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Hard Photoproduction at HERA - Theory - Michael Klasen LPSC (ex-ISN) Grenoble 16 January 2007

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Hard Photoproduction at HERA - Theory -. Michael Klasen LPSC (ex-ISN) Grenoble 16 January 2007. CERN / Fréjus. LPSC. ILL. ESRF. Outline. QCD F actorization Theorem Photon Spectra Photon Structure Jet Production Cone and cluster algorithms - PowerPoint PPT Presentation

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Page 1: Hard Photoproduction at HERA - Theory -

Hard Photoproduction at HERA- Theory -

Michael KlasenLPSC (ex-ISN) Grenoble

16 January 2007

Page 2: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 2

ESRF

ILLLPSC

CERN /Fréjus

Page 3: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 3

OutlineQCD Factorization Theorem

Photon SpectraPhoton Structure

Jet ProductionCone and cluster algorithmsSingle jets, dijets, three jets, and diffraction

Hadron ProductionFragmentationLight hadrons, heavy hadrons, and quarkonia

Prompt-Photon ProductionFragmentation and isolationInclusive photons and photons with jets

Related TopicsVirtual photonsPolarized photons

Page 4: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 4

ReferencesTopical review:

Klasen, Rev. Mod. Phys. 74 (2002) 1221

Diffractive jet production:Kaidalov, Khoze, Martin, Ryskin, EPJC 21 (2001) 521Klasen, Kramer, EPJC 38 (2004) 93; PRL 93 (2004) 232002;JPG 31 (2005) 1391; hep-ph/0608235 (EPJC, in press)

Heavy-quark production:Cacciari, Frixione, Nason, JHEP 0103 (2001) 6Heinrich, Kniehl, PRD 70 (2004) 094035Kramer, Spiesberger, EPJC 38 (2004) 309Kniehl, Kramer, Schienbein, Spiesberger,PRD 71 (2005) 014018Banfi, Salam, Zanderighi, EPJC 47 (2006) 113

Page 5: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 5

QCD Factorization Theorem

Direct Photons Resolved Photons

Page 6: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 6

Photon Spectra (1)

Bremsstrahlung:Weizsäcker-Williams (1934) approximation:

Subleading non-logarithmic terms (Kessler, 1975): 5%

Beamstrahlung (very dense bunches at LC):Transverse acceleration in EM-field ( ) of bunch:

Laser backscattering:Compton effect (Ginzburg et al., 1984):

Page 7: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 7

Photon Spectra (2)

LHC, s/A = 5.5 - 14 TeV

Page 8: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 8

Photon Structure (1)

Structure functions:

Evolution equations:

Factorization schemes: ,

Hadronic solutions:

Strong coupling constant:

[Albino, MK, Söldner-Rembold, PRL 89 (2002) 122004]

Page 9: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 9

Photon Structure (2)

Albino, MK, Söldner-Rembold, PRL 89 (2002) 122004

PDG, JPG 33 (2006) 1

Page 10: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 10

Jet Production (1)Direct-direct ( LEP):

Direct-resolved:

Resolved-resolved:

Hadronic cross-section:

Partonic cross-section:

Matrix elements:

Page 11: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 11

Jet Production (2)

Virtual loop corrections:Self-energies:

,Vertex corrections:

Real emission corrections:

Page 12: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 12

Cone and Cluster AlgorithmsJADE clustering algorithm (e+e--colliders):

Snowmass cone algorithm (pp-colliders): with

Broad, seedless jets Midpoint: start with > 1 GeV seeds, add > 100 MeV clusters

Durham kT-algorithm: with

IR-safe, no Rsep, applies to e+e-- and pp-colliders

N3 computing time (N searches of N2 table for dmin)

Take geometrical nearest neighbours, use Voronoi diagrams N ln N computing time [Cacciari, Salam, PLB 641 (2006) 57]

Page 13: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 13

Single Jets and DijetsSingle jets:

High statistics, single

scale ET

s from scaling violations:

Dijets:

Photon PDFs from xobs:

Page 14: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 14

Three JetsThree-body rest frame:

Three-jet cross section:

Energy/angular distributions:

Page 15: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 15

Diffractive Dijet ProductionHard diffraction: Does factorization hold?

Deep inelastic scattering: Yes Direct photoproductionHadroproduction: No Resolved photoproduction

Why next-to-leading order? tot = dir(x,M) + res(x,M)

At LO x = 1, but at NLO x 1

log(M)-dependence cancels

Diffr. hadroproduction of dijets:

CDF Coll., PRL 84 (2000) 5043

Page 16: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 16

KinematicsDiffractive processes at

HERA:

H1 Coll., EPS 2003 and DIS 2004

Inclusive DIS:

Diffractive DIS:

Experimental cuts:

Page 17: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 17

Diffractive Parton DistributionsDouble factorization:

G. Ingelman, P. Schlein, PLB 152 (1985) 256

Hard QCD factorization:

Regge factorization:

Pomeron flux factor:

Pomeron tracectory:

Page 18: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 18

Proof of Hard FactorizationDiffractive deep inelastic

scattering:

J.C. Collins, PRD 57 (1998) 3051

Light cone coordinates:q= (q,q,qT)

Leading regions:H: q O(Q)J: l (0,Q/2,0T)A: |k|« O(Q)

Soft gluon attachments:

Poles in k-plane:Final state: Upper half-planeInitial state: Lower half-plane

Page 19: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 19

Multipomeron ExchangesDirect photoproduction:

Modify the Regge trajectory

Resolved photoproduction:

Factorization breaking

X

X

Page 20: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 20

Diffractive Photoproduction of DijetsCross section:

Photon flux: Weizsäcker-Williams approximation

Page 21: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 21

Factorizable Multipomeron Exchanges

y-dependence: Photon flux

Small correlations due to exp. cuts

xIP-dependence: Pomeron flux

Subleading Reggeon contribution

Page 22: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 22

Two-Channel Eikonal ModelHadronic collisions:

Survival probability:

Opacity / optical density: Ki = 1

Kaidalov et al., EPJC 21 (2001) 521

Photoproduction:

Generalized vector meson dominance:JPC = 1: , , …

Fitted parameters (W = 200 GeV):Total cross section: tot (p) = 34

mbPomeron slope: B = 11.3 GeV-2

Transition probability: = 0.6

ZEUS Coll., EPJ C2 (1998) 247 H1 Coll., EPJ C13 (2000) 371

Survival probability:R |S|2 0.34

Kaidalov et al., PLB 567 (2003) 61

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16 January 2007 Michael Klasen, LPSC Grenoble 23

No Sign of Factorization Breaking at LO

x-dependence: Direct/resolved photons

At LO, R = 1 agrees better with data!

zIP-dependence: Gluon density in pom.

Smaller uncertainties in 1/ d/dzIP

Page 24: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 24

Non-Factorizable Multipomeron

Exchangesx-dependence: Direct/resolved

photons

Large K-Factor Survival probability

zIP-dependence: Gluon density in pom.

Reduced scale uncertainties at NLO

Page 25: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 25

ZEUS Analysisx-dependence: Direct/resolved

photons

At LO, R = 1 agrees better with data!

Other observables:

Excellent agreement for absolute

’s!

Page 26: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 26

Diffractive / Inclusive ProductionR = fg/IP fIP/p / fg/p with M12 = xzIPxIPW:

A. Kaidalov et al., PLB 567 (2003) 61

R = diffr. / incl. with full kinematics:

MK, G. Kramer, EPJC 38 (2004) 39

CTEQ6L CTEQ5M1

Page 27: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 27

But: Data also support direct suppression!

Page 28: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 28

Factorization Scale DependenceInclusive photoproduction:

MK, Rev. Mod. Phys. 74 (2002) 1221

Diffractive photoproduction:

MK, G. Kramer, EPJC 38 (2004) 39

Page 29: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 29

Hadronization Corrections

Observable and model dependent!

Page 30: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 30

ET-Distribution

Importance of large ET:Direct process dominatesIS singularity less importantHadronization corrections smallExperimentally directly

accessibleLess sensitive than x

Result:Suppressed result agreesUnsuppressed 50% too low

How can we learn more?Critical role of IS singularityTransition from p to DIS

Page 31: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 31

High- to Low-Q2 Transition in DISQ2-dependence:

MK, G. Kramer, PRL 93 (2004) 232002

zIP-dependence:

MK, G. Kramer, PRL 93 (2004) 232002

Page 32: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 32

Factorization Scale Dependence (1)

MK, G. Kramer, JPG 31 (2005) 1391

Page 33: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 33

Factorization Scale Dependence (2)

Q2-dependence:

MK, G. Kramer, JPG 31 (2005) 1391

zIP-dependence:

MK, G. Kramer, JPG 31 (2005) 1391

Page 34: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 34

Factorization Scheme Dependence

Q2-dependence:

MK, G. Kramer, JPG 31 (2005) 1391

zIP-dependence:

MK, G. Kramer, JPG 31 (2005) 1391

Page 35: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 35

Components of Parton Densities in Photon

SaS parameterizations allow for separation:Anomalous component: Resummation of IS singularityHadronic component: Vector meson dominance model

VMD component suppressed:10-4 for Q2 70 GeV2

10-2 for Q2 5 GeV2

Anomalous component dominates:Direct higher order contributions

Known from inclusive low-Q2 production

Page 36: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 36

Leading Neutron Production (1)Meson cloud model:

Pion flux factor:

Scattering process:

Page 37: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 37

Leading Neutron Production (2)Sea-quark and gluon density in pions:

Sutton, Martin, Roberts, Stirling, PRD 45

Dijet production with a leading neutron:

MK, G. Kramer, PLB 508 (2001) 259

Page 38: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 38

Leading Neutron Production (3)DIS: Fix R in

[MK, G. Kramer, hep-ph /

p: Find S = 0.48 (0.64)

0608235 (EPJC in press)]

Page 39: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 39

Hadron ProductionQCD factorization theorem:

Direct-direct ( LEP):

Direct-resolved:

Resolved-resolved:

Hadronic cross section:

Partonic cross-section:

Matrix elements:

Page 40: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 40

Fragmentation (1)Transition functions:

Evolution equations:

Fit to e+-e- cross sections:

Peterson (1983):

Mele and Nason (1991):

Page 41: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 41

Fragmentation (2)Available parameterizations:

Quality of the fits:

Comparison to LEP/SLC

data:

Page 42: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 42

Light Hadrons

Page 43: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 43

Heavy Hadrons (1)

Fixed flavor number scheme:Heavy flavors: mq > q = c,b,t

Active partons in PDFs and FFs: q = u,d,s and g

Applicability: tot, pT ≈ mq

Partonic processes:qq: gg:

Fixed-order next-to-leading-logarithm scheme:Cacciari, Greco, Nason, JHEP 05 (1998) 007Subtraction of ln(mq

2/pT2) ≠ massless calculation

Finite O(mq2/pT

2) terms initial condition of FFs

Page 44: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 44

Heavy Hadrons (2)Variable flavor number scheme:

Kniehl, Kramer, Schienbein, Spiesberger, EPJC 41 (2005) 199Kinematics of mass factorization:

Factorized partonic cross section:

Partonic splitting functions:

Page 45: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 45

Open Charm at the Tevatron

Kniehl et al., PRL 96 (2006) 012001CDF, PRL 91 (2003) 241804

Page 46: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 46

D*+jet in Photoproduction at HERA

Page 47: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 47

QuarkoniaThe two sides of QCD:

Quarks and gluons: Asymptotically free, carry colorHadrons: Color-singlets, non-perturbative, confinement

Simplest laboratory: Quarkonia Rich spectroscopy

Charmonia: c’(2S), X(3872) (?)Bottomonia: (1D)

Experimental data:C-/B-factories:BES, CLEO, Babar, BelleFixed target: HERA-B, E866Colliders: LEP, HERA, Tevatron, LHC-B

Review:N. Brambilla et al.: CERN Yellow Report, hep-ph/0412158

Page 48: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 48

NRQCD

Color singlet state:Created by soft gluon exchange with underlying event

Separation of mass scales: (vc2 = 0.3, vb

2 = 0.1)mc = 1.5 GeV (annihilation and production threshold)

mcvc = 0.9 GeV (size of bound state)

mcvc2= 0.5 GeV (splitting of resonances)

Double expansion in s and v (pertur. and relat. corrections)

Lagrangian: and are two-component heavy (anti-)quark spinorsL reproduces LQCD: ,

Gauge completion: [Nayak, Qiu and Sterman, PLB 613 (2005) 45]

Page 49: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 49

J/-Cross Section at the Tevatron

Similar situation for ’ and c, see M. Krämer, Prog. Part. Nucl. Phys. 47 (2001) 141

[Braaten (1995); Cho, Leibovich (1996)]

Page 50: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 50

J/-Cross Section at HERA and LEP

Cacciari, Krämer, PRL 76 (1996) 4128 MK et al., PRL 89 (2002) 032001

Page 51: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 51

J/- and -Polarization at the Tevatron (1)

Braaten, Kniehl, Lee, PRD 62 (2000) 094005 Braaten, Lee, PRD 63 (2001) 071501

Page 52: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 52

J/- and ’-Polarization at the Tevatron (2)

[http://www-cdf.fnal.gov/physics/new/bottom/]

Page 53: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 53

-Cross Section and -Polarization at the LHC

But: LO only [M. Krämer, Prog. Part. Nucl. Phys. 47 (2001) 141]

[Braaten (1995); Cho, Leibovich (1996)]

Page 54: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 54

NLO Quarkonium Production

Color-singlet model pT-spectrum: pJ/+jetKrämer, Zunft, Steegborn, Zerwas, PLB 348 (1995) 657Krämer, NPB 459 (1996) 3

NRQCD tot: pp/p QuarkoniumPetrelli et al., NPB 514 (1998) 245Maltoni, Mangano, Petrelli, NPB 519 (1998) 361

NRQCD pT-spectrum: Quarkonium + /jetKlasen, Kniehl, Mihaila, Steinhauser, NPB 713 (2005) 487Klasen, Kniehl, Mihaila, Steinhauser, PRD 71 (2005) 014016

Page 55: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 55

Virtual CorrectionsTypical Feynman diagrams:

Cross section:

Light box contribution:

Page 56: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 56

Real CorrectionsGluon emission: Light quark emission:

Page 57: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 57

Finite NLO Cross Section

Cross section:

Singularity cancellation:

Page 58: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 58

Prompt-Photon ProductionQCD factorization theorem:

Quark-box contribution:NNLOBut importantnumerically

Hadronic cross section:

Partonic cross sections:PHOX NLO programs

Importance:Higgs background

Page 59: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 59

Fragmentation and IsolationSplitting functions:

Evolution equations:

Fit to e+e- cross sections:

Hadronic activity in cone:

Isolation criterion:

IR-safe definition:

Page 60: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 60

Inclusive Photons

Page 61: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 61

Photons with Jets

Page 62: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 62

Related Topics

Virtual photons

Polarized photons

Prompt photons in hadron collisions

Page 63: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 63

Virtual PhotonsTransverse photon flux:

Longitudinal photon flux:

Pert. boundary cond. P2=Q2:

GRV interpolation:

Page 64: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 64

Polarized PhotonsPolarized photon flux:

Polarized splitting functions:

Polarized coefficient fct.:

Page 65: Hard Photoproduction at HERA - Theory -

16 January 2007 Michael Klasen, LPSC Grenoble 65

Hard Photoproduction at HERA

Strong coupling constantReal and virtual photon structureProton, pion and pomeron structure ( Absorption!)Jet definition and jet shapesUniversality of fragmentation functionsFactorization for heavy quarksColor-singlet vs. color-octet quarkonium formationIsolation of final state photons

Relevance for LHC-physics: Higgs, and more