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L-Tracker Fitter Status. James L. Popp UC Irvine February 6, 2005 MECO Collaboration Meeting. Outline. Goal : Develop pattern recognition with the longitudinal tracker beginning with simulated raw detector signals (cluster formation, etc.)

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L tracker fitter status

L-Tracker Fitter Status

James L. Popp

UC Irvine

February 6, 2005

MECO Collaboration Meeting


Outline

Outline

  • Goal: Develop pattern recognition with the longitudinal tracker beginning with simulated raw detector signals (cluster formation, etc.)

  • Summarize what we have fixed and are fixing in the existing L-tracker pattern recognition and fitter code developed at UCI

  • Discuss maximum likelihood fitter performance under ideal conditions

  • What happens to fitter results when finite spatial resolution is added

  • Conclusions & Plans

James L. Popp, UC Irvine L-Tracker Fitter Status


Code repairs

Code Repairs

  • Evident in early 2004: that the code we had was not performing as well as we expected with MECOtracker001.gmc

  • After many attempts to find a “quick fix” yielded little progress, we decided to break the code up into smaller parts and test each one.

  • Fitter & pattern recognition had

    • Numerous bugs

    • Designed too closely around a simplified detector

    • Geometry & absorber change

  • The size of the whole project required some

    coordinated division of labor:

    • Fitter (some issues remain)

    • “Helix” pattern recognition

    • Straw cluster recognition

    • Cluster reconstruction w/ realistic inefficiencies

    • etc.

James L. Popp, UC Irvine L-Tracker Fitter Status


Physics deadbeats in pittsburgh

Physics Deadbeats in Pittsburgh

  • Cleaned up fitter, after some consultation with TJ

  • Next…results using ideal position information

James L. Popp, UC Irvine L-Tracker Fitter Status


Longitudinal tracker

Longitudinal Tracker

Geometry: “Octagon with eight vanes” – tilted modules

Straws:2.6 m length  5 mm diameter, 25 mm thickness – 2800 straws

Three layers per plane, outer two resistive, inner conducting

Pads:30 cm  5 mm wide cathode strips affixed to outer straws

Position Resolution: in-plane perp to wires 0.2 mm, along wires 1.5 mm

James L. Popp, UC Irvine L-Tracker Fitter Status


L tracker setup current fitter studies

L-Tracker Setup: Current Fitter Studies

  • GMC/crd/tracker/MECOtracker001.gmc

  • Fitter tries to determine the most probable momentum entering tracker

    • Requires at least 5 module crossings (redundancy)

    • Uses no more than 8 (could be more)

James L. Popp, UC Irvine L-Tracker Fitter Status


Simulation reconstruction ideal conditions

Simulation & Reconstruction: ideal conditions

  • GEANT: Conversion in Al target

  • Cluster cuts: approx. 48%

    • Tracker: at least

      • 5 module crossings

      • 1 straw hit per crossing

    • Module crossing position

      • 1st module entry point (x,y,z)

    • Pitch angle cut: > 40 degrees

  • Input to fitter: momentum from simple

    helix fit to module crossings

  • Fitter cuts: approx. 35%

    • Likelihood function FWHM < 0.6 MeV

    • Max. scattering angle < 0.1 radians

    • Pitch angle: 45 – 60 degrees

    • Trigger energy deposition > 75 MeV

James L. Popp, UC Irvine L-Tracker Fitter Status


Mu e pitch angle

Mu-e: Pitch Angle

  • Reconstructed

    entry angle

  • True entry angle

James L. Popp, UC Irvine L-Tracker Fitter Status


Mu e momentum

Mu-e: Momentum

  • Reconstructed entry

    momentum

  • True entry momentum

  • Reconstructed minus

    true….next slide…

James L. Popp, UC Irvine L-Tracker Fitter Status


Mu e intrinsic resolution

Mu-e: Intrinsic Resolution

  • Mean (gaussian) = - 0.045 MeV/c

  • Standard deviation (gaussian) = 0.12 MeV/c

James L. Popp, UC Irvine L-Tracker Fitter Status


Mu e resolution

Mu-e Resolution

  • Noise/Signal = 0.05

  • Acceptance = 0.21

  • Signal window minimum = 103.3 MeV

James L. Popp, UC Irvine L-Tracker Fitter Status


Mu e conversion and dio

Mu-e Conversion and DIO

  • Protons on production target:

  • Muon stopping efficiency:

  • Experiment run time:

  • Observation time window efficiency: 0.49

  • MECO L-tracker acceptance: 0.21

  • Assume

    • Probability for mu-e conversion:

  • Expected number of mu-e events: 6.1

  • Table 5 – MECO memo 099:

    • Expected # DIO above 100 MeV =

James L. Popp, UC Irvine L-Tracker Fitter Status


Mue and dio energy spectra

Mue and DIO Energy Spectra

  • DIO: 859,800 events

    • Energy: 100 – 105 MeV

  • Mu-e: 81,626 events

  • Normalization

    • values in previous slide

James L. Popp, UC Irvine L-Tracker Fitter Status


Finite spatial resolution

In-plane

z

normal

Finite Spatial Resolution

  • Gaussian random variables

    • In-plane direction (perp wires)

    • z direction (parallel wires)

  • Standard deviations

  • Add random numbers to true module crossing (entry) points

Tracker module cartoon

James L. Popp, UC Irvine L-Tracker Fitter Status


Mu e pitch angle momentum

Mu-e: Pitch Angle & Momentum

  • Spatial resolution seems to have relatively small effect - deceptive

  • Leads to large scattering angle estimates when crossings are close together

James L. Popp, UC Irvine L-Tracker Fitter Status


Mu e intrinsic resolution1

Mu-e: Intrinsic Resolution

  • Spatial resolution – Gaussian fit

    • Perfect: mean = - 0.045 MeV/c, Standard deviation = 0.119 MeV/c

    • Finite: mean = - 0.054 MeV/c, Standard deviation = 0.154 MeV/c

James L. Popp, UC Irvine L-Tracker Fitter Status


Mu e resolution1

Mu-e Resolution

James L. Popp, UC Irvine L-Tracker Fitter Status


Spatial resolution lever arm effect

segments

Spatial Resolution: Lever arm effect

  • Vertical axis: scattering angle (radians)

  • Horizontal axis: minimum of 2 adjacent segments sharing the angle (cm)

James L. Popp, UC Irvine L-Tracker Fitter Status


Mu e likelihood function spatial resolution

Mu-e Likelihood Function: Spatial Resolution

  • Illustrate point further:

    • Left: No smearing

    • Right: Smearing – gaussians

James L. Popp, UC Irvine L-Tracker Fitter Status


Conclusions plans

Conclusions & Plans

  • Likelihood function: modified to include effect of spatial resolution

  • Cluster recognition routines are under development

  • Cluster reconstruction is not far from completion

  • Incorporate cluster angle (local crossing angle) in likelihood function

  • Simulate pad & crystal signals…

James L. Popp, UC Irvine L-Tracker Fitter Status


L tracker fitter status

END

James L. Popp, UC Irvine L-Tracker Fitter Status


Requirements resolution

Requirements – Resolution

  • The Tracker must provide precise momentum measurements to separate conversion signal events from muon decay in orbit (DIO) in a 1 T field.

  • The end point energy for DIO electrons coincides with the conversion signal, the end point spectrum falls as the 5th power of E, thus the level of DIO background in the signal region is sensitive to the resolution function; both the central (gaussian) region and high side tails

  • To obtain a signal / noise ratio of 20 for a nominal conversion signal of Rme = 10-16 requires an energy FWHM < 1 MeV

The resolution is dominated by multiple scattering, thus material must be kept to a minimum

Chamber r – f res. of 0.2 mm and z res. of 1.5 mm are adequate and achievable

DIO Background convolved with detector response

Acceptance wrt perfect detector for fixed 20:1 S/N

GEANT conversion signal simulation

James L. Popp, UC Irvine L-Tracker Fitter Status


Requirements rate handling efficiency

Requirements – Rate Handling, Efficiency

  • A beam intensity of ~1011 stopped muons / sec implies that the detector must be capable of operating in a high rate environment.

    • This has driven the choice of 5 mm diameter straws and fast gas as the basic detector element. Note that the multiple scattering contribution to the resolution drives us to use thin walled (25 mm) straws

    • The majority of DIO electrons are at low pTrelative to signal events, thus the active elements of the detector are at large radius with respect to the stopping target

  • The detector must have reasonable efficiency to make the most of the sensitivity provided by the intense stopped muon beam. This drives a close packed straw array.

  • Reconstruction efficiency will be discussed in detail later in the talk

James L. Popp, UC Irvine L-Tracker Fitter Status


Two geometry options

Two Geometry Options

  • Two geometries under consideration (details follow)

    • “Longitudinal” (or simply “L”) Tracker with straws (nearly) parallel to the DS axis

    • “Transverse” (or “T”) Tracker with straws perpendicular to the DS axis

    • The nature of the event information and the engineering challenges associated with the construction are quite different for each arrangement

  • We have formed a “Tracking Chamber Advisory Committee” to evaluate both variants and recommend a choice to the MECO Executive Committee

  • We do not have an ETA on this decision yet, although (currently) this system is not on the MECO critical path

James L. Popp, UC Irvine L-Tracker Fitter Status


Tracker studies

Tracker Studies

  • Existing Efforts

    • L Tracker prototypes at Houston and Osaka using different straw types

    • Front-end electronics work at Houston that is largely applicable to either the L or T variants

    • Simulations of performance in the presence of backgrounds at UCI (L Tracker) and NYU (T Tracker)

  • New Initiatives this year

    • T Tracker mechanical design at Syracuse University

    • Additional front-end electronics at UVA, LBL

    • Simulation software coordination via Berkeley

    • Trigger/DAQ/Back-end electronics design at BU, UMass, NYU

James L. Popp, UC Irvine L-Tracker Fitter Status


Tracker simulations

Tracker Simulations

  • Effects Modeled

    • GEANT3 detailed geometries including straw walls, wires, gas, manifolds

    • Noise hits fromg, p, n, at the nominal rate and doubled

    • Resolution – 200 mm per straw for T tracker

      200 mm (r-j) 1.5 mm (z) per cluster for L tracker, both with tails out to 2.5 mm at 1%

    • Delta ray effects on rates

    • Energy loss (Landau fluctuations) and Molieré scattering in the stopping target

    • Beginning to work with GEANT4 as well

  • Remaining to be done

    • Hit digitization in the L Tracker, straws and pads

    • L Tracker cluster recognition

    • B field effects on drift performance

    • Support structures

James L. Popp, UC Irvine L-Tracker Fitter Status


L tracker detector rates vs time

L Tracker Detector Rates vs. Time

Rate

[MHz]

Rate

[kHz]

Full time between proton pulses

Detection time interval

25

20

15

10

5

0

800

700

600

500

400

300

200

100

0

m-capture protons

beam electrons

m- decay

in flight

0 400 800 1200 700 900 1100 1300

time with respect to proton pulse arrival time [ns]

Very high rate from beam electrons at short times – potential problems with chamber operation

Protons from m capture are very heavily ionizing – potential problems with noise, crosstalk

Rates are similar (not identical) for T tracker, both highly dependent on radial position near inner edge

James L. Popp, UC Irvine L-Tracker Fitter Status


Tracker reconstruction

Tracker Reconstruction

  • Codes for reconstructing events in each geometry have been developed independently at different institutions, often with different underlying assumptions

  • We have begun integrating the two approaches, we are still in the early stages. See Yury’s talk for more on this effort.

  • All current tracker reconstruction efforts have been based solely upon drift distance or straw positions. Additional information remains to be exploited:

    • Both trackers:

      • Pulse height to remove protons – for “free” via the use of the Elefant readout chip.

    • L tracker

      • Pulse-height for Compton electron rejection

      • Pulse-height for proton rejection, r-f and z hit correlation

      • Comparison of r-f and z hit timing to match hits in the two views – good to a few ns

      • Straw number correlation with z position for valid helices, i.e. order of r-f hits in each module is correlated with z position due to tilt and to lesser extent to energy loss

      • Use of local (cluster) track angle and timing information in pattern recognition to reduce combinatoric search (improves speed)

      • Some of these implemented in background rejection already (e.g. local track angle to reduce mis-reconstruction background)

James L. Popp, UC Irvine L-Tracker Fitter Status


L tracker pattern recognition fitting

L Tracker Pattern Recognition & Fitting

  • Look for circles in r-f hits

  • Match with z hits – all combinations are tried

  • Hit positions are currently taken from detector crossing points, but these will ultimately be obtained via cluster finding

  • Following application of pre-selection cuts (following slide) raw helix info is passed to a maximum likelihood fitter.

James L. Popp, UC Irvine L-Tracker Fitter Status


L tracker event selection

L Tracker Event Selection

  • The energy of the GEANT primary electron at the entrance of the electron calorimeter is at least 75 MeV.

  • The agreement of the projected entry position at the electron calorimeter for the fitted track is within 20 cm of that given by the GEANT primary electron.

  • The maximum scattering angle at each detector element < 0.1 rad

  • 45 º < pitch angle < 60º

  • The fitting uncertainty is less than 600 MeV.

  • The total number of clusters is at least 6

  • There are no missing clusters on the track where it intercepts any detector element.

James L. Popp, UC Irvine L-Tracker Fitter Status


Mis reconstruction

Mis-reconstruction

  • Mis-reconstructed tracks like this one are potentially a source of background from very low energy DIO electrons that reconstruct many s above the actual energy

    • Difficult to study, since orders of magnitude more low energy electrons

    • Technique of increasing rates, then reducing observed background by weighting factor of (rT/rMC)n, where rT and rMC are the true and MC rates, and n is the number of noise signals used in the background event

    • One additional cut: event rejected if a lower momentum track is found

real e- from - decay

fake high p track

James L. Popp, UC Irvine L-Tracker Fitter Status


L tracker resolution

L Tracker Resolution

  • 2  107 reconstructed conversion events

  • The intrinsic resolution is 180 keV

James L. Popp, UC Irvine L-Tracker Fitter Status


L tracker signal vs background

L Tracker Signal vs. Background

  • DIO contribution is known spectrum convolved with “measured” signal resolution function

  • The acceptance is 19% for NBack / Nsignal = 0.05

  • For B(m→e) =10-16 this amounts to 5 conversion events and 0.25 DIO background in the signal region

James L. Popp, UC Irvine L-Tracker Fitter Status


Summary of l tracker results

Summary of L Tracker Results

  • Additional studies of straw material thickness, overall detector length, and minimum number of clusters on the candidate track

James L. Popp, UC Irvine L-Tracker Fitter Status


T tracker resolution with background

T Tracker Resolution with Background

  • Nominal background and 25 µm

  • Delta-ray and straw inefficiency

  • Kalman filter reconstruction

  • Tracker Resolution

     = 0.19 MeV/c

  • Plot is the difference between

    reconstructed input momentum

    and actual input momentum

    Average straw rate 550 kHz

    Straw eff. Overall acceptance

    100% 19.2 %

    97% 18.7 %

James L. Popp, UC Irvine L-Tracker Fitter Status


T tracker dio reconstruction with background

T Tracker DIO Reconstruction with Background

  • 1M DIO events (> 100 MeV/c)

    were generated

     20 times more than expected

    Fit by Norm x (Emax - E)5

  • 3 event found

    in search range > 103.5 MeV

    Background  3 / 20 = 0.2 event

    Muon Conversion Signal 

    5.5 events expected

    for Br = 10-16

    Background/Signal Ratio = 0.03

    (Same conditions)

James L. Popp, UC Irvine L-Tracker Fitter Status


Summary of t tracker results

Summary of T Tracker Results

  • Results at nominal background rate without and with delta-ray and straw inefficiencies of 3%

James L. Popp, UC Irvine L-Tracker Fitter Status


Proton contribution to tracker rates

Proton Contribution to Tracker Rates

Protons are very heavily ionizing – up to 50 times minimum ionizing

Protons below ~18 MeV absorbed in target

Rate hitting tracker reduced by absorbers – further optimization possible

Studies of response of chambers to low energy protons planned at TUNL at Duke University

105

103

10

all generated protons

100

10

1

protons hitting tracker

0 20 40 60 80 100

Proton energy [MeV]

James L. Popp, UC Irvine L-Tracker Fitter Status


L tracker fitter status

James L. Popp, UC Irvine L-Tracker Fitter Status


Muon electron conversion dio

Muon-electron conversion & DIO

  • Finite Spatial Resolution

James L. Popp, UC Irvine L-Tracker Fitter Status


Mue and dio finite spatial resolution

Mue and DIO: Finite Spatial Resolution

  • Yo mama

James L. Popp, UC Irvine L-Tracker Fitter Status


New l tracker design

New L-Tracker Design

James L. Popp, UC Irvine L-Tracker Fitter Status


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