2 and x.
• High- Q2 NC and CC: electroweak effects– NC: effect of Z exchange (different coupling of quark-antiquark)– CC: flavor-specific (sees positive and negative quarks differently)
• HERA-II with longitudinal polarization just started.– W should couple with only right-handed e+ (and left-handed e−).
• F2 measurement and PDF determination– Very steep rise of sea and gluon at low x.