# Presentation: 466949

## MINOS Experiment:Oscillation Results from the First Two Years of Running 

**MINOS Experiment:****Oscillation Results from the First Two Years of Running**** **

- Wine and Cheese Seminar, Fermilab, **19th July  2007**

- Niki Saoulidou, Fermilab,
- For the MINOS Collaboration

## Outline

- Introduction
- Experiment Overview
- Neutrino Beam and MINOS Detectors
- Beam Neutrino Data in the  :
- Near Detector
- Far Detector
- Far Detector Oscillation Analysis
- Summary / Outlook

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## Introduction 

**Neutrinos**  were invented in order to solve a **“mystery”** (energy non-conservation in beta decays)...
- Since their birth, they have created even more **mysteries** themselves ...
**Solar neutrino “problem”**(e‘s from the Sun  are less than   expected )
**Atmospheric neutrino “problem” **(“Too few numu problem”)
- The “problem”  of missing neutrinos can be nicely explained  if they  posses non-degenerate  masses, in which case they can **oscillate** between the different  flavors:
**3 active   (LEP/SLC) **
**n sterile (MiniBoone results do not see a signal in the allowed  LSND region )**
**Non zero neutrino masses is one (or the only) of the strongest experimental  evidence  we have so far for physics beyond the Standard Model!**

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## 3-Flavor Oscillation Formalism

**U=**

- If neutrinos oscillate, then the interaction eigenstates (or weak eigenstates, which is what we observe) can be expressed in terms of the mass eigenstates as follows:

**Atmospheric**

**Cross Mixing**** **

**Solar****  **

**Majorana phases  **

**0******** ****decays**

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## 2-Flavor Neutrino Mixing

- In certain experimental situations only one  contributes, in which case   one can write the oscillation probability as :

**Physics**

**Experiment**

- Different neutrino experiments , depending on what components of the mixing matrix they want to measure involve:
** ****Different baselines **
** ****Different neutrino energies  **
** ****Different neutrino flavors  **

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## SuperK : Atmospheric neutrinos        

**SuperK : Atmospheric neutrinos****        **

-    Study  and e produced in the upper atmosphere.
-   Observation    **: fewer muon neutrinos than expected**
**    ****: as many electron neutrinos as expected**

- Observed / Expected  CC interactions

**Phys.Rev.Lett. 93:101801,2004**

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## K2K:1st Long-Baseline Accelerator-based Experiment 

**K2K:1****st**** Long-Baseline ****Accelerator-based Experiment**** **

**112 Observed / 158.1 Expected**

** ****Goal was  to confirm SK result with accelerator muon neutrinos **

** ****L=250Km**

- 58 single-ring like events

**Phys.Rev.D 74, 072003,2006**

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## MINOS Collaboration

**   ****30 institutions**
**  ****175 physicists**

- Argonne • Athens • Benedictine • Brookhaven • Caltech • Cambridge • Campinas • Fermilab College de France • Harvard • IIT • Indiana • Minnesota-Twin Cities • Minnesota-Duluth • Oxford • Pittsburgh  • Rutherford Sao Paulo • South Carolina • Stanford • Sussex • Texas A&M Texas-Austin • Tufts • UCL • William & Mary • Wisconsin

**MINOS Near Detector Surface Building**** **

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## MINOS Experiment

**MINOS Experiment**

** ****MINOS (****M****ain ****I****njector ****N****eutrino ****O****scillation ****S****earch)  is**
** ****a ****two detector**** long baseline ********oscillation experiment. **

**Cross Section (******** & Beam Modeling (************) uncertainties to high accuracy cancel out between  the two Detectors **

**Basic Idea : 2 detectors “identical” in all their important features. **

**Intense Beam**

**Far Detector**

**Near Detector**

****

****

******(E)************near****(E)      ********        ********(E)************far****(E)**

********

********

********

********

********

********

********

****

- 735 km

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## MINOS Physics Goals

**Verify ******************** mixing hypothesis** and make **a precise (<10%)** measurement of the oscillation parameters **Phys. Rev. Lett. 97 (2006) 19180 **
**Search for sub-dominant ****************e** oscillations (not yet seen at this mass-scale)
- Search for/rule out exotic phenomena:
- Sterile neutrinos
- Neutrino decay
- Use magnetized MINOS Far detector to study neutrino and anti-neutrino oscillations  (unique capability of MINOS experiment)
- Test of CPT violation
- Atmosphericoscillations: PRD75,092003(2007),PRD73,072002 (2006)
- Cosmic rays, hep-ex/0705.3815

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##  NuMI Neutrino  Beam

** ****NuMI Neutrino  Beam**

**207m**

**      ****120 GeV protons strike the graphite target**
**    ****Initial intensity                     1.50 x 10****13****  ppp   every  2-4 sec**
**    ****Current intensity                    2.50 x 10****13**** ppp   every 2.4 sec **
**    ****Have also  reached                 4.05 x 10****13****  ppp   every 2.2 sec **
**     ****Goal for 2007 is to run stably at  ~  2.5 x 10****13****  ppp every 2.2  sec **
**     ****Goal for  (2008-9) :**
**Improve beam Power (by 30-40%)**
**  ****From multi-batch  slip-stacking to NUMI **
** ****2.2 sec cycle time during Mixed Mode (stacking)**

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##  NuMI: Neutrino Beam configurations

** ****NuMI: Neutrino Beam configurations**

-  One can obtain different neutrino spectra by moving the target (have taken data already for four different energy configurations).
-   These data (ME*,HE*) are used to perform systematic  studies in the Near Detector  and tune our Monte Carlo.
*** ME = medium energy, HE = high energy, MHE = medium-high resulting from different target positions*

-                Beam composition
- (events in low energy configuration):
**98.5%        (6.5%   ), 1.5%**

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## The  MINOS Detectors

**NEAR**
**0.98 kt**

**FAR**
**5.4kt**

** ****Basic Idea : Two detectors “identical” in all their important features. **
- Both detectors are tracking calorimeters composed of interleaved planes of steel and scintillator
-  2.54 cm thick steel planes
-  1 cm thick  & 4.1 cm wide scintillator strips (read out by WLS fibers)
-  1.3 T toroidal magnetic field.
-  Multi-Anode  Hamamatsu PMTs (M16 Far & M64 Near)
-  Muon momentum resolution  ~ 6 % from range  ( ~ 12 % from curvature )

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## The MINOS Calibration

**The MINOS Calibration**

- Calibration of ND and FD :
- Calibration detector     (overall energy scale)
- Light Injection system (PMT gain+Linearity)
- Cosmic ray muons          (strip to strip and detector to detector)
- Energy scale calibration:
**3.1 % absolute error in ND**
**2.3 % absolute error in FD**
**3.8 % relative**

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##  MINOS – NUMI Running

** ****MINOS – NUMI Running**

**Dataset used in the first   and current  analysis  ****(1.27x10****20**** POT’s) Run I**** **

**Running in higher energy beam configurations**

- Accelerator shutdown

**Additional Data Set used in current analysis   ****(1.23x10****20**** POT’s) Run IIa**

**Many thanks to our Accelerator Division colleagues!!**

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## Neutrino Event topologies

**NC Event**

**UZ**

**VZ**

**Long ******** ****track+ hadronic activity at vertex**

**Short, with typical EM shower profile**

**Short event, often diffuse**

**3.5m**

**1.8m**

**2.3m**

**Monte Carlo**

**E******** = ****E****shower****+P******

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## Event Selection Criteria – Near and Far

-  ********** ****CC****-like events are selected in the following way:**
- Event must contain at least one reconstructed track
- The reconstructed track vertex should be within the fiducial volume
- The fitted track should have negative charge (selects )
- Cut on likelihood-based Particle ID parameter which is used to separate CC and NC events.

- 

- 

**Calorimeter**

**Spectrometer**

**NEAR DETECTOR**

**FAR DETECTOR**

**Fiducial Volume**

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## Analysis Changes w.r.t. published (Phys.Rev.Lett.97(2006)19180) Analysis

- _Reconstruction – Event Selection__ _
**Improved track reconstruction : **
**More events satisfy pre-selection track quality related criteria**
**Improved Event Selection with the use of 2D PDFs (correlations are**
**taken into account) and more  Discriminating variables  :**
** ****2) Increased efficiency for selecting ************ ****CC   **
** ****3) Increased background rejection (less NC contamination)**
** ****Enlarged Far Detector Fiducial Volume and relaxed 30 GeV Energy**
** ****Cut on Analysis sample:**
** ****4) Increased overall neutrino selection efficiency **

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## Analysis Changes w.r.t. published (Phys.Rev.Lett.97(2006)19180) Analysis

- _Intranuclear Re-scattering -  Hadronization & ____Cross Section  Modeling _
**Updated/Improved Models  (show better agreement with world’s **
**data).**
**-We determine the  relationship  between hadronic true  and  visible**
**energy from the MC. These  changes  in  the  MC resulted in a 10%**
**decrease in the visible  shower energy in both Near and Far Detector**
**Data (original systematic uncertainty 11%)**
********MINER****A experiment will help better understand intranuclear*
* **Re-scattering effects and hadronization modeling *

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## Selecting Charged Current Interactions

-      Events are selected using a likelihood-based procedure, with six input variables and 2D Probability Density Functions (PDFs) that show discriminating power  between True CC and NC interactions:
**Track Topology Variables**
- Track Pulse Height Per Plane
- Number of Track Only Planes
- Number of Track Planes
- Goodness of Muon Track Fit
- Reconstructed Track Charge
**Event Variables**
- Reconstructed Kinematics Y distribution ( Y = Shower Energy / Neutrino Energy)
**Relative CC/NC Spectrum and CC/NC  Priors**

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## PID Improvement over old Analysis

**New PID has higher overall efficiency and higher background rejection (less contamination from NC interactions)**

- NEAR

- FAR

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## Near detector event reconstruction

**High rate** in **Near detector** results in multiple neutrino interactions per MI spill
- Events are separated by topology and timing

**Time (us)**

**One spill in the Near Detector**

**Individual events**

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## Near Detector : Data/MC

**Near Detector : Data/MC**

**Low Level ND Quantities agree quite well****.**

**Track Angles (X Y Z)**

**Plots normalized to area**

**Event Vertices (X Y Z)**

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## Near Detector  : Data/MCParticle IDentification Input Variables

**Input Variables used for CC-NC Separation agree well between Data and MC**

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## Near Detector  : Data/MCParticle IDentification Distribution

**Near Detector  : Data/MC****P****article ****ID****entification**** ****Distribution**

**Agreement between Data and MC very good, for all neutrino energies.**

**Cut to select **
**CC-like events**

**CC-like**

**NC-like**

**0-3 GeV**

**3-6 GeV**

**All Energies**

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## Near Detector:Data/MC (Hadron Production Tuning)

**LE**

**ME**

**HE**

-  Disagreement between Data /MC : “Dip” that moves with neutrino energy for different target positions, characteristic signature of beam modeling effect (hadron production)
-  MC tuning (on hadron xF and pT) improves the agreement between Data and MC.
-  Results from the MIPP experiment will help us further improve our understanding of the hadron production model.

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## Near Detector  : Data Stability 

- Beam is very stable and there are no significant intensity-dependent biases in event reconstruction.
- Run IIa Data are different (~7% lower at the peak) from RunI Data due to different target position (known identified effect)

**Energy spectrum by Month: Run I**

**Near Detector  : Data Stability **

**Energy spectrum by Month : Run IIa**

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## Near Detector Data :What did we learn

**The agreement between Data/MC of low level quantities indicates that there are no major detector/reconstruction effects not modeled by our MC.**
**The disagreement between Data/MC of the reconstructed neutrino energy spectrum  is related with the main uncertainties that we mentioned earlier (hadron production and cross sections modeling).**
**We would like to use a Near-Far extrapolation technique as insensitive to these systematics uncertainties as possible.**

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## Far Detector Beam Data: Blind Analysis 

** **Since May 20th 2005 running in the Low Energy configuration
-  Collaboration decided to perform Blind Analysis:
-  Unknown (energy biased) fraction of our Far Detector Data are “open” and we use them to  perform data quality checks.
-   Remaining fraction  of our Far Detector Data are “hidden” and final analyses will be performed on total sample once Box is opened.
-  Once data quality is assured and cuts and analysis decided on, box is opened
**After Box Opening for the first analysis we re-blinded our data using a different function.**

****** **
**Justice is Blind**

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## Far Detector Data : Typical Events

- In the Far detector we record events that satisfy either of the following trigger conditions:
** ****4/5  consecutive planes  **
- OR
**Sum of ADC >1500 (PH/plane = 800 ADC for muons) or  6 hits in any 4 consecutive plane window **
-                                       0R
**Events within +/-50 usec from a beam spill  (GPS “spill time” is send via internet to Far DAQ for triggering)**
-  Also events +/- 50 usec from “fake spill”. (“Fake spill” data used for background studies)
- Mostly record cosmic ray muons at a rate of 0.5 Hz .

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## Far Detector Live Time

**Run I**

**Run IIa**

**Special thanks to everyone who helped to maintain such a high livetime during this period!**

**Far Detector live time  is 99%**

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## Far Detector Data : Selecting Beam Induced Events

**Far detector neutrino events  have very distinctive topology and timing **

**Neutrino candidates are in 8.9us window**

**0.5 Hz cosmic mu rate**

- Time stamping of the neutrino events is provided by two GPS units (located at Near and Far detector sites).
- Analyzing 7.0 million “fake” triggers 0.8 non neutrino events are expected in the Analysis Sample.

**Far Detector Data : ****Selecting Beam Induced Events**

**Neutrino Candidates**

**COSMICS**

- X Angle Degrees

- Y angle Degrees

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## Far Detector Neutrino Events

- Cross Talk Hits

- Cross Talk Hits

-  Beam

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## Far Detector Beam Data vs Time and POT’s

- Neutrino events per POT’s are flat as a function of time.
- Neutrino events follow integrated POT’s nicely.

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## Far Detector Beam Data:Vertices and Timing 

**Far Detector Beam Data:Vertices and Timing**** **

- Timing and topological characteristics of beam neutrino event candidates in agreement with expectations.

**NUMI Only Mode**

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## There are two general methods for predicting the unoscillated Far Detector spectrum:

Near Detector “Data Driven”:

Measured ND spectrum is directly used to predict FD Unoscillated spectrum.
FD Prediction depends very weakly on details of the hadron production and cross section models.

Near Detector “Fit Based”:

Hadron production and cross section models are “tuned” by fitting the measured ND spectrum.
Tuned MC is then used as the FD unoscillated spectrum.
Disadvantage: If the models are “inadequate”, the description of the Near and Far Detector Data will be inadequate as well.

We have developed two different methods from each category. We choose as primary the “Data Driven” “Beam Matrix Method” since it gives the smallest systematic error.

**Near Detector “Data Driven”:**
- Measured ND spectrum is directly used to predict FD Unoscillated spectrum.
- FD Prediction depends **very weakly on details of the hadron production and cross section models.**
**Near Detector “Fit Based”:**
- Hadron production and cross section models are “tuned” by fitting the measured ND spectrum.
**Tuned MC is then used as the FD unoscillated spectrum.**
**Disadvantage: If the models are “inadequate”, the description of the Near and Far Detector Data will be inadequate as well.**
***We have developed two different methods from each category. We choose as primary the “Data Driven” “Beam Matrix Method” since it gives the smallest systematic error.***

**Predicting the Unoscillated FD Spectrum**

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## Use the “Beam Matrix” method with which beam modeling and cross sections uncertainties cancel (to a large extent) between the two detectors.

The “Beam Matrix” method uses  : 
The  ND reconstructed energy distribution  (Data),
The knowledge of pion/kaon 2-body decay kinematics and the geometry of our beamline, 
Our Monte Carlo to provide necessary  corrections due to energy smearing and acceptance.

**The “Beam Matrix” method uses  : **
- The  ND reconstructed energy distribution  (Data),
- The knowledge of pion/kaon 2-body decay kinematics and the geometry of our beamline,
- Our Monte Carlo to provide necessary  corrections due to energy smearing and acceptance.

**Predicting Unoscillated FD Spectrum: ****Beam Matrix Method**

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## Near

- Beam Matrix provides a very good representation of how the far detector spectrum relates to the near one.
- Beam Matrices that correspond to different hadron production models are very similar (spread in each column determined primarily by the geometry of the beamline)

**“****Beam**** Matrix ”Method :**** Near to Far extrapolation**

- Far

- =

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## Beam Matrix Method : Systematics

**Beam**** Matrix Method : Systematics**

- Ratio of true Spectra to nominal MC : shows the magnitude of the Change due to systematic uncertainty under study
- Ratio of predicted spectra to nominal MC : shows how accurately this method predicts the true spectra.

**Difference between Black and Red lines is a measure of the cancellation of the systematic uncertainty (zero difference means systematic has cancelled entirely between Near and Far)**

**Resonant Cross Section changed by +/-20%**

**Hadron Production Model changed by +/- 1 sigma**

**Beam Modeling & Cross Section Uncertainties Cancel to a large extent**

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## Remaining systematic uncertainties 

| Uncertainty | Shift in m2
(10-3 eV2) | Shift in 
sin2(2 |
| --- | --- | --- |
| Near/Far normalization 4% | 0.065 | <0.005 |
| Absolute hadronic energy scale 10%  | 0.075 | <0.005 |
| NC contamination 50% | 0.010 | 0.008 |
| All other systematic uncertainties | 0.041 | <0.005 |
| Total systematic (summed in quadrature) | 0.11 | 0.008 |
| Statistical error (data) | 0.17 | 0.080 |

- Beam and cross section uncertainties using the Beam Matrix Method cancel to a very large extent.
- The main remaining systematic uncertainties are Near/Far normalization, absolute hadronic energy scale and NC contamination.

**Remaining systematic uncertainties**** **

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## Predicting the Un-Oscillated Spectrum : Alternative  Methods

**Predicting the Un-Oscillated Spectrum : Alternative  Methods**

-     Results from all  four extrapolation methods in good agreement with each other at the few (<4%) percent level.

**- Beam Matrix**
**-  F/N**
**- NDFit**
**- 2DFit**

**Overflow bin**

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## Box opening

**Extensive checks on the open dataset in the FD completed.**
**Analysis methods fully validated on MC datasets.**
**Proceed to open the box and look at the full dataset**

**FD FULL DATA SET 2.50x10****20**** POT’s**

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## Far Detector CC-Like Event Selection

**Far Detector CC-Like Event Selection**

| Cut | Number of Events |
| --- | --- |
| Track in fiducial volume | 847 |
| Data quality cuts | 830 |
| Timing cut | 828 |
| Beam quality cuts | 812 |
| Track quality cut | 811 |
| Track charge<=0 | 672 |
| PID parameter>0.85 | 564 |
| Reco Enu<200 GeV | 563 
Final Analysis Sample |

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## FD CClike Events :     Observed vs Expected

| Data Sample | FD
Data | Expected
(Matrix Method; Unoscillated) | Data/Prediction
(Matrix Method) |
| --- | --- | --- | --- |
| CClike All  | 563 | 738  30 | 0.76 (4.4 ) |
|  CClike (<10 GeV) | 310 | 496  20 | 0.62 (6.2 )   |
| CClike (<5 GeV) | 198 | 350  14 | 0.57 (6.5  |

**FD CC****like**** Events :     ****Observed vs Expected**

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## Fit to the visible energy spectrum of the selected Far detector CC events to extract the mixing parameters Δm2 and sin22θ:

- Systematic uncertainties:
-      4%  N/F normalisation
-      10% Absolute shower energy scale
-      50% NC background Contamination

- common to near
- and far detectors

-        Statistical error       Systematic errors

**Oscillation Fit**

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## Strong energy-dependent suppression of μ events observed.
Consistent with the neutrino oscillation hypothesis.

**FD CC****like**** Events: Best Fit Spectrum**

- Strong energy-dependent suppression of μ events observed.
- Consistent with the neutrino oscillation hypothesis.

- Oscillation Hypothesis best fit

- No Disappearance  Hypothesis

- P(2,n.d.f) = 0.18

- 2 /n.d.f  = 41.2/34 = 1.2

- P(2,n.d.f)  is negligible

- 2 /n.d.f  = 139.2/36 =3.9

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## FD CClike Events: MINOS Allowed Region

**FD CC****like ****Events: MINOS Allowed Region**

- _Best Fit Values when fit Constrained to the Physical Region_

- 2 /n.d.f  = 41.2/34 = 1.2

- eV2/c4

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## Best Fit: No constraint to physical Region

**Best Fit: No constraint to physical Region**

- _Best Fit Values when fit Not Constrained to the Physical Region_

**The Feldman-Cousins Method is one that insures coverage.**
-  We have **already evaluated the effect when only statistical uncertainties are considered**, we plan to fully exploit the FC Method for our final results.
-  Given the initial statistical studies, **the Feldman – Cousins approach indicates that our current Confidence Intervals are slightly conservative (over-coverage)**

- 2 /n.d.f  = 40.9/34 = 1.2

- eV2/c4

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## FD CClike Events: MINOS Allowed Region

**FD CC****like ****Events: MINOS Allowed Region**

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## FD Distributions : Track Angles

**FD Distributions : Track Angles**

- Agreement between Data and oscillation  best fit very good.

**Neutrinos point ~3****0**** up in the FD!!**

**Mean:87.6**

**Mean:89.9**

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## FD Distributions :  Vertices

**FD Distributions :  Vertices**

- Agreement between Data and oscillation  best fit very good.

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## PID Input Variables

**FD FULL DATA SET 2.50x10****20**** POT’s**

**PID Input Variables**

- Agreement between Data and oscillation best fit very good

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## PID Distributions

**FD FULL DATA SET 2.50x10****20**** POT’s**

**PID Distributions**

- Agreement between Data and oscillation best fit very good

- NEW PID

- OLD  PID

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## FD CClike Events:Kinematic Distributions

**FD CC****like**** Events:Kinematic Distributions**

**FD FULL DATA SET 2.50x10****20**** POT’s**

- Agreement between Data and  oscillation  best  fit very good

- 2 /n.d.f = 30.8/20 = 1.5

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##  PRL  2006 – Current Results

-  PRL  2006 – Current Results

- Best Fit value changed due to :
- 1) Partially statistics (new events)
- 2)The systematic shift in Shower energy by 1 with the new Intranuclear Re-scattering Model.

**Run I+IIa   ****   **
**Run I (2006) Initial Analysis**

- }

- }

**Initial Analysis**

**RunI – RunIIa Contour Overlap = 56%**

**Probability  = 25%**

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- N.Saoulidou

## The MINOS new result increases further (w.r.t our previous one) the precision on the knowledge of the “atmospheric mass squared difference”, which is important for the next generation neutrino oscillation experiments. 	

The MINOS result is in agreement with previous measurements (SuperK and K2K). The fit of the Neutrino Energy Spectrum under the oscillation hypothesis yields a Probability of 18%.The fit to the Neutrino Energy Spectrum under the hypothesis of no disappearance  yields a negligible probability.

The systematic uncertainties of this measurement are well under control.

With the MINOS increased statistics, we will be able to test “exotic” models and possibly disfavor them with large significance!

Analyses of Neutral Current, Electron Neutrino Appearance, and Neutrino Cross Sections are underway...

Stay tuned!!

**Summary / Outlook**

**The MINOS new result increases further (w.r.t our previous one) the precision on the knowledge of the “atmospheric mass squared difference”, which is important for the next generation neutrino oscillation experiments. ****	**
- The MINOS result is in agreement with previous measurements (SuperK and K2K). The fit of the **Neutrino Energy Spectrum under the oscillation hypothesis yields a Probability of 18%.**The fit to the Neutrino Energy Spectrum under the hypothesis of **no disappearance  yields a negligible probability.**
- The systematic uncertainties of this measurement are well under control.
**With the MINOS increased statistics, we will be able to test “exotic” models and possibly disfavor them with large significance!**
**Analyses of Neutral Current, Electron Neutrino Appearance, and Neutrino Cross Sections are underway...**
**Stay tuned!!**

- Fermilab W&C  07-19-07

- N.Saoulidou

## Acknowledgements

**On behalf of the MINOS Collaboration, we would like to express our gratitude to the *****many Fermilab groups who provided technical expertise and support in the design, construction, installation and operation of the experiment.***
**We would also like to gratefully acknowledge financial support from the following institutions: DOE, NSF, University of Minnesota (and the Minnesota DNR for hosting us) and STFC (UK)**

- Fermilab W&C  07-19-07

- N.Saoulidou