[PPT] - Jet production in ultra-peripheral collisions with Pythia 8 COST PowerPoint Presentation

SLIDE 1

Jet production in ultra-peripheral collisions with Pythia 8

COST workshop on collectivity in heavy-ion collisions

Ilkka Helenius February 28th, 2019

In collaboration with Christine O. Rasmussen and Torbjörn Sjöstrand

SLIDE 2

Outline

Motivation

Ultra-peripheral collisions (UPCs) allows to study γp and

γA, complementary to pp and pA (collectivity?)

Provide a Monte-carlo event generator for UPCs validated

against HERA data

Model the factorization-breaking effects for diffractive

dijets in photoproduction [I.H. and C.O.R., arXiv:1901.05261 [hep-ph]] Outline

1. Event generation in Pythia 8
2. Photoproduction and ultra-peripheral collisions
3. Dynamical rapidity gap survival model for hard diffraction
4. Summary & Outlook

1

SLIDE 3

Pythia 8

A general-purpose Monte-Carlo event generator
Use theory where available (perturbative QCD),

add phenomenological models where not Authors (release 8.240):

Torbjörn Sjöstrand

Lund University

Christian Bierlich

Lund University & Niels Bohr Institute

Nishita Desai

CNRS-Universite de Montpellier

Ilkka Helenius

University of Jyväskylä

Philip Ilten

University of Birmingham

Leif Lönnblad

Lund University

Stephen Mrenna

Fermi National Accelerator Laboratory

Stefan Prestel

Lund University

Christine O. Rasmussen

Lund University

Peter Skands

Monash University

2

SLIDE 4

Event generation in Pythia 8

1. Hard scattering
Convolution of partonic

cross sections and PDFs

2. Parton showers
Generate Initial and Final

State Radiation (ISR & FSR) using DGLAP evolution

[Figure: S. Prestel]
3. Multiparton interactions (MPIs)
Use regularized QCD 2 → 2 cross sections
4. Beam remnants
Minimal number of partons to conserve colour and flavour
5. Hadronization
Using Lund string model with color reconnection
Decays into stable hadrons

3

SLIDE 5

Ultra-peripheral heavy-ion collisions

                  

b > 2RA

Photon flux from equivalent photon approximation

Described with a flux of quasi-real (low-Q2) photons

⇒ Corresponds to photoproduction in ep collisions

Flux in impact-parameter space from bmin(≈ RA + RB)

f A

γ (x) = 2αEMZ2

xπ [ ξ K1(ξ)K0(ξ) − ξ2 2 ( K2

1(ξ) − K2 0(ξ)

)] Z is nuclear charge, ξ = bminxm, m (per-nucleon) mass

4

SLIDE 6

Event generation in photoproduction

Direct processes

Cross section from convolution

dσbp→kl+X = f b

γ (x) ⊗ f p i (xp, µ2) ⊗ dσγi→kl

b b x xp p remn. k l

Resolved processes

Convolute also with photon PDFs

dσbp→kl+X = f b

γ (x) ⊗ f γ j (xγ, µ2)

⊗ f p

i (xp, µ2) ⊗ dσij→kl

Sample photon kinematics and

setup γp sub-system with Wγp

b b xγ x xp p remn. remn. k l

Evolve the sub-system as any hadronic collision (incl. MPIs)

5

SLIDE 7

Dijet photoproduction in ep collisions at HERA

ZEUS dijet measurement

Q2

γ < 1.0 GeV2

134 < Wγp < 277 GeV
Ejet1

T

> 14 GeV, Ejet2

T

> 11 GeV

−1 < ηjet1,2 < 2.4

Different contributions

Define

xobs

γ

= Ejet1

T eηjet1 + Ejet2 T

eηjet2 2yEe

to discriminate direct and resolved processes (=xγ in γ at LO parton level)

b b b b b b b b

ZEUS

b

Pythia 8.226 resolved direct 17 < Ejet1

T

< 25 GeV 500 1000 1500 2000 dσ/dxobs

γ

[pb]

b b b b b b b b

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 xobs

γ

ratio to Pythia

[ZEUS: Eur.Phys.J. C23 (2002) 615-631]

At high-xobs

γ

direct processes dominate

6

SLIDE 8

Dijets in ultra-peripheral collisions by ATLAS [ATLAS-CONF-2017-011]

Event selection

anti-kT with R = 0.4
plead

T

> 20 GeV, pjets

T

> 15 GeV, |ηjets| < 4.4 Event-level variables:

mjets =

√ (ΣiEi)2 −

Σi⃗

pi

2
yjets = 1

2 log

(

ΣiEi+Σipzi ΣiEi−Σipzi

)

HT = ΣipTi
xA = mjets

√s e−yjets

A

x

3 −

10

2 −

10

1 −

10 1

b / GeV ] µ [

A

x d

T

H d σ ∼

2

d

12 −

10

10 −

10

8 −

10

6 −

10

4 −

10

2 −

10 1

2

10

4

10

6

10

< 50 GeV

T

H 42 < )

1

10 × < 59 GeV (

T

H 50 < )

2

10 × < 70 GeV (

T

H 59 < )

3

10 × < 84 GeV (

T

H 70 < )

4

10 × < 100 GeV (

T

H 84 < )

5

10 × < 119 GeV (

T

H 100 < )

6

10 × < 141 GeV (

T

H 119 < )

7

10 × < 168 GeV (

T

H 141 < )

8

10 × < 200 GeV (

T

H 168 <

Preliminary ATLAS

1

2015 Pb+Pb data, 0.38 nb = 5.02 TeV

NN

s =0.4 jets R

t

k anti- > 20 GeV

lead T

p > 35 GeV

jets

m Not unfolded for detector response Data Pythia+STARlight scaled to data

Preliminary data compared to Pythia 6 where events

reweighted with photon flux from STARlight

In Pythia 8 photon flux can be set by the user

7

SLIDE 9

Dijets in ultra-peripheral collisions with Pythia 8

Dominant contributions

Large xA: resolved
Small xA: direct
Weak dependence on γPDF

Sensitivity to nPDFs

Data not public, estimate

the statistical uncertainty at different luminosities

Potential to constrain nPDFs

down to x ∼ 10−3

With lower pjets

T

can extend the low-x reach further

dσ/dxA [nb] PbPb,√sNN = 5.5 TeV anti-kT, R = 0.4 plead

T

> 20 GeV/c mjets > 35 GeV NNPDF2.3 EPPS16 Resolved Direct Ratio to NNPDF2.3 xA

GRV SaSgam

L = 0.38 nb−1 L = 10 nb−1

[I.H., arXiv:1811.10931 [hep-ph]] [see also Guzey, Klasen, arXiv:1902.05126 [hep-ph]]

8

SLIDE 10

Factorization breaking in hard diffraction

IP

z 0.2 0.4 0.6 0.8 ratio to NLO 0.5 1 1.5 [pb]

IP

/dz σ d 500 1000

H1

p γ

H1 VFPS data )

hadr

δ (1+ × 0.83 × NLO H12006 Fit-B

PDF

γ AFG

[H1: JHEP 1505 (2015) 056]

Factorization breaking
bserved at Tevatron
Similar results from pp

collisions at the LHC

Factorization-based

calculation overshoot the data in photoproduction regime by a factor of two

But good agreement in DIS

[CDF: PRL 84 (2000) 5043-5048]

9

SLIDE 11

Hard diffraction in photoproduction

Starting point: Assume factorization of the cross section

Direct:

dσ2jets= f b

γ(x) ⊗ dσγj→2jets ⊗ f I P j (zI P, µ2) ⊗ f p I P(xI P, t)

Resolved: dσ2jets= f b

γ(x) ⊗ f γ i (xγ, µ2) ⊗ dσij→2jets ⊗ f I P j (zI P, µ2) ⊗ f p I P(xI P, t)

Direct:

b b γ p p remn. jet jet P

Resolved:

b b γ p p remn. remn. jet jet P ✗ ✓

Dynamical rapidity gap survival for resolved events

1. Generate diffractive events with dPDFs (PDF selection)
2. Reject events where MPIs in

p system (MPI selection)

3. Evolve

IP system, allow MPIs for this subsystem

10

SLIDE 12

Hard diffraction in photoproduction

Starting point: Assume factorization of the cross section

Direct:

dσ2jets= f b

γ(x) ⊗ dσγj→2jets ⊗ f I P j (zI P, µ2) ⊗ f p I P(xI P, t)

Resolved: dσ2jets= f b

γ(x) ⊗ f γ i (xγ, µ2) ⊗ dσij→2jets ⊗ f I P j (zI P, µ2) ⊗ f p I P(xI P, t)

Direct:

b b γ p p remn. jet jet P

Resolved:

b b γ p p remn. remn. jet jet P ✗ ✓

Dynamical rapidity gap survival for resolved events

1. Generate diffractive events with dPDFs (PDF selection)
2. Reject events where MPIs in γp system (MPI selection)
3. Evolve

IP system, allow MPIs for this subsystem

10

SLIDE 13

Hard diffraction in photoproduction

Starting point: Assume factorization of the cross section

Direct:

dσ2jets= f b

γ(x) ⊗ dσγj→2jets ⊗ f I P j (zI P, µ2) ⊗ f p I P(xI P, t)

Resolved: dσ2jets= f b

γ(x) ⊗ f γ i (xγ, µ2) ⊗ dσij→2jets ⊗ f I P j (zI P, µ2) ⊗ f p I P(xI P, t)

Direct:

b b γ p p remn. jet jet P

Resolved:

b b γ p p remn. remn. jet jet P ✗ ✓

Dynamical rapidity gap survival for resolved events

1. Generate diffractive events with dPDFs (PDF selection)
2. Reject events where MPIs in γp system (MPI selection)
3. Evolve γIP system, allow MPIs for this subsystem

Originally for pp in [C.O. Rasmussen and T. Sjöstrand, JHEP 1602 (2016) 142]

10

SLIDE 14

Comparisons to HERA data

H1 2007:

[EPJC 51 (2007) 549]

Q2 < 0.01 GeV2
xIP < 0.03
Ejet1

T

> 5.0, Ejet2

T

> 4.0 GeV

−1.0 < ηjet1,2 < 2.0

Observables

Wγp (H1)
MX (ZEUS)
zobs

IP

=

∑

jet(Ejet+pjet z )

∑

i∈X(Ei+pi z)

xobs

γ

=

∑

jet(Ejet−pjet z )

∑

i∈X(Ei−pi z)

ZEUS 2008: [EPJC 55 (2008) 177]

Q2 < 1 GeV2, 0.2 < y < 0.85
xIP < 0.025
Ejet1

T

> 7.5, Ejet2

T

> 6.5 GeV

−1.5 < ηjet1,2 < 1.5

Default Pythia setup

dPDFs from H1 fit B LO
γPDFs from CJKL
pref

T0 = 3.00 GeV/c

(Tuned to HERA γp data)

11

SLIDE 15

Invariant mass distributions

H1 2007:

b b b b b

Data PDF MPI 1 2 3 4 5 dσ/dW [pb/GeV]

b b b b

170 180 190 200 210 220 230 240 0.5 1 1.5 2 W [GeV] MC/Data

ZEUS 2008:

b b b b b b b

Data PDF MPI 2 4 6 8 10 12 dσ/dMX [pb/GeV]

b b b b b b

15 20 25 30 35 40 45 0.5 1 1.5 2 MX [GeV] MC/Data

PDF selection overshoots the data by 20–50 %
Impact of the MPI rejection increases with W and MX
Stronger suppression in H1 analysis due to looser cuts
n Ejets

T

and xIP

12

SLIDE 16

xobs

γ

distributions

H1 2007:

b b b b b

Data PDF MPI 100 200 300 400 500 600 dσ/dxobs

γ

[pb]

b b b b

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.5 1 1.5 2 xobs

γ

MC/Data

ZEUS 2008:

b b b b b b

Data PDF MPI 100 200 300 400 500 dσ/dxobs

γ

[pb]

b b b b b

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 xobs

γ

MC/Data

Stronger suppression at low-xobs

γ

as more room for MPIs

ZEUS cuts force the cross section to high-xobs

γ

region χ2/ndf H1 2007 ZEUS 2008 H1 & ZEUS PDF selection 5.20 9.64 7.63 MPI selection 1.42 5.10 3.44

13

SLIDE 17

Hard diffraction in UPCs

Apply the dynamical rapidity gap survival model to UPCs in

pp and pPb (currently not applicable to γPb)

In pPb the photon flux from Pb dominates (p neglected)

p p γ p p P gap X gap Pb Pb γ p p P gap X gap

Kinematics similar to HERA

Ejet1(2)

T

> 8(6) GeV

Mjets > 14 GeV
xIP < 0.025

Pythia setup

Same PDFs as for HERA
Vary MPI parameter:

pref

T0 = 3.0 GeV (HERA γp)

pref

T0 = 2.28 GeV (LHC pp) 14

SLIDE 18

Invariant mass distributions

pPb √s = 5.0 TeV

PDF, pref

⊥0 = 3.00 GeV

MPI, pref

⊥0 = 3.00 GeV

PDF, pref

⊥0 = 2.28 GeV

MPI, pref

⊥0 = 2.28 GeV

0.5 1 1.5 2 2.5 3 3.5 4 4.5 dσ/dW [nb/GeV] 200 400 600 800 1000 1200 1400 0.2 0.4 0.6 0.8 1 1.2 1.4 W [GeV] Ratio to PDF

pp √s = 13 TeV

PDF, pref

⊥0 = 3.00 GeV

MPI, pref

⊥0 = 3.00 GeV

PDF, pref

⊥0 = 2.28 GeV

MPI, pref

⊥0 = 2.28 GeV

0.002 0.004 0.006 0.008 0.01 0.012 dσ/dW [nb/GeV] 500 1000 1500 2000 0.2 0.4 0.6 0.8 1 1.2 1.4 W [GeV] Ratio to PDF

Extended W range wrt. HERA, especially in pp (harder flux)
Stronger suppression from MPIs than at HERA
Two-fold effect from lower pref

T0 , increases cross section for

PDF selection but MPI selection rejects more events

15

SLIDE 19

xobs

γ

distributions

pPb √s = 5.0 TeV

PDF, pref

⊥0 = 3.00 GeV

MPI, pref

⊥0 = 3.00 GeV

PDF, pref

⊥0 = 2.28 GeV

MPI, pref

⊥0 = 2.28 GeV

10 2 10 3 10 4 dσ/dxobs

γ

[nb] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.2 0.4 0.6 0.8 1 1.2 1.4 xobs

γ

Ratio to PDF

pp √s = 13 TeV

PDF, pref

⊥0 = 3.00 GeV

MPI, pref

⊥0 = 3.00 GeV

PDF, pref

⊥0 = 2.28 GeV

MPI, pref

⊥0 = 2.28 GeV

10 1 10 2 dσ/dxobs

γ

[nb] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.2 0.4 0.6 0.8 1 1.2 1.4 xobs

γ

Ratio to PDF

Enhanced MPI-suppression towards at small-xobs

γ

since more momentum left for MPIs

The gap-survival effects more pronounced in UPCs at the

LHC compared to HERA ⇒ Ideal place to constrain models

16

SLIDE 20

Summary & Outlook

Photoproduction in Pythia 8

Good description of the HERA data
Can be applied also to ultra-peripheral collisions with

appropriate photon flux

Potential to constrain nPDFs with photo-nuclear dijets

Diffractive dijets in photoproduction

Implementation of dynamical rapidity gap survival model

for γp (and γγ), originally introduced for pp

⇒ Uniform framework to describe the observed

factorization breaking for hard diffraction in pp and ep

Applicable also for UPCs (currently with proton target)

17

SLIDE 21

Backup slides

SLIDE 22

PDFs for resolved photons

Comparison of different photon PDF analysis

xf(x, Q2)/αEM x CJKL GRV SaSgam Q2 = 10.0 GeV2 u-quark xf(x, Q2)/αEM x CJKL GRV SaSgam Q2 = 10.0 GeV2 gluon

Some differences between analyses, especially for gluon

⇒ Theoretical uncertainty for resolved processes

CJKL used as a default in Pythia 8, others via LHAPDF5 but
nly for hard-process generation

SLIDE 23

MPIs with resolved photons

Parametrization for γp

pT0 values between γγ

(using LEP data) and pp

Relevant energies:
HERA: Wγp ≈ 200 GeV
eRHIC: Wγp ≈ 100 GeV

Number of MPIs in different colliders

Non-diffractive events

with resolved photons

Less MPIs in ep than pp
Larger pT0
Point-like PDF in PS

pT0(√s) [GeV/c] √s [GeV] γγ γp pp

[A.U.] Number of interactions/Event RHIC: pp 200 GeV HERA: ep 300 GeV eRHIC: ep 145 GeV

SLIDE 24

Charged particle pT spectra in ep collisions at HERA

b b b b b b b b b b b b b b b b b b b b b b b b b b

H1

b

Pythia 8.226 resolved direct pref

T0 = 3.00 GeV/c

|η| < 1 10−2 10−1 1 10 1 10 2 10 3 d2σ/dηdp2

T [nb]

b b b b b b b b b b b b b b b b b b b b b b b b b b

2 4 6 8 10 12 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 pT [GeV/c] ratio to Pythia

[H1: Eur.Phys.J. C10 (1999) 363-372]

H1 measurement

Ep = 820 GeV, Ee = 27.5 GeV
< Wγp >

≈ 200 GeV

Q2

γ < 0.01 GeV2

Comparison to Pythia 8

Resolved contribution

dominates

Good agreement with the

data using pref

T0 = 3.00 GeV/c

⇒ MPI probability between pp and γγ

SLIDE 25

Charged particle pT spectra in ep collisions at HERA

b b b b b b b b b b b b b b b b b b b b b b b b b b b

H1 pref

T,0 = 2.28 GeV, χ2/n = 9.90

pref

T,0 = 2.70 GeV, χ2/n = 1.85

pref

T,0 = 3.00 GeV, χ2/n = 0.79

pref

T,0 = 3.30 GeV, χ2/n = 1.69

MPI off, χ2/n = 2.48 10−2 10−1 1 10 1 10 2 10 3 10 4 d2σ/dηdp2

T [nb]

b b b b b b b b b b b b b b b b b b b b b b b b b b

2 4 6 8 10 12 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 pT [GeV/c] MC/Data

[H1: Eur.Phys.J. C10 (1999) 363-372]

H1 measurement

Ep = 820 GeV, Ee = 27.5 GeV
< Wγp >

≈ 200 GeV

Q2

γ < 0.01 GeV2

Comparison to Pythia 8

Resolved contribution

dominates

Good agreement with the

data using pref

T0 = 3.00 GeV/c

⇒ MPI probability between pp and γγ

SLIDE 26

Charged particle pT spectra in ep collisions at HERA

b b b b b b b b b b b b b b b b b b b b b b b b b b b

H1 pref

T,0 = 2.28 GeV, χ2/n = 9.90

pref

T,0 = 2.70 GeV, χ2/n = 1.85

pref

T,0 = 3.00 GeV, χ2/n = 0.79

pref

T,0 = 3.30 GeV, χ2/n = 1.69

MPI off, χ2/n = 2.48 10−2 10−1 1 10 1 10 2 10 3 10 4 d2σ/dηdp2

T [nb]

b b b b b b b b b b b b b b b b b b b b b b b b b b

2 4 6 8 10 12 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 pT [GeV/c] MC/Data

pT0(√s) [GeV/c] √s [GeV] γγ γp pp

H1 measurement

Ep = 820 GeV, Ee = 27.5 GeV
< Wγp >

≈ 200 GeV

Q2

γ < 0.01 GeV2

Comparison to Pythia 8

Resolved contribution

dominates

Good agreement with the

data using pref

T0 = 3.00 GeV/c

⇒ MPI probability between pp and γγ

SLIDE 27

Charged-particle η dependence

b b b b b b b b b b

H1

b

Pythia 8.226 resolved direct pT > 2.0 GeV/c 500 1000 1500 2000 2500 3000 dσ/dη [nb]

b b b b b b b b b b

1
0.5

0.5 1 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 η ratio to Pythia

b b b b b b b b b b

H1

b

Pythia 8.226 resolved direct pT > 3.0 GeV/c 100 200 300 400 500 600 700 800 dσ/dη [nb]

b b b b b b b b b b

1
0.5

0.5 1 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 η ratio to Pythia

[H1: Eur.Phys.J. C10 (1999) 363-372]

Good agreement also for charged-particle η dependence
Resolved contribution dominates the cross section

SLIDE 28

Dijet in ep collisions at HERA

Pseudorapidity dependence of dijets

[Eur.Phys.J. C23 (2002) 615-631]

b b b b b b b

ZEUS

b

CJKL GRV SaSgam xobs

γ

< 0.75 1 < ηjet1 < 2.4 100 200 300 400 500 600 700 dσ/dηjet2 [pb]

b b b b b b b

1
0.5

0.5 1 1.5 2 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 ηjet2 ratio to CJKL

b b b b b b b

ZEUS

b

CJKL GRV SaSgam xobs

γ

> 0.75 1 < ηjet1 < 2.4 50 100 150 200 250 300 350 dσ/dηjet2 [pb]

b b b b b b b

1
0.5

0.5 1 1.5 2 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 ηjet2 ratio to CJKL

Simulations tend to overshoot the dijet data by ∼10 %
∼ 10 % uncertainty from photon PDFs for xobs

γ

< 0.75

SLIDE 29

Hard diffraction in DIS

e e γ∗ zP xP t p p remn. jet jet P

Diffractive dijets

Virtual photon interacts with

Pomeron from proton producing jets

Signature: scattered proton or

a rapidity gap between proton and Pomeron remnant Factorized cross section for diffractive dijets

DIS: dσ2jets+X = f IP

i (zIP, µ2) ⊗ f p IP(xIP, t) ⊗ dσie→2jets

where f p

IP is Pomeron flux and f IP j diffractive PDF (dPDF)

Factorization verifed by H1 and ZEUS at HERA

SLIDE 30

Theoretical uncertainties

Largest uncertainties arise from

LO ME (vary factorization and renormalization scales)
diffractive PDFs (H1fitB, ZEUS-SJ and GKG18A)

ZEUS 2008:

b b b b b b b

Data central Combined scale uncertainty 2 4 6 8 10 12 dσ/dMX [pb/GeV]

b b b b b b

15 20 25 30 35 40 45 0.5 1 1.5 2 MX [GeV] MC/Data

ZEUS 2008:

b b b b b

Data central Combined scale uncertainty 100 200 300 400 500 dσ/dzobs

P

[pb]

b b b b

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.5 1 1.5 2 zobs

P

MC/Data

Scale uncertainty around 20 %
Better agreement for the shape of zobs

IP

with ZEUS-SJ

SLIDE 31

Theoretical uncertainties

Largest uncertainties arise from

LO ME (vary factorization and renormalization scales)
diffractive PDFs (H1fitB, ZEUS-SJ and GKG18A)

ZEUS 2008:

b b b b b b b

Data GKG LO Fit A ZEUS NLO Fit SJ H1 LO Fit B 2 4 6 8 10 12 dσ/dMX [pb/GeV]

b b b b b b

15 20 25 30 35 40 45 0.5 1 1.5 2 MX [GeV] MC/Data

ZEUS 2008:

b b b b b

Data GKG LO Fit A ZEUS NLO Fit SJ H1 LO Fit B 100 200 300 400 500 dσ/dzobs

P

[pb]

b b b b

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.5 1 1.5 2 zobs

P

MC/Data

Scale uncertainty around 20 %
Better agreement for the shape of zobs

IP

with ZEUS-SJ

SLIDE 32

zobs

IP

distributions

H1 2007:

b b b b b

Data PDF MPI 100 200 300 400 500 dσ/dzobs

P

[pb]

b b b b

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.5 1 1.5 2 zobs

P

MC/Data

ZEUS 2008:

b b b b b

Data PDF MPI 100 200 300 400 500 dσ/dzobs

P

[pb]

b b b b

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.5 1 1.5 2 zobs

P

MC/Data

MPI suppression not dependent on zobs

IP

Better agreement with H1 data after MPI rejection
Shape a bit off in both cases, observable sensitive to
dPDFs
Jet reconstruction