Charge Symmetry Breaking In The Dd 4Heπ Reaction With WASA-at-COSY
Charge symmetry breaking in the dd 4Heπ0reaction with WASA-at-COSYMitglied der Helmholtz-GemeinschaftMaria Ż urek for the WASA-at-COSY CollaborationInstitute for Nuclear PhysicsForschungszentrum Jülich, GermanyInternational School of Nuclear Physics, 37th Course, Erice-Sicily
2Isospin SymmetryIsospin symmetry - Two sources of violation: Electromagnetic interactionLightest quark mass difference Window for probing quark mass ratiosNucleon mass difference: mn mp, static isospin symmetry breakingΔMpn ΔMem ΔMstr-0.7 0.3 MeV (from QED calculations)2.05 0.3 MeV (ΔMpn - ΔMem )Acces to ΔMstrEffective field theory: dynamic ISBπN scattering lengthe.g. a(π0p) - a(π0n) f(ΔMstr) (Weinberg 1977)Mitglied der Helmholtz-Gemeinschaft However: No direct measurement of π0N Large e.m. corrections in π N Latice (17)(24)–1.00(07)(14)Sz. Borsanyi at al., Science 27 March 2015Ab initio calculation of the neutron-proton mass differenceπNN production vertex20.09.2015M. Żurek - CSB with WASA2
3Charge Symmetry BreakingIsospin Symmetry BreakingDominated by pion mass difference Δmπ - e.m. effect Charge Symmetry BreakingSymmetry under the operation of PCS e iτ 2 π /2- Δmπ does not contributenp dπ0 forward-backward asymmetry Afb [1]ΔMstr (1.5 0.8 (exp.) 0.5 (th.)) MeV (LO) [2] dd 4He π0CSC σ 0CSB σ 0, σ MCSB 2σtotal measured at treshold [3]40p-wavecontributionindd HeπΧPTResult consistentat higher excess energies neededwith s-wave productionMitglied der Helmholtz-Gemeinschaft [1] Opper et al. PRL 91 (2003) 212302[3] Stephenson et al. PRL 91 (2003) 14230220.09.2015[2] Filin et al. Phys. Lett. B681 (2009) 423M. Żurek - CSB with WASA3
4WASA-at-COSY experimentHe4He3dd π0 (γγ)4HeBackground: dd (pnd,pnpn,tp) π0 dd 3Henπ0 (3·105 higher) dd 4Heγγ (physics background)Mitglied der Helmholtz-GemeinschaftFirst beam time in 2008 (2 weeks) Goal: σtotal @ Q 60 MeVAnalysis4He-3He separation: overall kinematic fit 2 hypotheses fitted: dd 4Heγγ and dd 3Henγγ (no constrain on π0) Optimized cuts on cumulated probability distribution20.09.2015M. Żurek - CSB with WASA4
5dd 3Henπ0 reaction measurementTwo-fold model ansatz:30 Quasi-free contribution: dd Heπ nspec Partial waves decomposition of the 3-body final state (limited to L 1)σtot (2.89 0.01stat 0.06sys 0.29norm) µbModel used for simulatingthe dd 3Henπ0 backgroundand for normalizationHefull modelincoherent sum3M3Henθpθqbeam πdirection0nφ3Heπ04 independent variables M3Hen, θp, θq, φquasi-freeMitglied der Helmholtz-Gemeinschaft3-bodyPhys. Rev. C 88 (2013) 01400420.09.2015M. Żurek - CSB with WASA5
6dd 4Heπ0 reaction measurementResults:Heπ04σtot/4π3Mitglied der Helmholtz-Gemeinschaft4LegendrePolynomialsP0 P2no acceptanceno acceptancePhys. Lett. B 739 (2014) 44–49Henπ0HeγγTotal cross section:Fit including p-wave:Heπ0: σ (118 18stat 13sys 8ext) pb4Heγγ: σ (920 70stat 100sys 70ext) pbdσ/dΩ (9.8 2.6) pb/sr · P0(cosθ*) (9.5 7.4) pb/sr · P2(cosθ*)4consistent with s-wave onlyHowever: not decisive due to limited statistics20.09.2015M. Żurek - CSB with WASA6
7dd 4Heπ0 reaction measurementChallenges: Better 4He-3He separation needed Better energy resolutionSolution:Time-of-Flight (ToF)Remove most of Forward Detectorup to Forward Veto Hodoscope Mitglied der Helmholtz-Gemeinschaft Particle identification methodbased on ToF-ΔEEkin reconstruction using ToF8 week long experimental run with an optimized detector setupGoal: σtotal and angular distribution at Q 60 MeV20.09.2015M. Żurek - CSB with WASA7
8Detector CalibrationToF Calibration dd 3Hen time peak position used Calibrate the data to the MC values for everydetector element as a function of θdd 3HenMitglied der Helmholtz-GemeinschaftdE Calibration Based on ToF MC: dE [GeV] vs ToF [ns] dEGeV(ToF) Data: dE [channels] vs ToF [ns] dEch(ToF) Run-wise correction, θ-dependency correctionKinetic Energy Reconstruction Based on Ekin(ToF1), Ekin(ToF2),Ekin(dEFWC1), Ekin(dEFWC2) χ 2 fit used to obtainthe best matching Ekin20.09.2015M. Żurek - CSB with WASAdEGeV(ToF)8
9Kinematic distributionpreliminaryMitglied der Helmholtz-Gemeinschaftdd 3Henπ0dd 3Henγdd 3Hen2 body reaction dd 3Hen dependency20.09.2015M. Żurek - CSB with WASA9
10Kinematic fit 2 hypotheses fitted: dd 4Heγγ and dd 3Henγγ (no constrain on π0)data data χ2 fit with energymomentum conservationconstrain on the plots: cumulatedprobability distribution for2 fitted hypotheses2D cut on cumulated probability distributionMitglied der Helmholtz-Gemeinschaftdata20.09.2015M. Żurek - CSB with WASA10
11Invariant mass distributionPhys. Lett. B 739 (2014) 44–49preliminaryHeπ04Henπ03HeγγMitglied der Helmholtz-Gemeinschaft4 Further optimization of 2D cut on cumulated probability distribution needed Introduction of ToF based particle identification method planned20.09.2015M. Żurek - CSB with WASA11
12Invariant mass distributionMitglied der Helmholtz-Gemeinschaftpreliminary20.09.2015M. Żurek - CSB with WASA12
13Summary Mitglied der Helmholtz-Gemeinschaft Charge Symmetry Breaking used to access quark mass effectsTheoretical tool: Chiral Perturbation TheoryResults of the dd 3Henπ0 reaction measurement publishedFirst results of the dd 4Heπ0 reaction measurement published Total cross section obtained Angular distribution not decisive to identify p-wave contribution8 weeks production run with an optimized detector setup performed.Data analysis in progress20.09.2015M. Żurek - CSB with WASA13
14Mitglied der Helmholtz-GemeinschaftBackup20.09.2015M. Żurek - CSB with WASA14
15Isospin Symmetry BreakingStatic ISBpion mass difference: m(π ) m(π0) - e.m. effectnucleon mass difference: mn mp – e.m. and strong effectΔMem (-0.7 0.3) MeVΔMstr (2.05 0.3) MeVMitglied der Helmholtz-GemeinschaftDynamic ISBπN scattering length, e.g. a(π0p) - a(π0n) f(ΔMstr)However:no direct measurement of π0Nlarge e.m. corrections in π NπNN production vertex20.09.2015M. Żurek - CSB with WASA15
16Charge Symmetry BreakingMeasurements of CSB observablesnp dπ0 forward-backward asymmetry Afbleading CSB term: πN rescatteringOpper et al., Afb (17.2 8.0 5.5) · 10-3(PRL 91 (2003) 212302)Mitglied der Helmholtz-GemeinschaftPion production in dd 4He π0CSC σ 0CSB σ 0, σ MCSB 2Complementary to np dπ0:different strength of CSB termsdd initial state more demanding20.09.2015Result: Stephenson et al.(PRL 91 (142302) 2003)σtot(Q 1.4 MeV) 12.7 2.2 pbσtot(Q 3.0 MeV) 15.1 3.1 pbResult consistent with s-wave productionM. Żurek - CSB with WASA16
17Next StepsTheory effortTheory collaboration working on a consistent analysis offorward-backward asymmetry in np dπ0 ΔMstr (1.5 0.8 (exp.) 0.5 (th.)) MeVcross section at threshold of dd 4Heπ0Mitglied der Helmholtz-GemeinschaftExperimental inputreaction dynamics of dd 3Henπ0 (CSC)In dd 4Heπ0: A. Nogga et al., Phys. Lett. B 639 (2006) 465Wienberg term is suppressed (NNLO & NNNLO calculations needed)Once the parameters are fixed the p-waves can be predictedparameter free to LO and NLO p-wave contribution in dd 4Heπ0 at higher excess energies NLO calculation expected uncertainty 20% - 30%20.09.2015M. Żurek - CSB with WASA17
18Mitglied der Helmholtz-GemeinschaftThe reaction dd 3Henπ0at pd 1.2 GeV/c20.09.2015M. Żurek - CSB with WASA18
19Data AnalysisBenchmark for 4Heπ0 : clean selection of 3He - π0 coincidences final step: kinematic fit to ensure overall energy and momentum conservation 3.4 x 106 fully reconstructed events, nearly full coverage of Dalitz plotsπHe4Mitglied der Helmholtz-Gemeinschaft020.09.2015 2 coincident photonsin calorimeter 3He in Forward DetectorM. Żurek - CSB with WASA19
20Data AnalysisFurther analysis 3-body final state, unpolarized:9 – 4 – 1 4 independent variablesM3Hen, θp, θq, φdN/dcosθCM / a.u.Luminosity:dd 3He nbased on G.Bizard et al.,Phys. Rev. C22 (1980) 1632 two-fold model ansatz: quasi-free contributiondd 3Heπ0 nspecLint (350 25) nb-1partial waves decomposition of the3-body final state (limited to L 1)full model incoherent sum cos θCMLuminosity determination: two-body reaction dd 3Heninterpolated data fromMitglied der Helmholtz-GemeinschaftHe3M3HenBizard et al., PRC22 (1980) 1632:perfect match of expected angular distributionθpθq0nPhys. Rev. C 88 (2013) 01400420.09.2015beam πdirectionφ3Heπ0M. Żurek - CSB with WASA20
21Resultsqf3-bodyMitglied der Helmholtz-Gemeinschaftσtot (2.89 0.01stat 0.06sys 0.29norm) µbModel used for simulatingthe dd 3Henπ0 backgroundin the dd 4Heπ0 measurementPhys. Rev. C 88 (2013) 01400420.09.2015M. Żurek - CSB with WASA21
22Mitglied der Helmholtz-GemeinschaftThe reaction dd 4Heπ0at pd 1.2 GeV/c20.09.2015M. Żurek - CSB with WASA22
23Experiment and data analysisBeam time in summer 2008Dedicated two-weeks run on dd 4Heπ0Goal: σtotal @ Q 60 MeVIntegrated luminosity L (4909 348sys ) nb-1Mitglied der Helmholtz-Gemeinschaft Conditions tuned to maximum achievable luminosityQuite stable experimental conditions Lavg 4*1030 cm-2s-1 can serve as a realistic basis for future runsExperimental setup: standard WASA setupTrigger: high threshold in FD, 1 neutral in CD – thresholdoptimized to beam intensity of 2-3·1010 deuterons in flat top20.09.2015M. Żurek - CSB with WASA23
24Experiment and data analysisMitglied der Helmholtz-Gemeinschaftdd π0 (γγ)4He20.09.2015Background:dd (pnd,pnpn,tp) π0dd 3Henπ0dd 4Heγγ (physics background)M. Żurek - CSB with WASA24
25Experiment and data analysisIdentification of 4He: weak cut on ΔE–ΔE in FWC and FTHOverall kinematic fit used:2 hypotheses fitted:Mitglied der Helmholtz-Gemeinschaftdd 4Heγγ and dd 3Henγγ (no constraint on 2γ invariant mass)optimized cuts on cumulated probability distributions20.09.2015M. Żurek - CSB with WASA25
26ResultsFitted with MC filtered distibution dd 4Heγγ: homogeneous 3-bodyphase space distributionpreliminaryHeπ04dd 3Henπ0: model from theprevious analysis 34Henπ0Energy dependence:HeγγMitglied der Helmholtz-GemeinschaftpreliminaryPreliminary total cross sections:4Heπ0:σ (118 18stat 13sys 8ext) pb4Heγγ:σ (920 70stat 100sys 70ext) pbMomentum dependence of the formationof the 4He state – not included!20.09.2015M. Żurek - CSB with WASA26
27Results – angular ied der Helmholtz-Gemeinschaftpreliminary20.09.2015M. Żurek - CSB with WASA27
28Resultsσtot/4πLegendrePolynomialsP0 P 2Fit including p-wave:no acceptanceno acceptancepreliminarydσ/dΩ (9.8 2.6) pb/sr · P0(cosθ*) (9.5 7.4) pb/sr · P2(cosθ*) consistent with s-wave onlyMitglied der Helmholtz-GemeinschaftHowever:not decisive due to limited statistics20.09.2015M. Żurek - CSB with WASA28
29Experiment and data analysisMitglied der Helmholtz-GemeinschaftBeam time in spring 2014Dedicated eight week run on dd 4Heπ0Goal: σtotal and angular distribution @ Q 60 MeV Conditions tuned to maximum achievable luminosityQuite stable experimental conditions Experimental setup: modified WASA setupTrigger: high threshold in FD, 1 neutral in CD – thresholdoptimized to beam intensity of 2-3·1010 deuterons in flat top20.09.2015M. Żurek - CSB with WASA29
30Time of Flight CalibrationFWC time readout alignment ToF(FWC1-FWC2) for 3He withθ 5o-6o for every FWC1 and FWC2element Alignament corrections obtained froma set of equations for ToF(FWC1FWC2) for every FWC elementMC: dd 3Hen time peak position for 6 θ-binsdd 3HenData: shitf to value from MC simulationMitglied der Helmholtz-Gemeinschaft1: calibration FVH element wise for 6 θ-bins FVH time readout alignment2: calibration FWC element wise for 18 θ-bins θ-dependency correction20.09.2015M. Żurek - CSB with WASA30
31Energy losses calibration in FWCBased on the ToFMC simulation: dE [GeV] vs ToF [ns] for 3Hein Forward Detector dEGeV(ToF)Data: dE [channels] vs ToF [ns] dEch(ToF)Mitglied der Helmholtz-GemeinschaftdEGeV(ToF)Linear dependency good quenchingsimulation in MC nonlinear responseof PM not visible20.09.2015 dEGeV(ToF(dEch)) dEGeV(dEch)M. Żurek - CSB with WASA31
32Energy losses calibration in FWCfrom MCfrom MCbeginning of the beamtime830 runs after beginning of the beamtime(about ¼ of all runs) Run correction to dE calibration for every FWC1 and FWC2 element need Separate calibration for 2nd part of the beamtimeMitglied der Helmholtz-Gemeinschaftel. 22 fwc2Before correction20.09.2015el. 22 fwc2After correctionM. Żurek - CSB with WASA32
33Kinetic energy calibration Minimization of χ2 : Ekin(ToF1), Ekin(ToF2), Ekin(dEFWC1), Ekin(dEFWC2) dependency from MC Data based uncertainties of ToF(dE) as a function of ToF(dE) (first ineration)6o θ 9oMitglied der Helmholtz-Gemeinschaft6o θ 9o20.09.2015M. Żurek - CSB with WASA33
34ToF vs Energy LossesMitglied der Helmholtz-Gemeinschaftdd 3Henπ0dd Hen320.09.2015dd 3HenγM. Żurek - CSB with WASA34
35Further data analysis Central Detector Calibration – run dependent (Michaela Schever) Kinematic Fit performed for 2 hypothesis:dd 3Henγγ and dd 4Heγγ Error parametrization (MC smearing to match data uncertainties in ToFand dE)Mitglied der Helmholtz-Gemeinschaft Cut on 2 dim spectra of p-value from fit20.09.2015M. Żurek - CSB with WASA35
r H e l m h o l t z-G e m e i n s c h a f t 3 Isospin Symmetry Breaking Dominated by pion mass difference Δm π - e.m. effect Charge Symmetry Breaking Symmetry under the operation of - Δm π does not contribute np dπ0 forward-backward asymmetry A fb [1] ΔM str (1.5 0.8 (exp.) 0.5 (th.)) MeV (LO) [2] dd 4He π0
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