Hallazgos

The FD data quality cuts are summarized in the first part of Table.6.5.

Table 6.5: data quality, containment and cosmic rejection cuts in LID and LEM regions. the detail of each variables will be discussed in the subsequent paragraphs.

variables cuts

Number of hits per plane nhit/nplane < 8

Number of hits in x-view planes ncellx > 5

Number of hits in y-view planes ncelly > 5

Difference between nhit in x and y view planes dnhit < 0.4

Cosine of the angle between the two leading showers dang > -0.95

Distance of the leading shower from vertex gap < 100 cm

Fraction of nhit on showers nhitfrac > 0.7

Distance from east wall minx0 > 15 cm

Distance from west wall maxx0 > 10 cm

Distance from bottom miny0 > 10 cm

Distance from top maxy0 > 150 cm

Distance from front minz0 > 35 cm

Distance from back maxz0 > 200 cm

Fraction of event transverse momentum ptp < 0.4, when maxyall < 25 cm,

Number of Hits per Plane: The cut requires the number of hits per plane to be less than 8. The number of planes is counted based on the most energetic shower instead of slice in order to reduce the uncertainty due to noise hits. This cut removes FEB flash issues in data, in which case multiple contiguous hits are seen on the same plane. The FBE flash

problem is often induced by high energy cosmic ray events. Fig.6.8 shows an event from

cosmic trigger data presenting a pattern for the FEB flash problem. The blue contiguous

boxes show the flash effect. Fig.6.9shows the distribution of the number of hits per plane

for LID and LEM selected events for signal (blue), beam background (red) and cosmic background (black) at “n-1” cut stage, at which all the cuts except for the number of hits per plane cut are applied. As cosmic background is livetime exposure normalized and beam events are POT normalized, cosmic background is much lower than the beam components.

Figure 6.8: Event display of a cosmic trigger event as an example that is removed by this cut based on the number of hits per plane variable. The blue boxes represent hits, while dash lines are reconstructed prongs.

(left) and LEM (right) selected regions for νe CC signal (blue), total beam background (red) and total cosmic background events (black). Magenta Lines are cut position. The cut removes events with average number of hits per plane greater than 8.

Total Number of Hits in X/Y-View Planes (nhit/nplane): This cut removes events show-

ing little energy deposition in either view. Fig. 6.10and Fig. 6.11shows the distribution

of total number of hits in X/Y-View planes. This cut requires that an event has at least 5 cells in both X-view and Y-view planes.

Figure 6.10: Distribution of total number of hits in X-View planes at ”n-1” cut stage in the LID (left) and LEM (right) selected region.

Difference between the Number of Hits in X (ncellx) and Y (ncelly) View Planes: This cut is designed to remove the events with a large difference between the number of hits deposited in X-view planes and in Y-view planes. For a well reconstructed beam event, a high symmetry between the number of hits in X and Y views is expected. The cut also has the power of rejecting cosmic ray events, since cosmic ray events tend to enter the detector at large angle with respect to the beam direction, which ends up with more

hits in X view than in Y view planes. Fig.6.12 shows an example of mis-reconstruction

Figure 6.11: Distribution of total number of hits in Y-View planes at ”n-1” cut stage in the LID (left) and LEM (right) selected regions.

jected by this cut. Fig.6.13 shows the distribution of this variable at “n-1” cut stage

in LID and LEM regions. The cut is at 0.4, which preserves the majority of the signal events.

Figure 6.12: Event display of a cosmic trigger event as an example of mis-reconstruction showing large difference between the number of hits in X-view and Y-view planes.

Cosine of the Angle between the Two Leading Showers (dang): The cut removes the interactions with the two most energetic prongs that have large angle to each other.

An example of such case is shown in Fig.6.14, which is probably an event with one

gapped prong due to bad channel issues, non-reporting APD due to noise, and is mis-

reconstructed into two prongs. Fig.6.15shows the distribution of the variable in LID and

planes at ”n-1” stage in the LID (left) and LEM (right) selected regions.

-0.95 radians, which is ∼170 degrees. This cut is not applied for the events with only one reconstructed prong.

Figure 6.14: Event display of a cosmic trigger event having two reconstructed prongs, repre- sented by green and red lines, which have a very large angle to each other.

Figure 6.15: Distribution of the cosine of the angle between the first two showers in LID selected region, LID > 0.95 (left) and LEM selected region, LEM > 0.8 (right).

Distance of the Leading Shower Start from the Main Vertex (gap): This cut removes interactions where the distance of the leading shower from interacting position is greater than 100 cm, which is ∼ 2 times larger than the radiation length of EM showers in the

NOνA detectors. Fig.6.16 shows an example of this pattern, which shows a distance of

∼120 cm between the vertex and prong start, in which the vertex is probably mislocated

due to several very noisy cells far away from the leading shower. Fig.6.17 shows the

distributions of this variable in LID and LEM selected regions. The cut at 100 cm is well above the majority of the signal (blue) events.

Figure 6.16: The event shows a large distance between the leading shower start and the main vertex.

Figure 6.17: Distribution of the distance of the leading shower from the main vertex in LID (left) and LEM (right) regions.

Fraction of the Hits associated to Showers (nhitfrac): This cut selects events in which at least 70% of the hits belong to showers. The events where a small fraction of hits is

reconstructed into a shower might have high contamination of noise hits. Fig.6.18shows

the distributions of this variable at “n-1” cut stage in the LID and LEM selected regions. The cut is at 0.7, which retains more than 98% of the signal events.

Figure 6.18: Distribution of the fraction of the hits on showers in LID (left) and LEM (right) regions.