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Upsilon Polarization Analysis Status CDF note 10628 v1.1. Matthew Jones Purdue University. Overview of Polarization Analysis. Angular distribution of muons is the superposition of signal + background Background dominated by heavy flavor Requiring one displaced track enhances background

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upsilon polarization analysis status cdf note 10628 v1 1

Upsilon Polarization AnalysisStatusCDF note 10628 v1.1

Matthew Jones

Purdue University

B Production and Decay Meeting

overview of polarization analysis
Overview of Polarization Analysis
  • Angular distribution of muons is the superposition of signal + background
  • Background dominated by heavy flavor
  • Requiring one displaced track enhances background
  • In sideband regions, the angular distribution of displaced track sample agrees well with angular distribution in complementary sample
  • Level of background calculated from fits to invariant mass distribution
  • Sufficient information to subtract angular distribution of background in a mass range that contains the ϒ(nS) signal

B Production and Decay Meeting

example 6 5 p t 8 5 gev c
Example: 6.5 < pT < 8.5 GeV/c

Background only

Background only

Signal + background

B Production and Decay Meeting

some of the recent changes
Some of the Recent Changes
  • Efficiency for muon matching cut found to depend on pT…
  • Peaking co-linear background suppressed by cut on
  • Revert to classic binned log-likelihood fit since Monte Carlo samples are large
  • Measure signal fraction in displaced track sample – accounted for in simultaneous fit.

B Production and Decay Meeting

muon 2 9 cut efficiency
Muonχ2<9 cut efficiency
  • Measured using μ+SVT sample
  • Simulated in Monte Carlo template generation

CMU

CMX

B Production and Decay Meeting

background properties
Background Properties
  • Peaking background suppressed by the cut
  • Included in Monte Carlo acceptance calculation
  • No loss of signal efficiency for

Component that peaks at large ΔpT

Kinematic limit

Also contributes to peaking in cosθ distribution in the S-channel helicity frame.

B Production and Decay Meeting

invariant mass fits
Invariant mass fits
  • Components:
    • Background: exponential or gamma function
    • Signal: single Gaussians
  • Fit for:
    • Prompt background scale factor
    • Signal fraction in displaced track sample (typically between 1 and 4%)
    • Mass shift and resolution

B Production and Decay Meeting

angular distribution in side bands
Angular distribution in side-bands
  • The displaced and non-displaced track samples have similar angular distributions:

Error bars: displaced (scaled)

Histogram: non-displaced

  • Drell-Yan contribution expected to be small (few %)
  • Not surprising if dominated by heavy flavor decays

B Production and Decay Meeting

sideband fits using unpolarized templates
Sideband fits using unpolarized templates
  • Predicted yield in bin i,j:
  • is the unpolarized acceptance and efficiency from the Monte Carlo.
  • Background parameters are not limited to physical range for a spin-1 particle decay.

B Production and Decay Meeting

projections of sideband fits
Projections of sideband fits
  • First in Collins-Soper frame:

B Production and Decay Meeting

projections of sideband fits1
Projections of sideband fits
  • Now in S-channel helicity frame:

B Production and Decay Meeting

signal background fit
Signal + Background fit
  • Mass bin contains signal + background
  • Relative fractions constrained from fit to mass distribution
  • Displaced track sample constrains background angular distribution

B Production and Decay Meeting

projections from 1s bin
Projections from ϒ(1S) bin

Collins-Soperframe

Displaced track sample

B Production and Decay Meeting

projections from 1s bin1
Projections from ϒ(1S) bin

S-channel helicity frame

B Production and Decay Meeting

angular variables
Angular variables

Background mass bins

1S

2S

3S

  • Angular distribution of signal is quite different from background shape.
  • Parabolic errors approximate confidence intervals from mncont() quite well.

B Production and Decay Meeting

angular invariant
Angular Invariant,
  • Similar in both reference frames
  • Would like to use difference to quantify systematic uncertainties on

Black: CS frame

Red: SH frame

B Production and Decay Meeting

1s results
ϒ(1S) Results

B Production and Decay Meeting

2s results
ϒ(2S) Results

B Production and Decay Meeting

3s results
ϒ(3S) Results

Getting ugly – may want to combine some adjacent bins.

B Production and Decay Meeting

differential cross section
Differential Cross Section
  • Only a cross check at this point
  • pT-dependent efficiencies included in unpolarized templates
  • pT-independent quantities:
    • Muon scale factors
    • Vertex cuts (suspicious old result)
    • Final state radiation

B Production and Decay Meeting

final state radiation
Final State Radiation
  • The fit scales the signal yield by the fraction of the single Gaussian in mass range
  • FSR simulated using PHOTOS
  • A Gaussian fit to the line shape with FSR accounts for only about 92% of the events
  • In Run I, this was determined to be (93±2)%

Final correction factor:

B Production and Decay Meeting

differential cross section1
Differential Cross Section

B Production and Decay Meeting

time dependence in j datasets
Time Dependence in J/ψ datasets

B Production and Decay Meeting

no time dependent efficiencies found
No time-dependent efficiencies found
  • Track reconstruction efficiency:
  • XFT efficiency for fiducial tracks:
  • Difficult to pin down CMU efficiency… claimed to be well understood for
  • No evidence for bias in angular distributions

B Production and Decay Meeting

systematic uncertainties
Systematic Uncertainties
  • Proposal:
    • Trivial stuff: uncertainties in efficiencies used to generate templates
    • Monte Carlo statistics: samples are generally large, but statistical precision should be quantified
    • Background model: compare ϒ decay angular distribution with background shape constrained using the sideband regions.
    • Alternative treatments:
      • parameterization with additional ad-hoc shape component
      • wider mass range for displaced track background proxy
  • This is the remaining work in progress.

B Production and Decay Meeting

summary
Summary
  • Complete, self-consistent analysis of angular distribution
  • No strong evidence for significant polarization
  • Difficult to see how this would agree with NRQCD or kT factorization models.
  • Systematic uncertainties to be evaluated
    • These studies might provide ways to demonstrably reduce possible bias

B Production and Decay Meeting