1. Cosmics at far position P.Sala, M.Antonello, A.Ferrari, D.Stefan, R. Sulej LNGS SC1

2. From report to PAC LNGS SC Slide: 2

3. Few trivial things lThree years of data tacking  6.6 10 20 pot  1.4 10 8 spills  220 s l4 10 5 ν  CC events collected at the far position in positive focusing mode  one every 400 spills lSignal events are of the order of 600 over three years lIntrinsic ν e order of 2000 events over three years, ν  O 200000 Background “types” and effects In a shielded situation, practically ALL background is (re-)generated by muons lCosmic photons in coincidence with beam spill  Direct background to nue search, reduce through reconstruction and/or veto (identify associated muon, distinguish nue from photon) lCosmic photons inside the drift time, trigger given by another cosmic event  Reduce via a light system capable of “segmenting” the LAr volume and veto lCosmic events inside drift time, trigger given by neutrino event  Can harm event reconstruction, reduce via light and veto Slide: 3 LNGS SC

4. Simulations lTwo-step FLUKA simulations: lStep 1: showering of primary cosmic rays in atmosphere, at the FNAL location. Double differential particle fluxes scored at various quotes in atmosphere and at ground. lStep 2: re-sample these particle distributions on a sphere around the detector and propagation around and inside the detector Slide: 4

5. Paola Sala, HSS06 5 Negative muons at floating altitudes: CAPRICE94 Open symbols: CAPRICE data Full symbols: FLUKA primary spectrum normalization ~AMS-BESS Astrop. Phys., Vol. 17, No. 4 (2002) p. 477

6. Paola Sala, HSS066 L3 Muons exp. data FLUKA simulation Vertical Horizontal (S.Muraro, PhD thesis Milano)

7. Paola Sala, HSS067 Comparison with AMS data Protons and leptons below the geomagnetic cutoff have been measured by the AMS experiment at altitudes 370-390 Km, latitude ±51.7 0 Astrop. Phys. 20,221 (2003) Downgoing proton flux, simulation(solid line) AMS data(triangles).  M is the geomagnetic latitude in radians

8. 1 st step : fluxes lparticles/cm^2/primary at FNAL elevation (225 m) Neu Pro Pio+ Pio- K0 Muo+ Muo- Pho Ele Total 5.9E-03 5..6E-04 3.4E-06 4.4E-06 4.9E-08 1.1E-02 8.7E-03 7.4E-03 1.8E-03 E>100 MeV 3.3E-03 4.4E-04 3.2E-06 4.0E-06 4.9E-08 1.1E-02 8.6E-03 2.2E-03 6.9E-04 E>200 MeV 1.5E-03 3.1E-04 2.9E-06 3.5E-06 4.8E-08 1.1E-02 8.4E-03 9.1E-04 3.4E-04 E>1 GeV 1.2E-04 6.8E-05 1.4E-06 1.4E-06 4.0E-08 8.3E-03 6.6E-03 7.7E-05 4.2 E-05 lThe photon flux listed here is relevant for un-shielded detectors only LNGS SC Slide: 8

9. Step 2 lSimulation restarted at 250m for different particle types, with thresholds at 100 MeV except for muons --> 30 MeV lSimulated exposure equivalent to about 150s for each particle type (less for muons) lConfiguration 1: detector on surface. Included: non-active LAr, Al, cryo, thermal insulation and its support, ``passerelle'' on top. lConfiguration 2: detector in a pit, covered by 3m of rock. For this configuration, for the moment we have only the contribution from primary MUONS and NEUTRONS, that we expect is the dominant one. the rest is coming. lEvents have been recorded in the usual T600 full simulation, plus some auxiliary data for quick retrieval of information. LNGS SC Slide: 9

10. Results underground Slide: 10 Hz 2m s (drift)In 220 s All events, Edep>100 MeV11600232500000 With ≥ 1 Photon > 100 MeV5701.2120000 With ≥ 1 Photon > 100 MeV, no  1.70.003370 All events, Edep>200 MeV10700212300000 With ≥ 1 Photon > 200 MeV2500.556000 With ≥ 1 Photon > 200 MeV, no  0.60.001140 lThe acquisition and event processing will have to deal with 3 millions of events, out of which less than one tenth are neutrinos lEvery neutrino event will have >5 muon tracks superimposed in the same chamber (4 chambers) lThere will be 56000 photons ON TIME with the spill, 140 of them isolated lThere will be 1.5 million photons with E>200 MeV collected “in drift” (0.5 in drift times 3 millions triggers), out of which 3000 have no associated muon

11. How do neutrino events look like? Slide: 11 Angular distribution of emitted leptons in the Booster beam Distribution is wide  angle wrt beam is not a good cut for cosmics Warning for internal veto: 45% of  events are NOT contained, need 2 anticoincidence hits to discriminate cosmics Energy distribution of electrons produced in “signal like” e events. Dashed is the cumulative distribution. 200 MeV corresponds to about 10% loss in efficiency WARNING: Simulation of interactions at these energies is subject to large uncertainties

12. Zenith of primary Slide: 12 Zenith angle distribution of primary particle in coincidence with a background event in the detector, underground location. Dashed line (right axis) is the Cumulative distribution. Average cosine is 0.778, Corresponding to 40 degrees NOT all the muons are vertical

13. Deposited energy LNGS SC Slide: 13 Spectrum of energy deposited by background events in the detector (cut at 100 MeV)

14. Slide: 14 dN/d(logE) GeV Energy of muons entering the detector About 15% are stopping inside

15. Cosmic Photon Energy Slide: 15 Energy distribution of the most energetic photon in each event, threshold at 100 MeV. GeV

16. Photon conversion distance Slide: 16 Distance of photon conversion vertex from parent muon, in cm, for cosmic background events in t600. Distance is perpendicular to the muon TRACK: it can be used to define a cylindrical “fiducial volume cut” around muon tracks. On the right the cumulative distribution cm

17. Photon conversion distance Slide: 17 Distance of photon conversion vertex from parent muon, in cm, for cosmic background events in t600. ONLY photons with E>200 MeV Distance is perpendicular to the muon TRACK: it can be used to define a cylindrical “fiducial volume cut” around muon tracks. On the right the cumulative distribution At 30 cm 2% are left  About 1000 photons “on time” survive, to be reduced through dE/dx or other cm

18. Examples LNGS SC Slide: 18 One background event: isolated photon

19. Example Slide: 19 Collection Induction 2 Background event with one muon + one pion- entering Pion interacts and produces pizero Pion - Muon 6630823

20. Example Slide: 20 Muon entering from top, accompanied by photon generated ouside Note the dispersion of the em shower  the “first” photon is not always the only one to be considered Wire chambers Cathode 7379926

21. Example LNGS SC Slide: 21

22. Example LNGS SC Slide: 22 9897540 One muon can have more than one accompanying photon

23. Slide: 23 Muon entering from side and crossing, many small photons around 7003983

24. We generated photons 0-1 GeV along Z direction Look for Pair conversions that can mimic a neutrino interaction (activity at the vertex) Pair conversions with a “one-mip” like energy deposition Comptons Photon identification : preliminary work We used the same algorithm that was optimized for the signal type events (FNAL and CERN). The procedure is exactly the same. (see later) A semi-automatic procedure was used, where the conversion point and the shower direction are taken from MC, the shower reconstruction, topology and dE/dx are automatic NEXt : apply to simulated background events

25. Example of event with: no activity at the vertex 2 mip Initial part of the cascade is marked as dark blue: 2.5 cm in 3D, dE/dx: 3.97 MeV/cm OK

26. Example of event classified as „activity at the vertex” Coll Ind 2 Ind 1 Collection enlarged part of the cascade 2 clusters within 3 cm (10 wires) 3 cm Induction 2 enlarged part of the cascade dE/dx from 2.5 cm of the initial part of the cascade: 7.48 MeV/cm activity at the vertex > 2 mip

27. Two other examples classified as events with activity at the vertex. Collection Ind2 Zoom - Collection Zoom – Ind2 Collection Ind2 Zoom - Collection Zoom – Ind2 dE/dx from 2.5 cm of the initial part of the cascade: 3.96 MeV/cm dE/dx from 2.5 cm of the initial part of the cascade: 4.8 MeV/cm

28. for photon momentum > 0.2 GeV/c: 87% events have no activity at the vtx. dE/dx > 3.5 MeV/cm: 708events/765events: 93% dE/dx < 3.5 MeV/cm && activity at the vtx: 21 events/765 events: 3% (0 comptons) 3.5 MeV/cm Info. dE/dx is measured along the higher electron momentum - photons along z dir. photons p > 0.2 GeV/c

29. for photon’s momentum > 0.3 GeV/c: 88% events have no activity at the vtx. dE/dx > 3.5 MeV/cm: 610events/650events: 94% dE/dx < 3.5 MeV/cm && activity at the vtx: 16 events/650 events: 2% (0 comptons) 3.5 MeV/cm - photons along z dir. photons p > 0.3 GeV/c

30. photons p > 0.2 GeV/c Examples of dangerous photons (slide 7, slide 8, slide 9): dE/dx < 3.5 MeV/cm && activity at the vtx. Collection Induction 2 In total there are 21 events 18 are asimmetric as on the event on the left 2 photons converted in such a way that the electron with higher momentum goes along collection wire, so they have dE/dx = 0 MeV/cm 1 has electromagnetic activity close enough to have more than one cluster at the beginning and dE/dx lower than threshold (3.5 MeV/cm) (slide 9).

31. Collection Induction 2 Collection - zoom dark blue: hits taken to compute dE/dx : 2.1 MeV/cm Collection Induction 2 Collection - zoom

32. Two other interesting examples photon with momentum 0.36 GeV/c e+: 281 MeV/cm and e-: 76 MeV/cm x primary vtx dE/dx = 0 because initial dir of electron with higher energy is along collection wire 3.3 MeV/cm Only one event this type: 2 clusters within 3 cm and dE/dx lower than 3.5 MeV/cm.

33. LNGS SC33

34. Preliminary results from the visual scanning of MC e events lThree independent scanners. lPreliminary results on the first 100 events. Slide: 34 Scanning of intrinsic e events100 events T600: 420 t fiducial mass91 events e events with hadronic activity at vertex80 e events with ‘’isolated ‘’ electron candidate78 e events with electron at vertex showering70 Recognized e MC events54 As a first hint only ~59% of e CC MC events with vertex inside the fiducial mass and activity at vertex can be recognized with the previous selection criteria

35. Results from the scanning of low energy MC e CC events Intrinsic e spectrum with E < 1.3 GeV (56 %) lPreliminary results on the 175 scanned events. Slide: 35 Scanning of intrinsic e events E < 1.3 GeV175 events T600: 420 t fiducial mass160 events e events with hadronic activity at vertex117 e events with ‘’isolated ‘’ electron candidate112 e events with electron at vertex showering98 Recognized e MC events80 ●only ~50% of e CC MC events with vertex inside the detector fiducial volume have activity at vertex and can be recognized with the previous selection criteria ●25 % of the events in the fiducial volume shows no detectable hadronic activity at vertex!

36. MC event 3 (NO) Slide: 36 Collection view Induction1 view Induction2 view Incoming neutrino 62 cm 43 cm 142 cm 44 cm 94 cm 44 cm E = 0.51 GeV E dep = 0.49 GeV A e q.e. without activity at interaction vertex.

37. MC event 8 (OK) Slide: 37 Collection viewInduction1 viewInduction2 view 94 cm 64 cm Incoming neutrino 95 cm 64 cm 74 cm 60 cm E = 1.16 GeV E dep = 0.50 GeV lDIS event with backward going electron.

38. LNGS SC Slide: 38