Studia symulacyjne

1. Studia symulacyjne Rekonstrukcja energii, Q2, przypadki wielopionowe Paweł Przewłocki Warszawska Grupa Neutrinowa

2. Pomiary związane z ND280 • Spektrum energetyczne • Metody rekonstrukcji energii neutrina • Badanie tła pochodzącego od produkcji pizer w oddziaływaniach NC • Szacowanie przekrojów czynnych NCpizero na podstawie CCpi+ (łatwiej rekonstruowalne) • Tło pizerowe w SuperK – przypadki wielopionowe

3. Generator and statistics • Generator: Nuance 3.006 • Medium: water • With and without nuclear reinteractions (FSIs) • 500,000 evts generated • 210873 cc and 83378 nc events – QE • 112776 cc  and 42856 nc events – RES • 27187 cc  and 9250 nc events – DIS • And others, more exotic (diffractive, coherent, elastic on electrons)

4. Beam structure (after interactions) All QE All DIS

5. Neutrino energy reconstruction • Via total momentum • Sum of outgoing particles’ momenta should give us momentum of the neutrino (assuming the nucleon is at rest – no fermi momentum) • For QE we’ve got another formula • We also assume no fermi momentum here and a clean QE event – muon and proton only ν Outgoing particles) μ θ ν p

6. Advantages and drawbacks • QE formula needs only observables associated with muon track – but it is in principle valid only for QE interactions • QE formula is therefore senseless for NC events – no muon • Total momentum formula suffers from the fact that not all the final states are visible in the detector • Both methods are impaired by neglecting the fermi motion of the target nucleon (this results in some smearing of the reconstructed energy) • What particles are visible – first guess: muons, electrons, protons, pizeros, pi charged

7. True (MC) vs total mom (no FSI) • All particles visible – just to show that it works (smearing due to Fermi motion) Ereco [GeV] Ereco [GeV] Solid – MC Energy Dashed - reconstructed Solid – MC Energy Dashed - reconstructed [GeV] E MC [GeV]

8. True (MC) vs total mom vis(no FSI) Visibility as described before Ereco [GeV] Solid – MC Energy Dashed - reconstructed [GeV] E MC [GeV] Totally invisible events (NC of course, CC have at least a muon)

9. True (MC) vs QE formula (no FSI) CC events only Ereco [GeV] Solid – MC Energy Dashed - reconstructed E MC [GeV]

10. Wondering which are QEs and which nonQEs on the scatterplot? Orange dots denote ideal reconstruction nonQEs QEs The large smearing here is because of Fermi motion (apart from the fact that Nuance includes deexcitation particles in the final state but this is negligible)

11. Quality of reconstruction plots Total mom vis All evts QE formula CC Ereco - EMC

12. Quality of reconstruction comparison Solid – QE formula, Dashed – Total visible momentum CC QE CC, all channels QE formula works better for QE, total momentum is better for others

13. The problem • Sometimes the reconstruction error is REALLY huge: diff: 167.7042 enu (reco): 170.1219 cos: -0.8033161 pmu: 0.5125948 14 0.1056796E-06 0.000000 2.417668 2.417668 2112 -0.9664943E-02 -0.1033968 -0.1701247 0.9334740 0.1993157 13 0.7104180E-01 -0.2968962 -0.4117757 0.5233710 0.5125948 2212 -0.8070657E-01 0.1934993 2.659319 2.827771 2.667571 22 -0.4696306E-02 0.1602426E-03 -0.4013904E-02 0.6180000E-02 0.6180000E-02 id px py pz E p the difference Surprisingly large error in comparison with the Fermi motion distorsion (max. ~250MeV)

14. Investigation • Simple QE simulator with and without Fermi motion • Fermi motion in [0, 250MeV] • Incoming neutrino energy in [0, 5GeV] CMS Muon and proton Neutrino plus proton

15. Muon cosine vs muon momentum cos cos No fermi smearing Fermi max 250MeV P [GeV] P [GeV]

16. Muon pz vs muon momentum smearing Fermi max 250MeV No fermi

17. No doubts where the smearing comes from Fermi max 1GeV

18. Does this cause the errors? • Average error as a function of total muon momentum, in the region denoted on slide 6 Error in % Multiplicity in the same bins Error (forget the bars)

19. Does this cause the errors? • Average error as a function of sine of ‘angle’ on pz vs p plot Error in % sine sine Multiplicity in the same bins Error (forget the bars)

20. Rozwiązanie • Wyjście poza obszar dozwolony powoduje niekontrolowane zachowanie się mianownika we wzorze rekonstrukcyjnym • Powinniśmy brać pod uwagę te przypadki, które znajdują się w obszarze dozwolonym • Dla naszej próbki błąd powyżej +50% ma 0.6% przypadków

21. Rekonstrukcja Q2 • Badanie tła pochodzącego od produkcji pizer w oddziaływaniach NC • Szacowanie przekrojów czynnych NCpizero na podstawie CCpi+ (łatwiej rekonstruowalne) • Źródła różnic w rozkładach qsq dla przypadków pizerowych i pi+ • Różnice teoretyczne • Różnice wynikające z pędu Fermiego i FSI

22. Qsquare considerations Outgoing lepton Neutrino Qsq = four-momentum transfer Nucleon • Ideal qsquare – from lepton vertex • Observable qsquare – from hadron vertex, assuming nucleon doesn’t have a fermi momentum • We have to take into account additional nucleons in the hadron vertex (calculating it in a real detector environment is a totally different issue:-) Hadrons

23. Qsquare – true and observable • Zakładamy rekonstruowalność wszystkich cząstek • Odpowiednia liczba nukleonów w stanie początkowym • Widać rozmycie spowodowane pedem Fermiego (co powoduje wejście Qsquare w wartości ujemne) All events Qsq [GeV^2] Solid – lepton qsq, dashed – hadron qsq

24. Qsquare – true and observable NC 1pizero CC 1piplus Qsq [GeV^2] Qsq [GeV^2] Solid – lepton qsq, dashed – hadron qsq

25. Let’s include FSIs • Solid – no FSIs, Dashed – FSIs included (hadron qsq) • FSIs smear qsq distribution a little, but nothing unexpected All Qsq [GeV^2]

26. FSIs: single pi production evts Solid – no FSIs, Dashed – FSIs included NC 1pizeronoFSI: 28685evts,FSI: 21484evts CC 1piplus,noFSI: 109421evts,FSI: 86276evts Qsq [GeV^2] Turning on FSIs means that some pis are absorbed, that’s why the number of evts gets smaller

27. Co dalej? • Uwzględnienie efektów detektorowych – widzialność cząstek (PID, cięcia na energię) • Liczymy na dalsza współpracę z wrocławianami:-)

28. Tło wielopionowe • Single pi zero NC production is the main background to CC nu_e interactions producing electrons • When we see a single pi zero it doesn’t have to be a single pion event; it can also be a multipion event (π0+nπ+/-), with other (charged) pions being low-energetic and this way invisible to us in water Čerenkov detector like SK • Let’s estimate how much we miss by taking into account only single pion events • In other words – how many multipion events look like a single pizero? Total: 500000 evts

29. Čerenkov visibility criteria • To see a charged particle in a Čerenkov detector such as SuperK, it has to have energy of at least 1.5 times its mass • When there are other rings in the vicinity, the realistic threshold is something about 1.5*m+50MeV (we need a distinguishable ring) • Pi zero is always visible by its decay into two gammas

30. Results – visibility applied FSI, +50MeV Single visible pizeros Multi pi background Pizero momentum [MeV]

31. Conclusion • 4% is not a large contribution, at least in the first phase of the experiment • But in the phase of precise measurements even 4% may be significant • Measurements in ND280, perhaps in future 2km LAr detector?