Deutsches Elektronen-Synchrotron(DESY), Hamburg,

NIKHEF, Amsterdam

Double parton scattering session:experimental introduction

Jonathan Gaunt, Paolo Gunnellini

MPI@LHC 2016San Cristobal de las Chiapas

November 2016, Mexico

Paolo Gunnellini MPI@LHC2016 November 2016 1

Introduction and outlook

Many interesting experimental talks:ATLAS results on double parton scattering→ Ewelina LobodzinskaDPS measurements at the CMSexperiment→ Ramandeep KumarMeasurement of four-jet production atCMS→ Paolo GunnelliniStudy of DPS processes at LHCb→ An Liupan

N.B. 17 + 3 min. for each talk!

Prospects for the future:

1 DPS energydependence

2 New sensitivechannels?

3 New sensitiveobservables?

4 New phasespace?

N.B. Very personal and (CMS-) biased view!

Paolo Gunnellini MPI@LHC2016 November 2016 2

Experimental overview

σDPSAB = m

2σAσBσeff

Internal structure of the protonDPS background for any physics channel

→ Which channels can be used to look for DPS signals?

FEATURES OF THE FINAL STATE:

→ High multiplicityof physics objects

Credits: Paolo Bartalini

Paolo Gunnellini MPI@LHC2016 November 2016 3

Is this not a clear evidence of DPS?

ATLAS - CMS: DPS fraction 5-8%→ Diff. cross sections of DPS-sensitive observables

LHCb: DPS fraction 60 - 80%→ Total production cross section for sensitive channels S∆

0 0.5 1 1.5 2 2.5 3

Dat

a / M

C

0.60.8

11.21.41.61.8

22.2

Uncertainty

S∆0 0.5 1 1.5 2 2.5 3

Dat

a / M

C

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Uncertainty

S∆0 0.5 1 1.5 2 2.5 3

Dat

a / M

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Uncertainty

S∆

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S)

∆d(

evt

dN .ev

tN

1

-210

-110

1

-1 Ldt = 5 fb∫ = 7 TeV s CMS

PYTHIA8MADGRAPH5 + PYTHIA8MADGRAPH5 + PYTHIA8, no MPIPOWHEG2 + PYTHIA6POWHEG2 + PYTHIA6, no MPIData

Paolo Gunnellini MPI@LHC2016 November 2016 4

Is this not a clear evidence of DPS?

More results (and new final states) continue to appear

Tplight

rel∆0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

MC

/Dat

a

0.20.40.60.8

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Tp

light

rel

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) d

σ(1

/

-110

1

10

2 b + 2 j + X→ (7 TeV), pp-13 pb

2 b jets: > 20 GeV

Tp

| < 2.4η|

2 other jets: > 20 GeV

Tp

| < 4.7η|

CMS Data

POWHEG+P8 CUETS1 MPI off

Similar amount of DPS contribution as inW+dijet (∼ 7-9%)!

Collection of several measurements (jet, charmand vector-boson sector) allows studies on

channel-dependencePaolo Gunnellini MPI@LHC2016 November 2016 5

Experimental strategy for DPS measurements (I)

Investigation of sensitive channels (same-sign WW, J/ψ+D,Λ)Analysis cuts which increase DPS sensitivity

Currently, measurements scan different (and complementary) regions of phase spacePaolo Gunnellini MPI@LHC2016 November 2016 6

Experimental strategy for DPS measurements (II)

1st step

Correcteddistributions

DPS-sensitivevariables

2nd step

Data interpretationand unambiguous

definitionof signal and

background templates

3rd step

Extraction of the DPSfraction and study of

the processdependence

Compare the data to your own favourite predictions!4th (future) step: possibility to measure sensitive corners of phase space

Paolo Gunnellini MPI@LHC2016 November 2016 7

Role of the quantity σeff

Is the value for σeffa useful input?How can one reducethe exp. unc.?Should one try alsoa global extraction?

Combined extraction in differentchannels/energies?

Paolo Gunnellini MPI@LHC2016 November 2016 8

LHCb results

Focus on associated charm production with some differentialcross sections available→ double J/ψ

→ Z + charm mesons→ Y + charm mesons

From Vanya last year’s MPI@LHC:”10% of ”hard” events has additional charm!”

→ Why does LHCb use the CDF result for σeff ?

→ I had some rumours that some results at 13 TeV will be presented. :)

Paolo Gunnellini MPI@LHC2016 November 2016 9

Status of DPS analysis in Run II

Not much more available at 13 TeV in termsof DPS understanding for the time being!

POSSIBLE (EXPERIMENTAL) REASONS:Poor low-PU runs (∼ 2 pb−1 - in RunI was 36 pb−1)Jets (especially) at low pT not very well understoodPeople are generally happy with evaluation of DPS crosssections for background estimation through the pocketformula → little contamination, large uncertainties for σeffnot an issueMissing person power

Paolo Gunnellini MPI@LHC2016 November 2016 10

Inputs for discussion during conference

HOW TO MAKE DPS ANALYSES(EVEN MORE) ATTRACTIVE?

New ideas and new channels to be looked forDevelopment of new theoretical approachesPossibility of using more sophisticated models to be tested inspecific channelsGoing further: triple parton scattering.... more ideas to be collected during this week’s discussions!

Paolo Gunnellini MPI@LHC2016 November 2016 11

Inputs for discussion during conference

HOW TO MAKE DPS ANALYSES(EVEN MORE) ATTRACTIVE?

New ideas and new channels to be looked forDevelopment of new theoretical approachesPossibility of using more sophisticated models to be tested inspecific channelsGoing further: triple parton scattering.... more ideas to be collected during this week’s discussions!

We hope to have a nice discussion during the DPS session!

Paolo Gunnellini MPI@LHC2016 November 2016 12