Antiproton Annihilation on Argon Nuclei in LArIAT William Foreman, University of Chicago On Behalf of the LArIAT Collaboration DPF 2017 – Fermilab Wednesday, August 2, 2017
Motivation: Neutron-Antineutron Oscillation § Feature of many BSM theories § For bound neutrons, signature is decay products from subsequent annihilation of oscillated neutron with a neighboring nucleon τ bound = R · τ 2 free arXiv:1109.4227, Super-K Neutron-Antineutron Oscillation Search (2015) 2 Aug 2017 W. Foreman (UChicago), DPF 2017 2
Search for n-nbar in a LArTPC G. Karagiorgi, DUNE Collab. Mtg 2017 § Star-like topology & final state energy (E f ~ 2m p c 2 ) distinguishes from primary background Simulated n-nbar § DUNE expected to set τ (free) event in DUNE limit of ~1.7 × 10 9 s at 90% CL over 10yrs, a x5 improvement on existing limit by Super-K of 2.7 × 10 8 s See poster by Georgia Karagiorgi, and talk on 8/3 by Joshua Barrow! J. Hewes, DUNE Collab. Mtg 2017 2 Aug 2017 W. Foreman (UChicago), DPF 2017 3
Antiproton Annihilation Annihilation star first pbar observed in photographic emulsion experiment in 1955 at UC Berkeley (Chamberlain, Segrè, Wiegand, Ypsilantis, Goldhaber) 2 Aug 2017 W. Foreman (UChicago), DPF 2017 4
Antiproton Annihilation Annihilation star first pbar observed in photographic emulsion experiment in 1955 at UC Berkeley (Chamberlain, Segrè, Wiegand, Ypsilantis, Goldhaber) Mixed reviews in the press… “New Atom Particle Found; Termed a Negative Proton” New York Times “Grim New Find at UC.” Berkeley Gazette 2 Aug 2017 W. Foreman (UChicago), DPF 2017 5
Antiprotons in LArIAT § Antiproton annihilation at rest is our best proxy to n-nbar signals in data LArIAT Data Preliminary π - (48.4%) p- (0.007%) § LArIAT produces some pbars e- (40.9%) μ - (2.2%) in our tertiary beamline K- (0.035%) (~0.007%!), which can stop and annihilate with surface Ar nucleons § A sample of pbar-Ar events in LArAT will: § Provide a test-bed for n-nbar reco algs over LArTPC data Lariat Negative Beamline § Help constrain nuclear Composition (MC + Data) models used to simulate n- -100A, 64 GeV pions nbar final states 2 Aug 2017 W. Foreman (UChicago), DPF 2017 6
Selecting Antiprotons in the LArIAT Beamline 2 Aug 2017 W. Foreman (UChicago), DPF 2017 7
Beamline Mass Calibration with Protons Time of flight [ns] Events LArIAT Run II d LArIAT Run II p e, μ , π p + Pos Tertiary Beam Pos Tertiary Beam Entries: 262776 Entries: 262776 Preliminary Preliminary p/pbar selection K region: 750-1150 MeV/c 2 K + d π + µ + e + Reconstructed beamline mass [MeV/c 2 ] Wire chamber track momentum [MeV/c] 2 Aug 2017 W. Foreman (UChicago), DPF 2017 8
Looking for Antiprotons in Negative Beam All Run II negative Selecting events in beam data proton mass range Time of flight [ns] LArIAT Run II LArIAT Run II Neg Tertiary Beam Neg Tertiary Beam Proton Mass Cut Entries: 724019 Entries: 1532 Preliminary Preliminary Wire chamber track momentum [MeV/c] Wire chamber track momentum [MeV/c] 2 Aug 2017 W. Foreman (UChicago), DPF 2017 9
Wire Chamber Track Matching TPC Wire chambers LArIAT Run II Proton candidates Preliminary 2 Aug 2017 W. Foreman (UChicago), DPF 2017 10
Wire Chamber Track Matching First ~5cm TPC Wire chambers LArIAT Run II Proton candidates Preliminary Preliminary 2 Aug 2017 W. Foreman (UChicago), DPF 2017 11
Wire Chamber Track Matching χ 2 /NDF = 1.47 LArIAT Run II χ 2 /NDF = 0.93 LArIAT Run II N = 1351(17) N = 2062(46) Pos Beam Pos Beam μ = -0.0552(9) μ = 1.46(1) Proton candidates Proton candidates σ = 1.319(24) σ = 0.89(2) Preliminary Preliminary C = 326(18) C = 324(51) Peak: 3.125 Mean: 11.44 § Good matching seen in Std. dev: 10.84 LArIAT Run II proton sample Pos Beam Proton candidates Preliminary § Currently optimizing selection cuts 2 Aug 2017 W. Foreman (UChicago), DPF 2017 12
Event Selection Breakdown Event cuts Run 1 Neg Run 2 Neg Run 3 Neg Total events 430,792 5,330,568 1,442,706 Beam event w/ TPC info 81,103 1,518,837 725,503 1.2s < T < 5.5s RawDigits size > 0 1 TOF & 1 Pz 36,692 724,019 378,232 15ns < TOF < 75ns 200 MeV/c < Pz < 1400 MeV/c Proton mass cut 273 1,532 523 700-1300 MeV/c 2 Identifiable pbar ~2 ~50 ~50 events (by eye) Golden stopping pbar ~1 ~15 ~15 events (by eye) WC-to-TPC match These by-eye steps to be replaced α < 20 deg by WC-to-TPC matching, etc… -3cm < dx < 6cm -6cm < dy < 6cm Reject thru-going MaxMatched = 3 2 Aug 2017 W. Foreman (UChicago), DPF 2017 13
Antiproton Candidate Event Examples Annihilation in-flight Annihilation at rest LArIAT LArIAT Raw Wire Data Raw Wire Data Collection Plane Collection Plane Induction Plane Induction Plane 2 Aug 2017 W. Foreman (UChicago), DPF 2017 14
A Few More… LArIAT: Raw Wire Data LArIAT: Raw Wire Data LArIAT: Raw Wire Data Collection Plane Collection Plane Collection Plane Induction Plane Induction Plane Induction Plane LArIAT: Raw Wire Data LArIAT: Raw Wire Data LArIAT: Raw Wire Data Collection Plane Collection Plane Collection Plane Induction Plane Induction Plane Induction Plane 2 Aug 2017 W. Foreman (UChicago), DPF 2017 15
Next steps Stage 1: Event Selection Stage 2: Stage 3: Ø Beam mass cut (done) Energy at Final state Ø WC track matching (in prog.) annihilation reconstruction Ø dE/dx LArIAT Data 2D Reco Anticipated results: § Charged pion multiplicity § MIP vs. EM-like ratio of deposition Sum up visible energy along § Visible final-state energy track 2 Aug 2017 W. Foreman (UChicago), DPF 2017 16
Take-Aways § LArIAT has observed ~O(100) antiproton annihilations in LAr for the first time! § ~30 of these come to rest before annihilating § Now beginning work on reconstructing these events in the TPC – stay tuned! 2 Aug 2017 W. Foreman (UChicago), DPF 2017 17
Thanks! 2 Aug 2017 W. Foreman (UChicago), DPF 2017 18
Backup 2 Aug 2017 W. Foreman (UChicago), DPF 2017 19
Anticipated deliverables q Charged pion multiplicities q Neutral pion multiplicities Ø challenging due to topology of π 0 à 2 γ showers q Total visible energy Ø MIP-like vs. EM-like total deposition J. Hewes, G. Karagiorgi, K. MC Truth n-nbar topology in 40 Ar Terao @ DUNE Collab Mtg ‘17 Event Momentum Num. of primary particles Event Energy 2 Aug 2017 W. Foreman (UChicago), DPF 2017 20
Systematic Uncertainty Budget in Signal Efficiency in Super-Kamiokande N-Nbar Search arXiv:1109.4227, Super-K Neutron-Antineutron Oscillation Search (2015) 2 Aug 2017 W. Foreman (UChicago), DPF 2017 21
Beamline Selection Plots (Neg Beam) Run IIA Run I Run II 2 Aug 2017 W. Foreman (UChicago), DPF 2017 22
Recommend
More recommend
