Review of nal-state structure of pp interactions at the LHC · Review of nal-state structure of pp...

Review of final-state structureof pp interactions at the LHC

Paolo Gunnellini

DESY (Deutsches Elektronen Synchrotron), Hamburg

QCD at cosmic energiesKalchida (Greece)

May 2016

Paolo Gunnellini QCD at cosmic energies May 2016 1

Outline

1 Final states at the LHC2 Generalities on Monte Carlo event

generators3 Generator tuning and machinery

Available tunesOur understanding of QCD exp. dataCurrent issues and incompatibilities

4 Comparison between predictionsand measurements

Diffractive selectionsHard QCD events and multijet scenariosVector-boson final statesTop-antitop final states

5 Universality of tunes?6 Summary and conclusions

DISCLAIMER: Mainly results from ATLAS and CMS!


Hard scattering at the LHC

To simulate proton-proton collisions, physicists generally use

Monte Carlo event generators

Ingredients of the hard scattering

→ Factorization theorem→ Parton distribution functions→ Matrix element calculation

..starting from lowest order in αS butmight include additional real and

virtual corrections

σab→F (Q2) =∫

dx1dx ′1 f 1a (x1,Q

2) f 2b (x ′1,Q

2) σ̂ab(x1, x′1,Q

2)

Total Cross Section Partonic Cross Section

Parton Distribution Functions

with x = longitudinal proton momentum fraction carried by the partonQ2 = scale of the scattering


The underlying event at the LHC


Final states at the LHC

What can be produced in proton-proton collisions?

From soft to hard..

Soft particles

Jets

Heavy flav. jets

Vector boson

Top quark

Vector boson pair

Higgs

.......

pp

80 µb−1

W

35 pb−1

Z

35 pb−1

t̄t tt−chan WW H

total

VBF

VH

tt̄H

Wt

2.0 fb−1

WZ

13.0 fb−1

ZZ ts−chan t̄tW t̄tZ

σ[p

b]

10−1

1

101

102

103

104

105

106

1011Theory

LHC pp√s = 7 TeV

Data 4.5 − 4.9 fb−1

LHC pp√s = 8 TeV

Data 20.3 fb−1

LHC pp√s = 13 TeV

Data 85 pb−1

Standard Model Total Production Cross Section Measurements Status: Nov 2015

ATLAS Preliminary

Run 1,2√s = 7, 8, 13 TeV

Huge collection of measurements about these final states..in this talk only

some of them with focus on our understanding of the experimental results!


MC generator types

Pure matrix element (ME) simulationMC integration of cross section + PDFNo hadronization nor UE

Useful for theoretical studies, no exclusive events generated

Event generatorsCombination of ME and parton showersGenerator for fixed-order ME combined with leadinglog (LL) parton shower MC

Exclusive events, useful for experimentalists


MC generator types


Details of the Monte Carlo generators

Example: multijet final state

PYTHIA8 and HERWIG++: LO MC generators with extra jets from PS & MPI

SHERPA, MADGRAPH: matrix element with N-jets (extra real emission)

POWHEG: matrix element with a hard emission @ NLO (real & virtual)

PYTHIA, HERWIG SHERPA MADGRAPH@LO POWHEG


The Underlying Event at the LHC

Hard scattering

Initial and Final StateRadiation

Multiple Parton Interactions(MPI)

Beam-beam remnants

Hadronization

In general, the UE is asofter contribution but..some MPI can be hard!

Double PartonScattering

[TeV]s

0.04 0.1 0.2 1 2 3 4 5 10

[mb]

eff

σ

5

10

15

20

25

30

35

40 CMS (W + 2 jets)ATLAS (W + 2 jets)CDF (4 jets)

+ 3 jets)γCDF ( + 3 jets)γCorrected CDF (

+ 3 jets)γD0 (UA2 (4 jets - lower limit)AFS (4 jets - no errors given)

PA= σA

σpptot

PB = σB

σpptot

σDPSAB ∝ m

2PAPBσ

pptot

σDPSAB = m

2σAσB

σeff

σeff � σpptot

Need for correlations!Paolo Gunnellini QCD at cosmic energies May 2016 11

How do we deal with that?

Montecarlo event generators (PYTHIA, HERWIG, SHERPA..)

Parameters need to be adjusted (tuned) to describe data

MPI

Primordial kT

Parton shower

Hadronization

e.g. p0T = pref

T · (E/Eref )ε

Proton matter distribution profileColour reconnection

e.g. Width of the gaussian used for modelling theparton primordial kT inside the proton

e.g. Strong coupling valueRegularization cut-offUpper scale

e.g. Length of fragmentation stringsStrange baryon suppression

How does one tune all these?Choice of parameter ranges and sensitive observablesPredictions for different parameter choices and interpolation of the MC responseData-MC difference and minimisation over parameter space


Some ”official” tunes from the authors..

PYTHIA 8

HERWIG++

Monash Tune - PDF: NNPDF2.3LO (EPJ C74 (2014) 8)

UE-EE-5C - PDF: CTEQ6L1 (JHEP 1310 (2013) 113)

PYTHIA 8 Monash HERWIG++ UE-EE-5C(soft) MPI UE pp(p̄) data at various

√s UE pp(p̄) data at various

√s

Value of measured σeff

Primordial kT pT spectrum of lepton pair pT spectrum of Z boson

from Z decays in hadronic collisions in hadronic collisions

Parton shower Event shapes in pp̄ interactions Jet multiplicity, jet rates and

(taken from previous tune) shapes at various colliders

Hadronization Particle multiplicities in hadronic Particle production at

Z decays in e+e− collisions various colliders

General approach is a ”factorized” tuning procedure with only some ofthe components investigated

N.B. For the DPS simulation, generators normally useparameters of soft MPI and extrapolate to harder scales


Can they be refined?

How well do they describe observables at different energy?

→ Nch and psumT as a function of the leading charged particle

TRANS MIN: sensitive to MPI

TRANS MAX: sensitive to MPI and PS

TRANS DIF: sensitive to PS

TRANS AVE: sensitive to MPI and PS

PURPOSE: Tuning MPI and colourreconnection parameters

PTmax Direction

Δφ

“TransMAX” “TransMIN”

“Toward”

“Away”

“Toward-Side” Jet

“Away-Side” Jet

Jet #3

Leading Object Direction

Δφ

“Toward”

“Transverse-1” “Transverse-2”

“Away”


Results of the energy-dependence tuning

Charged particle mult. in the MAX reg. @ 0.9 (left) and 7 (right) TeV

b

b

b

b

bb b b b b

bb

bb

b

CDF datab

PYTHIA8 Tune 4CCUETP8S1-CTEQ6L1CUETP8S1-HERAPDF1.5LOCUETP8M1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9TransMAX charged-particle density

√s = 900GeV

(1/Nevents)dNch/d

ηd

φ

2 4 6 8 10 12 14 16 18 20

0.6

0.8

1

1.2

1.4

pmaxT [GeV]

MC/data

b

b

b

b

bb b b b b

bb

b b

b

CDF datab

HERWIG++ Tune UE-EE-5CCUETHppS1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

TransMAX charged-particle density√s = 900GeV

(1/Nevents)dNch/d

ηd

φ

2 4 6 8 10 12 14 16 18 20

0.6

0.8

1

1.2

1.4

pmaxT [GeV]

MC/data

b

b

b

b

b

bb

bb b

b b bb b

b

b

CMS datab

PYTHIA8 Tune 4CCUETP8S1-CTEQ6L1CUETP8S1-HERAPDF1.5LOCUETP8M1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

TransMAX charged-particle density√s = 7 TeV

(1/Nevents)dNch/d

ηd

φ

5 10 15 20 25

0.6

0.8

1

1.2

1.4

pmaxT [GeV]

MC/data

b

b

b

b

b

bb

bb b

b b bb b

b

b

CMS datab

HERWIG++ Tune UE-EE-5CCUETHppS1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

TransMAX charged-particle density√s = 7 TeV

(1/Nevents)dNch/d

ηd

φ

5 10 15 20 25

0.6

0.8

1

1.2

1.4

pmaxT [GeV]

MC/data

New tunes!PYTHIA 8 (CUETP8)

HERWIG++ (CUETHpp)

with various PDFs

Better constrain of theenergy extrapolation

CR changes with thechoice of the PDF

Rising part andplateaux region are

well predictedby the new tunes

(arXiv 1512.00815)


Tune performance at the new energy

2.5− 2− 1.5− 1− 0.5− 0 0.5 1 1.5 2 2.5

η /

dch

N d⋅

evN

1/

1

1.5

2

2.5

3

3.5

4

DataPYTHIA 8 A2PYTHIA 8 MonashHERWIG++ UE-EE5EPOS LHCQGSJET II-04

| < 2.5η| > 500 MeV, T

p 1, ≥ chn

= 13 TeVsPreliminary ATLAS

η2.5− 2− 1.5− 1− 0.5− 0 0.5 1 1.5 2 2.5

MC

/ D

ata

0.8

1

1.2

5 10 15 20 25 30

>φ dη

/dch

N2<

d

0

0.5

1

1.5

2

2.5 PreliminaryATLAS

= 13 TeVs

Transverse region

|< 2.5η > 0.5 GeV, |T

p

> 1 GeV leadT

p

DATA (uncorrected) EPOS

PYTHIA 8 A14 PYTHIA 8 A2HERWIG++ EE5 PYTHIA 8 Monash

[GeV]leadT

p5 10 15 20 25 30

MC

/Dat

a

0.70.80.9

11.11.21.3

0

1

2

3

4

5

6

7

8

-3 -2 -1 0 1 2 3

dN

ch/d

ηη

pp √s = 13 TeV inelastic

CMS

dataPYTHIA8 CUETP8S1EPOS LHC

(GeV)T

Leading Track p2 4 6 8 10 12 14 16 18 20 22 24

data

/MC

0.4

0.6

0.8

1

1.2

1.4

1.6

HIST_data_syserror

Stat. UncertaintyStat. + Syst. Uncertainty

HIST_data_syserror

2 4 6 8 10 12 14 16 18 20 22 24

(G

eV)

)φ∆(∆η∆/⟩

T pΣ⟨

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8 CMSPreliminary

(13 TeV)-1281 nbdata

Pythia8 + CUETP8M1

Pythia8 + Monash

EPOS

Herwig + CUETHS1

transMIN

√s = 13 TeV

TOP:dN/dη

ATLAS-CONF-2015-028,

PLB751 (2015)

BOTTOM:Nch vs plead

T

ATLAS-PHYS-2015-019,

CMS-FSQ-15-007

Current tunesreproduce the

data at 13 TeV!

May the energydependence of

the MPI beimproved in the

generators?

p0T = pref

T · (E/Eref )ε


What about other observables? (arXiv 1512.00815)

Min. Bias observables X

bb b

b b b b bb b

ALICE datab

CUETP6S1CUETP8S1-CTEQ6L1CUETP8S1-HERAPDF1.5LOCUETP8M1

0

1

2

3

4

5

6

7Charged-particle multiplicity,

√s = 7 TeV

dNch/d

η

-1 -0.5 0 0.5 1

0.6

0.8

1

1.2

1.4

η

MC/data

Incl. jet cross sections

Forward region

Z-boson observables

UE vs pjetT

DPS observables




bb b

b b b b bb b

ALICE datab


0

1

2

3

4

5

6


√s = 7 TeV

dNch/d

η

-1 -0.5 0 0.5 1

0.6

0.8

1

1.2

1.4

η

MC/data


Forward region X

b

bb b

b bb b b

b bb

b bb b b

bTOTEM datab


0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Charged-particle multiplicity,√s = 7 TeV

dNch/d|η|

5.4 5.6 5.8 6 6.2 6.4

0.6

0.8

1

1.2

1.4

|η|MC/data

Z-boson observables

UE vs pjetT

DPS observables




bb b

b b b b bb b

ALICE datab


0

1

2

3

4

5

6


√s = 7 TeV

dNch/d

η

-1 -0.5 0 0.5 1

0.6

0.8

1

1.2

1.4

η

MC/data


Forward region X

b

bb b

b bb b b

b bb

b bb b b

bTOTEM datab


0

0.5

1

1.5

2

2.5

3

3.5

4

4.5


dNch/d|η|

5.4 5.6 5.8 6 6.2 6.4

0.6

0.8

1

1.2

1.4

|η|MC/data

Z-boson observables

UE vs pjetT X

b

b

b

b

b

bb b b b b

b bb

bb

b b

CMS datab

CUETP6S1CUETP8S1-CTEQ6L1CUETP8S1-HERAPDF1.5LOCUETP8M1CUETHppS1

0

0.2

0.4

0.6

0.8

1

TransAVE Nch density,√s = 2.76 TeV

〈d2Nch/d

ηd

φ〉

10 20 30 40 50 60 70 80 90 100

0.6

0.8

1

1.2

1.4

pT (leading charged-particle jet) [GeV]

MC/Data

DPS observables




bb b

b b b b bb b

ALICE datab


0

1

2

3

4

5

6


√s = 7 TeV

dNch/d

η

-1 -0.5 0 0.5 1

0.6

0.8

1

1.2

1.4

η

MC/data

Incl. jet cross sections X

bb

bb

bb

bb

bb

bb

bb

bb

bbbbbbbbbbbbbbbb

b

CMS datab

PH+CUETP8M1PH+CUETP8S1-HERAPDF1.5LO

10−3

10−2

10−1

1

10 1

10 2

10 3

10 4

10 5

10 6

10 7

CMS, Inclusive jets,√s = 7 TeV, 0.5 < |y| < 1.0

d2σ/dpTdy[pb/GeV]

10 2 10 3

0.5

1

1.5

2

2.5

pT [GeV]

MC/data

Forward region X

b

bb b

b bb b b

b bb

b bb b b

bTOTEM datab


0

0.5

1

1.5

2

2.5

3

3.5

4

4.5


dNch/d|η|

5.4 5.6 5.8 6 6.2 6.4

0.6

0.8

1

1.2

1.4

|η|MC/data

Z-boson observables

UE vs pjetT X

b

b

b

b

b

bb b b b b

b bb

bb

b b

CMS datab


0

0.2

0.4

0.6

0.8

1


〈d2Nch/d

ηd

φ〉

10 20 30 40 50 60 70 80 90 100

0.6

0.8

1

1.2

1.4


MC/Data

DPS observables




bb b

b b b b bb b

ALICE datab


0

1

2

3

4

5

6


√s = 7 TeV

dNch/d

η

-1 -0.5 0 0.5 1

0.6

0.8

1

1.2

1.4

η

MC/data


bb

bb

bb

bb

bb

bb

bb

bb

bbbbbbbbbbbbbbbb

b

CMS datab


10−3

10−2

10−1

1

10 1

10 2

10 3

10 4

10 5

10 6

10 7


d2σ/dpTdy[pb/GeV]

10 2 10 3

0.5

1

1.5

2

2.5

pT [GeV]

MC/data

Forward region X

b

bb b

b bb b b

b bb

b bb b b

bTOTEM datab


0

0.5

1

1.5

2

2.5

3

3.5

4

4.5


dNch/d|η|

5.4 5.6 5.8 6 6.2 6.4

0.6

0.8

1

1.2

1.4

|η|MC/data

Z-boson observables X

b

b bb b

bbb

b

b

b

b

b

b

b

b

b

b

CMS datab

CUETP8M1PH+CUETP8M1PH+CUETP8S1-HERAPDF1.5LO

10−6

10−5

10−4

10−3

10−2

10−1Z boson pT in leptonic decay

1/

σd

σ/dpT(Z

)[1/GeV]

1 10 1 10 2

0.6

0.8

1

1.2

1.4

pT(Z) [GeV]

MC/Data

UE vs pjetT X

b

b

b

b

b

bb b b b b

b bb

bb

b b

CMS datab


0

0.2

0.4

0.6

0.8

1


〈d2Nch/d

ηd

φ〉

10 20 30 40 50 60 70 80 90 100

0.6

0.8

1

1.2

1.4


MC/Data

DPS observables




bb b

b b b b bb b

ALICE datab


0

1

2

3

4

5

6


√s = 7 TeV

dNch/d

η

-1 -0.5 0 0.5 1

0.6

0.8

1

1.2

1.4

η

MC/data


bb

bb

bb

bb

bb

bb

bb

bb

bbbbbbbbbbbbbbbb

b

CMS datab


10−3

10−2

10−1

1

10 1

10 2

10 3

10 4

10 5

10 6

10 7


d2σ/dpTdy[pb/GeV]

10 2 10 3

0.5

1

1.5

2

2.5

pT [GeV]

MC/data

Forward region X

b

bb b

b bb b b

b bb

b bb b b

bTOTEM datab


0

0.5

1

1.5

2

2.5

3

3.5

4

4.5


dNch/d|η|

5.4 5.6 5.8 6 6.2 6.4

0.6

0.8

1

1.2

1.4

|η|MC/data

Z-boson observables X

b

b bb b

bbb

b

b

b

b

b

b

b

b

b

b

CMS datab

CUETP8M1PH+CUETP8M1PH+CUETP8S1-HERAPDF1.5LO

10−6

10−5

10−4

10−3

10−2

10−1Z boson pT in leptonic decay

1/

σd

σ/dpT(Z

)[1/GeV]

1 10 1 10 2

0.6

0.8

1

1.2

1.4

pT(Z) [GeV]

MC/Data

UE vs pjetT X

b

b

b

b

b

bb b b b b

b bb

bb

b b

CMS datab


0

0.2

0.4

0.6

0.8

1


〈d2Nch/d

ηd

φ〉

10 20 30 40 50 60 70 80 90 100

0.6

0.8

1

1.2

1.4


MC/Data

DPS observables X

b b bb b

bb

b

b

b

b

b

b

b

CMS datab

CUETP8M1CUETHppS1

10−1

1

Normalized ∆S in pp→ 4j,√s = 7 TeV

(1/

σ)d

σ/d

∆S

0 0.5 1 1.5 2 2.5 3

0.6

0.8

1

1.2

1.4

∆SMC/data


Further look at UE/DPS comparisons (arXiv 1512.00815)

Tune name σeff value (mb)

CUETP8M1 26.0+0.6−0.2

CUETHppS1 15.2+0.5−0.6

Dedicated tune to DPS-sensitiveobservables in four-jet final state

CDPSTP8S2 → σeff = 19.0+4.7−3.0 mb

b

b

b

b

b

b

bbbbbb b

b bb b b b b b b b b b b b b

b

bb

b bb

ATLAS datab

CDPSTP8S2-4j

0

0.2

0.4

0.6

0.8

1

1.2

TransAVE Nch density,√s = 7 TeV

〈d2Nch/d

ηd

φ〉

2 4 6 8 10 12 14 16 18 20

0.6

0.8

1

1.2

1.4

pT (leading track) [GeV]

MC/Data

b b bb b

bb

b

b

b

b

b

b

b

CMS datab

CUETP8M1CUETHppS1

10−1

1

Normalized ∆S in pp→ 4j,√s = 7 TeV

(1/

σ)d

σ/d

∆S

0 0.5 1 1.5 2 2.5 3

0.6

0.8

1

1.2

1.4

∆S

MC/data

Not able to describe both UE and DPS observables at with the same set of tunes

Indication for need of a refinement of the current MPI model?


High multiplicity scenarios

Low multiplicities → mainly softer MPI componentsHigh multiplicities → contribution of harder MPI

= 7 TeVsCMS, pp | < 1.9ch.jetη |

(GeV/c)T

p5 10 15 20 25 30 35 40 45 50

)-1

(GeV

/cT

/dp

ch.je

tdN

ch.je

t1/

N -510

-410

-310

-210

-110

1

10

80≤ ch50 < N

(GeV/c)T

p5 10 15 20 25 30 35 40 45 50

MC

/dat

a

0

1

2

3 dataPYTHIA8 MPI-offPYTHIA8 4CPYTHIA6 Z2*Herwig++ 2.5 UE_EE_3M

= 7 TeVsCMS, pp > 0.25 GeV/cch.particle

T| < 2.4, pch.particleη|

chN20 40 60 80 100 120

>(G

eV/c

)T

<p

1

1.5 dataPYTHIA8 MPI-offPYTHIA8 4CPYTHIA6 Z2*Herwig++ 2.5 UE_EE_3M

all ch. particles

chN20 40 60 80 100 120

MC

/dat

a

0.5

1

1.5

2

= 7 TeVsCMS, pp | < 1.9ch.jetη |

(GeV/c)T

p5 10 15 20 25 30 35 40 45 50

)-1

(GeV

/cT

/dp

ch.je

tdN

ch.je

t1/

N -510

-410

-310

-210

-110

1

10 data

PYTHIA8 4C

PYTHIA6 Z2*Herwig++ 2.5 UE_EE_3M

140≤ ch110 < N

(GeV/c)T

p5 10 15 20 25 30 35 40 45 50

MC

/dat

a0

1

2

3

b

b

b

b

b

b

b

b

b

b

b

CMS datab

CUETP8S1-CTEQ6L1CDPSTP8S1-4jCUETP6S1Monash

10−4

10−3

10−2

10−1

1

CMS,√s = 7 TeV, |ηch.jet| < 1.9, 110 < Nch ≤ 140

1/Nch.jetdNch.jet/dpT[GeV/c]

−1

5 10 15 20 25 30 35 40 450.60.8

11.21.41.61.8

pT [GeV/c]

MC/Data

1- Charged-particlemeasurement

2- Jet measurement

Good agreement forUE tunes at lowmultiplicities but

worse for increasingmultiplicities

→ Better descriptionat high multiplicitiesfor the DPS tunes!

Normalized jet pT spectrumat different multiplicities(top and bottom right)

Charged particle spectra pTas a function of multiplicity

(bottom left)

Eur.Phys.J. C73 (2013) 2674


Diffractive-enhanced final states (I)

Diffractive dissociation cross sections as a functionof the fraction of the dissociated mass in differentranges dominated by different components→ Test of models for diffractive scenarios

Xξ

10log

-6 -5.5 -5 -4.5 -4 -3.5 -3 -2.5 -2

(m

b)Xξ

10/d

log

σd

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

< 0.5YM10

log

(7 TeV)-1bµ16.2

CMS (a)

Xξ

10log

-6 -5.5 -5 -4.5 -4 -3.5 -3 -2.5 -2 (

mb)

Xξ10

/dlo

gσd

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Data PYTHIA version:

=0.08)ε P8-MBR (=0.104)ε P8-MBR (

P8-4C P6-Z2*

< 1.1YM10

0.5 < log

(7 TeV)-1bµ16.2

CMS (c)

Best description is provided by MBR generator (arXiv.0203141) whichfully simulates the diffractive components and is tuned to Tevatron data

It uses different hadronization parameters to describe charged particle pT spectra

LEFT: SD-enhanced, RIGHT: DD-enhanced Phys. Rev. D 92 (2015) 012003


Diffractive-enhanced final states (II)

η2− 1.5− 1− 0.5− 0 0.5 1 1.5 2

η/d

ch)

dNev

ents

(1/N

0.4

0.6

0.8

1

1.2

1.4

1.6CMSPreliminary

| < 2.4η 1 in |≥ chN > 0.5 GeV

Tp

(13 TeV)

SD selectiondataPYTHIA8 CUETM1PYTHIA8 CUETS1PYTHIA8 CUETM1 MBRPYTHIA8 4C MBR

bb

b

b

b

b

b

b

b

b

b

b

b

b

Datab

CUETP8M1CUETP8M1-MBR

CUETP8M1-PomFlux

10−1

1

10 1

Charged hadron p⊥ for |η| = 0.1 at√s = 7 TeV

d2Nch/d

ηdp⊥[(GeV

/c)

−1]

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

0.6

0.8

1

1.2

1.4

p⊥ [GeV/c]

MC/Data

η2− 1.5− 1− 0.5− 0 0.5 1 1.5 2

η/d

ch)

dNev

ents

(1/N

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2CMSPreliminary

| < 2.4η 1 in |≥ chN > 0.5 GeV

Tp

(13 TeV)

SD selectiondataPYTHIA8 CUETM1PYTHIA8 CUETS1PYTHIA8 CUETM1 MBRPYTHIA8 4C MBR

bb

bbbbbbb

b

b

bb

bb

bb

bb

bb

bb

b bb

bb b

bb b b

b

Datab

CUETP8M1CUETP8M1-MBR

CUETP8M1-PomFlux

10−4

10−3

10−2

10−1

1

10 1

Charged hadron p⊥ for |η| < 2.4 at√s = 7 TeV

(1/2

πp⊥)d2Nch/d

ηdp⊥[(GeV

/c)

−2]

1 2 3 4 5 6

0.6

0.8

1

1.2

1.4

p⊥ [GeV/c]

MC/Data

SD-enhancedselection: activity

in one region,veto in the other

MBR diffraction model andparameters help to improve

the SD observables, due to abetter description of low

trans.mom. region

CMS-FSQ-15-008

Need for differenthadronization parameters fordiffractive observables than

for nondiffractive?

Ongoing work!


Jet observables at 13 TeV

(GeV)T

Jet p

200 300 1000 2000

dy

(pb/

GeV

)T

/ dp

σ2 d

-310

-110

10

310

510

710

910

1110

1310

1510)6|y|<0.5 (x10

)50.5<|y|<1.0 (x10)41.0<|y|<1.5 (x10)31.5<|y|<2.0 (x10)22.0<|y|<2.5 (x10)12.5<|y|<3.0 (x10)03.2<|y|<4.7 (x10

NP×CT14

(13 TeV)-172 pb

R = 0.7Tanti-k

CMSPreliminary

Inclusive jet cross section in differentrapidity bins

Various cone sizes probe different aspectsof parton evolution

Jets clustered with R = 0.7 are describedby NLO fixed-order calculations andpredictions from NLO MC generators

LO MC event generators are not able toreproduce the measurement

(GeV)T

Jet p200 300 1000 2000

Ratio

to C

T14

0.5

1

1.5

2

2.5DataHERAPDF1.5NNPDF3.0MMHT2014Exp. uncert.Theory uncert.

(13 TeV)-172 pb

CMSPreliminary

R = 0.7Tanti-k|y| < 0.5

(GeV)T

Jet p

200 300 1000 2000

Ratio

to P

H+P8

CUE

TM1

0.5

1

1.5

2

2.5DataPH+P8 CUETS1-CTEQ6L1PH+P8 CUETS1-HERAPDFP8 CUETM1Hpp CUETS1Exp. uncert.

(13 TeV)-172 pb

CMSPreliminary

R = 0.7Tanti-k|y| < 0.5

→ Fixed-order NLO ME corr. for NP effects with diff. PDF sets→ MC generators with LO or NLO dijet ME + PS and UE sim.

CMS-PAS-SMP-15-007 ATLAS-CONF-2015-034


Jet observables at 13 TeV

(GeV)T

Jet p

200 300 1000 2000

dy

(pb/

GeV

)T

/ dp

σ2 d

-310

-110

10

310

510

710

910

1110

1310

1510)6|y|<0.5 (x10

)50.5<|y|<1.0 (x10)41.0<|y|<1.5 (x10)31.5<|y|<2.0 (x10)22.0<|y|<2.5 (x10)12.5<|y|<3.0 (x10)03.2<|y|<4.7 (x10

NP×CT14

(13 TeV)-172 pb

R = 0.4Tanti-k

CMSPreliminary

Inclusive jet cross section in differentrapidity bins

Various cone sizes probe different aspectsof parton evolution

Jets clustered with R = 0.4 are notdescribed by NLO fixed-order calculationsbut only by predictions from NLO MCgenerators

Effect of missing PS contributions relevantfor smaller cones

(GeV)T

Jet p200 300 1000 2000

Ratio

to C

T14

0.5

1

1.5

2

2.5DataHERAPDF1.5NNPDF3.0MMHT2014Exp. uncert.Theory uncert.

(13 TeV)-172 pb

CMSPreliminary

R = 0.4Tanti-k|y| < 0.5

(GeV)T

Jet p

200 300 1000 2000

Ratio

to P

H+P8

CUE

TM1

0.5

1

1.5

2

2.5DataPH+P8 CUETS1-CTEQ6L1PH+P8 CUETS1-HERAPDFP8 CUETM1Hpp CUETS1Exp. uncert.

(13 TeV)-172 pb

CMSPreliminary

R = 0.4Tanti-k|y| < 0.5

[GeV]T

p210×4 210×5 210×6 210×7 210×8R

atio

w.r

.t. N

LO p

QC

D (

CT

10)

0.4

0.6

0.8

1

1.2

1.4

integrated luminosity not includedRelative uncertainty of 9% in the

| < 0.5y|

PreliminaryATLAS

13 TeV

-178 pb

=0.4R jets, tanti-k

DATA (syst., total)

CT10

MMHT

NNPDF3

Non-pert. corr.×NLOJET++

maxT

p = R

µ = F

µ


Multijet observables (I)

[TeV]12m

-110×3 1 2 3 4 5 6 7

* [p

b/T

eV]

yd12

m/dσ2 d

-1710

-1410

-1110

-810

-510

-210

10

410

710

1010

uncertaintiesSystematic

Non-pert. & EW corr.

)y* exp(0.3 T

p=µCT10, NLOJET++

)-0010×* < 0.5 (y ≤0.0 )0-310×* < 1.0 (y ≤0.5 )0-610×* < 1.5 (y ≤1.0 )0-910×* < 2.0 (y ≤1.5 )-1210×* < 2.5 (y ≤2.0 )-1510×* < 3.0 (y ≤2.5

ATLAS

-1 dt = 4.5 fbL∫ = 7 TeVs

= 0.4R jets, tkanti-

Inclusive dijet cross section indifferent rapidity bins as a

function of dijet mass

Jets clustered with R = 0.4 arereproduced by NLO fixed-ordercalculations

JHEP05(2014)059

Th

eo

ry/d

ata

1

1.5

2 * < 0.5y

= 0.530CTobsP = 0.306HERA

obsP

1

1.5

2 * < 1.0y ≤0.5


obsP

[TeV]12m

-110×3 1 2 3 4

1

1.5

2 * < 1.5y ≤1.0


obsP

Th

eo

ry/d

ata

1

2

3 * < 2.0y ≤1.5


obsP

1

2

3 * < 2.5y ≤2.0


obsP

[TeV]12m

-110×8 1 2 3 4 5

1

2

3 * < 3.0y ≤2.5


obsP

NLOJET++)y* exp(0.3

Tp=µ


CT10

HERAPDF1.5

exp. onlyepATLJet13

exp. onlyHERAPDF1.5

uncertaintyStatistical


ATLAS -1 dt = 4.5 fbL∫

= 7 TeVs



Multijet observables (II)

[TeV]12m

-110×3 1 2 3 4 5 6 7

* [p

b/T

eV]

yd12

m/dσ2 d

-1710

-1410

-1110

-810

-510

-210

10

410

710

1010



)y* exp(0.3 T

p=µCT10, NLOJET++

)-0010×* < 0.5 (y ≤0.0 )0-310×* < 1.0 (y ≤0.5 )0-610×* < 1.5 (y ≤1.0 )0-910×* < 2.0 (y ≤1.5 )-1210×* < 2.5 (y ≤2.0 )-1510×* < 3.0 (y ≤2.5

ATLAS

-1 dt = 4.5 fbL∫ = 7 TeVs


Inclusive dijet cross section indifferent rapidity bins as a

function of dijet mass

Jets clustered with R = 0.4 arereproduced by MC eventgenerators using NLO dijet MEbut sensitivity to UE tunes

JHEP05(2014)059

Th

eo

ry/d

ata

0.8

1

1.2* < 0.5y

0.8

1

1.2* < 1.0y ≤0.5

[TeV]12m

-110×3 1 2 3 4

0.8

1

1.2 * < 1.5y ≤1.0

Th

eo

ry/d

ata

0.5

1

1.5

2* < 2.0y ≤1.5

0.5

1

1.5

2* < 2.5y ≤2.0

[TeV]12m

-110×8 1 2 3 4 50.5

1

1.5

2 * < 3.0y ≤2.5

POWHEGBorn

Tp=µCT10,

EW corr.

+ PYTHIA shower

AUET2B

Perugia 2011

uncertaintyStatistical


ATLAS -1 dt = 4.5 fbL∫

= 7 TeVs



Multijet observables (III))

[fb/G

eV

](1

)

T / d

(pσ

d

410

310

210

110

1

10

210

310

410

510

610

Data

0.9)×HEJ (

1.0)×BlackHat/Sherpa (

1.0)×NJet/Sherpa (

>100 GeV(1)

Tp

ATLAS1 20.3 fb1=8 TeV, 95 pbs

[GeV](1)

Tp

210×23

103

10×2

Th

eo

ry/D

ata

0

0.5

1

1.5

2

systematic uncertainty

Total experimental

uncertainty

PDF)⊕NLO (scale

) [fb/G

eV

](1

)

T / d

(pσ

d

410

310

210

110

1

10

210

310

410

510

610

Data

0.6)×Pythia 8 (

1.4)×Herwig++ (

1.1)×MadGraph+Pythia (

>100 GeV(1)

Tp

ATLAS1 20.3 fb1=8 TeV, 95 pbs

[GeV](1)

Tp

210×23

103

10×2

Th

eo

ry/D

ata

0

0.5

1

1.5

2

systematic uncertainty

Total experimental

Four-jet scenarios also well describedin a wide region of the phase space

JHEP 12 (2015) 105Phys.Rev.D89(2014)092010

| < 4.7η| jet:nd, 2st1

> 50 GeVT

p

jet:th, 4rd3 > 20 GeV

Tp

4j+X→, pp -1 = 7 TeV, L = 36 pbsCMS,

SHERPAPOWHEG+P6 Z2'MADGRAPH+P6 Z2*PYTHIA8 4CHERWIG++ UE-EE-3Total Uncertainty

| < 4.7η| jet:nd, 2st1

> 50 GeVT

p

jet:th, 4rd3 > 20 GeV

Tp

4j+X→, pp -1 = 7 TeV, L = 36 pbsCMS,

SHERPAPOWHEG+P6 Z2'MADGRAPH+P6 Z2*PYTHIA8 4CHERWIG++ UE-EE-3Total Uncertainty

Jet #pt50 100 150 200 250 300 350 400 450 500

50 100 150 200 250 300 350 400 450 500

MC

/Dat

a

0.20.40.60.8

11.21.41.61.8

2Leading jet

Jet #pt50 100 150 200 250 300 350 400 450 500

50 100 150 200 250 300 350 400 450 500

MC

/Dat

a

0.20.40.60.8

11.21.41.61.8

2Subleading jet

Jet #pt50 100 150 200 250 300 350 400 450 500

MC

/Dat

a

0.20.40.60.8

11.21.41.61.8

2

Third jet

(GeV)T

Jet p50 100 150 200 250 300 350 400 450 500

MC

/Dat

a

0.20.40.60.8

11.21.41.61.8

2Fourth jet


Z boson observables

Jets associated to a Z boson

Measurement of differential cross sections for different jet multiplicities→ Crucial test of our QCD predictions!

1 [GeV]≥ jets

, NTH

4−10

3−10

2−10

1−10

1

10

Data (25ns)

2j NLO + PS)≤aMC@NLO + PY8 (

CMS Preliminary (13 TeV)-12.5 fb

(R = 0.4) JetsTanti-k

| < 2.4 jet

> 30 GeV, |yjet

Tp

channelµµ →*γZ/

(jets

) [p

b/G

eV]

T/d

Hσd

1 [GeV]≥ jets

, NTH200 400 600 800 1000

aMC

@N

LO/D

ata

0.5

1

1.5

Stat. unc. (gen)

3 [GeV]≥ jets

, NTH

5−10

4−10

3−10

2−10

Data (25ns)

2j NLO + PS)≤aMC@NLO + PY8 (

CMS Preliminary (13 TeV)-12.5 fb

(R = 0.4) JetsTanti-k

| < 2.4 jet

> 30 GeV, |yjet

Tp

channelµµ →*γZ/

(jets

) [p

b/G

eV]

T/d

Hσd

3 [GeV]≥ jets

, NTH200 400 600 800 1000

aMC

@N

LO/D

ata

0.5

1

1.5

Stat. unc. (gen)

jetsN

0 1 2 3 4

) [p

b]je

ts)+

Nµµ

→(Z

(σ

1

10

210

310

410 DataSherpaMadgraph

+ jets-µ+µ →Z

-113 TeV, 85 pbPreliminary

, R=0.4tanti-k

> 30 GeVjet

Tp

| < 2.5jet

|y

ATLAS

jetsN0 1 2 3 4

Dat

a / P

red.

0.60.8

11.21.4

4≥ 3 ≥ 2 ≥ 1 ≥ 0 ≥

CMS-SMP-15-010ATLAS-CONF-2015-041

Predictions describe measurements as long as the multiplicity matchesthe number of partons in the matrix element


Top observables (I)

Underlying event in top pair events

Measurement of event content in terms of charged particle multiplicity and pT

→ Test of final-state universality of UE contribution

t

t

t t W+

b

b

μ+ νμ

q

q

W-‐

CMS-TOP-15-017

CMS Preliminary

(13 TeV)-12.2 fb

[GeV]ch

Tp

0 5 10 15 20 25

MC

/Dat

a

0.5

1

1.5

) [/G

eV]

ch Tp/d

(ev

dN

ev1/

N

4−10

3−10

2−10

1−10

1

overall

away

transverse

toward

Powheg + Pythia 8tt

(CUETP8M1)

CMS Preliminary

(13 TeV)-12.2 fb

[GeV]ttT

p20 30 40 100 200 300

MC

/Dat

a

0.8

1

1.2

[GeV

]⟩

ch Tp ⟨

1.5

2

2.5

3

3.5

4

4.5

detector-level data Powheg + Pythia 8 (CUETP8M1)tt

2 Powheg + Pythia 8 (CUETP8M1) (2Q)tt2 Powheg + Pythia 8 (CUETP8M1) (Q/2)tt

Powheg + Herwig++ (EE5C) tttransverse

Predictions of POWHEG NLO matrix-element interfaced to P8 tunes from hadronicevents are able to reproduce all measured observables in each considered region


Top observables (II)

Top pair in lepton + jets final states

Measurement of differential cross sections as a function of top pair pT and jetmultiplicity → Test of reliability of predictions in top sector

) [GeV]t(tT

p

]-1

[pb

GeV

)t(t

Tdp

σd

2−10

1−10

1

(13 TeV)-12.3 fbl+jets particleCMS

Preliminarydata

stat⊕sys stat.MG5_aMC@NLO P8 [FxFx]MG5_aMC@NLO P8 [MLM]Powheg P8Powheg H++MG5_aMC@NLO P8MG5_aMC@NLO H++

) [GeV]t(tT

p0 100 200 300 400 500

data

theo

ry

0.81

1.21.4

n-jets

d n-

jet

σd

10

20

30

40

50

(13 TeV)-12.3 fbl+jets particleCMS

Preliminarydata

stat⊕sys stat.MG5_aMC@NLO P8 [FxFx]MG5_aMC@NLO P8 [MLM]Powheg P8Powheg H++MG5_aMC@NLO P8MG5_aMC@NLO H++

additional jets0 1 2 3 >=4

data

theo

ry1

1.5

2

NLO predictions describe well the measurements but sensitivity tomatching scheme and PS generator

CMS-TOP-16-008


Parton shower and MPI tuning

TUNING OF PYTHIA 8 TO OBSERVABLES MEASURED IN DIFFERENT PROCESSES

Study of the interplay between MPI and parton showerVarious PDF sets investigated

ObservablesTrack jet propertiesJet shapesDijet decorrelationsMultijetsZ boson pT

tt̄ gap and jet shapesTrack-jet and jet UE

Extremely important for:testing the universality of the parton shower in leptonic and hadronic collisions

testing the performance of UE simulation for different hard scattering processes

ATL-PHYS-PUB-2014-021


Parton shower and MPI tuning

Significant improvement of description of observables in:Drell-Yan (left), top-antitop (center) and jet substructure (right) sectors

bb b b b b b b b b b b b b b b b b b

bb

b

b

b

b

b

ATLAS Simulation

ATLAS Datab

AU2 CTEQ6L1MonashA14-CTEQA14-MSTWA14-NNPDFA14-HERA

10−7

10−6

10−5

10−4

10−3

10−2

10−1Z pT “dressed” muons

1σ

fid.

dσ

fid.

dp T

1 10 1 10 20.70.75

0.80.85

0.90.95

1.01.05

1.1

Z pT

MC

/Dat

a

b

b

b

b

bb

bb

bb b b b b b b b b

ATLAS SimulationATLAS Datab


0.7

0.75

0.8

0.85

0.9

0.95

1.0

Gap fraction vs. Q0 for veto region: |y| < 0.8

f gap

50 100 150 200 250 300

0.96

0.98

1.0

1.02

1.04

Q0 [GeV]

MC

/Dat

ab

b

b

b

b

bb

b

b

b

b

b

b

b

ATLAS Simulation

ATLAS Datab


0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Cambridge-Aachen jets, R = 1.2, 300 GeV < p⊥ < 400 GeV

1/σ

dσ

/d

τ 21

0.2 0.4 0.6 0.8 1 1.2

0.6

0.8

1

1.2

1.4

N-subjettiness τ21

MC

/Dat

a

αS values are similar for all PDF usedquite high for the hard processeslower for initial- and final-state radiationsignificantly lower than previous tunes for ISR and FSR

Damped shower needed to describe gap fraction in t̄tevents and pZ

T simultaneouslyPaolo Gunnellini QCD at cosmic energies May 2016 36

Tuning higher-order ME matched to parton showers

OBSERVABLES: gap fraction, jet shapes and jet multiplicity in t̄t events

GENERATORS: PYTHIA 8 standalone, MADGRAPH aMC@NLO andPOWHEG + PYTHIA 8

Different steps of tuning:

tuning of ISR and FSR separately, then simultaneous tune toaccount for their interplay

application of tune to matched generators

tune of the matched MADGRAPH aMC@NLO + PYTHIA 8

(Some of the) Outcomes

Significant improvement in the description of t̄t observables

Parameters of simultaneous ISR-FSR tune do not differ much fromthe separate tunes

Tune of matched MADGRAPH+PYTHIA 8 has similar parametersto standalone PYTHIA 8

ATL-PHYS-PUB-2015-007, ATL-PHYS-PUB-2015-048


Summary and conclusions

High energy physics strongly relies on predictions from MonteCarlo event simulation

Very sophisticated tunes are available and are able to describe a wide range ofobservables at different collision energies

Actual measurements are sensitive to ME, UE and PS contributions and are ableto disentangle them

Tunes obtained at 7 TeV (or below) are able to reproduce data at 13 TeV in agood level of agreement

It is difficult to reproduce data relative to some corners of the phase space withina unique set of parameters (e.g. DPS-sensitive observables, diffraction)

Need for more sophisticated models/parametrizations?

New measurements, moreadvanced simulation..

Stay tuned!


Summary and conclusions

High energy physics strongly relies on predictions from MonteCarlo event simulation

Very sophisticated tunes are available and are able to describe a wide range ofobservables at different collision energies

Actual measurements are sensitive to ME, UE and PS contributions and are ableto disentangle them

Tunes obtained at 7 TeV (or below) are able to reproduce data at 13 TeV in agood level of agreement

It is difficult to reproduce data relative to some corners of the phase space withina unique set of parameters (e.g. DPS-sensitive observables, diffraction)

Need for more sophisticated models/parametrizations?

New measurements, moreadvanced simulation..

Stay tuned!

THANK YOU FOR YOUR ATTENTION


BACKUP SLIDES


A double parton scattering (DPS)

Two different x values for thetwo partons in each proton

Impact parameter b

σDPSA,B = m

2

∫dx1dx ′1σ̂A(x1, x

′1)

∫dx2dx ′2σ̂B (x2, x

′2)

∫d2b f (x1, x2, b) f (x ′1, x

′2, b)

DPS Cross Section Double parton distribution functions

Partonic cross sections

If the partons are assumed to be uncorrelated:

f (x1, x2, b) = f (x1)f (x2)F (b)

The two scatterings factorize in the cross section formula:

σDPSAB =

m

2

∫dx1dx ′1σ̂Af (x1)f (x ′1)

∫dx2dx ′2σ̂B f (x2)f (x ′2)

∫d2b [F (b)]2

It is thus defined: σeff = 1∫d2b [F (b)]2


Combined fits to whole MPI spectrum

Combined fits of observables sensitive to soft, semi-hard and hard MPI

b b bb b

bb

b

b

b

b

b

b

b

CMS datab

DPS-UE-MB Tune

10−1

1

Normalized ∆S in pp→ 4j in |η| < 4.7 at√s = 7 TeV

(1/

σ)d

σ/d

∆S[1/rad]

0 0.5 1 1.5 2 2.5 3

0.8

0.9

1.0

1.1

1.2

∆S (rad)

MC/Data

b b bb

b

bb

b

b

b

b

b

b

b

CMS datab

DPS-UE-MB-Weighted Tune

10−1

1

Normalized ∆S in pp→ 4j in |η| < 4.7 at√s = 7 TeV

(1/

σ)d

σ/d

∆S[1/rad]

0 0.5 1 1.5 2 2.5 3

0.8

0.9

1.0

1.1

1.2

∆S (rad)

MC/Data

bb b

b b b b bb b

ALICE datab

DPS-UE-MB Tune

0

1

2

3

4

5

6

7Pseudorapidity

√(s) = 7 TeV, INEL > 0

dN/d

η

-1 -0.5 0 0.5 1

0.6

0.8

1

1.2

1.4

η

MC/Data

bb b

b b b b bb b

ALICE datab


0

1

2

3

4

5

6

7Pseudorapidity

√(s) = 7 TeV, INEL > 0

dN/d

η

-1 -0.5 0 0.5 1

0.6

0.8

1

1.2

1.4

η

MC/Data

b

b

b

b

bb b

b b b b b b b b

bb

CMS datab

DPS-UE-MB Tune

10−2

10−1

1TransMIN charged particle density

√s = 7 TeV

(1/Neven

ts)dNch/d

ηd

φ

5 10 15 20 25

0.6

0.8

1

1.2

1.4

pTmax[GeV/c]

MC/Data

b

b

b

bbb b

b b b b b b b bb

b

CMS datab


10−2

10−1

1

TransMIN charged particle density√s = 7 TeV

(1/Neven

ts)dNch/d

ηd

φ

5 10 15 20 25

0.6

0.8

1

1.2

1.4

pTmax[GeV/c]

MC/Data

No hope to get the measurements well described altogether


Why do we actually tune?

Not only for fun!

1 Correct description of the dataPile-up simulationEvaluation of detector effects and unfoldingEstimation of background (in MC-driven approach)Models are not ”allowed” to fail

2 Good physics predictionsCorrect evaluation of physics effectsModels are ”allowed” to fail

The danger is overtuning!


Review of nal-state structure of pp interactions at the LHC · Review of nal-state structure of pp...

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