1. Wrong sign muons detection in a
Monolith-like
structure
Marco Selvi
(Bologna University and INFN Ph.D. student)
In collaboration with M. Garbini, H. Menghetti

2. Overview Wrong sign muon physics The Monolith Detector
Background rejection power
Charge Identification
WSM from hadrons
Various detector structures
Test beam results
Conclusions

3. study of matter effects, CP violation
Physics at a n-Factory
Circulating 50 GeV m+ in a NuFactory (1021 decays in 5 years)
Beam made by nm and ne (m e+ ne nm)
Search at LBL for wrong sign muons (m-) coming from
ne oscillated into nm
q13, sign of Dm2,
study of matter effects, CP violation

4. nm CC rate (background)
m+ e+ ne nm
nm CC at 732 km
nm m+ + X

5. nm CC rate (signal) m+ e+ ne nm nm 1.1 105 nm CC at 732 km nm m- + X
oscillation nm
nm CC at 732 km
nm m- + X

6. n The Monolith Detector Large mass 34 kton
Magnetized Fe spectrometer B = 1.3 Tesla
Time resolution ~ 1 ns (for up/down discrimination)
Space resolution ~ 1 cm (rms on X-Y coordinates)
Momentum resolution sp/p ~ 20% from track curvature for outgoing m
~ 6% from range for stopping m
Hadron E resolution sEh /Eh ~ 90%/Eh 30%
14.5 m B B
~52000 m2 of detector : Glass Spark Counters
13 m Fe n
2.2 cm Fe
8 cm
29.5 m

7. Backgrounds
Two main sources:
Fake WSM (due to charge misidentification)
WSM from hadrons

8. Charge identification
Generate interaction using Pythia + q.e. + 1p corrections (Lipari code).
Simulate the whole event in Geant:
Multiple scattering with Moliere theory option ON (not just gaussian approximation)
Full B field description
Fit muon track using GEANE and Kalman filter approach (a real reconstruction, not just smearing)
both for signal and background

9. B field details n n n n

10. Long PC event example (m-)

11. background event example (m+)

12. n Wrong event example Large angle scattering
Overestimated in GEANT (~30) ...see OPERA
Recognizable via Kalman filter (change in slope)

13. Charge identification: results
Selection cuts:
Pm (from range) > 7.5 GeV
In each region:
At least 4 points
Track lenght > 300 cm
Same charge assigned in each region
Fractional bkg.
1 x 10-6
Efficiency
35%

14. Wrong sign muons
from hadrons

15. Wsm from hadrons

16. Wsm from hadrons
Large Magnetic Detector people showed (see Sitges Workshop Cervera’s talk)
that it is possible to reject such bkg up to
~ 2 x with 24% efficiency
just using two cuts:
Pm > 5. GeV
Qt > 1.4 GeV
Qt = Pm sin2q

17. ... What can Monolith say? Pm cut may be easily reproduced:
good muon momentum resolution
Qt depends on hadronic angular resolution
in LMD analysis they assume to have the same performances of MINOS (MINOS proposal - chapter 7)
in MONOLITH: it has to be checked !!

18. Angular resolution: true vertex
3cm read-out strips
From true vertex to true shower’s center of gravity
From true vertex to rec. shower’s center of gravity n
MINOS assumes to know the true vertex

19. Vertex resolution Transverse resolution sx = 5.6 cm
Longitudinal res. sy = 5.8 cm
Vertical res. sz = 5.1 cm

20. Ang. Resolution: reconstr. vertex
From true vertex to true shower’s center of gravity
From reconstructed vertex to rec. shower’s center of gravity n

21. hadronic angular resolution
Assuming vertex known: comparable with MINOS
Monolith fit
23.
10.6

22. hadronic angular resolution
Reconstructing vertex: about twice MINOS
Monolith fit
32.
8.2

23. e nm CC ne CC nm ne NC First approach
Just use a hard momentum cut (Pm >20 GeV)
and forget about the angular resolution.
Fractional bkg and efficiency
Charge misid.
nm CC
ne CC
nm ne NC e
MONOLITH
11 % 35
100 .6 30
LMD
24 % 38 6
5.6

24. Sin2(2q13) sensitivity Oscillation probability:
Pne-nm= s232 sin2(2q13) sin2(1.27 Dm2 L/E)
Fix q23=45°, change q13 and Dm2
Compare number of signal events (efficiency corrected) with the error in the surviving background events (statistical + 5% syst.)
Draw a 4s region

25. Sin2(2q13) sensitivity – 4s
Strong muon momentum cut Pm > 20 GeV

26. Second approach
Use LMD cuts (Pm >5. GeV; Qt > 1.4 GeV) and take into account the different smearing
3 times higher fractional “hadronic” backgrounds
Monolith fit
32.
8.2
e = 16%

27. Sin2(2q13) sensitivity – 4s Strong muon momentum cut Pm > 20 GeV
Qt > 1.4 GeV

28. Improvements Higher granularity Planes orientation
... perform the same cuts (Pm >5. GeV; Qt > 1.4 GeV) and modify the fractional bkg accordingly with the obtained hadronic direction smearing
Efficiencies are considered to be the same (16.5%)
Very conservative hypothesis: improvements are expected in both cases

29. Horizontal plates – 4 cm thick
Monolith fit
23.
12.

30. Sin2(2q13) sensitivity – 4s Strong muon momentum cut Pm > 20 GeV
Qt > 1.4 GeV
4 cm horiz plane
Pm > 5 GeV
Qt > 1.4 GeV

31. Vertical planes – 8 cm thick
...Against ~5 cm

32. Vertical plates – 8 cm thick
Monolith fit
15.
12.

33. Sin2(2q13) sensitivity – 4s Strong muon momentum cut Pm > 20 GeV
Qt > 1.4 GeV
8 cm VERT plane
Pm > 5 GeV
Qt > 1.4 GeV

34. Baseline: 3500 km Bkg ~ L-2 (fluxes)
Signal ~ L-2 (fluxes) x L2 (oscillation) = L0
... up to O(3000 km)
Baseline 732 km
8 cm VERT plane
Pm > 5 GeV ; Qt > 1.4 GeV
Baseline 3500 km

35. 100 kton detectors Baseline 732 km Mass: 34 kt 8 cm VERT plane
Pm > 5 GeV
Qt > 1.4 GeV
Mass: 100 kt

36. Test-beam
with a iron-RPC
calorimeter

37. Experimental setup 2,4,6,8,10 GeV Iron (5cm) + RPC (2cm) e, p, m
Cherenkov
Scintillators

38. Event display: m Use the muon direction as the true beam direction:
Uncertainty 1 degree

39. Event display: p

40. Direction reconstruction

41. hadronic angular resolution
Resolution better than the requested one.
Baby-Monolith fit
10.4
10.1

42. hadronic angular resolution
MC and Data comparison:
5cm thick plates
3cm strip width

43. hadronic angular resolution
MC and Data comparison:
10cm thick plates
3cm strip width
... Also 10cm agrees with MINOS fit (reference one) !!!

44. One word (slide) about
atmospherics

45. Vertical vs horizontal layers for atmospheric neutrinos (FAQ)
Selected atm. n’s events for fixed L/E resolution
Lower reconstruction efficiency along the vertical direction with vertical plates
About the same efficiency at small L/E (where the 1st minimum is expected):
Events near the horizon filtered by resolution requirements!
Horizontal plates
Vertical plates
8 cm iron
(contained events full simulation)
Pay on mixing, but marginally on Dm2

46. Comment about LMD How will this muon track be measured?
What has been simulated:

47. Comparing structures
LMD: Iron rod diameter: 6 cm Scint. rod diameter: 2 cm
MONOLITH hor 4cm
2 cm
2 cm
4 cm
Identical structures but LMD has less active volume !

48. Right treatment of the resolution
MINOS fit:
3d !!!

49. Conclusions
We demonstrate that a full simulation of a realistic detector gives, in the worst case (horiz. 8cm plates), a 3 times lower sensitivity
Among improvements, the better seems PLATES ORIENTATION (Moreover, it allows a good toroidal B field (not charge symmetric) ... Better S/N ratio !!)
Test beam results confirm that vertical orientation (no matter about segmentation) satisfies the requested performances
Atmospherics are reconstructed with the correct resolutions and efficiencies also with vertical plates!!