Measurement of low energy neutrino cross-sections with the ... - opera

Measurement of low energy neutrino cross-sections with the ... - opera

Measurement of low energy neutrino cross-sectionswith the PEANUT experimentAndrea RussoNapoli Universityon behalf of the PEANUT collaboration

Index• Physics goals of PEANUT experiment• The detector• Emulsion Cloud Chambers• Automated microscopes for emulsion scanning• Data Analysis and Event reconstruction• Monte Carlo simulation of neutrino interactions in thedetector• Cross section measurement• Perspectives of ECC in future ν experiments• Conclusions2

Physics goalsFor Charged Current neutrino interactions three dynamics are possible• Deep Inelastic Scattering (‏DIS‏)‏ , Quasi Elastic Scattering (QE) and(‏RES‏)‏ • Resonance (Delta particle) productionFew GeV region (

Hybrid detector: Emulsion-lead targets and(‏detector scintillating fibre tracker (SFTPEANUT detectorEmulsion-lead targets arehoused in “miniwalls”, made by4 rows and 3columnsPEANUT in thenear detectorhall of MINOSFibre tracker planes (shown in green) trackcharged particles produced in ν interactionswith high precision (a few hundred micron)and providetiming information4NUFACT 09A. Russo– Napoli University

The NuMI beamNuMI neutrino beam uses 120 GeVprotons from the Main Injectoraccelerator, aimed 58 mraddownward towards Soudan mine.NuMI spectum in Low EnergyconfigurationIt can be operated in High Energy,Medium Energy and Low EnergyconfigurationsTotal number of NuMI protons(blue line) and the protonsper week (green) deliveredon the target.5NUFACT 09A. Russo– Napoli University

Emulsion Cloud Chambers (ECC) in PEANUT detectorTarget made of a sandwich of lead plates (passivetarget) and nuclear emulsions (active trackerdetector): Emulsion Cloud ChambersModular detector: each module (calledbrick) is made of a sandwich of 56 leadplates (passive target) and 57 emulsionsfilms.8.3kg10X 0Neutrino Beam75mm125mm100mmECC combines high density of leadand high-precision trackingperformances of emulsion: suitablefor low energy neutrino physicsEmulsion films:300micron thickPb plate : 1mmNUFACT 09A. Russo– Napoli University6

Nuclear emulsion filmsProduced by Fuji Film,same films as in OPERA detectorNuclear emulsion is a film made of AgBrcrystals in organic gelatine. Theyrecord the passage of charged particleswith an accuracy better than 1 μmmipfogcharged particles crossing emulsionsionize AgBr atoms. Fixing anddevelopment treatments turnionized atoms into black grainsCompton electronNUFACT 09A track is defined as a sequence ofaligned black grains(to show the grain density, the pictureshows an exposure parallel to the film)• sensitivity~ 36 grains per 100 µm for mip tracks• background~ 9 grains per 1000 μm 37A. Russo– Napoli University

European Scanning System (ESS)Emulsion ScanningS-UTS (Japan)Design based on two different approachesCommercial hardware,software-based approachHard-coded algorithmPerformances:>90% tracking efficiency for small angle tracksSpatial and angular resolutions are ≅1μm , ≅2 mrad8NUFACT 09A. Russo– Napoli University

Reconstruction of neutrino events in PEANUT• Trigger + select events “on time” with NuMI beam spill cycle• Electronic detector information are processed by a software reconstruction program that reconstructscharged tracks crossing the detector– After a few weeks exposure, bricks were removed from the detector, exposed to cosmic rays, anddeveloped• Two analysis procedures were followed1) Scanback analysis:Bricks analysis• Scanning of the two most downstream films of the bricks in search for tracks related to neutrino events(confirmed by SFT).• These tracks are followed up in the brick up to the neutrino interaction vertex• neutrino vertex reconstruction2) General scan• Full surface scanning of all the films of the brick and reconstruction of all neutrino event candidates• Selection of neutrino events on the basis of the confirmation of SFTThese two procedure allow to select CC neutrino interactions with a purity ≅98%NUFACT 09A. Russo– Napoli University9

Scan-back approachEmulsion track matchedwith SFT detector,followed up to the νinteraction pointν vertexGeneral-scan approachLarge surface scanning3D Track reconstructionin emulsionNeutrino vertexreconstruction10NUFACT 09A. Russo– Napoli University

Neutrino events in PEANUT: an exampleHits in scintillatingfibre planes andreconstructed tracksSame eventreconstructed inemulsion11NUFACT 09A. Russo– Napoli University

Neutrino event data and MC-data comparisonData-MC comparison performed on all aspects of the reconstruction of ν eventsDetailed MC study shows thatour ν event selection is strongly biasedin favour of CC interactions even withoutmuon identification. Contaminationfrom NC events is reduced from ≅17%to ≅1% requiring ν event candidates tobe confirmed by SFTIngredients of MC:•70% DIS, 19% QE, 11% RES•No neutral current eventsMultiplicity of SFT tracks in ν eventsSFT data reconstructionResiduals between SFT and emulsion tracksDataMC12NUFACT 09A. Russo– Napoli University

Neutrino event data and MC-data comparisonDataMCMuon slope distribution(muon defined as emulsiontrack in ν event matched withSFT track. This selection(‏purity ensures ≅98%Charged multiplicityat neutrino verticesDataMC13NUFACT 09A. Russo– Napoli University

Cross-section measurements• The measured charged multiplicity distribution is sensitive to the ratio of DIS, QE and RES wrt tothe total CC cross section• These ratios can be obtained minimizing the difference between the multiplicity distributions in MCand data, with the ratio of Resonances to Quasi Elastic kept fixed to 0.58. The ratio of DIS wrt tototal CC cross section acts as a free parameter in this minimization• The best-fit values are:f QE= 0.20 +0.06 -0.07(‏‎0.02(syst (stat) ±f DIS= 0.68 +0.09 -0,07(‏‎0.02(syst (stat) ±f RES(‏‎0.02(syst 0.04(stat) ± = 0.12 ±The expected values are (see Phys. Lett. B66 (1977) 291, Phys. Rev. D23 (1981) 2499, Phys. Lett. B78(1978) 510):f QE= 0.19 ± 0.04f DIS= 0.70 ± 0.04f RES= 0.11 ± 0.02The main source of systematic error comesfrom the uncertainty on the ratio RES/QE14NUFACT 09A. Russo– Napoli University

Perspectives of ECC in future ν experimentsECC could be used to study few GeVs neutrino beams (currentlydone in T2K). Micrometric resolution of emulsion allows to measureprecisely:1) neutrino event topology2) pseudo-rapidity distributions of charged particles(‏μm‏)‏ Track position resolution(‏mrad‏)‏ Track slope resolutionCross section measurements:In PEANUT QE,RES and DIS cross sections measured with ≅15%(‏statistics precision (precision limited by15NUFACT 09A. Russo– Napoli University

Kinematical measurements in ECCRelevant kinematical variables (i.e. P T, hadron momentum distribution, energy ofelectromagnetic component of shower) in ν interactions can be measuredMultiple Coulomb Scattering in lead plates exploited in momentum measurementΘ 2 = δ 2 + (14MeV/βp) 2 X/X 0Coulomb scattering term(‏mrad Measurement error (≅2Transverse angular deviationAn ECC is ≅ 10 X 0charged-particle momentum canbe measured withprecision < 25% up to 4GeV(‏‎1/P(GeVExample: momentummeasurement for4GeV simulatedpions in ECC16NUFACT 09A. Russo– Napoli University

Neutrino beam monitoringBoth ν μand ν edetectable in ECCfew percents contamination in non pure ν beams measurableReconstruction of electromagneticshowersin emulsion: a 6GeV electronshown hereΑ few ν ecandidatesfound in PEANUT bricksNeural network approach allows to have>90% efficiency and 2GeV e.m. showersNUFACT 09See JINST 2:P02001,2007A. Russo– Napoli University17

Conclusions• PEANUT experiment was designed to investigate neutrino interactions at low energies (i.e. few(‏GeV• Hybrid detector: scintillating fibre tracker and ECC target• A sample of 147 ν μCC events has been analysed• MC simulation based on the neutrino event generator used in the OPERA experiment (optimized onthe data of NOMAD experiment) shows good agreement between data and the expectations• Charged multiplicity in ν μCC interactions has been measured and DIS, RES, and QE contributionsto total CC cross section has been estimated. All values are compatible with expectations based onpast measurements• A paper on PEANUT results is in preparation• This kind of detector can be used to monitor ν beams in future experiments• Cross sections, relevant topological and kinematical variables, v econtamination in non pure beamscan be measured18


Emulsion ScanningTwo scanning systems, developed byEuropean and Japanese scanninglaboratoriesEuropean Scanning System (ESS)S-UTS (Japan)20

Monte Carlo simulationA dedicated Monte Carlo simulation is used to estimate the performances ofPEANUT detector. It provides both:1. Simulation of ECC targets2. Simulation of Scintillating Fiber TrackerHits inemulsiondetectorHits in theelectronicdetector21

Vertices' distribution in brickz vertexdataMean = -3.5*10e4 μmRMS = 1.8*10e4 μmExpectedMean = -3.8*10e4 μmRMS = 1.9*10e4 μmExpectedMeanX = 6.0*10e4 μmRMSX = 3.3*10e4 μmMeanY = 5.0*10e4 μmRMSY = 2.8*10e4 μm22

(‏detector MC Data comparison (electronicTX angle distributionMCDATATY angle distribution23

(‏ESS‏)‏ The European Scanning SystemDeveloped by European emulsion laboratories:scanning speed: ~ 20 cm 2 /hspatial precision: ~ 0.5 μmZ stage (Micos)0.05 μm resolutionCMOS cameraFull Camera Link1280×1024 pixels256 gray levelsEmulsion filmOptical system:50x objectiveXY stage (Micos)0.1 μm resolution24

Performances of the ESSScanning speed: 20 cm 2 /h/side(‏μm‏)‏ Position resolutionTracking efficiency up to 95%for small angle tracksEfficiency(‏μm‏)‏ Angular resolution25

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