Physics Generators existing at BNL

Tobias Toll, BNLEIC R&D Simulation Workshop

BNL 10/8/12

Monday, October 8, 2012

https://wiki.bnl.gov/eic/index.php/Simulations

For information about generators,on how to use, references etc.

https://wiki.bnl.gov/eic/index.php/Computing

Information about how to get started and using the EIC computing at BNL:

EIC computing at BNL

If you don’t have an RCF accounthttps://www.racf.bnl.gov/docs/getstart/newuserform

‣ email John McCarthy & ElkeTo add EIC to existing RCF accoint:

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Monday, October 8, 2012

Why simulate?

Physics simulators crucial for IR design and predicting feasibility of making key EIC measurements.

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Monday, October 8, 2012

Why simulate?

Deliverables Obserables MC generator

Polarised gluon distribution Δg

Scaling violation in inclusive DIS

PEPSI+LEPTO

Polarised quark and antiquark densities

semi-incl. DIS for pions and kaons

PEPSI+LEPTO

Sivers and unpolarised TMDs for quarks and

gluon

SIDIS with transv. polarisation/ions; di-hadron

(di-jet) heavy flavoursgmc_trans

GPDs, 3D structure of quarks and gluon in

b-pL space

Exclusive DIS: vector mesons and DVCS

MILOU

EIC e+p Physics Programme,Key measurements

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Monday, October 8, 2012

Why simulate?

Deliverables ObservablesMC

generator

integrated gluon distributions

F2, L Pythia6+EPS09

kT dependent gluons; gluon correlations

di-hadron correlations

Pythia6/DPMJetIII hybrid

b-dependence of gluon

distribution and correlations

Diffractive VM production and DVCS, coherent and incoherent

parts

Sartre

EIC e+A Physics Programme, Key measurements

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Monday, October 8, 2012

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What is an MC generator?

T. Toll MC@NLO 8

Text

Monday, October 8, 2012

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What is an MC generator?

T. Toll MC@NLO 9

DokshitzerGribovLipatovAltarelliParisiTextText

Monday, October 8, 2012

What is an MC generator?Hard scattering pQCD or QED Matrix Element, at LO, NLO...

Initial state QCD radiations: collinear

(DGLAP), non-collinear (CCFM, RCBK) ...

Input distribution: PDF, uPDF, GPD, TMD...

Final State brems-strahlung PS,

vacuum/medium

Lund Strings, Clusters,

independent, medium

...

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Monday, October 8, 2012

What is an MC generator?Hard scattering pQCD or QED Matrix Element, at LO, NLO...

Initial state QCD radiations: collinear

(DGLAP), non-collinear (CCFM, RCBK) ...

Input distribution: PDF, uPDF, GPD, TMD...

Final State brems-strahlung PS,

vacuum/medium

Lund Strings, Clusters,

independent, medium

...

Radiative corrections(see Elke’s talk)

Hadronic remnant

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The Generators

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Pythia6

http://home.thep.lu.se/~torbjorn/Pythia.htmlSjostrand, Torbjorn et al. JHEP 0605 (2006) 026 hep-ph/0603175 FERMILAB-PUB-06-052-CD-T, LU-TP-06-13

by T. Sjöstrand

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Multi-purpose generator in ep, all sorts of collinear LO ME

Collinear factorisation (DGLAP) PS

Lund fragmentation (JETSET)

Can simulate non-collinear effects with initial Gaussian gluon and

quark kT distributions.

Code modified to include radiative corrections via RADGEN (by Elke).

Monday, October 8, 2012

Pythia6

xB

-510 -410 -310 -210 -110 1

)2 (G

eV2 Q

1

10

210

310

410

510

610

710

810

y = 0.

01

y = 0.

95 y = 0.

05

y = 0.

6

!Ldt = 10 fb-1 20 GeV on 250 GeV

http://home.thep.lu.se/~torbjorn/Pythia.htmlSjostrand, Torbjorn et al. JHEP 0605 (2006) 026 hep-ph/0603175 FERMILAB-PUB-06-052-CD-T, LU-TP-06-13

by T. Sjöstrand

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Multi-purpose generator in ep, all sorts of collinear LO ME

Collinear factorisation (DGLAP) PS

Lund fragmentation (JETSET)

Can simulate non-collinear effects with initial Gaussian gluon and

quark kT distributions.

Code modified to include radiative corrections via RADGEN (by Elke).

Monday, October 8, 2012

LEPTOMulti-purpose DIS generator. For ep: LO DIS, QCDC & PGF

Often used as part of other software packages, e.g.: PEPSI & DJANGO

Initial state radiation from either DGLAP, or dipoles (ARIADNE)

Fragmentation from Lund model (JETSET)

Rapidity gaps simulated with soft colour interactions

Uses LHAPDF for PDF

Ingelman, G. et al. Comput.Phys.Commun. 101 (1997) 108-134 hep-ph/9605286 DESY-96-057

by G. Ingelman et. al.

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Monday, October 8, 2012

PEPSI DIS generator with polarised proton, based on LEPTO 4.3.

Includes LO DIS, QCDC, PGF + electro-weak interactions

Polarised density functions are set in LEPTO

Code modified to include radiative corrections via

RADGEN (by Elke)

Various parametrisations of Δq(x, Q2) and Δg(x, Q2)

-0.04

-0.02

0

0.02

0.04

-0.04

-0.02

0

0.02

0.04

-0.04

-0.02

0

0.02

0.04

10 -2 10 -1 1

DSSVDSSV andEIC 5 GeV on 100 GeV& 5 GeV on 250 GeV

all uncertainties for !"2= 9x!u x!d

x!s

x

Q2 = 10 GeV2

x!g

x

-0.2

-0.1

-0

0.1

0.2

0.3

10 -2 10 -1 1

L. Mankiewicz, A. Schäfer and M. Veltri, Comp. Phys. Comm. 71, 305-318 (1992)

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Uncertainty bands on helicity parton distributions, presently (blue) andwith EIC data (red), using projected inclusive and semi-inclusive

EIC data sets

Monday, October 8, 2012

gmc_transSIDIS generator for ep with polarized

proton, with TMDs,

Choice of TMD parameterisations:Sivers, Collins, Boer-Mulders

Produces a single hadron, not a full event:e+p→e+h, h = π+, π-, π0, K+, K-

Polarized cross-section used to generate angular distribution of produced hadron

x-410 -310 -210 -110 1

UT

A

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

< 20, 0.8 < z < 1.0210 < Q < 20, 0.1 < z < 0.2210 < Q

< 2, 0.8 < z < 1.021 < Q < 2, 0.1 < z < 0.221 < Q

Written for the HERMES collaboration

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Sivers asymmetry as a function of x for different Q2 and z values and integrated over pT, at the positivity bound, showing the precision scaled for 10 fb-1

Monday, October 8, 2012

MILOUA DVCS generator: ep→eϒp, based on

GPDs at evolved at NLO: DVCS, Bethe-Heitler and interference

Optional: protons dissociation and initial-state QED radiative effects and radiative

corrections

t-dependence parametrised as an exponential:

A. Freund and M. McDermott [All ref.s in: http://durpdg.dur.ac.uk/hepdata/dvcs.html]

EIC pseudo data20 GeV on 250 GeV!Ldt = 100 fb-1

0 1 2 3 4 5 6

0.5

0.0

0.5

! (rad) ! (rad)0 1 2 3 4 5 6

0.5

0.0

0.5

A UTsin

(!"!

s)

A UTsin

(!"!

s)

Q2 = 4.4 GeV2xB = 8.2 10-4t = -0.25 GeV2

Q2 = 13.9 GeV2xB = 8.2 10-4t = -0.25 GeV2

#2 = +1.5#2 = 0#2 = -1.5

dσ

d|t| = e−B(Q2)·|t|

Perez, E. et al. hep-ph/0411389 DESY-04-228

Maintained at BNL by Salvatore Fazio

16DVCS polarised asymmetry AUT for T-polarised photonsMonday, October 8, 2012

DJANGOHUsed by EIC primarily to simulate the effects of radiative

corrections in both ep and eA

DIS generator with both QED and QCD radiative effects

Contains HERACLES MC for complete one-loop electroweak radiative corrections and scattering

For high hadronic mass HERACLES uses an interface to LEPTO,for low mass to SOPHIA

Fragments partons via the Lund model in JETSET.

Can be used with nuclear PDFs as well

by H. Spiesberger MZ–TH/05–15

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Sartre

Diffraction in e+A collisions with the EIC

The e+A Working Group(Dated: Draft: April 30, 2009)

Abstract to be added ...

Contents

I. Introduction 1

II. All-twist saturation picture of diffractionin nuclei 3A. Comparison to HERA data 6B. The nuclear diffractive structure function 7

III. Leading-twist nuclear shadowing andcoherent diffraction in DIS with nuclei 10

IV. Kinematics of Diffractive Events 12

V. Key Measurements 13

VI. Detection of Diffractive Events 14A. Overview of Methods 14B. Forward Spectroscopy 15

1. Angular Divergence of the Beam 152. Measuring Small Scattering Angles 163. Existing Forward Spectrometer of

Relevance for EIC 16C. Large Rapidity Gap (LRG) Method 18D. Nuclear Breakup and Implications for EIC 19

VII. Simulations 20A. Triggering on Diffractive Events 20B. Acceptance Coverage 21C. Reproducability of HERA Plots 22

VIII. Detector and Machine Requirements 23

IX. Summary 23

References 25

I. INTRODUCTION

The phenomenon of diffraction is familiar to us frommany areas of physics and is generally understood to arisefrom the constructive or destructive interference of waves.One such example, a plane wave impinging on a singleslit is shown in Fig. 1. In the strong interactions, diffrac-tive events have long been interpreted as resulting fromscattering of sub-atomic wave packets via the exchange ofan object called the Pomeron (named after the Russianphysicist Isaac Pomeranchuk) that carries the quantumnumbers of the vacuum. Indeed, much of the strong in-teraction phenomena of multi-particle production can beinterpreted in terms of these Pomeron exchanges.

FIG. 1:

In the modern strong interaction theory of Quan-tum ChromoDynamics (QCD), the simplest model ofPomeron exchange is that of a colorless combinationof two gluons, each of which individually carries colorcharge. In general, diffractive events probe the com-plex structure of the QCD vacuum that contains color-less gluon and quark condensates. Because the QCD vac-uum is non–perturbative and because much of previouslystudied strong interaction phenomenology dealt with softprocesses, a quantitative understanding of diffraction inQCD remains elusive.

Significant progress can be achieved throught the studyof hard diffractive events at collider energies. These al-low one to study hadron final states with invariant massesmuch larger that the fundamental QCD momentum scaleof ∼ 200 MeV. By the uncertainity principle of quantummechanics, these events therefore provide considerableinsight into the short distance structure of the QCD vac-uum.

A QCD diagram of a diffractive event is shown inFig. 2. It can be visualized in the proton rest frame asthe electron emitting a photon with virtuality Q2 andenergy ω, that subsequently splits into a quark–anti-quark+gluon dipole; other wave packet dipole configura-tions are also feasible. These dipoles interact coherentlywith the hadron target via a colorless exchange. Thefigure depicts this as a colorless gluon ladder, which asdiscussed previously, is a simple model of Pomeron ex-change.

Because the spread in rapidity between the dipole and

|t | (GeV2) |t | (GeV2)0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

)2 /d

t (nb

/GeV

e’ +

Au’

+ J/!)

!(e

+ A

u "d

)2 /d

t (nb

/GeV

e’ +

Au’

+ #)

!(e

+ A

u "d

J/$ #

"Ldt = 10 fb-11 < Q2 < 10 GeV2x < 0.01|#(edecay)| < 4p(edecay) > 1 GeV/c%t/t = 5%

"Ldt = 10 fb-11 < Q2 < 10 GeV2x < 0.01|#(Kdecay)| < 4p(Kdecay) > 1 GeV/c%t/t = 5%

104

103

102

10

1

10-1

10-2

105

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103

102

10

1

10-1

10-2

coherent - no saturationincoherent - no saturationcoherent - saturation (bSat)incoherent - saturation (bSat)

coherent - no saturationincoherent - no saturationcoherent - saturation (bSat)incoherent - saturation (bSat)

New event generator for exclusive diffractive vector meson and DVCS production in ep and eA (and UPC)

Uses the dipole models bSat and bNonSat

DGLAP gluon evolution, with Gaussian proton shape and Woods-Saxon nuclear shape

Uses Gemini++ for nuclear break-up

Outlook: Coherent inclusive diffraction

T. Ullrich and TT

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Based on Dual Parton Model, with soft and perturbative pomeron exchanges and AGK cutting rules

In ee, ep, pp, pA, eA, and AA. From a few GeV to highest cosmic ray energies

Only applicable for photo-production!

Uses FLUKA for intra-nuclear cascade and evaporation

Uses Lund model (JETSET) for fragmentation

Uses a Glauber model based on Woods-Saxon for initial nucleus

DPM-JetIII

S. Roesler, R. Engel and J. Ranft, arXiv:hep-ph/0012252

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Monday, October 8, 2012

e-

e-

A

σ

A’

New Pythia-DPM-JetIII hybridUsed primarily by EIC to simulate

dihadron correlations

Uses ME and PS from Pythia6, with nPDF EPS09

Nuclear geometry (WS) from DPMJet, as well as Nuclear evaporation/nuclear

fission/fermi break-up

Energy loss effects to simulate fragmentation effects in cold nuclear

matter (Salgado & Wiedermann)

By Liang Zheng with Elke and J.H.

2 2.5 3 3.5 4 4.50

0.020.040.060.08

0.10.120.140.160.18

eAueAu - sat

eAu - nosateCa

pTtrigger > 2 GeV/c

1 < pTassoc < pT

trigger

|!|<4

ep Q2 = 1 GeV2

!"!"

C(!"

)

C eAu

(!"

)

2 2.5 3 3.5 4 4.50

0.05

0.1

0.15

0.2EIC stage-II# Ldt = 10 fb-1/A

20Rad. Corr. in progress

Monday, October 8, 2012

New Pythia-DPM-JetIII hybrid4 contributions to decorrelation:

1. Higher order effects, like (a) initial state PS and (b) NLO hard gluon+loop

2. Non-collinear effects, like (a) intrinsic kT of gluon. Also, (b) combination, with non-collinear initial state radiations and Matrix Elements.

3. Saturation vs. 4. Multiple scattering (not in eA)

Can turn on/off 1(a), and has (crude) mechanism for 1(b) & 2(a)

CASCADE contains 1(a) & 2(a), (b)Only for ep & pp

In progress: CASCADE for eA (H. Jung & TT)

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Monday, October 8, 2012

• CASCADE (H. Jung et. al.)Multi-purpose DIS. kT-factorised ME, CCFM evolution, uPDFs. Saturation included in initial state and by bound in evolution.Jung, H. et al. Eur.Phys.J. C70 (2010) 1237-1249 arXiv:1008.0152 [hep-ph] DESY-10-107

• MC@NLO (S. Frixione, TT)Only Heavy Quarks in photo-production for ep. Coll. ME calculated at NLO and matched with PS. LHAPDF.Toll, Tobias et.al. Phys.Lett. B703 (2011) 452-461 arXiv:1106.1614 [hep-ph] CERN-PH-TH-2011-128

• RAPGAP (H. Jung)Multipurpose. Simulates hard diffractive DIS. DGLAP.Jung, Hannes Comput.Phys.Commun. 86 (1995) 147-161

Other resources

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Monday, October 8, 2012