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HERA Physics and Gustav Kramer Alice Valk árová , Charles University, Prague. 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.. - PowerPoint PPT Presentation
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HERA Physics and Gustav Kramer
Alice Valkárová, Charles University, Prague
2nd April 2013 Festkolloquium - G.Kramer 1
2nd April 2013 Festkolloquium - G.Kramer 2
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
2nd April 2013 Festkolloquium - G.Kramer 3
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
2nd April 2013 Festkolloquium - G.Kramer 4
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
2nd April 2013 Festkolloquium - G.Kramer 5
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
2nd April 2013 Festkolloquium - G.Kramer 6
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
2nd April 2013 Festkolloquium - G.Kramer 7
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
2nd April 2013 Festkolloquium - G.Kramer 8
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
2nd April 2013 Festkolloquium - G.Kramer 9
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
2nd April 2013 Festkolloquium - G.Kramer 10
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
2nd April 2013 Festkolloquium - G.Kramer 11
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
2nd April 2013 Festkolloquium - G.Kramer 12
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
2nd April 2013 Festkolloquium - G.Kramer 13
),(),,,()( 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
2nd April 2013 Festkolloquium - G.Kramer 14
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
2nd April 2013 Festkolloquium - G.Kramer 15
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
2nd April 2013 Festkolloquium - G.Kramer 16
• 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!