ep-Physics at High Q

2

Recent Results and Future Perspectives Testing QCD and Electroweak Theory at HERA

Hans-Christian Schultz-CoulonUniversität Dortmund

[for the H1 and ZEUS collaboration]

Les Arcs, March 2002

HERA Kinematics

q

Protonp

Q2 = -(k – k')2

P X

k'k

P'

= xP

W±γ,Z0

q

Electron (e±) Electron (e±) Neutrino

Q

2

: four-momentum transferQ

2

:

[spatial resolution ~ 1/Q]

x: fractional momentum x: of the struck quark

y = Q

2

/sx: Inelasticityy =

[√s: cms energy]

E

p

=920 GeV

E

e

=27.5 GeV

[before 1998: E

p

=820 GeV]

Q

2

= 16950 GeV

2

Electrons

Protons

r

φφφφ

rz

view

view

NC DIS Event

[as seen in a typical HERA detector]

Neutral Current DIS Cross Section

F

˜

2

x q

i

x Q

2

,( )

q

i

x Q

2

,( )

+

[ ]

A

i

⋅

i

∑

=

Proton

γ,Z0e±

e±

q

q

SF

d

2

σ

NC

e

±

( )

dxdQ

2

------------------------2

πα

2

xQ

4

------------- Y

+

F

˜

2

Y

+−

–

xF

˜

3

y

2

F

L

–

[ ]

=

Y

±

1 1

y

–

( )

2

±( )

=

{ }

Helicity structure

A

i

Q

q2

2Q

q

v

e

v

q

χ

Z

–

Q

q

v

e

v

q

χ

Z

v

e2

a

e2

+

( )

v

q2

a

q2

+

( ) χ

Z

( )

2

+ +=

B

i

2Q

q

a

e

a

q

χ

Z

– 4

v

e

a

e

v

q

a

q

χ

Z

( )

2

+=

χZ1

4 sW2

cW2

------------------- Q2

Q2

MZ2

+----------------------

=

xF̃3 x qi x Q2,( ) qi– x Q

2,( )[ ] Bi⋅i

∑=

Proton structure

[electroweak couplings & propagator]

FL: influence smallFL: related to gluon density[contribution only @ high y]

Hard process

[LO: FL=0]

LO picture:

[fitted in NLO]

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

10

103

104

H1 e+p 94-00 prelim.

H1 e-p

ZEUS e+p 99-00 prelim.

ZEUS e-p 98-99 prelim.

SM e+p (CTEQ5D)

SM e-p (CTEQ5D)

y < 0.9

Q2 (GeV2)

dσ/d

Q2 (

pb/G

eV2 )

Neutral Current DIS Cross SectionNLO QCD Fit toHERA & Fixed Target DIS Data etc.

10-3

10-2

10-1

1

10

102

103

104

105

102

103

104

Q2 (GeV2)

H1 e–pZEUS e-p 98-99 prelim.

SM e–p (CTEQ5D)

H1 e+p 94-00 prelim.ZEUS e+p 99-00 prelim.

SM e+p (CTEQ5D)

x=0.08 (x10000)

x=0.13 (x2500)

x=0.18 (x500)

x=0.25 (x100)

x=0.40 (x5)

x=0.65

σ∼N

CNC �reduced�Cross Section

σ̃NC± 1

Y+---- xQ

4

2πα2------------- d

2σNCe

±( )dxdQ

2-----------------------≡

σ̃NC±

F̃2 f+− y( )F̃3 g y( )FL+=

Extraction of:

� xF3 (@ large Q2)� quark densities

~

0

0.5

1

1.5

0

0.5

1

1.5

10-2

1 10-2

1

0

0.5

1

1.5

10-2

1 10-2

1

H1

Col

labo

ratio

n

σ~

NC

Q2 = 100 GeV2 Q2 = 120 GeV2 Q2 = 150 GeV2 Q2 = 200 GeV2

σ~

NC

Q2 = 250 GeV2 Q2 = 300 GeV2

x

Q2 = 400 GeV2

x

Q2 = 500 GeV2

x

σ~

NC

Q2 = 650 GeV2

x

Q2 = 800 GeV2

e+p high y, H1 preliminary

e+p low Q2, H1 96/97e+p, H1 preliminary 99/00

H1 97 PDF Fit: σ~

NC (FL=0)H1 97 PDF Fit: σ

~

NC (FL=FQCD

L )

2 Q2 =FL ExtractionMethodσσσσ̃NC

+ 1Y+-----

xQ4

2ππππαααα2-------------

d2σσσσNC

dxdQ2

-----------------≡≡≡≡

x

� Substantial FL contri-bution only at low xi.e. @ high y = Q2/xs

� Subtraction methodtaking F2 from QCD Fit(at low y region)

FL=0

FL=FLQCD

FL

Y+

y2----- F2 Aσ̃NC–[ ]≡

Normalization factor taken from data with y<0.6

[negligible contribution of FL]

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

100 200 300 400 500 600 700800

Q2 / GeV2

F L

0.002 0.004 0.008 x

fixed y=0.75

FQCD

L (H1 97 PDF Fit)

FL = F2 (H1 97 PDF Fit)

H1

Col

labo

ratio

n

e+p H1 preliminary 99/00e−p H1 preliminary 98/99

FL ~ 20% of F2[i.e. < 10% contribution for y < 0.6]

xF3 Extraction Method[Using NC e+p and e-p cross section]

~

xF̃3Y+

Y–----- σ̃NC

e–( ) σ̃NC

e+( )–[ ]⋅=

σ̃NCe

+( ) 1Y+----- Y+F̃2 Y– – xF̃3 y

2FL–[ ]=

σ̃NCe

–( ) 1Y+----- Y+F̃2 Y+ – xF̃3 y

2FL–[ ]=

xF̃3 q x Q2,( ) q– x Q

2,( )[ ]∼

sensitivity to valence quark densities

additional factor needed if e+p and e-p data taken at different beam energies

sensitive only @ high Q2

where γZ interference is sizeable

Q2=1500 GeV2xF∼

3

Q2=3000 GeV2

Q2=5000 GeV2xF∼

3

Q2=8000 GeV2

Q2=12000 GeV2

x

xF∼

3

Q2=30000 GeV2

x

H1 H1 97 PDF FitZEUS prel.

0

0.2

0.4

0

0.2

0.4

0

0.2

0.4

10-1

10-1

xF̃3 Qeae 2Qqaqx qi qi–[ ]{ } χZ⋅ 2veae 2vqaqx qi qi–[ ]{ } χZ( )⋅ 2+=

xF3 Qeae xF3γZ{ } χZ⋅∼

xF3

contribution to xF3: <3%

� rises with Q2 (@ fixed x)due to propagator

� agreement of data withprediction from QCD fit

χZ1

4 sW2

cW2

------------------- Q2

Q2

MZ2

+----------------------

=

~

~

x

xF3 γZ

Q2=1500 GeV2

Q2=5000 GeV2

Q2=12000 GeV2

H1 97 PDF FitH1 Data

0

1

2

0 0.2 0.4 0.6

F3γZ

0

1

∫ 2Qqaq qi qi–[ ] 2Quau Nu 2Qdad Nd53--- 1 α s/π–( )⋅=+=

0

1

∫=

F3γZ

0.02

0.65

∫ 1.88 0.44±=

F3γZ

0.02

0.65

∫ 1.11=

H1 measurement:

H1 QCD Fit:

xF3γγγγZ

agreement within2 standard deviations

� Q2 dependence (from scaling violation) expected to be small

� direct comparison of measure-ments at different Q2 possible

[sum rule a la Gross Llewellyn-Smith]

Proton

W

e-(e+)

SF

ν(ν)_

-(+)

u-type(d-type)

d-type(u-type)

10-7

10-6

10-5

10-4

10-3

10-2

10-1

103

104

HERA Charged CurrentCross Section

H1 e+p 94-00 prelim.

H1 e-p

ZEUS e+p 99-00 prelim.

ZEUS e-p 98-99 prelim.SM e+p (CTEQ5D)

SM e-p (CTEQ5D)

y< 0.9

Q2 (GeV2)

dσ/d

Q2 (

pb/G

eV2 )

d2σCC

e+( )

dxdQ2

------------------------πα2

4sW2

---------1

Q2 MW2+( )

2----------------------------- u c 1 y–( )2

d s+( )–+[ ]=

d2σCC

e–( )

dxdQ2

-----------------------πα2

4sW2

---------1

Q2 MW2+( )

2----------------------------- u c 1 y–( )2

d s+( )–+[ ]=

ChargedCurrent

Cross Section

Probes u-quark density

Probes d-quark density

CC DIS Event[as seen by the other typical HERA detector]

1

2

0.5

1

0.2

0.6

Q2 = 280 GeV2 Q2 = 530 GeV2 Q2 = 950 GeV2

Q2 = 1700 GeV2 Q2 = 3000 GeV2 Q2 = 5300 GeV2

Q2 = 9500 GeV2 Q2 = 17000 GeV2

H1 e–pZEUS e–p 98-99 prelim.

SM e–p (CTEQ5D)

0.1 0.10.01 0.01

1

2

0.2

0.6

0.05

0.10

0.15

Q2 = 280 GeV2 Q2 = 530 GeV2 Q2 = 950 GeV2

Q2 = 1700 GeV2 Q2 = 3000 GeV2 Q2 = 5300 GeV2

Q2 = 9500 GeV2 Q2 = 17000 GeV2

x

H1 e+p 94-00 prelim.ZEUS e+p 99-00 prelim.

SM e+p (CTEQ5D)

0.1 0.10.01 0.01

x (u+c)(1-y)2x (d

_+s

_)

(1-y)2x (d+s)x (u

_+c

_)

x

σ CC

∼

σ CC

∼

σ̃CC± 4sW

2Q

2MW

2+( )

2

πα2------------------------------------------=

d2σCC

e±( )

dxdQ2

-------------------------

σσσσ̃CC–

x u c 1 y–( )2 d s+( )+ +[ ]=

σσσσ̃CC+

x u c 1 y–( )2d s+( )+ +[ ]=

Reduced CC Cross Section

e-p e+p

[Sensitivity to u/d quark densities]

Knowledge of d/u Ratio

M.Botje

Large uncertainty at high x[dependence on parameterisation][e.g. due to nuclear corrections]

Can be further constrained with NC and CC HERA data.

Fit to� HERA ep data

[H1 1994, ZEUS 1994]� Fixed Target proton

and deuteron data [E665, NMC, BCDMS, SLAC]

� Neutrino data [CCFR] � Drell-Yan data [E866]

Constrained byW-AsymmetryDIS data

DIS data onlyConstrained by

H1 Preliminary

0

0.2

0.4

0.6

0.8x=0.25xu

v

0

0.2

0.4

0.6x=0.25xd

v

0

0.1

0.2

0.3

0.4x=0.4xu

v

0

0.05

0.1

0.15

103

104

x=0.4

Q2 (GeV2)

xdv

0

0.02

0.04

0.06

103

104

x=0.65

Q2 (GeV2)

xuv

H1 94-00 combined

NLO QCD Fit: H1 only

H1 97 PDF Fit

CTEQ5M

MRST

Valence Quark Distribution

NLO QCD fit using high Q2,neutral/charged current,e+p and e-p data.

Quark densitiesdetermined via localextraction method fordata points where thexqv contribution is >70%.

@ high x

More statistics needed to constrain behaviour of dv, uv further.

xqv σmeas

xqvσ

---------

fit⋅=

HERA UpgradeZEUS Microvertex Detector

H1:� Lumi System� Triggering� Fwd/Bwd Silicon� Forw. Tracking

ZEUS:� Lumi System� Triggering� Microvertex� Forw. Tracking

- - -

x

x

x

x

x

x

Ls [cm-2s-1mA-2]

∆x [mm]

2002From a first

Design:1.8 x1030cm-2s-1mA-2

Delivered HERA luminosity 1994 – 2000

Days of running

Inte

grat

ed L

umin

osity

(pb

-1)

94-97 e+

98-99 e-

99-00 e+

02.11.

20

40

60

80

100

200 400 600 800

20

40

60

80

100

PostUpgrade Luminosity

2000:

70 pb-1LPeak

~ 1.7 x1031cm-2s-1

spec. Lumi[cm-2s-1mA-2]

Lumi[cm-2s-1]

int. Lumi [pb-1/y]

20000.7 x 1030 1.7 x 1031 70

[Ie=50 mA, Ip=100 mA, #Bunches ~200]

PostUpgr.1.5 x 1030 6 x 1031 240

[Ie=60 mA, Ip=140 mA, #Bunches ~200]

New beam optics with stronger focusingprovides expected improvement

lumi scan[low currents]

Peak Peak

HERA B

H1

HERMES

ZEUS

Laser

Laser

electrons

Spin Rotator (new)

Spin Rotator (new)

SpinRotator(exists)

TPOL

LPOL

Polarimeter

Polarimeter

Polarization for H1 and ZEUS

� utilises Compton scattering� measures spatial asymmetry

� utilises Compton scattering� measures energy weighted asymmetry

Goal: <2% accuracy per bunch per minute

0

10

20

30

40

50

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1Polarisation

σ obs

(P)

/ pb

Q2 (GeV 2)

(d2 σ/

dxdQ

2 ) / (

d2 σ em /d

xdQ

2 )e-L

e-R

e+L

e+R

0

0.5

1

1.5

2

2.5

3

10 102

103

104

105

[Q2>1000 GeV2]

NC

σ̃NC± σ̃NC 0,

±Pσ̃NC P,

±+=

Possibility to

Disentangle individual quark densities Measure EW couplings vu, vd, au, ad

σ̃NC±

f q q EW couplings, ,( )=Four independent equations one each for Qe= ±1 and P= ±1.

NC

CC

σ̃CC±

1 P±( )σ̃CC P 0=( ),±

=

e-p → νX

�+: Probe dv quark distribution (P= +1)-: Probe uv quark distribution (P= -1)

PolarisationUtilising

Exploit sensitivityto EW couplings athigh Q2

10-7 10-6 10-5 10-4 10-3 10-2 10-1 100100

101

102

103

104

105

106

107

108

109

fixedtargetHERA

x1,2 = (M/14 TeV) exp( ±y)

Q = M

LHC parton kinematics

M = 10 GeV

M = 100 GeV

M = 1 TeV

M = 10 TeV

66y = 40 224

Q2

(GeV

2 )

x

LHC

HERA @ high x, high Q2

Fixed Target

Test of QCD evolution over 4 order of magnitude. important for LHC and e.g. the prediction of Higgs/W cross sections.

+

EW Couplings vu,au

0.16

0.18

0.2

0.22

0.47 0.5 0.53ac (au)

v c (v

u)LEP 2002Preliminary

68.3 95.5 99.5 %CL

SM

HERA IIP= 0.5

1σ

4 x 250 pb-1

[Qe=±1, P=±1]

HERA:

Complementarymeasurement[HERA: u,d quark couplings][LEP: c,b quark couplings]

Precision compati-ble with LEP results

Conclusions

Neutral and charged current cross section consistent with SM

Electroweak effects used as tool to extract proton structure @ high x

HERA II: Test of QCD evolution up to highest Q2

Constrain valence quark distributions at high xDetermine EW couplings vu,au,vd,ad