Spin PWG

This is a feed of Drupal items targeting the "Spin" Audience.

Concerning the 'floating' mass peak and Zgg

 Objective:

Explore the pt-dependent mean mass position in data and MC and perhaps draw some conclusions about the quality of our simulations.

Details:

Special Attention Ought to be Paid to Zgg

The collaboration has concerns about the SMD, and not without reason.  They, they SMDs, have been notoriously hard to understand and model.

Mean pT in z bins

I looked into the mean transverse momentum for pions and jets in each of my z bins. First, here’s a comparison of data (black points) and Monte Carlo (red lines) for the BJP1 trigger:

It looks good to me, so I went on to compare simulations for jet patch and minimum-bias triggers:

In hindsight, this plot makes perfect sense — the trigger hardens the pT spectrum for the jets, so each JP z bin (which integrates over 10-25 GeV) has a higher average jet p_{T} than the MB version.

Now, this 3 GeV p_{T} shift means that we’re biasing the sample in each z bin towards higher x. This is almost certainly the source of the observed trigger bias in the Monte Carlo asymmetries for π+. So, what’s the next step?

Cut Variation Tests

Goal:

To test the stability of the cross section measurement to changes in the analysis cuts and, if necessary, assign a systematic uncertainty for cut variations.

Early Studies

  

Preliminary Result

Longitudinal double-spin asymmetries for inclusive charged pion production opposite a jet

Jigsaw Fits (2nd try)

 Following up from this post concerning the modeling of the invariant m

Paper Proposal

Cross section and longitudinal double-spin asymmetr

2005 Charged Pion

  

Candidate Level Comparisons

Objective:

Data/Filtered Pythia Inv. Mass Distributions

Details

Data Vs. T2 Platinum (see here)

Cuts:

Run 6 Data / Monte Carlo Comparison

Partonic Cross Sections

xsec = {
'3_4' : 1.302,
'4_5' : 3.158E-01,
'5_7' : 1.372E-01,
'7_9' : 2.290E-02,
'9_11' : 5.495E-03,
'11_15' : 2.220E-03,
'15_25' : 3.907E-04,
'25_35' : 1.074E-05,
'35_45' : 5.000E-07,
'45_55' : 2.857E-08,
'55_65' : 1.451E-09
}

Normalization Procedure

I calculated the integrated luminosity for my dataset (5.43 pb^-1) and scaled all event- and jet-level histograms by that amount (in mb^-1 to match the partonic xsec numbers above). For the track histograms I added a multiplicative factor of 0.82 to account for imperfect PID efficiency in the data. I neglected PID contamination.

Run 9

Collect documentation on run 9 here.

Goals

<z> Details

<z> Details

 

A_LL Details

Details on the A_LL result and the systematic studies:

The result in numbers:

Bin <p_T> [GeV]

Neutral Pion Paper: 2005 ALL & <z>

Neutral Pion Paper for 2005 data: Final Results.

There are two spin plots planned for the paper, one with the 2005 A_LL and one with the <z>.

Group Meeting Update

Progress towards a measurement of A_{LL} for charged pion production opposite a trigger jet using data from the 2006 STAR run. Goal is to present this measurement as a function of z, defined here as p_{T}(pi) / p_{T}(trigger jet).

Update 2008-08-28: added data/MC comparison plots

Jigsaw Fits (1st try)

Goal:

Data Sets

For the cross section analysis I am using a number of Monte Carlo samples along with one data set.  The details of each of these sets can be found below:

 

Cross Section Analysis

On the pages listed below I'm going to try to keep track of the work towards measuring the cross section for inclusive pion production in pp collisions from run 6.  I'll try to keep the posts