Alexander A. Savin

Hadron Structure and QCD 2004, 18-22 May 2004, St.Petersburg, Russia

2/27A.Savin – Jets at HERA -

Kinematic variablesKinematic variables

222 kkqQ 22 )( pqW

2)( kps

kp

qpy

Bjorken scaling variable

inelasticity

Photon virtuality

*P center-of-mass energy squared

ep enter-of-mass energy squared

Pq

Qx2

2

e+(-)

p(820)

3/27A.Savin – Jets at HERA -

)( 01S

)( 11S

1S

1S

Boson-gluon fusionQCD Compton

1 jet

2 jets

Jets at HERAJets at HERA

4/27A.Savin – Jets at HERA -

Three jetsThree jets

5/27A.Savin – Jets at HERA -

Detecto

r Sim

ulatio

n

Parton Level

Hadron Level

LO:ARIADNELEPTOPYTHIARAPGAP

NLO:DISENTDISASTER++MEPJETNLOJETS

GEANTCDM+LUND etc

Uncertainties: pdf FR , hadronisation detector

Events simulationEvents simulation

6/27A.Savin – Jets at HERA -

i

j

Jet FindingJet Finding Breit FrameBreit Frame

La

b F

ram

eB

reit

Fra

me

Bre

it F

ram

e

DIS Event

PT

PL

2,iTi Ed

2

222,

2,

))()((},min{

REEd jTiTij

Inclusive mode,combine if: jiij ddd

Exclusive mode:

combine until cutij yy

Longitudinally invariantkT cluster algorithm

02 qxP

)cos1}(,min{2 222 ijjiij EE

Qy

7/27A.Savin – Jets at HERA -

DGLAP:

BFKL:

Bjxxx ...21

Bjxxx ...21

222,

21, ... Qkk TT

no ordering in kT

Unordered parton evolution, e.g. CCFM (Cascade)

Ariadne/LEPTO

Different parton-shower models: BFKL/DGLAP-like

DGLAP vs BFKLDGLAP vs BFKL

8/27A.Savin – Jets at HERA -

High Pt jets at Pt > Q probe the photon structure.

resolveddirect

In the BFKL both are taken in account due to arbitrary ordering of the kT

E

eEx jets

jetTobs

jets

2

)8.0(75.0obsx )8.0(75.0obsx

Real and virtual photon structureReal and virtual photon structure

9/27A.Savin – Jets at HERA -

Comparison with NLO

GeVE

GeVW

GeVQ

pb

jetT

jet

755

5.21

28595

1

1.2422

1

H1

Real photon structure: inclusive jet PHP at high EtReal photon structure: inclusive jet PHP at high EtNon-perturbative effects: multiple interactions and hadronisation are small

10/27A.Savin – Jets at HERA -

5.1||,3:

5

4.2||

280130

1

120

*

22

1

GeVpD

GeVE

GeVW

GeVQ

pb

T

jetT

jetZEUS

Real photon structure: dijet PHP with charmReal photon structure: dijet PHP with charm

11/27A.Savin – Jets at HERA -

Comparison with NLO

ZEUS

GeVEE

y

GeVQ

pb

jetT

jetT

jet

5.6,5.7

03

55.02.0

20001.0

6.38

2,1,

22

1

Virtual photon structure: dijet DIS at hight Et Virtual photon structure: dijet DIS at hight Et

12/27A.Savin – Jets at HERA -

Comparison with Herwig and Cascade

H1

GeVE

GeVEE

y

GeVQ

pb

t

jetT

jetT

jet

6

5,5

05.2

85.01.0

802

6.38

2,1,

22

1

Virtual photon structure: dijet DIS at hight Et Virtual photon structure: dijet DIS at hight Et

13/27A.Savin – Jets at HERA -

5.1||,3:

5.6;5.7

4.2||

65.02.0

104

*

2,1,

1

GeVpD

GeVEE

y

pb

T

jetT

jetT

jetZEUS

Virtual photon structure: dijet DIS with charmVirtual photon structure: dijet DIS with charm

14/27A.Savin – Jets at HERA -

Uncertainties:-NLO QCD due to terms beyong NLO;-NLO QCD due to -statistical and correlated systematic uncertainties(fits);-hadronisation etc.

)( Zs MPDF

New results on PDFs using jets in global PDF fits!

15/27A.Savin – Jets at HERA -

GeVE

GeVQ

pb

BreitjetT

Breitjet

HAD

8

8.12

5.0cos7.0

125

6.38

,

22

1

ZEUS

22,

22,

)(

)(cos

HADZHADT

HADZHADTHAD PEP

PEP

Structure of the proton: inclusive jets in DIS Structure of the proton: inclusive jets in DIS

16/27A.Savin – Jets at HERA -

Use jet data to tie down the high-x region in PDFanalysis

The improvement in the determination of the gluondistribution at moderate to high-x is striking

Structure of the proton: jets in the PDF fitStructure of the proton: jets in the PDF fit

17/27A.Savin – Jets at HERA -

22 105 GeVQ 22 2010 GeVQ 22 3520 GeVQ 22 7035 GeVQ 22 10070 GeVQ

8.25.1 LAB

GeVE

y

GeVQ

pb

LABjetT

LABjet

5

8.21

6.02.0

1005

1.21

,

22

1

H1

Structure of the proton: inclusive jets in DIS Structure of the proton: inclusive jets in DIS

18/27A.Savin – Jets at HERA -

7.01.0

855 22

y

GeVQH1

222,

21, ... Qkk TT

DGLAP

22., Qp jetforwt

The probability for

is low

BFKL

Low xBj,high Q2 ,

high pt,jet2 in the

p-direction25.0

035.0

79.274.1

5.3

2

2,

,

Q

p

E

Ex

GeVp

jett

p

jetjet

jet

jett

Forward jets Forward jets

19/27A.Savin – Jets at HERA -

0cos

22

1

6

32

25

7.38

2

2,

22

1

HAD

jetT

jetT

jet

Q

E

GeVE

GeVQ

pb

ZEUS

Comparison with NLO

to suppress

Forward jets Forward jets

20/27A.Savin – Jets at HERA -

Jet

Jet

Gap

-remnant P- remnant

0

2

R

R

-2.4 2.4

dd

ddf

gap

/

/)(

Dijet events with Rapidity Gap

All Dijet events

Interjet energy flowInterjet energy flow

H1GeVW

GeVQ

pb

233165

01.0

6.622

1

Color singlet added

21/27A.Savin – Jets at HERA -

Ratios: R2/1 and R3/2

GeVE

GeVQ

pb

jetT

jet

5

5.21

500010

2.8222

1

ZEUS

Multijet productionMultijet production

22/27A.Savin – Jets at HERA -

Multijet production: ratio 3jets/2jetsMultijet production: ratio 3jets/2jets

23/27A.Savin – Jets at HERA -

At high ET,jet and ycut not too low,fragmentation effects are small –subjet multiplicity in pQCD

kT inclusive - for jetskT exclusive - for subjets

2

222,

2,2

,

))()((},min{

1

REE

Ey jTiT

jetTij

Jets substructureJets substructure

24/27A.Savin – Jets at HERA -

GeVE

pbjetT 17

2.82 1

ZEUS

PHP and DIS

Jets substructureJets substructure

25/27A.Savin – Jets at HERA -

s measurements

26/27A.Savin – Jets at HERA -

sat HERA

27/27A.Savin – Jets at HERA -

Considerable progress in jets studying in ep: precise measurements, NLO etc

One may expect more new information about photon and proton pdfs by including more jet data in global PDF fits.

In many cases the theoretical uncertainties are still dominant