hera measurements for the lhc

HERA measurements for the LHC

Katerina Lipka, DESY

for the H1 and ZEUS Collaborations

Standard Model at the LHC 2013

World-only ep collider

protons

electrons

Deep Inelastic Scattering at HERA

Central Tracker

• HERA I : 1992-2000

• HERA II: 2003-2007

• collider experiments

H1 & ZEUS,√smax= 318 GeV

• integrated Luminosity

~0.5 fb-1/ experiment

Ep=460-920 GeV Ee=27.6 GeV

HERA switched off June 2007, analyses ongoing on the way to final precisionH1 and ZEUS combine experimental data accounting for systematic correlations HERA performs the QCD analysis of (semi) inclusive DIS data (HERAPDF)H1 and ZEUS collaborations provide/support the PDF Fitting Tool (HERAFitter)

2

HERA Kinematics

E1

E2

s = τs = x1x2s

x1,2 =M√

s× exp(±y)

Q = M

Q2 =-q2 boson virtuality x=-q2/2p·q Bjorken scaling variable s=(k+p)2 center of mass energy

y transferred energy fraction Y± = 1±(1-y)2

Kinematics reconstructed from the scattered lepton (or hadronic final state)

Reconstruction of x1 and x2 not straightforward

fi(x)

DIS at HERA: clean lepton probe

Proton-proton collision at LHC

3

HERA Kinematics

fi(x)

DIS at HERA: clean lepton probe HERA covers low, medium x range of the LHCQ2 evolution via QCD

4

HERA

TEVATRON

LHC

DGLAP

HERA data: backbone for PDF determination

E1

E2

s = τs = x1x2s

x1,2 =M√

s× exp(±y)

Q = M

Proton-proton collision at LHC

4

Structure functions in DIS and proton PDFs

DIS cross sections provide an access to parton distribution functions in proton

LO : F2 ∝�

i

(qi(x) + qi(x))

LO : F3 ∝�

i

(qi(x)− qi(x))

NLO : FL ∝ x · αS · g(x,Q2)

d2σe±P

dxdQ2=

2πα2

xQ4[Y+F2 ∓ Y−xF3 − y2FL]

dominant contribution

γ/Z interference

contribution from gluon

γ, Z Exchange: Neutral Current ep → e X

σe+pCC ∝ x{(u + c) + (1− y)2(d + s)}

σe−pCC ∝ x{(u + c) + (1− y)2(d + s)}

W± Exchange: Charged Current ep → ν X

sensitive to individual quark flavours

5

HERA Inclusive DIS Measurements at highest Q2]2

[pb/

GeV

2/d

Qd

-710

-510

-310

-110

10

]2 [GeV2Q310 410

p CCH1 ep CC+H1 e

p CC HERA IIZEUS ep CC HERA II+ZEUS e

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

p NCH1 ep NC+H1 e

p NC HERA IIZEUS ep NC HERA II+ZEUS e

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

y < 0.9 = 0eP

HERA

[%] eP-100 -50 0 50 100

[pb]

CC

0

20

40

60

80

100

120p Scattering±HERA Charged Current e

2 > 400 GeV2Q y < 0.9

X p +e

X p e

HERAPDF 1.5

HERAPDF 1.5

H1 ZEUS

H1 ZEUS

NC and CC cross sections at large scales:SM: zero cross section for a RH e- or LH e+

Final HERA legacy textbook measurements in electroweak physics

Electroweak unification Good agreement with the SM

Inclusive HERA I and II dataprecision NC: ~1.5%, CC: ~4%

Charged Current

Neutral Current

arXiv:1208.6138JHEP 1209:061 (2012)EPJC 62 (2009) 625EPJC 70 (2010) 945EPJC 61 (2009) 223

6

http://arxiv.org/abs/1208.6138

http://arxiv.org/abs/1208.6138

Recent results on DIS NC Cross Sections

precision 1.5% for Q2 < 500 GeV2

arXiv:1208:6138

JHEP 1209:061 (2012)

sensitivity to valence compositiongluon distribution via scaling violations

xF γZ3 ∝ x · qval

F γZ2 ∝ q · q

JHEP 1209:061 (2012)

Q2=1500 GeV2

7

Recent results on DIS CC Cross Sections

JHEP 1209:061 (2012)

HERA II: improvement in precision: e+ (e-) p by a factor of 3 (10) luminosity wrt. HERA I

improved sensitivity to quark flavour composition 8

Combined HERA DIS Cross Sections

H1 and ZEUS

HER

A In

clus

ive

Wor

king

Gro

upA

ugus

t 201

0

x = 0.02 (x300.0)

x = 0.032 (x170.0)

x = 0.05 (x90.0)

x = 0.08 (x50.0)

x = 0.13 (x20.0)

x = 0.18 (x8.0)

x = 0.25 (x2.4)

x = 0.40 (x0.7)

x = 0.65

Q2/ GeV2

r,N

C(x

,Q2 )

HERA I+II NC e+p (prel.)HERA I+II NC e-p (prel.)

HERAPDF1.5 e+pHERAPDF1.5 e-p

±

10-2

10-1

1

10

10 2

10 3

10 2 10 3 10 4 10 5

0

0.5

1

1.5

2

0

0.5

1

0

0.2

0.4

0.6

0.8

H1 and ZEUS

r,C

C(x

,Q2 )

Q2 = 300 GeV2

-

Q2 = 500 GeV2 Q2 = 1000 GeV2 Q2 = 1500 GeV2

Q2 = 2000 GeV2 Q2 = 3000 GeV2

10-2 10-1

Q2 = 5000 GeV2

10-2 10-1

Q2 = 8000 GeV2

x

HER

A In

clus

ive

Wor

king

Gro

upA

ugus

t 201

0

10-2 10-1

Q2 = 15000 GeV2

10-2 10-1

Q2 = 30000 GeV2

x

HERA I+II CC e-p (prel.)HERAPDF1.5

Neutral Current Charged Current

Preliminary H1 and ZEUS measurements are combined accounting for correlationsImpressive precision up to high Q2 and high xQCD analysis of combined HERA NC and CC data: HERAPDF 9

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 1

0.2

0.4

0.6

0.8

1

HERAPDF1.5 (prel.)

exp. uncert.

model uncert. parametrization uncert.

x

xf 2 = 10 GeV2Q

vxu

vxd

0.05)×xS (

0.05)×xg (

HER

A S

truc

ture

Fun

ctio

ns W

orki

ng G

roup

July

201

0

H1 and ZEUS HERA I+II Combined PDF Fit

0.2

0.4

0.6

0.8

1

Model assumptions:

Qmin2=3.5 GeV2 , αs(MZ)=0.1176

mc=1.4 GeV; mb=4.75 GeV; fs(Q02)=0.31

HERA parton density functions

DGLAP evolution (QCDNUM, arXiv:1005.1481)

Heavy quarks: massive

Variable Flavour Number Scheme

Scales: µr = µf = Q2 , starting scale 1.9 GeV2

Experimentally uncertainty (Δχ2 =1)

Parameterization at starting scale:

HERAI +HERAII (prel.)

HERAPDF1.5: most precise DIS data, recommended HERA PDF set

10

HERA parton density functionsHERAPDF1.5 NLO and NNLO most precise DIS data, proper treatment of correlation of errors, allows for model studies

0

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

HERAPDF1.5 NNLO (prel.)

exp. uncert.


x

xf 2 = 10000 GeV2Q

vxu

vxd

0.05)×xS (

0.05)×xg (

HER

APD

F St

ruct

ure

Func

tion

Wor

king

Gro

upM

arch

201

1

H1 and ZEUS HERA I+II PDF Fit

0

0.2

0.4

0.6

0.8

1

NNLO

Describes LHC data very well, used in ATLAS, CMS and LHCb analyses

Available in LHAPDF with eigenvectors for uncertainties and αs variation

Final combination of HERA inclusive data and QCD analysis on the way (HERAPDF2.0)11

Precision QCD: Jets at HERA

i 1

0×

NC

/Je

t -210

1

210

410

610

810

1010

T,JetP710 20 50

DijetTP710 20 50

[GeV]TrijetTP 710 20 50

2 < 200 GeV2 150 < Q (i = 10)

2 < 270 GeV2 200 < Q (i = 8)

2 < 400 GeV2 270 < Q (i = 6)

2 < 700 GeV2 400 < Q (i = 4)

2 < 5000 GeV2 700 < Q (i = 2)

2 < 15000 GeV2 5000 < Q (i = 0)

had cNLO

= 0.118sCT10, QCDNUMNLOJet++ and fastNLO

Inclusive Jet Normalised

DijetNormalised

TrijetNormalised H1

Preliminary

(Multi)-jet production directly sensitive to the strong coupling constant

< 1% experimental error

Nuclear Physics B 864 (2012) 1

αS(MZ)=0.1206 (exp) (theory)+ 0.0023- 0.0022

+ 0.0042- 0.0035 αS(MZ)=0.1163 (exp) (theory)+ 0.0011

- 0.0011+ 0.0042- 0.0042

Measure αs running in a single experimentdifferent measurement methods agree

PhotoproductionQ2~0

DIS, 150 GeV2 < Q2 < 15000 GeV2

12

Additional Constraints on PDFs: Charm at HERA

c, b

g(x)

γe

p

c, b

stringent test of QCD, direct probe of the gluon

use different tagging methods:- meson reconstruction,- large mass and long lifetime

combination: - orthogonal uncertainties- take into account correlations

0

0.2

0

0.5

0

0.5

0

0.5

red

cc_

H1 VTX

H1 D* HERA-II

H1 D* HERA-I

ZEUS c µ X

ZEUS D* 98-00

ZEUS D* 96-97

ZEUS D0

ZEUS D+ H1 and ZEUSQ2=2.5 GeV2 Q2=5 GeV2 Q2=7 GeV2

Q2=12 GeV2 Q2=18 GeV2 Q2=32 GeV2

Q2=60 GeV2 Q2=120 GeV2 Q2=200 GeV2

Q2=350 GeV2

10-4 10-3 10-2

Q2=650 GeV2

10-4 10-3 10-2

Q2=2000 GeV2

HERA

10-4 10-3 10-2

x

Eur. Phys. J. C 73:2311 (2013), [arXiv:1211.1182]

13


c, b

g(x)

γe

p

c, b

stringent test of QCD, direct probe of the gluon

use different tagging methods:- meson reconstruction,- large mass and long lifetime

combination: - orthogonal uncertainties- take into account correlations

0

0.2

0

0.5

0

0.5

0

0.5

red

cc_

H1 VTX

H1 D* HERA-II

H1 D* HERA-I

ZEUS c µ X

ZEUS D* 98-00

ZEUS D* 96-97

ZEUS D0

ZEUS D+ H1 and ZEUSQ2=2.5 GeV2 Q2=5 GeV2 Q2=7 GeV2

Q2=12 GeV2 Q2=18 GeV2 Q2=32 GeV2

Q2=60 GeV2 Q2=120 GeV2 Q2=200 GeV2

Q2=350 GeV2

10-4 10-3 10-2

Q2=650 GeV2

10-4 10-3 10-2

Q2=2000 GeV2

HERA

10-4 10-3 10-2

x

Eur. Phys. J. C 73:2311 (2013), [arXiv:1211.1182]

Q2=18 GeV2

HERA

H1 and ZEUS

H1 VTX

H1 D* HERA-II

H1 D* HERA-I

ZEUS c µ X

ZEUS D* 98-00

ZEUS D* 96-97

ZEUS D0

ZEUS D+

x

red

cc_

10-3 10-20

0.2

0.4

0.6

Precision ~ 5% at medium Q2 reached 14


Inclusion of charm: reduced uncertainty on gluon, charm and light sea...mostly due to better constrained charm-quark mass

Eur

. Phy

s. J

. C 7

3:23

11 (2

013)

, [ar

Xiv

:121

1.11

82]

15


Consistent with the world averagemc(mc)wa = 1.275 ±0.025 GeV

perform PDF fit varying mc in

FFNS coefficients

Determination of mc(mc) MS at NLO Study mc -choice in variable flavor number schemes

Different schemes prefer different Mc

Eur

. Phy

s. J

. C 7

3:23

11 (2

013)

, [ar

Xiv

:121

1.11

82]

16

Additional Constraints on PDFs: Charm at HERAStudy mc -choice in

variable flavor number schemes

Different schemes prefer different Mc

Prediction for W+ (W-, Z ) production at the LHC

Uncertainty due to differences in charm treatmentin PDFs significantly reduced by using optimal Mc

Eur

. Phy

s. J

. C 7

3:23

11 (2

013)

, [ar

Xiv

:121

1.11

82]

17

HERAFitter: Open-Source Modular Tool for QCD AnalysisDeveloped at HERA, extended to LHC and theory groupsStudy the impact of different data on PDFs and test different theory approaches

experimental input

processes: NC, CC DIS, jets, diffraction, heavy quarks (c,b,t)Drell-Yan, W production

theoretical calculations/toolsHeavy quark schemes: MSTW, CTEQ, ABMJets, W, Z production: fastNLO, ApplgridTop production NNLO (Hathor)QCD Evolution DGLAP (QCDNUM) kT factorisationAlternative tools NNPDF reweightingOther models Dipole model + Different error treatment models + Tools for data combination (HERAaverager)

H1 and ZEUS

Q2 / GeV2

r,N

C(x

,Q2 )

x=0.0002x=0.002

x=0.008

x=0.032

x=0.08

x=0.25

HERA I NC e+pZEUSH1

+

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1 10 10 2 10 3 10 4

[GeV]T

p210 310

/d|y

|T

(CTE

Q 6

.6)/d

p0

2/d

|y|/d

T/d

p2 d 0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2(CL90)PDF jets. R =0.4 (0.0<|y|<0.3) tanti-k

DataCTEQ 6.6HERAPDF 1.0

HERAPDF 1.5

GJR 2008

ATLAS Preliminary

[GeV]jetT

p100 200 300 400 500 600 700

[pb/

GeV

]je

tT

dpje

t/d

y2 d

-1510

-1310

-1110

-910

-710

-510

-310

-11010

310

510

710

910

1110D0 RunII

NLOjet++ (HERAPDF1.5)

)6| < 0.4 (x 10jet|y

)3| < 0.8 (x 10jet0.4 < |y

| < 1.2 jet0.8 < |y

)-3| < 1.6 (x 10jet1.2 < |y

)-6| < 2.0 (x 10jet1.6 < |y

)-9| < 2.4 (x 10jet2.0 < |y

+ nonperturbative corr.

Tevatron inclusive jet cross sections

experiments: HERA, Tevatron, LHC, fixed target

0

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

HERAPDF1.5 NNLO (prel.)

exp. uncert.


x

xf 2 = 10 GeV2Q

vxu

vxd

0.05)×xS (

0.05)×xg (

HER

APD

F St

ruct

ure

Func

tion

Wor

king

Gro

upM

arch

201

1


0

0.2

0.4

0.6

0.8

1

PDF or DPDF,...

αS (MZ),mc,mb,mt, fs,..

Theory predictions

Benchmarking

Comparison of schemes

HER

AFi

tter

18

Open source code, available at https://www.herafitter.org/HERAFitterVersion 0.3.0 released in March 2013.

HERAFitter: Open-Source Modular Tool for QCD Analysis

Joined effort of experimentalists, theorists and tool-developers Successfully used by the LHC experiments

19

Summary

HERA data are unique and of particular importance for PDF determination

• HERA II inclusive DIS cross section measurements are published

• H1+ZEUS combination and analysis towards HERAPDF2.0 ongoing

• HERA jet and charm data provide additional constrains on αS and charm-quark mass

HERA Expertise in QCD analysis preserved in HERAFitter development

• developed and supported by several experiments and theory groups

• allows experimentalists to perform QCD analysis and test theory approaches

• open source program, project open for further support

20

Back up

Determination of parton density functions

x-dependence of PDFs is not calculable in perturbative QCD:

parameterize at a starting scale Q20 : f(x)=AxB(1-x)C(1+Dx+Ex2)

evolve these PDFs using DGLAP equations to Q2>Q20

construct structure functions from PDFs and coefficient functions:

predictions for every data point in (x, Q2) – plane

χ2- fit to the experimental data

Structure function factorization: for the exchange of Boson V (γ, Z, W±)

calculable in pQCDfrom measured cross sections

PDF

FV2 (x,Q2) =

�

i=q,q,g

� 1

xdz × CV,i

2 (x

z, Q2, µF , µR, αS)× fi(z, µF , µR)

µi measured value at point i

δi statistical, uncorrelated systematic error

γjj – correlated systematic error

bj – shift of correlated systematic error sources

mi _ true value (corresponds to min χ2)

Measurements performed sometimes in slightly different range of (x,Q2)

swimming to the common (x,Q2) grid via NLO QCD in massive scheme

Combination ProcedureMinimized value:

HERAPDF: Fit Improvements

0

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

HERAPDF1.5 (prel.)

exp. uncert.


x

xf 2 = 10 GeV2Q

vxu

vxd

0.05)×xS (

0.05)×xg (

HER

APD

F St

ruct

ure

Func

tion

Wor

king

Gro

upM

arch

201

1

H1 and ZEUS HERA I+II 10 parameter PDF Fit

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

HERAPDF1.5f (prel.) exp. uncert. model uncert. parametrization uncert.

HERAPDF1.5 (prel.)

xxf 2 = 10 GeV2Q

vxu

vxd

0.05)×xS (

0.05)×xg (

HER

APD

F St

ruct

ure

Func

tion

Wor

king

Gro

upM

arch

201

1

H1 and ZEUS HERA I+II 14 parameter PDF Fit

0

0.2

0.4

0.6

0.8

1

HERAPDF1.5f : 14-parameter fit gluon more flexible at low-x

Small difference in total uncertainty → swap between parametrisation and experimental uncertainties

1.5 1.5 flexible

HERAPDF1.5f:

Two parametrisations are studied: a 10-parameter fit which corresponds to the preliminaryPDF fit of the NC and CC combined HERA I and HERA II data, HERAPDF1.5 [3], and a 14-parameter fit, HERAPDF1.5f, which allows more flexibility, in particular for the low-x gluondistribution. At the starting scale Q2

0 = 1.9 GeV2 the PDFs are parametrized as follows:

xg(x) = AgxBg · (1− x)Cg − A′

gxB′

g(1− x)C′

g (1)xuv(x) = Auvx

Buv · (1− x)Cuv · (1 +Duvx+ Euvx2) (2)

xdv(x) = AdvxBdv · (1− x)Cdv (3)

xU(x) = AUxBU · (1− x)CU (4)

xD(x) = ADxBD · (1− x)CD (5)

The parameters Ag, Auv , Adv are constrained by the sum rules. It is assumed that BU = BD,C ′

g = 25, AU = AD(1− fs), where fs is the strangeness fraction.

In the 10-parameter fit additional four constraints are enforced: A′

g = B′

g = 0, Bdv = Buv

and Duv = 0. In both, the 10- and 14-parameter fits these choices define the central fit, whilefurther parameters are considered when evaluating the parametrization uncertainty, as describedin section 2.3.

Greater flexibility in the gluon density helps to avoid a parametrisation bias, when addingmore data that is sensitive to the gluon density, like charm or jet production. Therefore, the14-parameter fit is preferred and used for HERAPDF1.6.

1.3 Theoretical predictions

The NLO cross sections of jet production were calculated using the NLOJET++ program [13].The FastNLO [14] interface was used to efficiently convolute the matrix elements from NLO-JET++ with the fitted PDFs.

In the prediction for the normalized jet cross sections [4] QCDNUM has been used to calcu-late the corresponding inclusive cross sections. For the factorisation and renormalisation scalesthe same variables as in relevant publications are used, the combination of Q2 and transversejet energy measured in the Breit frame ET (µf = µr =

√

(Q2 + E2T )/2) for the H1 measure-

ments and transverse jet energy measured in the Breit frame (µf = µr =√

E2T ) for the ZEUS

measurements.

2 Determination of uncertainties

The total uncertainty of the parton density functions and the αsaccounts for the experimenaluncertainties of the measurements and the variations of model and parametrisation assumptions,as described in the following.

2




gxB′

g(1− x)C′

g (1)xuv(x) = Auvx



xU(x) = AUxBU · (1− x)CU (4)

xD(x) = ADxBD · (1− x)CD (5)




g = B′

g = 0, Bdv = Buv






√



E2T ) for the ZEUS

measurements.



2




gxB′

g(1− x)C′

g (1)xuv(x) = Auvx



xU(x) = AUxBU · (1− x)CU (4)

xD(x) = ADxBD · (1− x)CD (5)




g = B′

g = 0, Bdv = Buv






√



E2T ) for the ZEUS

measurements.



2




gxB′

g(1− x)C′

g (1)xuv(x) = Auvx



xU(x) = AUxBU · (1− x)CU (4)

xD(x) = ADxBD · (1− x)CD (5)




g = B′

g = 0, Bdv = Buv






√



E2T ) for the ZEUS

measurements.



2

HERAPDF1.5 (10 parameter fit)




gxB′

g(1− x)C′

g (1)xuv(x) = Auvx



xU(x) = AUxBU · (1− x)CU (4)

xD(x) = ADxBD · (1− x)CD (5)




g = B′

g = 0, Bdv = Buv






√



E2T ) for the ZEUS

measurements.



2




gxB′

g(1− x)C′

g (1)xuv(x) = Auvx



xU(x) = AUxBU · (1− x)CU (4)

xD(x) = ADxBD · (1− x)CD (5)




g = B′

g = 0, Bdv = Buv






√



E2T ) for the ZEUS

measurements.



2

HERAPDF1.7: DIS+ low energy+jets+charm

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 1

0.2

0.4

0.6

0.8

1

HERAPDF1.7 (prel.) exp. uncert. model uncert. parametrization uncert.

HERAPDF1.6 (prel.)

x

xf 2 = 10 GeV2Q

vxu

vxd

0.05)×xS (

0.05)×xg (

HER

APD

F St

ruct

ure

Func

tion

Wor

king

Gro

upJu

ne 2

011

HERA I+II inclusive, jets, charm PDF Fit

0.2

0.4

0.6

0.8

1Flexible parametrization

heavy flavours:

mc=1.5±0.15 GeV

αS (MZ)=0.119

steeper gluon as HERAPDF1.6

Including the jet and the charm data: decouple the gluon from αS and mc

FV2 (x,Q2) =

�

i=q,q,g

� 1

xdz × CV,i

2 (x

z, Q2, µF , µR, αS)× fi(z, µF , µR)

Heavy Quarks and PDF Fits

Factorization:

i - number of active flavours in the proton: defines the factorization (HQ) scheme

• i fixed : Fixed Flavour Number Scheme (FFNS)

only light flavours in the proton: i = 3 (4)

c- (b-) quarks massive, produced in boson-gluon fusion

Q2 » mHQ2 : can be less precise, NLO coefficients contain terms ~

• i variable: Variable Flavour Number Scheme (VFNS)

- Zero Mass VFNS: all flavours massless. Breaks down at Q2 ~mHQ2

- Generalized Mass VFNS: different implementations provided by PDF groups smooth matching with FFNS for Q2 →mHQ

2 must be assured

ln� Q

mHQ

�

QCD analysis of the proton structure: treatment of heavy quarks essential

HQ contributions to the proton structure function F2 : (e.g. charm)

Direct test of HQ schemes in PDF fits

Heavy Quark Production at HERAHeavy quarks in ep scattering produced in boson-gluon fusion

Contribution to total DIS cross section:

charm: ~ 30% at large Q2

beauty: at most few %

Gluon directly involved: cross-check of g(x) from NC and CC DIS cross sections

c (b)

c (b)

g(x)

γe

p

/ GeVmodelcm

1.2 1.3 1.4 1.5 1.6 1.7 1.8

2

600

700

800

900

1000

flexible param standard param

/ndf

2

1

1.2

1.4

1.6

H1 and ZEUS (prel.)

(prel.)cc2HERAPDF1.0 + F

RT standard

0.018 GeV±(opt)=1.572 modelcm

/ GeVmodelcm

1.2 1.3 1.4 1.5 1.6 1.7 1.8

2

520

540

560

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600

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660

680

flexible param standard param

/ndf

2

0.9

0.95

1

1.05

1.1

1.15

H1 and ZEUS (prel.)

HERAPDF1.0 RT standard

0.100 GeV±(opt)=1.308 modelcm

Charm Mass as a Model Parameter in PDF

F2+charmF2

Strong dependence on mc Weak dependence on mc

Study the sensitivity of the PDF fit to the value of mc

PDF fit to inclusive DIS PDF fit to inclusive DIS + charm data

Prediction using mc=1.4 GeV

Error band: PDF uncertainty

Experimental error

Parametrization variation

Model assumptions

including mc variation

Heavy Quarks in PDFs and W/Z at LHC

√s=14 TeV

rapidity

NLO ⊗ HERAPDF1.0

Prediction of W± cross section @ LHC: dominant uncertainty due to PDF

mc variation in PDF: significant uncertainty on W@LHC in central region

/ GeV modelcm

1.2 1.4 1.6 1.8

/ nb

+W

52

54

56

58

60

62

64

RT standard

) = 7 TeVs (+W(prel.)cc

2HERAPDF1.0 + F

HER

A In

clus

ive

Wor

king

Gro

up

Aug

ust 2

010

Vary the charm mass in the PDF. Use resulting PDFs for LHC predictions

Larger mc → more gluons, less charm → more light quarks → larger σW

Charm at HERA and W/Z at LHC

/ GeV modelcm

1.2 1.4 1.6 1.8

/ nb

+W

52

54

56

58

60

62

64

RT standard


2HERAPDF1.0 + F

HER

A In

clus

ive

Wor

king

Gro

up

Aug

ust 2

010


Only one HQ scheme mc variation in PDF

1.4 < mc < 1.65 GeV

3% uncertainty on W prediction


/ GeV modelcm

1.2 1.4 1.6 1.8

/ nb

+W

52

54

56

58

60

62

64

RT standard RT optimised ACOT-full S-ACOT- ZMVFNS


2HERAPDF1.0 + F

HER

A In

clus

ive

Wor

king

Gro

up

Aug

ust 2

010


Several HQ schemes mc variation in PDF

1.4 < mc < 1.65 GeV

3% uncertainty on W prediction

Using different HQ schemes:

+ 7% uncertainty

Large uncertainty on σW prediction due to HQ treatment in PDFs


(HERA)PDF and top quark at the LHC Top quark at CMS: cross section @ approx. NNLO

mtpole (GeV)

t t_

(pb)

approx. NNLO (Langenfeld et al.) × HERAPDF15NNLO

only PDF uncertainties (68% CL):experimentalparametrizationmodel variations: Q2 > 5 GeV2

CMS (Prel.) CMS-PAS-TOP-11-005 (2011)

0

200

400

600

140 150 160 170 180 190

Dominant uncertainty: variation of Q2min imposed on data used in the fit

top quark production at the LHC has potential to constrain the high-x gluon

Q2=4mt2

thanks A. Cooper-Sarkar

HERAPDF1.5NNLO

PDF fits using HERA jet data: fixed αS

0

0.2

0.4

0.6

0.8

12 =10 GeV2Q

vxu

0

0.2

0.4

0.6

0.8

1

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00.20.4

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-0.4-0.2

00.20.4

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

12 =10 GeV2Q

vxd

HERAPDF1.6 (prel.) Exp. uncert. Model uncert. Param uncert. HERAPDF1.5f (prel.)

0

0.2

0.4

0.6

0.8

1

-0.4-0.2

00.20.4

-410 -310 -210 -110 1x-0.4-0.2

00.20.4

-0.4-0.2

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0.4

0.6

0.8

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10121416

H1 and ZEUS HERA I+II PDF Fit with Jets

HER

APD

F St

ruct

ure

Func

tion

Wor

king

Gro

upM

arch

201

1

Inclusion of jet data into the PDF fit using fixed αS does not have large impact

Inclusive DIS data: combined HERAI+HERAII

Jet data:H1 high Q2 , EPJ C65 (2010) low Q2, EPJ C67 (2010)

ZEUS incl. jets PLB547 (2002) incl.+2jets NP B765 (2007)

PDF Fit: - flexible parametrisation- αs(MZ) fixed

13

PDF fits with free αS (MZ)

0

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

HERAPDF1.5f (prel.) )

Z(Ms free

exp. uncert. model uncert. parametrization uncert.

x

xf 2 = 10 GeV2Q

vxu

vxd

0.05)×xS (

0.05)×xg (

HER

APD

F St

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Func

tion

Wor

king

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arch

201

1


0

0.2

0.4

0.6

0.8

1

no jet data

14

0

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

HERAPDF1.5f (prel.) )

Z(Ms free


x

xf 2 = 10 GeV2Q

vxu

vxd

0.05)×xS (

0.05)×xg (

HER

APD

F St

ruct

ure

Func

tion

Wor

king

Gro

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arch

201

1


0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

HERAPDF1.6 (prel.) )

Z(Ms free


x

xf 2 = 10 GeV2Q

vxu

vxd

0.05)×xS (

0.05)×xg (

vxu

vxd

0.05)×xS (

0.05)×xg (

HER

APD

F St

ruct

ure

Func

tion

Wor

king

Gro

upM

arch

201

1

H1 and ZEUS HERA I+II PDF Fit with Jets

0

0.2

0.4

0.6

0.8

1

no jet data + jet data

PDF fits with free αS (MZ)

Inclusion of jet data into the PDF fit decouples the gluon and αS (MZ)

14

αS (MZ) from PDF fits including HERA jet data

)Z

(MS

0.114 0.116 0.118 0.12 0.122 0.124 0.126

m

in2

- 2

0

5

10

15

20H1 and ZEUS (prel.)

HERAPDF1.5fHERAPDF1.6

HER

APD

F St

ruct

ure

Func

tion

Wor

king

Gro

up

Mar

ch 2

011

)Z

(Ms

0.11 0.12 0.13)

Z(Ms

0.11 0.12 0.13

exp. uncert.th. uncert.

World averageS. Bethke, Eur. Phys. J. C64, 689 (2009)

jets 98-00TZEUS incl. kPhys. Lett. B 649, 12 (2007)

jets 96-97TZEUS incl. kPhys. Lett. B 547, 164 (2002)

multijetsT k2H1 low QEur. Phys. J. C67, 1 (2010)

multijetsT norm. k2H1 high QEur. Phys. J. C65, 363 (2010)

HERAPDF1.6Preliminary

H

ERA

PDF

Stru

ctur

e Fu

nctio

n W

orki

ng G

roup

Mar

ch 2

011

H1 and ZEUS (prel.)Scan of the αS (MZ) in the PDF fit

+ jet data

no jet data

PDF and αS (MZ) determined in the common fit:αS (MZ)= 0.1202 ± 0.0013exp ± 0.0007model/param ± 0.0012had+0.0045scale

From including the Jet data in the PDF fit: determine gluon and αS (MZ) 15

hera measurements for the lhc

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