HERA Physics and Gustav Kramer Alice Valkárová, Charles University, Prague 2nd April 2013Festkolloquium - G.Kramer1

HERA Physics and Gustav Kramer

Alice Valkárová, Charles University, Prague

2nd April 2013 Festkolloquium - G.Kramer 1


Gustav Kramer has more than 5000 citations to his papers….(h-ind. 38).A lot of citations to G.Kramer and co-authors in H1 and ZEUS publications!

• Photoproduction dijets, inclusive..

• Fragmentation functions, charm

• Isolated photons in DIS

• Diffraction, dijets, factorization

Dijet photoproduction


direct photoproduction photon directly involved in hard scattering

xγ=1 (at parton level)

hadron –like component (resolved) photon fluctuates into hadronic

system, which takes part in hadronic scattering

xγ<0.2 (at parton level)point –like component of resolved

photon dominates in the region of

0.2<xγ<1

In LO!Q2 ~ 0 GeV2

xγ - fraction of photon’s momentum in hard subprocess

hadronsz

jetszOBS

pE

pExx

)(

)(

Photoproduction, NLO QCD calculations


Measurement of the Inclusive Di-Jet Cross Section in Photoproduction and Determination of an Effective Parton Distribution in the Photon, H1 Collab., C. Adloff et al., Eur. Phys. J. C1 (1998) 97-107 , 09/97

Q2<4 GeV2

H1 – untagged photoproduction

Hadronization correction not takeninto account……

H1

Compared to KK NLO calculations

Low Q2 - dijets


Program for NLO QCD calculations JETviP (Kramer,Poetter) (the only program with resolved contribution included). G. Kramer and B. Poetter, Eur. Phys. J. C 5 (1998) 665

used for comparison with dijet photoproduction.

H1 Collab., A. Aktas et al., Eur. Phys. J. C37 (2004) 141-159

Measurement of Dijet Production at Low Q2 at HERA

M. Klasen and G. Kramer, Phys. Lett. B 366 (1996) 385

The asymmetric ET

cuts avoid regions of instability in the NLO calculations!

Incorporation of resolved component toNLO brings predictions closer to the data!

Inclusive photoproduction of jets


ZEUS Coll., Inclusive –jet photoproduction at HERA and determination of αs, Nucl.Phys.B 864,1 (2012)

(reference to:M.Klasen,T.Kleinwort,G.Kramer, Eur.Phys.J C1,(1998),1.)

Untagged photoproduction


Charged Particle Cross Sections in Photoproduction and Extraction of the Gluon Density in the Photon H1 Collab., C. Adloff et al., Eur. Phys. J. C10 (1999) 363

B.A.Kniehl,G.Kramer, Z.Physik C62 (1994),53.

Inclusive particle production at HERA: Resolved and direct quasireal photon contributions in NLO QCD

Inclusive particle photoproduction

Testing the universality of fragmentation functions – B.A.Kniehl,G.Kramer,B.PoetterNucl.Phys. B597 (2001), 337. 150 citations

Tagged photoproduction


Three different parameterisations of the FF areused which are obtained from NLO fits to e+e-data: KKP,KRETZER and AKK

Charged Particle Production in High Q2 Deep-Inelastic Scattering at HERA

H1 Collab., Phys.Lett.B654:148-159,2007.

B.A.Kniehl,G.Kramer,B.Potter,Nucl.Phys.B582(2000)514 with 314 citations….

S.Albino,B.A.Kniehl,G.Kramer,Nucl.Phys.B725(2005) 181

KKP

AKK

Fragmentation functions

In Breit frame,the measured normalized distribution of the scaled momentum 1/N dn/dxp,

N is the total number of events, dn is the total number of charged

tracks with scaled momentum xp in the interval dxp,x p=p h/(Q/2)

Charm production


Measurement of Inclusive and Dijet D*-Meson Cross Sections in Photoproduction at HERA

H1 Collab., F.D. Aaron et al.,Eur. Phys. J. C72 (2012) 1995

B.A. Kniehl, G. Kramer, I. Schienbein and H.Spiesberger, Eur. Phys. J.C62 (2009), 365

Single differential D* cross sections compared to NLO calculations

Difficult, due to the presence of two scales, mass of quark and pT


Observation of isolated high-ET photons in deep inelastic scattering

ZEUS Collab. Phys.Lett. B596 (2004), 86

Isolated photons and jets in DIS

Photon plus jet cross-sections in DIS ep CollisionsA. Gehrmann-De Ridder, G. Kramer, H.Spiesberger, Nucl. Phys. B 578 (2000) 326

Photons with 5 GeV < ETγ < 10 GeV accompanied by

jet

Quark radiative diagrams

Lepton radiative diagrams

LO


H1 Collab., F.D. Aaron et al., Eur.Phys.J.C54:371,(2008).

A. Gehrmann-De Ridder, G. Kramer and H.Spiesberger, Nucl. Phys. B 578 (2000) 326

The production of isolated photons in DIS with at least one jet compared to NLO calculations

Measurement of isolated photons accompanied by jets in deep inelastic ep scattering, ZEUS collab.,Phys.Lett.B 715 (2012),88.

The GKS predictions describe shapes quitewell…

Isolated photons and jets in DIS

Diffraction


Diffraction was not expected to play so important role at HERA experiments!

W

Two classes of diffractive events:

Q2~0 → photoproductionQ2>>0 → deep inelastic scattering (DIS)

Large rapidity gap

HERA: ~10% of low-x DIS events are

diffractive

Diffraction and questions of factorization


),(),,,()( 2*2

_

* QxtxQxfXpp iIP

D

ipartoni

D

QCD factorization theoretically proven for DIS (Collins, 1998)It allows the extraction of DPDFs from the (DIS) data

pp ep

S2=σ (data)σ (theory)

Exporting DPDFs from HERA toTevatron does not work!

Factorisation broken -> S2 ~ 0.1.

Dif → DPDFs – obey DGLAP, universal for

diff. ep DIS (inclusive,dijet,charm)

i* → universal hard scattering cross section

(same as in inclusive DIS)

Factorisation in dijet photoproduction (resolved component similar to hadron-hadron collisions) - interactions of spectators filling rapidity gap?

Factorization in photoproduction checked by both H1 and ZEUS….

Factorization in diffractive photoproduction


H1 -diffractive dijet photoproduction results compared to Frixione and Kramer-Klasen NLO QCD calculations.

Data suppressed by factor ~ 0.58

The same conclusion also for ZEUS, however without suppression!

H1 Collab., Eur.Phys.J. C70 (2010) 15

Factorization in diffraction


Eur.Phys.J. C70 (2010) 91-106

M.Klasen, G.Kramer, Suppression factors in diffractive photoproduction of dijets

Suppression factor R

An attempt to explain the differencein conclusions of both experiments.

The hint that suppression depends on ET of jets….(e.g. H1 Collab. Eur.Phys.J. C70 (2010) 15)

This puzzle not solved yet, new H1experimental results will come soon…(DIS 2013, Marseille).

Summary


• both HERA experiments profited a lot from the close relations with G.Kramer and his group

• H1 and ZEUS used frequently the predictions of G.Kramer and co-authors for the interpretation of the experimental results

In the name of both experiments - best wishes for the next fruitful years and good health!

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HERA Physics and Gustav Kramer Alice Valkárová, Charles University, Prague 2nd April 2013Festkolloquium - G.Kramer1