# Presentation: 865269

## Cosmic Ray Backgrounds

**Leon Mualem**
**University of Minnesota**

## Ground Level Components

**Muons**
- Vertical Diff flux @1GeV ~30/m**2**/s/sr/GeV
- Vert Integral Flux > 1GeV = 80/m**2**/s/sr*2000m**2**sr=0.2MHz
- Angular distribution ~cos**2**(θ)
- ~E**-1**,E**-2**,E**-3** (1,10,100 GeV/c)
**Neutrons**
- Vertical Diff flux @1GeV ~1/m**2**/s/sr/GeV
- Vert Integral Flux > 1GeV = 0.4/m**2**/s/sr*2000m**2**sr=0.8kHz
- Angular distribution ~exp(-8(secθ-1))
- ~E**-2.7**
**Photons **
- Vertical Diff flux @1GeV ~1/m**2**/s/sr/GeV
- Vert Integral Flux > 1GeV = 0.4/m**2**/s/sr*2000m**2**sr=0.8kHz
- Angular distribution ~exp(-8(secθ-1)) -> exp(-1.1(secθ-1))
- ~E**-2.7**

## Ground-level neutrons and photons
Detector: 15.7x15.7x134m ~2000 m2 effective area)
Generate neutron and photon fluxes with 
zenith angle random in cosθ, bins of 0.1
random energy (flat 1-4GeV) 
random azimuthal angle
random position on detector
Analyze with PJL standard 
    selections

- Detector: 15.7x15.7x134m ~2000 m2 effective area)
- Generate neutron and photon fluxes with
**zenith angle random in cos****θ, bins of ****0.1**
**random energy (flat 1-4GeV) **
**random azimuthal angle**
**random position on detector**
- Analyze with PJL standard
-     selections

**Simulations of Cosmic Ray Induced Backgrounds**

- 15.7m

- 15.7m

- 134m

## Neutrons

**Data from Ashton, “*****CR at ground level”*****, ed. Wolfendale (1974)**
**Atten. Length: ~120 g/cm****2**
**I(****θ****) = I(0)exp(-8(sec ****θ**** -1))**

## Neutron Selection Probability(Using Standard Analysis)

- Probability of
- selecting a neutron
- as a function of
- zenith angle:  P(θ)

## Neutron Rate vs. Angle

- Integral neutron
- rate (neutrons/s)
- as a function
- of angle:
- R(θ)=I(0)*
-    exp(-8(secθ-1))*
-    acceptance(θ)*
-    dcos θ

## Selected Neutron Event Distribution

- N(θ)=
-  P(θ)*R(θ)*T
- Total Events
-     =0.30 in
- 5 year
-   exposure
- (500s live)

## Electrons and photons

**Data from Daniels and Stephens; Revs Geophys. And Space Sci. 12, 233(****1974****)**
**~cos****2****θ**** for ****θ****< 60****o**
**Median energy ******** 10s of MeV**
**Attenuated as **
**             ****~exp(-x/175g.cm****-2****)**

## Photon Background

**Considered likely to be selected as electron event –EM interactions**
**Angular suppression not as strong as neutrons**
**Difficult to simulate correctly (easily)**
- Photons are from hadronic interactions production of π0; Associated particles should aid rejection
- Need to start with parent particles –N or P
- Photons can be seen from relatively far away
- Need to simulate large volume (X0=300m!)
**Estimate upper limit by simply simulating the photons as was done for neutrons**

## Photon Selection Probability(Using Standard Analysis)

- Probability of
- selecting a photon
- as a function of
- zenith angle:  P(θ)

## Photon Rate vs. Angle

- Integral photon
- rate (photons/s)
- as a function
- of angle:
- R(θ)=I(θ)*
-    acceptance(θ)
-    *dcos θ

## Selected Photon Event Distribution

- N(θ)=
-  P(θ)*R(θ)*T
- Total Events
-     =2600 in
- 5 year
-   exposure
- (500s live)

## Photon reduction possibilities

**Where can we go from here?**
- 2600 events is an unacceptable level of background
**Additional reduction**
- Containment/Fiducial cuts
- Interaction length ~80cm, current cut 15cm
-  increase, and increase on front/back faces
- Angular cuts
- currently at 45 degrees for no impact on FOM
- Correlated events
- How much flux comes in clusters, CORSIKA simulation
- Overburden
- Attenuation length ~125g/cm**2 **** ;  **~ 60cm

## Photon background vs. Overburden depth

**Reduction from 2560 events of photon background vs. depth**

## Potential side effects

**Better climate control**
- (handy in Northern Minnesota)
**Vastly improved SuperNOvA detection**

| Depth | Signal | EM bkd | Neutron  | S/sqrt(b) |
| --- | --- | --- | --- | --- |
| 0m | 1500 | 10,000 | 3,000 | 13 |
| 1m | 1500 | 1800 | 424 | 30 |
| 2m | 1500 | 320 | 60 | 77 |
| 3m | 1500 | 57 | 8.5 | 185 |
| 4m | 1500 | 10 | 1.2 | 450 |

## Find the SuperNOvA

- ~15min of data
- With typical ~10s
- supernova signal
- 10ms time bins
- NO OVERBURDEN

## Find the SuperNOvA

- ~15min of data
- With typical ~10s
- supernova signal
- 100ms time bins
- NO OVERBURDEN

## Find the SuperNOvA

**Find the SuperNOvA**

- ~15min of data
- With typical ~10s
- supernova signal
- 1s time bins
- NO OVERBURDEN

## Find the SuperNOvA

- ~15min of data
- With typical ~10s
- supernova signal
- 10ms time bins
- 1m OVERBURDEN

## Find the SuperNOvA

- ~15min of data
- With typical ~10s
- supernova signal
- 100ms time bins
- 1m OVERBURDEN

## Find the SuperNOvA

**Find the SuperNOvA**

- ~15min of data
- With typical ~10s
- supernova signal
- 10ms time bins
- 3m OVERBURDEN

## Find the SuperNOvA

- ~15min of data
- With typical ~10s
- supernova signal
- 10ms time bins
- 3m OVERBURDEN

## Conclusions

**EM background appears substantial**
- Possible help
- Increase cuts, length, angle, correlations
- Reduces signals
- Probably not enough
- Ostrich Solution
- Doesn’t affect signals
- Substantial increase in Supernova sensitivity
- ....