Studia symulacyjne Rekonstrukcja energii, Q 2, przypadki wielopionowe Paweł Przewłocki Warszawska Grupa Neutrinowa

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

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

Beam structure (after interactions) DIS QE All

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 weve got another formula We also assume no fermi momentum here and a clean QE event – muon and proton only Neutrino energy reconstruction μ p ν ν Outgoing particles) θ

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

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

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

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

Wondering which are QEs and which nonQEs on the scatterplot? QEs nonQEs Orange dots denote ideal reconstruction 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)

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

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

The problem Sometimes the reconstruction error is REALLY huge: diff: enu (reco): cos: pmu: E E E E E E E E E-02 id px py pzE p the difference Surprisingly large error in comparison with the Fermi motion distorsion (max. ~250MeV)

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

Muon cosine vs muon momentum P [GeV] cos smearingNo fermi Fermi max 250MeV

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

No doubts where the smearing comes from Fermi max 1GeV

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

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

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

Rekonstrukcja Q 2 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

Qsquare considerations Ideal qsquare – from lepton vertex Observable qsquare – from hadron vertex, assuming nucleon doesnt 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:-) Qsq = four-momentum transfer Neutrino Outgoing lepton Nucleon Hadrons

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

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

Lets include FSIs All Qsq [GeV^2] Solid – no FSIs, Dashed – FSIs included (hadron qsq) FSIs smear qsq distribution a little, but nothing unexpected

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

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

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 doesnt have to be a single pion event; it can also be a multipion event (π 0 +nπ +/-), with other (charged) pions being low- energetic and this way invisible to us in water Čerenkov detector like SK Lets 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? No FSIFSI NC1pizero total NC1pizero 0 pichrgd (84%) (79%) NC1pizero 1 pichrgd 3100 (9%)3218 (12%) NC1pizero 2 pichrgd 1652 (5%)1723 (7%) Total: evts

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

Results – visibility applied FSI, +50MeV Multi pi background Single visible pizeros All events visible as single pizero Events that fake single pizero (being in fact a multipi) noFSI (0.5%) noFSI, +50MeV (1.5%) FSI (1.8%) FSI, +50MeV (3.7%) Pizero momentum [MeV]

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?