introduction to neutrino event generator...ν ∈ (100 mev, ~tev ) • target nucleus used:...

Introduction to Neutrino Event Generator

NguyenThi HongVanIFIRSE,Quy Nhon

VSoN 2018

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Neutrino Physics: current status and open questions

• Observation of 𝜈𝑜𝑠𝑐𝑖𝑙𝑙𝑎𝑡𝑖𝑜𝑛𝑠à Neutrinos have masses àexistence of physics beyond SM : impact on particle phys, astroparticle phys. And cosmology.

• There are still many unknown problems with neutrinos:• What are masses of neutrinos?• Are neutrinos their own anti-particles? (Majorana or Dirac particles)?

• What is the neutrino mass hierarchy?• Is there CP-violation in leptonic sector?• Are there more than three neutrinos?• Why are neutrinos much lighter than other fermions?

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SearchwithBetaandDoubleBetadecays

SearchwithNeutrinooscillationexperiments

Phys. Tasks at neutrino oscillation experiments• Studyingνμ à νe transition(appearance)andνμ à νμ transition(dis-appearance)forbothneutrinoandanti-neutrinomodes.

• Understandingofdifferencesobservedbetweenneutrinosandantineutrinosinacceleratorexperiments.

• Measurementofθ13 mixingangle.• Precisionmeasurementsofotheroscillationparameters(∆m2

32,θ23,isθ23 maximal?).• SearchingforCPviolationintheleptonicsector.

• Searchingforthesignof∆m232.

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Tasks of Neutrino event generators• Simulate neutrino interactions: each generator is expected to simulate all

possible interactions using appropriate models. • Simulate signals and backgrounds observed in the detector à background

can be extracted from real data.• A bridge to compare between real data and theories in order to extract

neutrino oscillation parameters.• Reduce systematic uncertainties in measuring physics observation by

reducing uncertainties caused by the understanding of neutrino interactionswith nucleus.è precision of the Nu event generators is required to better understand

neutrino interactions.• Can be used to evaluate systematic uncertainties in extracting the physicsresults.

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Neutrino event generators

• What?àNeutrinoeventgeneratorsaresoftwares simulatingneutrinointeractions.

• Howdotheywork?

Inputs OutputsNeutrinoEvent

Generatorsq Neutrinotypeq Targetq Nuenergyorfluxq Interactionmodeq Otherparameters

…

NEUT,GENIE,Neugen,NuWro,GiBUU,…

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q ROOT fileq Kinematics of

out-going particlesq Other variablesq …

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Examples of Neutrino Event Generators

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NEUT• Developped initially for Kamiokande exp. then for Super-K, K2K, SciBooNE and T2K.• Used for Super-K and T2K MC official production• Mainly written in Fortran

GENIE• Developed by an international collaboration• Universal neutrino event generator• Written in C++ and well maintained, open source

NuWro• More theory oriented. Developed by people from Wroclaw University• Written in C++.

Challenges with Neutrino Scattering

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• 𝒱 beams are not mono-energeticà 𝒱 flux, and at a given E𝒱, there

is a contribution from multi processes.• 𝒱 cross-section is not well-constrained

in a region interested.• Targets used in 𝒱 experiments are

nucleus à nuclear effects are included in cross-section and kinematics of out-going particles: à MC generators need to be included

these effects.

Neutrino flux and cross-section

• Frequency of neutrino interations when the flux is uniform:

f = 𝜙 1𝑡𝑖𝑚𝑒∗𝑎𝑟𝑒𝑎2

∗ 𝑁 ∗ 𝜎[𝑎𝑟𝑒𝑎2]

• In reality, 𝒱flux is non-monoenergetic: f = N *∫ dE𝒱 𝜙(E𝒱) * 𝜎(𝐸𝒱)• Neutrino event generators are used to predict flux, to simulate

detector response and to generate interactions.

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Cross-sectionNumberofscatteringcentersFlux

Example of Neutrino flux and Event rate

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T2KINGRID

T2KINGRID

Flux EventRate=FluxxCross-section

Cross-section of neutrino-nucleus interaction

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• For a (A,Z) nuclear, the cross section of neutrino-nucleus interaction is incoherent sum of the interaction probability on each single nucleon in the nucleus.

Impulse Approximation:

• Neuclons aremadeofquarksà needformfactor

• Hadronic degreesoffreedomcanbe:quarks,nucleons,nuclei.

Basic Neutrino interactions

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Charge Current Quasi Elastic (CCQE) Neuclon changes but doesn’t break-up 𝓥 + n à ℓ − +𝒑

CCSingleMesonResonance(RES)Neuclon excitestoresonancestates𝓥 +Nà ℓ − +N’+𝝅(𝜼, 𝜥)

DeepInelasticScatteringNeuclon breaksup

𝓥 +Nà ℓ − +N’+m.𝝅(𝜼, 𝜥)

Cross-sectionofNeutrinoandAnti-neutrino

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Cross-section calculated by NUANCE

FromSamZeller,basedonP.Liparietal,Phys.Rev.Lett.74(1995)4384

• Eν in (100 MeV, 1 GeV): Cross-sections are predicted with a precision of about 20-30%• Eν in(1 GeV, 10 GeV): all types of interaction are important!• Eν> 10 GeV: cross-section is proportional to Eν

Procedures of Neutrino Event Generation

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AtmosphericneutrinoFluxCross-Section1. Fix the energy of

neutrino:

Distribution of E𝓥 can be determined from 𝓥flux andTotal 𝓥 cross-section:𝜙(E𝒱) * 𝜎(𝐸𝒱)

Procedures of the neutrino event generation

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2.Fixtheinteractionmode:

• Interaction mode is selected by using the each individual interaction cross-section

• In order to select one of the Interactions it is necessary to know the cross-sections for each mode.

From Hayato

Procedures of the neutrino event generation

3. Simulate primary interaction:

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• Fix the number of particles in the final state• Fix the types and 4-momenta ( direction ) of each particle

4. Simulate secondary interaction in nucleus• Simulate the interaction in the target nucleus • Fix the properties of each particle outside of the target

nucleus.

Neutrino Interactions: go into details1. Charged current quasi-elastic scattering: 𝓥µ+ n →µ- + p2. Neutral current elastic scattering: 𝓥µ + N à 𝓥µ + N3. Single π,η,K resonance productions: 𝓥µ + N à l + N’ + π (η, K)4. Coherent pion productions: 𝓥µ + X à 𝓥µ + X + π0

5. Deep inelastic scattering : 𝓥µ + N à l + N’ + mπ(η,K)

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l: lepton; N, N’: nuclons; m: integer Pion (π)

π +(ud); π-(du)π0 (uu /dd)Mπ ~ 140 MeV

Eta (η)

η = 𝑢u+dd−2𝑠s6

Mη ~ 548 MeV

Kaon (K)K+ = us;K- = suK0 = ds/sdmK ~ 495 MeV

Proton(p)p =uudmp ~940MeV

Neutron (n)n = uddmn ~ 940 MeV

Neutrino interactions: Feynman Diagram

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CCQE

𝓥µ+ n →µ- + p

CC1pi

𝓥µ + N à l + N’ + π (η, K)

Basics of kinematic variables

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FromJ.Zmuda

Basics of kinematics: convenient variables

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FromHayato Q2[GeV]

W[GeV]

NEUTCC1pi

Q2 vsW

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Neutrino Interactions: Quasi-Elastic Scattering

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W+

n

CCQE

NCQE

• Quasi-elastic (QE) scattering can produce a single lepton and a single nuclon.

• QE scattering is an important channel for ν oscillation experiments:

• QE gives largest contribution to the cross-sectionof neutrino-nucleon interaction in a low region energy of neutrino ( < 1 GeV ).

• QE is two body reaction à the incident neutrino energy can be reconstructed from kinematics of the charged lepton.

CCQE: incident neutrino energy reconstructed

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FromHayato

CC Quasi Elastic Scattering

• Cross-sectioncalculatedfromtheory:Freenucleon:C.H.L.Smith,Phys.Rep.3,261(1972)

• (Phys.Rep.3,261(1972))

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MV = 0.84 GeV/c2

AxialFormFactorVector Form Factor

Nuclons aremadeofquarksàparameterizedwithFormFactor

In NEUT: MA = 1.1 or 1.2 GeV/c2

CC Quasi Elastic Scattering

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MA = 1.21 MA = 1.21

Cross-section from NEUTNeutrino mode Anti-neutrino mode

Neutrino Interactions: single pion production

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Charged Current

Neutral Currentν + N à ℓ(ν) +N∗

𝜋(𝛾) + 𝑁′

Excitation of baryon resonance

Decay of baryon resonance

Neutrino Interactions: single pion production

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Charged Current

Neutral Current

ν + N à ℓ(ν) +N∗𝜋(𝛾) + 𝑁′

Main background of the nucleon decay:Particles in the final state are the same as the ones from nucleon decay

Main background for the search of νµ à νe at T2KIn the NC scattering, π0 and γproductioncan be mimicked as νe

Major contamination to the energy spectrum measurementIn the CC scattering, 𝜋 production can be absorbed in the nucleus:

• 𝜋 can be considered as missing energy, à background in searching for νμ à νμ disappearance

• CC1pi can be mimicked as CCQE.

Single meson and photon production via resonance

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ν + N à ℓ + Δ(N*)N’ + 𝜋(Κ, 𝜂)

ν + N à ℓ + Δ(N*)Κ + Λ

ν + N à ℓ + Δ(N*)N’ + 𝛾

Can be background of the ν𝜇à νe appearance ! 𝛾

Meson

Photon

𝑫𝒆𝒍𝒕𝒂 𝜟Δ++ =uuu;Δ+ =uudΔ0=udd;Δ- =dddmΔ =1232MeV

Single meson production via resonance

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Eν [GeV] Eν [GeV]

ν + N à ℓ + ΔN’ + 𝜋

Effect of Delta absorbtion is about 20%

Deep InelasticScattering

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ν + N àl + hadrons

Hadrons

• Understood as neutrino – quar interaction. • A dominant interaction in high Eν region (>

several GeV).• Eν is calculated as energy of lepton +

energy of hadrons.

Coherent pion production

• ν +Xàν +X+π0

• Pionproduction without breaking the target nucleus. • Cross-section is smaller than the resonance-mediated

production. • Recently,cross-sectionofchargedcurrentcoherentpionproduction(ν + 12Cà l± + 12C+π0)wasfoundtobeverysmallin~<GeV region.

• Experimently observed in higher Eν

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νν

π

Go in to detail with NEUT

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Introduction to NEUT• NEUT is a program simulating neutrino interactions with

Eν ∈ (100 MeV, ~TeV)• Target nucleus used: primarily proton and Oxygen then also rather well

tested with Carbon ( at K2K, SciBooNE )

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Works carriedoutbyNEUT:• Provide cross-sections to estimate the interaction rates or to select the

interaction mode.• Simulates primary neutrino interaction with nucleon and nucleus targets.• Simulates meson interactions in the target, especially in detail for the low

momentum pion.• Simulates nucleon re-scattering in the target nucleus.

NEUT: Summary of interaction modes• Quasi elastic scattering (QE):

• Models: Llewellyn-Smith (Nucl.Phys.B43 605(1972),erratum-ibid.B101 547(1975)).• MA = 1.1 or 1.2 GeV/c for form factor

• Meson production via resonance (RES)• Models: Rein & Sehgal (Ann. of Phys. 133(1981))• MA is set to be 1.1 or 1.2 GeV/c• Recently Δà N𝛾 decay is considered.

• Pion coherent (COH) • Models: Rein & Sehgal (Nucl.Phys.B223:29,1983)

• Deep inelastic scattering (DIS)• GRV94 pdf with Bodek-Yang correction• GRV98 pdf with Bodek-Yang correction7/10/18 NTHVan- VSoN2 33

Practice with NEUT: download and install

• Download: NEUT can be checked out from assembla via svn with a permission of Hayato (hayato@icrr.u-tokyo.ac.jp):

• svn co https://subversion.assembla.com/svn/neut−devel/tags/neut_5.4.0

• Required environment for NEUT installation: need to install CERNLIB and ROOT.

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NEUT: how does it work?

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NEUT inputs: card file

• Thecardfileisusedtospecifythedifferentmodels,parameters,andmodesthatNEUTcanrunwith

• Inputparametersaredefinedincardfileslocatedhere:src/neutsmpl/Cards/

• Whensettingupyourcardfile,checkcarefullythat:

• Your parameter starts at the first column• There is no “C” in front of the line

(otherwise it will be considered as a comment).

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NEUT inputs: card fileOutputparameters:

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• EVCT-NEVT:Thenumberofeventstogenerate.• NEUT-RAND:Howtoseedtherandomnumber

generator:1togenerateaseedfromtheclock,2toreadinfromafile.

• NEUT-QUIET:Verbositylevel:0-2(0printseverything,1printsinteractionmodeandneutrinoenergy,2printsmainlyPythiaoutput).

TargetParameters• NEUT-NUMBNDN:Thenumberofbound

neutronsinthematerial.Foranucleus,simplythenumberofneutronsinthenucleus.

• NEUT-NUMBNDP:Thenumberofboundprotonsinthematerial.

• NEUT-NUMATOM:Theatomicmassnumberofthenucleus(NUMATOM=NUMBNDN+NUMBNDP)

• NUCRES-RESCAT:Setto1(default)toincludenuclearre-scatteringefects (finalstateinteractions)ashadronicparticlesleavethenucleus.

• NEUT-NUMFREP:Thenumberoffreeprotons.AsNEUTisdesignedforwater,itallowsformoleculeswithhydrogenatoms.Thesearetreatedasfreeprotons

NEUT inputs: CardfileBeamParameters

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• EVCT-IDPT: The pdg code of the incoming neutrino type (±12,±14,±16).• EVCT-MPV: Option for neutrino momentum selection. Set to 1 for a fixed momentum, 2

to select from a uniform flat distribution, and 3 to select from an input flux histogram.• EVCT-PV: When using a monochromatic beam, select the neutrino energy in MeV.

When using a flat distribution, set EVCT-PV min max (again, in MeV).• EVCT-FILENM: Input filename for flux histogram.• EVCT-HISTNM: Name of histogram in flux input file.• EVCT-INMEV: Set to 0 if the flux histogram is in GeV, or 1 if it is in MeV.• EVCT-MDIR: Set to 1 to use a fixed direction beam, 2 to use a random direction for

each event.• EVCT-DIR: Define the beam direction x y z.

NEUT inputs

• NEUT-MODE 0 : all interactions selected• NEUT-MODE > 0 : neutrino mode• NEUT-MODE < 0: anti-neutrino mode• 0 < |NEUT-MODE|< 30: CC interactions• 30 < |NEUT-MODE|<60: NC interactions• NEUT-MODE = -1: select all modes with

their weights set in NEUT-CRS (for neutrino) and NEUT-CRSB (for anti-neutrino)

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Interaction modes

NEUT inputs

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Procedure of generating neutrino events

1. Reads the card file with neutcore/necard.F2. Fills the interaction model with neutcore/nefillmodel.F3. Creates the root output file4. Read input flux histogram (if any)5. Start the loop over the generated events

• Set the vertex position; the neutrino direction and energy.• Draw the event rate (if there is an input flux histogram)• Generate events with neutsmpl/nevecgen.F• Call neutcore/nevent.F to compute the kinematics for each event• Consider other effects (radiative corrections, nucleon re-scattering)

6. Saves all the infomation in the ROOT output file

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Usingthisexecutable“neutroot2”in src/neutsmpl/

Practice with NEUT: basic steps1. ssh –X –Y -p 7022 vson@iop1.myftp.org pass: vson12342. Go to “groupA/neut_5.4.0 ”3. Set up environment: source setup_env_neut540.sh4. go to src/neutsmpl5. Run compilation: /bin/csh Makeneutsmpl.csh6. If the installation is successful, in side the “src/neutsmpl” directory there

should be a binary file named “neutroot” or “neutroot2”.7. Generate neutrino events: . / neutroot2 cardfile.card output.root 8. Analyzing the output using basic_histo.cc:

make basic_histos ./basic_histo input_file.root output_file.root

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Practice with NEUT: define parameters in card fileWe have 4 groups: run with default card of Neut_5.4.0 and for CCQE: “neut_5.4.0/src/neutsmpl/Cards/neut_5.4.0_nd5_C_ccqe.card”• Group A: neutrino mode, off axis flux flux: nd5_tuned13av1.1_13anom_run1-7c_fine.root, histo: enu_nd5_tuned13a_numu• Group B: neutrino mode, on axis fluxflux: nd34_tuned_11bv3.1_250ka.root, histo: ing3_tune_numu• Group C: anti-neutrino mode, off axis flux flux: nd5_tuned13av1.1_13anom_run5c-7b_antinumode_fine.root, histo: enu_nd5_tuned13a_numub• Group D: anti-neutrino mode, on axis flux flux: run5c_tune_INGRID_13a_1_1.root), histo: ing3_tune_numub

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Practice with NEUT: Analyze the output

• Consult“neut_5.4.0/src/neutsmpl/basic_histos.cc” asarootmacroforanalyzingtheoutputfiletocreatebasichistograms.

• “vectorbranch”,whichcontainsinformationabouttheincomingandoutgoingparticles.

• “vertexbranch”:forinteractionvertexinformation.• Gettingtheparticlesinformation:

• nvect->Npart():numberofparticlesineachevent• vect->PartInfo(p_index):togettheinfoofeachparticleofindex“p_index”:

• vect->PartInfo(p_index)->fP:momentum4-vector• vect->PartInfo(p_index->fPID:pdg codeofparticle• ….

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PracticewithNEUT:Analyzetheoutput

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LoadNEUTlibraries

OpentheoutputFilecreatedbyneutroot2 Linkthebranches

Practice with NEUT: Analyze the output

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Defineyourhistograms

PracticewithNEUT:Analyzetheoutput

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Loop over events

Loop over all particles in an event

Fillyourhistograms

PracticewithNEUT:Analyzetheoutput

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Openafiletosavehistograms

Save your histograms

PracticewithNEUT:analyzetheoutput

• root-b-q'make_histos_standalone_neut540_ccqe_simple.cc(“your-root-file-from-NEUT.root”,”your-root-file-save-basic-histograms.root")'

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Back-upSlides

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HistograminROOT

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