Andrea Albert

Long Baseline Scanning Results

8/5/08

Tanal is a Monte Carlo program that simulates how a Liquid Argon Time
Projection Chamber (LAr TPC) would record and display neutrino events.
Events simulated in a 250 X 250 X 250cm^3^ TPC in the off-axis NuMI beam
\~800 km from Fermilab were scanned for TPCs with 5mm and 10mm wire
spacings. The purpose was to determine if ~e~ event identification and
background rejection efficiency were significantly reduced using 10mm
wire spacing compared to 5mm. For each set 1999 ~e~ and events were
made. All events with \>3.5GeV visible energy were rejected to avoid
spending time on obvious events and also because at 800 km the
probability of -\> ~e~ oscillations are highest for those lower
energies. Additionally, only events where an electron materialized
within 2cm of the primary vertex were scanned. A second set was scanned
where an electron event occurred within 5cm of the vertex. A summary of
scanning methods, results, and analysis of the results are contained in
this report.

I.  *Scanning Methods*

The scanner must decide whether an event is a charged current ~e~ (CCe),
charged current (CCmu), or neutral current (NC). Since -\> ~e~
oscillations are being studied, CCe events constitute the signal while
CCmu and NC are background events we wish to reject as efficiently as
possible. The NC events will most likely constitute the largest fraction
of this background. A scale for the desired NC rejection is set by the
number of ~e~ in the NuMI beam in order to keep the signal significantly
above the background. The NuMI beam is \~0.7% ~e~ and thus we wish for
the NC background to be no greater than 0.7%.

i.  CCe Events

A CCe event is identified as an event with a single electron produced at
the primary vertex. The simplest CCe event is a charged current
quasi-elastic scattering (CCe QE) $\nu_{e} + n \rightarrow e^{-} + p$.
Resonance (RES) and Deep Inelastic Scattering (DIS) can also occur
producing additional particles: protons, pions, electrons, photons, etc.

Most identification errors occur when a photon conversion into an
electron-positron pair is mistaken for a single electron. The e^-^ and
e^+^ may be on top of each other making it hard to distinguish them.
Also, in RES and DIS events a single electron can be on top of other
electrons or protons making it difficult to identify CCe events, thus
reducing the signal identification efficiency.

**Electron ID**- Look for a collimated electromagnetic shower

MIP at the beginning is typically \~1

**Proton ID**- High dE/dx -\> short tracks with high MIP

Longer track with high MIP at end

![](media/image1.png){width="4.926388888888889in"
height="2.4833333333333334in"}

*Image 1- single electron and proton (CCe QE)*

![](media/image2.png){width="4.375in" height="1.6152777777777778in"}

*Image 2- single electron and proton (CCe QE)*

**Photon Conversion ID**- Look for a gap from the primary vertex where
the photon traveled before converting.

MIP at beginning typically \~2

May also see e^-^ and e^+^ splitting into separate tracks

![](media/image3.png){width="3.7263888888888888in"
height="2.501388888888889in"}

*Image 3- photon conversions (NC)*

![](media/image4.png){width="4.3069444444444445in"
height="4.184722222222222in"}

*Image 4- photon conversion (NC)*

ii. CCmu

A CCmu event is identified as an event with a muon produced at the
primary vertex. Like with the CCe events, RES and DIS scattering can
occur creating additional particles. The simplest CCmu event is also
charged current quasi-elastic, however in this case a muon is created
instead of an e^-^, $\nu_{m} + n \rightarrow m^{-} + p$. Muons are
usually easy to identify since they have long straight tracks with
MIP\~1. Sometimes protons or pions can have long tracks that look like
muons, but there is usually a reaction or an increase in energy (higher
MIP) at the end. Occasionally a muon can decay into an e~­~^-^ at the end
of its track. Also, sometimes the muon track is not very long.

**Muon ID**- Long, straight tracks

Low MIP for entire track

Possible e^-^ decay at end

![](media/image5.png){width="4.779861111111111in" height="2.875in"}

*Image 5- muon (CCmu RES)*

![](media/image6.png){width="254.33263888888888in"
height="3.990972222222222in"}

*Image 6- muon-looking proton (CCe QE)*

![](media/image7.png){width="4.174305555555556in"
height="3.7715277777777776in"}

*Image 7- a shorter-tracked muon with an electron conversion (CCmu DIS)*

iii. NC

NC events are neutrino events that do not produce a muon or electron.
They are the most varied events. Image 3 and Image 4 are examples. A NC
is identified by its lack of muon or single electron emerging from the
primary vertex. When many particles are present this can be difficult.

![](media/image8.png){width="4.246527777777778in" height="2.175in"}

*Image 10- A complicated NC event (NC DIS)*

**Conclusion**- A CCe event has a single electron produced at the
primary vertex (other particles may also be produced)

A CCmu event has a muon produced at the primary vertex (other particles
may also be produced)

A NC event does not have an electron or muon emerging from the primary
vertex.

-   *Scanning Results*

    i.  Electron event within 2cm of vertex

**5mm pitch**

train05_1.eye

Num: CCe 111 CCmu 379 CCtau 0 NC 1509

Number of events 93

\*\*\* Your selection \*\*\*

  ---------------------- ---------------- ---------------- ----------------
                         CCe              CCmu             NC

  true CCe               64               0                3

  true CCmu              1                3                0

  true NC                7                2                13
  ---------------------- ---------------- ---------------- ----------------

CCe Efficiency 95.5% NC rejection 99.54% CCmu rejection 99.74%

**10mm pitch**

train10_1.eye

Num: CCe 115 CCmu 399 CCtau 0 NC 1485

Number of events 103

\*\*\* Your selection \*\*\*

  ---------------------- ---------------- ---------------- ----------------
                         CCe              CCmu             NC

  true CCe               75               0                1

  true CCmu              0                2                0

  true NC                11               2                12
  ---------------------- ---------------- ---------------- ----------------

CCe Efficiency 98.7% NC rejection 99.26% CCmu rejection100.00%

Note that the background rejections include the energy and electron
position cuts made. The CCe efficiency is based only on the scanned
events.

The NC scanning efficiency is 59.09% with the 5mm spacing and 48.0% with
the 10mm spacing. Since we would like the NC background to be no worse
than the ~e~ contamination in the beam (\~0.7%) the 0.28% rejection
difference may be significant. More scanning is needed to get better
statistics on the NC rejection.

ii. Electron event within 5cm of vertex

**5mm pitch**

trainv2_05_2.eye

Num: CCe 126 CCmu 384 CCtau 0 NC 1489

Number of events 154

\*\*\* Your selection \*\*\*

  ---------------------- ---------------- ---------------- ----------------
                         CCe              CCmu             NC

  true CCe               86               2                6

  true CCmu              0                5                4

  true NC                6                3                42
  ---------------------- ---------------- ---------------- ----------------

CCe Efficiency 91.5% NC rejection 99.60% CCmu rejection 100.00%

**10mm pitch**

trainv2_10_2.eye

Num: CCe 157 CCmu 399 CCtau 0 NC 1443

Number of events 176

\*\*\* Your selection \*\*\*

  ---------------------- ---------------- ---------------- ----------------
                         CCe              CCmu             NC

  true CCe               80               5                17

  true CCmu              0                12               1

  true NC                11               3                47
  ---------------------- ---------------- ---------------- ----------------

CCe Efficiency 78.4% NC rejection 99.24% CCmu rejection 100.00%

CCe identification is 13.1% better with the 5mm spacing than the 10mm
spacing.

The NC efficiency is 82.35% with the 5mm spacing and 77.05% with the
10mm spacing. The NC rejection difference between the two pitches
(0.36%) is larger in this set.

**Conclusion**- With the 2cm cut \~3% more events are initially rejected
than with the 5cm cut, but the CCe efficiency is roughly the same for
both pitches. However, the difference in NC rejection is significant
considering the desired NC rejection. With the 5cm cut more events are
scanned, but the CCe efficiency decreases and the NC rejection
difference is larger. From these initial results the 5mm is obviously
better, but more scanning is needed to better understand the effect of
the wire spacing on the NC rejection.

-   *Mistakes Analysis*

A detailed analysis of each incorrectly identified event was performed
to determine if any patterns arose. This was done on the most recently
performed scans where an electron event was required to occur within 5cm
of the vertex when the scanner was most experienced.

Confusing a CCmu for a NC event (or vice versa) is not very significant
since both constitute the background. Therefore, the fraction of these
background mistakes versus signal for background (or vice versa) was
found. Also, it was believed that DIS were the most difficult to
identify so the fraction incorrectly tagged events that were DIS was
found.

i.  5mm pitch

Scanning file: trainv2_05_2.tpc

Events created: 1999

Events scanned: 154

  ------------------------------------------ ----------------------------
  Wrong ID                                   21/154

  signal-bkg confusion                       14/21

  DIS                                        13/21
  ------------------------------------------ ----------------------------

Of the 154 events scanned, 21 were incorrectly tagged. Of these 21, 14
were mistaking signal for background (or vice versa).

Also, 61.9% of the misidentified events were DIS.

ii. 10mm pitch

Scanning file: trainv2_10_2.tpc

Events created: 1999

Events scanned: 176

  ------------------------------------------ ----------------------------
  Wrong ID                                   29/176

  signal-bkg confusion                       27/29

  DIS                                        15/29
  ------------------------------------------ ----------------------------

Roughly the same percentages of events were tagged incorrectly with the
10mm pitch as with the 5mm pitch. However, a higher fraction of the
wrongly tagged events were mistaking signal for background (or vice
versa).

This time only 51.7% of the misidentified events were DIS.

**Conclusion**- The 5mm spacing reduced the number of non-DIS mistakes
by 10%. DIS events cause the majority of the mistakes made and will most
likely produce an upper limit on the CCe efficiency and background
rejection. With the 5cm cut, the 10mm wire spacing resulted in a 26%
increase in confusion between signal and background.