Physics at HERA - KEKresearch.kek.jp/group/riron/workshop/KEKPH2005/K.TOKUSHU...CC Cross-Sections...

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


ＤＥＳＹ/ＨＥＲＡ

ZEUSH1

HERA: （27.5GeV ｅｖｓ 920GeV ｐ）the world largest electron microscope


A view of the HERA ring tunnel

Proton ring

Electron ring


The corner stone（定礎）In 1984


H1

Experiments started in 1992


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

QWavelengthResolution h→－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)

( )22fi qqQ −−≡


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


Introduction: Deep Inelastic Scattering

x = Q2/2p.q

Described by 2 kinematic variables

p

∑=f

f QxxqeF ),( 222

:),( 2Qxq f quark distribution function

3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 9x

Q2 (

GeV

2 )

Kinem

atic

limit

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

.004

E′

ZEUS e−p 98−99

ZEUSe

eθ = 0.64 rad

= 1

0 G

eV

Statistics

x

Q2 (

GeV

2 )

Kinem

atic

limit

y=1

y=0.

004

ZEUS 1996-97


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


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）


At high Q2 (Q2~MWZ2),

σNC ～ σCC

αNC~αCCElectroweak unification

Good agreement with the SM

( )222

2

2

ExchangeMQdQdσ

+

′∝

α

Measurements of NC/CC Cross sections

HERA-I Final Results

•NC(e+p) < NC(e-p)γZ interference

•CC(e+p)<CC(e-p)u,d-quark distribution in the proton

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

10

103

104

ZEUS

ZEUS e+p CC 99-00

ZEUS e−p CC 98-99

SM e+p CC (CTEQ6D)

SM e−p CC (CTEQ6D)

ZEUS e+p NC 99-00

ZEUS e−p NC 98-99

SM e+p NC (CTEQ6D)

SM e−p NC (CTEQ6D)

Q2 (GeV2)

dσ

/dQ

2 (

pb

/Ge

V2)

Mw = 80.3 ±2.1(stat)±1.2(syst)±1.0(PDF) GeV(from ZEUS e−p data)


“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

EXCLUDED L3 indir. limitPreliminary

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＜0.85×10-16cm

No signal for Leptoquarks

LQ

e

q

λ

e pLQ

LQ––

q

q–g

p p e e

Excess in 1994-1997 data (e+p)


{ } { }[ ]32

22

4

2

2

2

)1(1)1(12 xFyFyxQdxdQ

d pe −−−+=±

mπασ

[ ][ ]∑

∑

−+−=

++++−=

qZeeffZeff

qZeeffZefff

QxqxQxxqPavavPaaeQxxF

QxqxQxxqPavavPvveeQxF

),(),(}42{),(

),(),(}))((2{),(

22223

2222222222

+

= 22

2

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 GeV

ZEUS e+p 96−97 √s=300 GeV

e−p ZEUS-S √s=318 GeV

e+p ZEUS-S √s=300 GeV


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


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 >

200

GeV

2 ) (p

b)

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>400GeVWith ~ 200 pb-1 for each polarized beam,

CC Expectations


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


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 >

200

GeV

2 ) (p

b)

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


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/G

eV2 )

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/ dQ2

dσ/ 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]


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 GeV2

y< 0.9

3/March/2005 K.Tokushuku(KEK) @ KEKPH2005 21Q2 (GeV 2)

e-L

e-R

e+L

e+R

a)

0

0.5

1

1.5

2

2.5

3

10 102

103

104

105

(d2 σ

/dxd

Q2 )

/ (d

2 σem

/dxd

Q2 )

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 )

Kinem

atic

limit

y=1

y=0.

004

ZEUS 1996-97


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


HERA Kinemati

c 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.


Scaling violation

DGLAP evolution （Dokshitzer, Gribov, Lipatov, Altarelli, Parisi）

( ) ( ) ( ) ( )[ ]∫∑ ⋅+⋅=∝1

222

22

2 ,,2

)(ln x

qgqqs

qq QygyxPQyqyxP

ydyQe

QddF

πα

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


• 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 e

m

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


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 e

m -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


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


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


•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


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 e

m -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 0009.00005.0

+−±=sα

)model(0018.0(exp)0049.01166.0 ±±=sα


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 e

m

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 e

m

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


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


S.F.measurements with 1 fb-1

• Expected precision in F2 and gluon determination


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


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.

Date post:	24-Aug-2020
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