Upsilon polarization analysis status cdf note 10628 v1 1
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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

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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


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