search for heavy neutral lepton: 22q final state - hadronisation … · 2019. 6. 4. · search for...

Search for Heavy neutral lepton: 2µ2q final stateHadronisation study & validation

Haifa Sfar2,1

1Universiteit Antwerpen2CERN

Searching for long-lived particles at the LHC5th workshop of the LHC LLP Community

28-05-2018

Haifa Sfar Search for Heavy neutral lepton: 2µ2q final stateSearching for long-lived particles at the LHC 5th workshop of the LHC LLP Community 28-05-2018 1

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Outline

1 Introduction

2 Problematic

3 Charged Particle Multiplictiy from e+e− Pythia8/Data

4 Charged Particle Multiplictiy from pp (HNL) Pythia8/Data

5 Particle Composition in the Jets at√s = 10.54 GeV from e+e− Data


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IntroductionCharged Particle Multiplicity

the hadronisation model in pythia8 was tuned by studying some observablesof the hadronic Z decays obtained from measurments come from LEP andSLD e+e− annihilation data at

√s = 91.2GeV : the monash 2013 tune.

Good description of charged particle multiplicity at√s = 91.2 GeV.


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IntroductionParticle Composition in the hadronic Z Decays at

√s = 91.2GeV

Good description of particle composition in the jets.If we go at low c.m.energy do we still have a good description of data withthis tuning ?


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IntroductionEnergy scaling

The energy scaling of the monash 2013 Tune is from 14 GeV to 200 GeV.Below the Z pole, the measurements mostly come from TASSOexperiment,few measurements come from HRS(29 GeV) and TOPAZ (57.8GeV).


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Problematic

Charged particles multiplicity is well tuned at√s = 91.2 GeV and scaled from

14 to 200 GeV.Do we have good/reasonable agreement between data and MC for the< NCh > and π±,K± and pp̄ multiplicity measurments below 14 GeV ?We have to compare these measurments quentities from Pythia8.2 with Datafrom e+e− low c.m.energy experiments.


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Previous Experiments : Overview

Different phase spaces were covered by several experiments in the past. Wecite here some of them.

Accelerator Place Dates√s[GeV ] Experiment

ACO LAL, Orsay 1973− 1988 0.5 M3NADONE Frascati 1973 1− 3 MASPEAR SLAC Stanford 1981 2.6− 7.8 SLAC-LBLDORIS DESY 1981 3− 11 PLUTO, LENACESR Cornell 1979 3− 12 CLEO,CUSBPETRA DESY 1980− 1984 12− 47 TASSO,JADESLC SLAC Stanford 1989− 1998 ≈ 91 SLD, MARK IILEP CERN 1989− 2000 88− 209 L3,DELPHIPEPII SLAC 1998− 2008 10.54 BaBarKEKB KEK,Japon 1999− 2008 10.52 Belle


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Charged Particle Multiplictiy : Datae−e+ annihilation process

The phase space from 2.5 to22 GeV c.m.energy is coveredby these experiments :

SPEAR(SLAC-LBL-Mark I)DORIS (LENA)PETRA (JADE)PETRA (TASSO)

These values are fullycorrected to the total phasespace.

fit function

< nch >= a + b × exp (c ×√

ln(s

Λ2 ))

a = 2.5, b = 0.007, c = 2.4, Λ = 0.3 GeV


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Charged Particle Multiplictiy : Datae−e+ annihilation process

We selected several c.m.enery from different experiments to compare withMonte Carlo (MC) pythia8 values.We selected the experiments that cover the needed range and also thesewhich have less systematic uncertainty than others.

Experiment√s < nch > stat uncert syst uncert

SLAC-LBL 2.60 3.75 ±0.42 25%SLAC-LBL 5.10 4.43 ±0.23 25%LENA 9.3 7.28 ±0.11 10%TASSO 14 9.08 ±0.05 ±0.25TASSO 22 11.22 ±0.007 [±0.25,±0.45]JADE 22 10.1 ±0.7 ±0.6


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Charged Particle Multiplictiy : Pythia8.2e−e+ annihilation process

Samples were generated using pythia8.235.It is e−e+ annihilation process with different c.m.energy following to thetable cited in the previous slide.It has the Monash2013 parameters for hadronisation by default.Not possible to go below 5 GeV for such process : Pythia limit.The decay products of KS and Λ are included in this study.


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Charged Particle Multiplictiy : Data + pythia8.2e−e+ annihilation process

We combine pythia results with values from the other experiments, in a wayto reproduce the summarizing plotThe aim of the study at 14 and 22 GeV c.m.energy is to compare our MCresults to the Monash tune results and we can see that they agree.We stopped at 5 GeV because it was not possible to go below that valueusing e−e+.


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Charged Particle Multiplictity Pythia8.2HNL process

The HNL samples used for this analysis are generated by Madgraph +pythia8.2.

Prompt Decay of HNL to Z 0 νµ.Prompt Decay of HNL to W± µ±.The configuration file used to hadronize the LHE files is :Hadronizer_TuneCUETP8M1_13TeV_generic_LHE_pythia8_cff .py .

The decay products of Ks and Λ are included in this study.


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Charged Particle Multiplictity Pythia8 + DataHNL process

< Nch > from W* can not be compared to < Nch > from e−e+ / Z 0. Weaim just to see how it looks like.


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Particle Composition in Jets at√s = 10.54 GeV

The decay products of Ks and Λ are included in this study.


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Particle Composition in Jets at√s = 10.54 GeV

Particle Pythia8.2 BABAR CLEO ARGUS HERWIGπ± 6.061 6.87± 0.11± 0.16 8.3± 0.4 6.38± 0.12 6.31K± 0.9981 0.972± 0.012± 0.016 1.3± 0.2 0.888± 0.030 1.01p/p̄ 0.2838 0.265± 0.008± 0.002 0.40± 0.06 0.271± 0.018 0.46

We have underestimation of π± comparing to Babar of ∼ 9%.Small overestimation p/p̄ ∼ 3%.Good description of K±


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Summary

We have reasonable agreement of charged particles multiplicity with Data.We have understimation of π± of 9% and we have small overestimation p/p̄∼ 3%.Pythia is not appropriate as a dedicated model for physics at energies wellbelow 10 GeV. However it still has decent limits towards low energies 3-10GeV.


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search for heavy neutral lepton: 22q final state - hadronisation … · 2019. 6. 4. · search for...

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