Transcript Muon Detection in the MINOS Calibration Detector

Muon Identification in the
MINOS Calibration Detector
Anna Holin
05 December 2005
University College London
Introduction
This talk will focus on the following:
a short MINOS experiment overview
 a description of the MINOS calibration
detector (CalDet)
 why muons are so important for the
calibration of the MINOS detectors
 muon identification - analysis of a CalDet run
 future plans

MINOS Experiment Overview
Far Detector
MINOS is an experiment dedicated to increasing
our understanding of the nature of neutrinos and
trying to determine neutrino oscillation parameters.
Near Detector
A beam of mostly muon neutrinos is generated at
the Main Injector at Fermilab:
120 GeV beam of protons incident upon target
=> produces a shower of mostly pions and kaons
=> focussed by two parabolic horns down a 675 m evacuated pipe => hadrons decay to muons
and muon neutrinos => hadron absorber removes remaining hadrons and 240 m of rock
removes muons => beam of muon neutrinos. MINOS started data taking in March 2005.
Near Detector
Energy spectra of incoming
neutrinos can be changed by
adjusting the positions of the
target and the horns.
980 tonnes
282 planes of steel (3.8mx4.8m)
1.5T magnetic field
Necessary to have two detectors:

one close to the neutrino source – the near detector,
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and the other one far away – the far detector,
so that oscillations have sufficient time to develop, even if m2 is small.
Near detector provides a zero reference point => results are extrapolated to Far detector.
Far Detector
Near detector event rates
extrapolated to Far detector and
compared to real results => this
should allow to measure neutrino
oscillation parameters like m2 .
5400 tonnes
486 iron/scintillator planes
of 8m diameter
1.5T magnetic field
Far detector was planned as two self-sufficient halves and was built in two phases,
which allowed to commence taking cosmic ray data already in August 2003.
CalDet
The Minos Callibration Detector located
at CERN in the East Hall test beam
complex (beams T7 and T11).
Data taking 2001-2003.
12 tonnes
60 steel planes / 24 strips each
1m x 1m
no magnetic field
2 Čerenkov counters
Main Goals:
Time of Flight system

Ensure that the separate parts of the detector work together

Light injection and cosmic ray calibration procedures validated and optimised

Electronic and hadronic responses of detectors determined – energy scale for MINOS

Near and Far detector electronics compared to each other
dE
dx
CalDet - Callibration
Callibration is crucial. Important calibration elements in CalDet:
Electronics calibrated using known quantities of charge injected
and read out,
 Response of pixels on every PMT homogenised using the light
injection system (LI),
 Development of methods to reduce / account for PMT crosstalk,

Beam muons of given energy travel the same distance through all
three detectors => for CalDet beam energy is known a priori => this
can be translated into an absolute energy range for all detectors,
which is crucial for measuring muon momentum in the Near and
Far detectors.

In CalDet, muons of energies <2GeV stop in the detector – they
interact with less than the 60 planes of the detector, which is an
ideal oportunity to measure dE/dX.
Therefore it is important to isolate the muons from the CalDet data
in order to find the absolute energy scale for all detectors.
Muon Identification Analysis 1
Analysis for run 40618 at momentum 1.8GeV (run with only 1 Cerenkov detector):
This sequence shows how muons can be identified by applying various cuts to the data.
Main cut applied: only the 2 middle strips in detector plane 0 (strips 11 and 12)
All Particles
Electrons
Muons + Pions
Kaons
Protons
Muon Identification Analysis 2
This is the same histogram as before, but showing only the curves for all
particles and for the muons + pions:
All Particles
Muons + Pions
Muon Identification Analysis 3
Now find the “trackiness” by analysing how many events hit a certain number of strips in a
plane – muons tend to hit only around one strip (of 24) in a given plane, but pions tend to
shower and hit many strips in a given plane, thus providing a good way of finding the muons:
Muon Identification Analysis 4
Now we can create a 2-D histogram of the number of hit strips from the previous histogram
versus the number of hit planes:
Muon Identification Analysis 5
We know that in CalDet, at particle momentum 1.8 GeV, on-momentum muons are expected to
have a peak interaction with ~51 planes.
And indeed around this value in this histogram, the particles interact with maximum ~2.5 strips.
So to identify the on-momentum muons, we could apply a cut at the “minimum” number of hit
planes = 41 to the original histogram, thus getting…
Muon Identification Analysis 6
Applying a cut to show only the particles that have hit more than 41 planes:
All Particles
Muons + Pions
Muons
Muon Identification Analysis 7
This is not ideal because when pions decay into muons, there will actually be two peaks:
 one corresponding to the on momentum muons,
 and one to muons that were emitted in the opposite direction in the pion’s restframe.
In the Pion restframe:
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
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In the laboratory frame:




Muon Identification Analysis 8
Recreating a 2-D histogram of the number of hit strips versus the number of hit
planes, as before, but changing the number of bins and applying colour, we get:
Muon Identification Analysis 9
Applying this new cut, i.e. removing all the particles that hit more than 2.5 strips per
plane, we can identify muons in the original muon/pion histogram:
All Particles
Muons + Pions
Muons
Future Plans
The MINOS NuMi beam has just collected a number of 1e20
protons on target, which was the goal set by the collaboration so as to
open the first box and begin analysis on the data. So the first
measurements will be made in a few weeks,

The 4-day MINOS collaboration meeting will take place in January
(5-8 January 2006),
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The main things that I am going to be working on in the near future
are:
Chris Smith is coming to UCL in the new term, and I will probably
be working with him on analyzing data,

Jenny asked me to work on writing a paper describing the results
presented in Leo Jenner's thesis so that his findings can be published.

Thank You.