1

Cosmics at far position

P.Sala, M.Antonello, A.Ferrari, D.Stefan, R.

Sulej

LNGS SC

From report to PAC

LNGS SC Slide: 2

Few trivial things

l Three years of data tacking 6.6 1020 pot 1.4 108 spills 220 sl 4 105 νCC events collected at the far position in positive focusing

mode one every 400 spillsl Signal events are of the order of 600 over three yearsl Intrinsic νe order of 2000 events over three years, ν O 200000

Background “types” and effectsIn a shielded situation, practically ALL background is (re-)generated by

muons l Cosmic photons in coincidence with beam spill

Direct background to nue search, reduce through reconstruction and/or veto (identify associated muon, distinguish nue from photon)

l Cosmic photons inside the drift time, trigger given by another cosmic eventReduce via a light system capable of “segmenting” the LAr volume

and vetol Cosmic events inside drift time, trigger given by neutrino event

Can harm event reconstruction, reduce via light and veto Slide: 3LNGS SC

Simulationsl Two-step FLUKA simulations:l Step 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.

l Step 2: re-sample these particle distributions on a sphere around the detector and propagation around and inside the detector

Slide: 4

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

Paola Sala, HSS06 6

L3 Muonsexp. data

FLUKA simulation

Vertical Horizontal

(S.Muraro, PhD thesis Milano)

Paola Sala, HSS06 7

Comparison with AMS data Protons and leptons below the geomagnetic cutoff have been measured by the AMS experiment at altitudes 370-390 Km, latitude ±51.70 Astrop. Phys. 20,221 (2003)

Downgoing proton flux, simulation(solid line) AMS data(triangles). M is the geomagnetic latitude in radians

1st step : fluxes

l particles/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

l The photon flux listed here is relevant for un-shielded detectors only

LNGS SC Slide: 8

Step 2

l Simulation restarted at 250m for different particle types, with thresholds at 100 MeV except for muons --> 30 MeV

l Simulated exposure equivalent to about 150s for each particle type (less for muons)

l Configuration 1: detector on surface. Included: non-active LAr, Al, cryo, thermal insulation and its support, ``passerelle'' on top.

l Configuration 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.

l Events have been recorded in the usual T600 full simulation, plus some auxiliary data for quick retrieval of information.

LNGS SC Slide: 9

Results underground

Slide: 10

Hz 2m s (drift)

In 220 s

All events, Edep>100 MeV 11600 23 2500000

With ≥ 1 Photon > 100 MeV 570 1.2 120000

With ≥ 1 Photon > 100 MeV, no

1.7 0.003 370

All events, Edep>200 MeV 10700 21 2300000

With ≥ 1 Photon > 200 MeV 250 0.5 56000

With ≥ 1 Photon > 200 MeV, no

0.6 0.001 140l The acquisition and event processing will have to deal with 3 millions of

events, out of which less than one tenth are neutrinosl Every neutrino event will have >5 muon tracks superimposed in the same

chamber (4 chambers)l There will be 56000 photons ON TIME with the spill , 140 of them isolatedl There 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

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 cosmicsWarning 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

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

Deposited energy

LNGS SC Slide: 13

Spectrum of energy deposited by background events in the detector (cut at 100 MeV)

Slide: 14

dN

/d(l

ogE)

GeV

Energy of muons entering the detector

About 15% are stopping inside

Cosmic Photon Energy

Slide: 15

Energy distribution of the most energetic photon in each event, threshold at 100 MeV.

GeV

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 cm

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

Examples

LNGS SC Slide: 18

One background event: isolated photon

Example

Slide: 19

Collection

Induction 2

Background event with one muon + one pion- enteringPion interacts and produces pizero

Pion -

Muon

6630823

Example

Slide: 20

Muon entering from top, accompanied by photon generated ousideNote the dispersion of the em shower the “first” photon is not always the only one to be considered

Wire chambers

Cathode

7379926

Example

LNGS SC Slide: 21

Example

LNGS SC Slide: 22

9897540

One muon can have more than one accompanying photon

Slide: 23

Muon entering from side and crossing, many small photons around

7003983

We generated photons 0-1 GeV along Z directionLook 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

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

Example of event classified as „activity at the vertex”

CollInd 2Ind 1

Collectionenlarged 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

Two other examples classified as events with activity at the vertex.

CollectionInd2

Zoom - CollectionZoom – Ind2

CollectionInd2

Zoom - CollectionZoom – 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

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

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

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).

Collection Induction 2

Collection - zoom

dark blue: hits taken to compute dE/dx : 2.1 MeV/cm

Collection

Induction 2

Collection - zoom

Two other interesting examples

photon with momentum 0.36 GeV/ce+: 281 MeV/cm and e-: 76 MeV/cm

xprimary 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.

33LNGS SC

Preliminary results from the visual scanning of MC ne events

l Three independent scanners.l Preliminary results on the first 100 events.

Slide: 34

Scanning of intrinsic ne events 100 events

T600: 420 t fiducial mass 91 events

ne events with hadronic activity at vertex 80

ne events with ‘’isolated ‘’ electron candidate

78

ne events with electron at vertex showering

70

Recognized ne MC events 54

As a first hint only ~59% of ne CC MC events with vertex inside the fiducial mass and activity at vertex can be recognized with the previous selection criteria

Results from the scanning of low energy MC ne CC events

l Intrinsic ne spectrum with En < 1.3 GeV (56 %)l Preliminary results on the 175 scanned events.

Slide: 35

Scanning of intrinsic ne events En < 1.3 GeV

175 events

T600: 420 t fiducial mass 160 events

ne events with hadronic activity at vertex 117

ne events with ‘’isolated ‘’ electron candidate

112

ne events with electron at vertex showering

98

Recognized ne MC events 80● only ~50% of ne 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!

MC event 3 (NO)

Slide: 36

Collection view

Induction1 view

Induction2 view Incoming neutrino

62 cm

43 c

m

142 cm

44 c

m

94 cm

44 c

m

En = 0.51 GeV Edep = 0.49 GeV

l A ne q.e. without activity at interaction vertex.

MC event 8 (OK)

Slide: 37

Collection view

Induction1 view

Induction2 view

94 cm

64 c

m

Incoming neutrino

95 cm

64 c

m

74 cm

60 c

m

En = 1.16 GeVEdep = 0.50 GeV

l DIS event with backward going electron.

LNGS SC Slide: 38