Measurements of the proton structure at HERA

Measurements of the proton structure at HERA

Ian C. Brock on behalf of the H1 and ZEUS collaborationsUniversity of Bonn!Blois 2014

Outline

• Introduction

• Recent FL measurements

• ZEUS and H1 NC/CC combinations

• HERAPDF 2.0

• F2b and F2c

• Summary

2

Many interesting and recent measurements not discussed due to lack of time: 22 papers in ZEUS/H1 combination!

HERA

• e± p collisions at √s = 318 GeV

• ∼0.5 fb-1 per experiment

• HERA 1:

• 1996 - 2000

• HERA 2 (longitudinal e± polarisation)

• 2004 - 2007

3

p 920 GeV

e±

27.5 GeV θ w.r.t. p beam η = -ln tan θ/2

DIS events and kinematics

• Characterise events:

• Q2

• Bjorken x, (0 < x < 1)

• Inelasticity y, (0 < y < 1)

4

!

!

!

!"#$%&'()*+,

%&'()*+,

%&'()*+,

-./*(0')

1*+)+,*'2)1*+)+,*'2)

-./*(0')

NC - scattered e

Q2 = s x yDIS ⇒ scattered e in detector

Q2 ≿1 GeV2

CC - scattered ν

Basic equations

• e±p cross-section and structure functions

• (Unpolarised) reduced cross-sections often used:

5

d2�(e±p)

dx dQ2=

2⇡↵2

xQ

4

⇥Y+F2(x,Q

2)⌥ Y�xF3(x,Q2)� y

2FL(x,Q

2)⇤

Y± = 1± (1� y)2

�r(or �) =d

2�

dx dQ

2· xQ

4

2⇡↵

2Y+

= F2(x,Q2)� y

2

Y+FL(x,Q

2)

Kinematic regions

6

Parameterise structure functions as a function of x Use DGLAP equations to evolve from HERA to LHC

Evolution depends on order: LO, NLO, NNLO

LHCTevatronHERA

Fixed target

FL

• FL proportional to cross-section of long. polarised photons

• 0 at lowest order!

• FL term in cross-section multiplied by y2

• Go to high y

• Make use of Q2 = s x y

• For given Q2 and x, vary s(y) to decouple F2 and FL

• HERA ran with Ep = 460 and 575 GeV in 2007 in order to vary s

7

� = F2(x,Q2)� y

2

Y+FL(x,Q

2)

FL

• ZEUS: include high-precision HERA 1 data (with shifted vertex to improve low Q2 measurement)

• H1: reanalyse and extend to lowest possible E′e

8

DESY-14-053, arXiv:1404.6376

DESY-13-211, EPJ. C 74 (2014) 2814

1 10 210 310

-0.2

0

0.2

0.4

4 1

0u

x 0.28

0.43

0.59

0.88

1.29

1.69

2.24

3.19

4.02

5.40

6.87

9.58

12.1

15.7

24.3

30.3

40.2

54.1

73.6

98.6

184

H1 and ZEUSLF

]2 [GeV2Q

HERAPDF1.5 NNLO

CT10 NNLO

MSTW08 NNLO

ABM12 NNLO

NNPDF2.3 NNLO

JR09 NNLO

H1ZEUSH1ZEUSH1ZEUS

1 10 210 310

-0.2

0

0.2

0.4 Reasonable precision ∼10% per point

Limited int. lumi.: 11.8 pb-1 at √s = 225 GeV 5.4 pb-1 at √s = 252 GeV

Combined cross-sections

• Complete set of H1 and ZEUS NC and CC measurements

• HERA 1 and HERA 2 datacombined

• Also includes latest FL andhigh x measurements

• 1307 data points!

• Correlated syst. uncertaintiesproperly taken into account

9H1prelim-14-041, ZEUS-prel-14-005

Good 𝜒2: 1685/1620 d.o.f.

Combined cross-sections

10

H1 and ZEUS preliminary

0

0.2

0.4

0.6

0.8

1

1.2

103

104

Q2/GeV2

mr,

NC

(x,Q

2 )

|

HERA NC e-p (prel.) 0.4 fb-1

3s = 318 GeVZEUS HERA IIZEUS HERA IH1 HERA IIH1 HERA I

x=0.008

x=0.032

x=0.08

x=0.25


0

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(x,Q

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+

HERA NC e+p (prel.) 0.5 fb-1

3s = 318 GeVZEUS HERA IIZEUS HERA IH1 HERA IIH1 HERA I

x=0.0002

x=0.002

x=0.008

x=0.032

x=0.08

x=0.25

x=0.008 x=0.08

H1prelim-14-041, ZEUS-prel-14-005

Electroweak effects

11H1prelim-14-041, ZEUS-prel-14-005


0

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mr,

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(x,Q

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3s = 318 GeV


HERA NC e- p (prel.) 0.4 fb-1

x=0.008

x=0.032

x=0.08

x=0.25]2

[pb/

GeV

2/d

Qmd

-710

-510

-310

-110

10

]2 [GeV2Q310 410

p CC±H1 ep CC+H1 e

p CC HERA II±ZEUS ep CC HERA II+ZEUS e

p CC (HERAPDF 1.5)±SM ep CC (HERAPDF 1.5)+SM e

p NC±H1 ep NC+H1 e

p NC HERA II±ZEUS ep NC HERA II+ZEUS e

p NC (HERAPDF 1.5)±SM ep NC (HERAPDF 1.5)+SM e

y < 0.9 = 0eP

HERA

HERAPDF 2.0

• Use ZEUS + H1 combined cross-sections (only) to extract PDFs:

• Low Q2 data constrain sea and gluon

• High Q2 NC and CC data constrain valence quarks

• Main tool used is HERAFitter (see next talk)

• Up-to-date theory treatment (especially of heavy flavour) included

• NLO + NNLO PDFs determined12

HERAPDF 2.0 (NC data)

13

0

0.5

1

1.5

0

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1

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H1 and ZEUS preliminaryQ2 = 3.5 GeV2

mr,

NC

(x,Q

2 )

+

Q2 = 5 GeV2 Q2 = 6.5 GeV2 Q2 = 8.5 GeV2

Q2 = 12 GeV2 Q2 = 15 GeV2 Q2 = 20 GeV2 Q2 = 25 GeV2

Q2 = 35 GeV2 Q2 = 45 GeV2

10-3 10-1

Q2 = 60 GeV2

10-3 10-1

Q2 = 90 GeV2

10-3 10-1

xQ2 = 120 GeV2

10-3 10-1

x

HERA NC e+p (prel.) 26 pb-1

3s = 225 GeVHERAPDF2.0 (prel.)NNLO, Q2 = 3.5 GeV2NNLO, Qmin0

0.5

1

1.5

0

0.5

1

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0

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1

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0

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1

1.5

H1 and ZEUS preliminaryQ2 = 3.5 GeV2

mr,

NC

(x,Q

2 )

+

Q2 = 5 GeV2 Q2 = 6.5 GeV2 Q2 = 8.5 GeV2


Q2 = 35 GeV2 Q2 = 45 GeV2

10-3 10-1

Q2 = 60 GeV2

10-3 10-1

Q2 = 90 GeV2

10-3 10-1

xQ2 = 120 GeV2

10-3 10-1

x


3s = 251 GeVHERAPDF2.0 (prel.)NLO, Q2 = 3.5 GeV2NLO, Qmin0

0.5

1

1.5

0

1

0

1

0

1

0

1

0

1

H1 and ZEUS preliminaryQ2 = 2 GeV2

mr,

NC

(x,Q

2 )

+

Q2 = 2.7 GeV2 Q2 = 3.5 GeV2 Q2 = 4.5 GeV2

Q2 = 6.5 GeV2 Q2 = 8.5 GeV2 Q2 = 10 GeV2 Q2 = 12 GeV2


Q2 = 35 GeV2 Q2 = 45 GeV2

10-3 10-1

Q2 = 60 GeV2

10-3 10-1

Q2 = 70 GeV2

xQ2 = 90 GeV2

10-3 10-1

Q2 = 120 GeV2

10-3 10-1

x


3s = 318 GeVHERAPDF2.0 (prel.)NLO, Q2 = 3.5 GeV2NLO, Qmin

0

0.5

1

1.5

0

0.5

1

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10 -2 10 -1

0

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10 -2 10 -1


Q2 = 150 GeV2

mr,

NC

(x,Q

2 )

+

Q2 = 200 GeV2 Q2 = 250 GeV2

Q2 = 300 GeV2 Q2 = 400 GeV2 Q2 = 500 GeV2

xQ2 = 650 GeV2 Q2 = 800 GeV2

x



10 -2 10 -1

0

0.5

1

1.5

0

0.5

1

1.5

10 -2 10 -1

0

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10 -2 10 -1


Q2 = 150 GeV2

mr,

NC

(x,Q

2 )

+

Q2 = 200 GeV2 Q2 = 250 GeV2

Q2 = 300 GeV2 Q2 = 400 GeV2 Q2 = 500 GeV2

xQ2 = 650 GeV2 Q2 = 800 GeV2

x



10 -2 10 -1

0

1

2

0

1

0

1

0

0.5

0

0.2

H1 and ZEUS preliminaryQ2 = 150 GeV2

mr,

NC

(x,Q

2 )

+

Q2 = 200 GeV2 Q2 = 250 GeV2 Q2 = 300 GeV2



Q2 = 3000 GeV2 Q2 = 5000 GeV2 Q2 = 8000 GeV2

10-2 10-1

Q2 = 12000 GeV2

10-2 10-1

xQ2 = 20000 GeV2

10-2 10-1

Q2 = 30000 GeV2

10-2 10-1

x



Low Q2

High Q2

√s = 225 GeV √s = 251 GeV √s = 318 GeV


1.14

1.16

1.18

1.2

1.22

1.24

0 5 10 15 20 25 30

Q2 cut / GeV2

χ2 /dof

HERAPDF2.0 (prel.)NLONNLO

χ2/dof = 1386/1130

χ2/dof = 1156/1001

Figure 24: The χ2 per degree of freedom vs the minimum Q2 of data entering the QCD fit forthe NLO and NNLO fits.

30


HERAPDF 2.0 NNLO (2 of many plots!)

14

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 1

2 = 3.5 GeVmin2 HERAPDF2.0 (prel.) NNLO Q

exp. uncert.

model uncert. parametrization uncert.

x

xf 2 = 10 GeV2fµ

vxu

vxd

0.05)×xS (

0.05)×xg (


0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 1

2 = 10 GeVmin2 HERAPDF2.0 (prel.) NNLO Q

exp. uncert.


x

xf 2 = 10 GeV2fµ

vxu

vxd

0.05)×xS (

0.05)×xg (


Figure 30: The parton distribution functions from HERAPDF2.0(prel.) at NNLO,xuv, xdv, xS = 2x(U + D), xg, at Q2 = 10 GeV2, for the Q2min = 3.5 GeV2 fit (top) and theQ2min = 10 GeV2 fit (bottom) The gluon and sea distributions are scaled down by a factor 20.The experimental, model and parametrisation uncertainties are shown separately.

36

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 1


exp. uncert.


x

xf 2 = 10 GeV2fµ

vxu

vxd

0.05)×xS (

0.05)×xg (


0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 1


exp. uncert.


x

xf 2 = 10 GeV2fµ

vxu

vxd

0.05)×xS (

0.05)×xg (


Figure 30: The parton distribution functions from HERAPDF2.0(prel.) at NNLO,xuv, xdv, xS = 2x(U + D), xg, at Q2 = 10 GeV2, for the Q2min = 3.5 GeV2 fit (top) and theQ2min = 10 GeV2 fit (bottom) The gluon and sea distributions are scaled down by a factor 20.The experimental, model and parametrisation uncertainties are shown separately.

36


Q2min = 3.5 GeV2 Q2min = 10 GeV2

HERAPDF 2.0

• Preliminary version released (NLO + NNLO); LO to come

• Still studying:

• Start from 3.5 or 10 GeV2 for default fit

• Gluon parametrisation?

• Number of free parameters?

• Heavy flavour scheme: RTOPT or ACOT

15

F2b and F2c

• ZEUS has finalised inclusive measurement of F2b and F2c

• Uses secondary vertex decay-length significance and jet mass to separate b, c, and light flavour

16

S-20 -15 -10 -5 0 5 10 15 20

En

trie

s

210

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510

S-20 -15 -10 -5 0 5 10 15 20

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trie

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trie

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510

S-20 -15 -10 -5 0 5 10 15 20

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trie

s

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S-20 -15 -10 -5 0 5 10 15 20

En

trie

s

10

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510

S-20 -15 -10 -5 0 5 10 15 20

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trie

s

10

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510

S-20 -15 -10 -5 0 5 10 15 20

En

trie

s

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610

S-20 -15 -10 -5 0 5 10 15 20

En

trie

s

310

410

510

610

ZEUS < 1.4 GeVvtx1 < m < 2 GeVvtx1.4 < m

< 6 GeVvtx2 < m vtxNo restriction on m

-1ZEUS 354 pb

Monte Carlo

LF

CharmBeauty

|S|4 6 8 10 12 14 16 18 20

En

trie

s

210

310

410

|S|4 6 8 10 12 14 16 18 20

En

trie

s

210

310

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|S|4 6 8 10 12 14 16 18 20

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trie

s

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|S|4 6 8 10 12 14 16 18 20

En

trie

s

310

410

510

|S|4 6 8 10 12 14 16 18 20

En

trie

s

310

410

510



-1ZEUS 354 pb

Monte Carlo

LF

Charm

Beauty

S-20 -15 -10 -5 0 5 10 15 20

En

trie

s

210

310

410

510

S-20 -15 -10 -5 0 5 10 15 20

En

trie

s

210

310

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510

S-20 -15 -10 -5 0 5 10 15 20

En

trie

s

210

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510

S-20 -15 -10 -5 0 5 10 15 20

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trie

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En

trie

s

10

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310

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510

S-20 -15 -10 -5 0 5 10 15 20

En

trie

s

10

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310

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510

S-20 -15 -10 -5 0 5 10 15 20

En

trie

s

310

410

510

610

S-20 -15 -10 -5 0 5 10 15 20

En

trie

s

310

410

510

610



-1ZEUS 354 pb

Monte Carlo

LF

CharmBeauty

DESY-14-083, arXiv:1405.XXXX

Reduced cross-sections & F2b / F2c

17

0

0.2

0.4

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0

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0.4

0.6

0

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0

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0.2

0.4

0.6

0

0.2

0.4

0.6

x -410

-310 -210

x -410

-310 -210

x -410

-310 -210

cc r

σ

0

0.2

0.4

0.6

0

0.2

0.4

0.6

0

0.2

0.4

0.6

ZEUS2 = 7 GeV2Q 2 = 12 GeV2Q 2 = 18 GeV2Q

2 = 32 GeV2Q 2 = 60 GeV2Q 2 = 120 GeV2Q

2 = 650 GeV2Q

-1ZEUS vtx 354 pb-1ZEUS D* 363 pb-1 354 pb+ZEUS D

HERA

)2 (GeV2Q

10 2103

10

+ 0

.03 i

bb 2

F0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22 -1ZEUS vtx 354 pb

-1ZEUS e 363 pb

-1 114 pbµZEUS

-1+vtx 126 pbµZEUS

-1H1 vtx 246 pb

HERAPDF 1.5

ABKM NNLO

MSTW08 NLO

MSTW08 NNLO

CTEQ6.6 NLO

JR09

x=0.032 i=0

x=0.013 i=1

x=0.005 i=2

x=0.002 i=3

x=0.0013 i=4

x=0.0005 i=5

x=0.0002 i=6

x=0.00013 i=7

BeautyCharm

Redu

ced

cros

s-se

ctio

n

Stru

ctur

e fu

nctio

n

DESY-14-083, arXiv:1405.XXXX

Beauty-quark mass

• Use σrb and HERA 1 cross-sections to extract mb

• Similar method already used for mc

18

) (GeV)b

(mbm3.5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5

2χ

586

588

590

592

594

596

598

600ZEUS

Inclusive DIS + beauty QCD fit

[GeV]µ10 210

) [G

eV]

µ( bm

2

2.5

3

3.5

4

4.5

5ZEUS

PDG with evolved uncertaintyZEUSDELPHI 3-jetsDELPHI 4-jets NLOALEPHOPALSLD

mb(mb) = 4.07± 0.14 (fit)+0.01�0.07 (mod.)

+0.05�0.00 (param.)

+0.08�0.05 (theo.)GeV

DESY-14-083, arXiv:1405.083

Summary

• ZEUS and H1 NC cross-sections combined

• Much improved precision!

• Updated measurements of FL and cross-sections at high x

• HERAPDF 2.0 (prelim.) recently released

• NLO and NNLO PDFs available; publication in preparation

• ZEUS inclusive F2b and F2

c measurements finalised

• Most precise F2b over wide kinematic range

• Use σrb data to extract mb(mb) at hadron collider for 1st time

19

Backup

DIS events and kinematics

• Characterise events:

• Q2

• Bjorken x, (0 < x < 1)

• Inelasticity y, (0 < y < 1)

21

Q2 = s x y

Very high Q2 event

Kinematic regions

22

Before LHC With LHC

Use DGLAP equations to evolve from HERA to LHC

Typical NC event selection

• Electron or high ET trigger

• Scattered electron with E > 10 GeV

• Cut on Σ(E - pZ) ≈ 2Ee (calorimeter) for DIS events

• Cut on event vertex (tracker)

23

High-x cross-sections

• Extend analysis to x ≈ 1 by using electron ET or modified Jacquet-Blondel method to measure x

24DESY-13-245, arXiv:1312.4438

ZEUS

DA

TA/T

HEO

RY

1

1.2=7252Q =8752Q =10252Q

1

1.2 =12002Q =14002Q =16502Q

1

1.5=19502Q =22502Q =26002Q

1

2 =30002Q =35002Q

0 0.2 0.4 0.6 0.8 1

=41502Q

1

2=52502Q =70002Q 2 in GeV2Q

-1p, 185 pb-ZEUS e

(Integrated)-1p, 185 pb-ZEUS e

HERAPDF 1.5

0 0.2 0.4 0.6 0.8 1

2

4 =95002Q

0 0.2 0.4 0.6 0.8 1

=15500 2QABM11/HERAPDF 1.5

CT10/HERAPDF 1.5

MSTW 2008/HERAPDF 1.5

NNPDF 2.3/HERAPDF 1.5

x

ZEUS

DA

TA/T

HEO

RY

1

1.2=7252Q =8752Q =10252Q

0.8

1

1.2 =12002Q =14002Q =16502Q

0.5

1

=19502Q =22502Q =26002Q

1

2 =30002Q =35002Q

0 0.2 0.4 0.6 0.8 1

=41502Q

1

2=52502Q =70002Q

68% CI?, 2 in GeV2Q

-1p, 142 pb+ZEUS e

(Integrated)-1p, 142 pb+ZEUS e

HERAPDF 1.5

0 0.2 0.4 0.6 0.8 1

1

2

3=95002Q

0 0.2 0.4 0.6 0.8 1

=15500 2QABM11/HERAPDF 1.5

CT10/HERAPDF 1.5

MSTW 2008/HERAPDF 1.5

NNPDF 2.3/HERAPDF 1.5

x

GMVFNS schemes: RTOPT and ACOT etc.

25

HERAPDF PDF parametrisations

26

Comparison of PDFs

27

HERAPDF 2.0

28

0.2

0.4

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1

-410 -310 -210 -110 1

2 = 3.5 GeVmin2 HERAPDF2.0 (prel.) NLO Q

exp. uncert. model uncert. parametrisation uncert.

x

xf 2 = 10 GeV2fµ

vxu

vxd

0.05)×xS (

0.05)×xg (


0.2

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1

-410 -310 -210 -110 1



x

xf 2 = 10 GeV2fµ

vxu

vxd

0.05)×xS (

0.05)×xg (


NLO NNLOQ2min = 3.5 GeV2

HERAPDF 2.0

29

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 1

2 = 10 GeVmin2 HERAPDF2.0 (prel.) NLO Q


x

xf 2 = 10 GeV2fµ

vxu

vxd

0.05)×xS (

0.05)×xg (


0.2

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0.6

0.8

1

-410 -310 -210 -110 1



x

xf 2 = 10 GeV2fµ

vxu

vxd

0.05)×xS (

0.05)×xg (


NLO NNLOQ2min = 10 GeV2

HERAPDF 2.0 (linear x scale)

30

0.2

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1

0 0.2 0.4 0.6 0.8 1



x

xf 2 = 10 GeV2fµ

vxu

vxd

xS

xg


0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1



x

xf 2 = 10 GeV2fµ

vxu

vxd

xS

xg


Vary Q2minNLO NNLO

HERAPDF 2.0 (log x scale)

31

0.2

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x

xf 2 = 10 GeV2fµ

vxu

vxd 0.05)×xS (

0.05)×xg (


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1

-410 -310 -210 -110 1



x

xf 2 = 10 GeV2fµ

vxu

vxd 0.05)×xS (

0.05)×xg (

H1 and ZEUS preliminaryNLO NNLO

Vary Q2min

HERAPDF 1.0 & 1.5 vs. 2.0 (linear x scale)

32

0.2

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0 0.2 0.4 0.6 0.8 1


HERAPDF1.0 NLO

x

xf 2 = 10 GeV2fµ

vxu

vxd

xS

xg


0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1


HERAPDF1.5 NNLO

x

xf 2 = 10 GeV2fµ

vxu

vxd

xS

xg


Q2min = 3.5 GeV2

HERAPDF 1.0 & 1.5 vs. 2.0 (log x scale)

33

0.2

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HERAPDF1.0 NLO

x

xf 2 = 10 GeV2fµ

vxu

vxd 0.05)×xS (

0.05)×xg (


0.2

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1

-410 -310 -210 -110 1


HERAPDF1.5 NNLO

x

xf 2 = 10 GeV2fµ

vxu

vxd 0.05)×xS (

0.05)×xg (


Q2min = 3.5 GeV2

Measurements of the proton structure at HERA

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Transcript of Measurements of the proton structure at HERA