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 is an experiment dedicated to increasing

our understanding of the nature of neutrinos and

trying to determine neutrino oscillation

parameters.

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.

MINOS Experiment Overview

Near Detector

Far Detector

Energy spectra of incoming neutrinos can be changed by adjusting the positions of the target and the horns.

Near Detector

Necessary to have two detectors: one close to the neutrino source – the near detector, 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.

980 tonnes

282 planes of steel (3.8mx4.8m)

1.5T magnetic field

Near detector event rates

extrapolated to Far detector and

compared to real results => this

should allow to measure neutrino

oscillation parameters like m2 .

Far Detector

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.

5400 tonnes

486 iron/scintillator planes

of 8m diameter

1.5T magnetic field

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

Time of Flight system Main Goals: 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

dxdE

CalDet - CallibrationCallibration 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 1Analysis 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 2This 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 3Now 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 4Now 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 6Applying 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:

In the laboratory frame:

Muon Identification Analysis 8Recreating 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 9Applying 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),

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.