Material y Método

6.4.1 Identification and calorimetric energy reconstruction of 1 GeV/𝒄 beam pions and muons

Measurements of charged pion interactions with argon nuclei are an important physics goal of the ProtoDUNE-SP experiment. Accurate measurement of these interactions allows a more precise understanding of neutrino interactions producing final-state pions, a key study channel of the DUNE experiment. Reconstructing these final state pions and any particles produced by their secondary interactions is important for estimations of neutrino energy. This section describes the results obtained from ProtoDUNE-SP Run 5387 taken on Oct. 18, 2018 corresponding to approximately 12 hours of exposure to a 1 GeV/𝑐 beam. The electron drift lifetime of this run was approximately 14 ms as measured by the purity monitor.

Selection of events with reconstructed beam pions: the beam line instrumentation as described in section3can be used to find events where the beam line has delivered a pion to the TPC. For the 1 GeV beam energy runs considered here, the beam line PID conditions for pions and muons can

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DUNE:ProtoDUNE-SP Cosmics MC

Expectation

Figure 60. Stopping muon 𝑑𝐸/𝑑𝑥 distributions for the ProtoDUNE-SP cosmic-ray data and MC. The black curves in(a)and(b)are the predicted most probable values (using the Landau-Vavilov function) of 𝑑𝐸/𝑑𝑥 versus residual range and(c)is the 𝑑𝐸/𝑑𝑥 distribution for the stopping muon sample. The histograms in (c) are normalized such that the maximum frequency is one.

be found in table2. At a beam momentum of 1 GeV/𝑐 the measured TOF of pions and muons is indistinguishable so the PID will select both pions and muons. Events are first removed for periods of unstable HV or one or more inactive TPC readout boards. The Pandora pattern recognition framework, described in section4.5.2is used to reconstruct the particle trajectories in the TPC as well as identify a reconstructed particle as a likely candidate for the beam line track. To remove events where a track has been incorrectly identified as the primary beam particle, quality cuts are placed on the distance and angle between the end of the beam line particle’s reconstructed trajectory and the start of the assigned reconstructed TPC beam particle track. These cuts remove backgrounds that are not aligned with the measured beam line track such as cosmic rays and secondary particles produced by the beam particle interacting upstream of the TPC. The cuts used for data are as follows:

• Beam quality cuts: angle

The cosine of the angle between the beam line track and reconstructed TPC track is required to be > 0.93.

• Beam quality cuts: position

◦ 0 cm ≤ ( 𝑋^Start− 𝑋^End ) ≤ 10 cm,

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◦ −5 cm ≤ (𝑌_TPC^Start− 𝑌_Beam^End ) ≤ 10 cm,

◦ 30 cm ≤ (𝑍_TPC^Start− 𝑍_Beam^End ) ≤ 35 cm,

where 𝑋_TPC^Startis the start position in X of the reconstructed candidate beam track in the TPC before SCE corrections. 𝑋_Beam^End is the projected X location of the intersection of the track from the beam line instrumentation with the TPC. The cuts are not centered around zero due the SCE shifting the start points of the reconstructed TPC tracks.

A replica selection is also placed on beam MC events where the true simulated beam particle is either a pion or muon. In MC the truth information of the beam particle is used in place of the beam line information. The cuts used for MC are as follows:

• Beam quality cuts: angle

The cosine of the angle between the true beam particle and reconstructed TPC track is required to be > 0.93.

• Beam quality cuts: position

◦ −3 cm ≤ ( 𝑋_TPC^Start− 𝑋_Beam^End ) ≤ 7 cm,

◦ −8 cm ≤ (𝑌_TPC^Start− 𝑌_Beam^End ) ≤ 7 cm,

◦ 27.5 cm ≤ (𝑍_TPC^Start− 𝑍_Beam^End ) ≤ 32.5 cm.

Here 𝑋_Beam^End is the projected X location of the true beam particle’s intersection with the TPC and 𝑋_TPC^Startis same as for data.

0.6 0.7 0.8 0.9 1.0 1.1 1.2

Reconstructed Track Length/CSDA Range 0.0

0.2 0.4 0.6 0.8 1.0 1.2 1.4

Relative Frequency

DUNE:ProtoDUNE-SP

Cut to select stopping muons Beam Pions and Muons (1 GeV/c)

Figure 61. The ratio of track length (SCE corrected) and continuous-slowing-down-approximation (CSDA) length for data candidates under the assumption the particle is a muon. The cut to select the stopping muons is indicated. The histogram is normalized such that the maximum frequency is one.

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Selection of stopping muons: the track lengths of the selected beam particles can be used to separate the beam pions and muons. As 1 GeV/𝑐 pions have an expected interaction length in argon of

~1 m the majority of pions will interact before coming to a stop via ionization energy loss. Whereas 1 GeV/𝑐 muons will stop predominantly via ionization energy losses with an expected path length in argon of ~4 m. The measured beam momentum is used to approximate the stopping range of each particle under the assumption it is a muon using the continuous-slowing-down-approximation (CSDA) range [64]. The distribution of the beam tracks’ reconstructed lengths divided by their calculated CSDA ranges is shown in figure61. Requiring the ratio

0.9 < Track Length CSDA Stopping Range

< 1.1, (6.10)

selects a subsample of stopping particles, predominantly muons. A replica selection cut is placed on the MC sample using the simulated momentum for the true beam particle in each event as input to the ratio calculation.

Beam Stopping Muons (1 GeV/c)

(b)

Figure 62. Pion (a)and stopping muon(b) 𝑑𝐸/𝑑𝑥 distributions for the ProtoDUNE-SP beam data after applying the calibration derived using cosmic-ray muons. The distribution for replica selections on a beam Monte Carlo sample with space charge effect simulated is also shown. The histograms are normalized such that the maximum frequency is one.

Calorimetric energy information of beam pions: the charge signal calibration produced from stopping cosmic-ray muons collected during the same run period described in section6.3is applied to the selected beam tracks to calculate the true deposited energy as a function of distance (𝑑𝐸/𝑑𝑥) along their trajectory. Figure 62(a) shows the distribution of 𝑑𝐸/𝑑𝑥 values of all hits on the collection plane from the selected beam pion candidates. That is, all candidates that are not selected by the stopping muon cut (eq. (6.10)) described above. The selected particles are MIPs. The MPVs of the calibrated data and MC samples agree to better than 1%.

Calorimetric energy information of beam stopping muons: figure62(b)shows the distribution of calibrated 𝑑𝐸/𝑑𝑥 values of all hits on the collection plane from the beam muon candidates selected by the stopping particle cut (eq. (6.10)). As with the pions, the MPVs of the data and MC samples agree to better than 1%. The distribution of the 𝑑𝐸/𝑑𝑥 vs residual range for the selected

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Stopping Beam Muons - Data (1 GeV/c)

(a) Stopping Beam Muons - MC (1 GeV/c)

0 50 100 150 200

Stopping Beam Muons - MC (1 GeV/c)

(b)

Figure 63. 𝑑𝐸/𝑑𝑥 vs residual range for selected stopping muons in the 1 GeV/𝑐 beam after applying the calibration derived using cosmic-ray muons, in data(a)and MC(b). The expected most probable value of 𝑑𝐸/𝑑𝑥 is plotted as a function of residual range for both.

stopping muons is shown for data in figure63(a)and for MC in figure63(b). A clear Bragg peak is seen at low residual range, as expected. The measured distribution displays good agreement with the theoretical MPV curve for a stopping muon in argon, in both the minimum ionization region and Bragg peak region of residual range.

6.4.2 Identification and calorimetric energy reconstruction of 1 GeV/𝒄 beam protons