Ben Snook and Charles Maguire Vanderbilt Universitymaguirc/CMS-HI/pizeroInJEX_16July2010V0.pdf ·...

The π0 Reconstruction in the July Exercise

Ben Snook and Charles Maguire

Vanderbilt University

July 16, 2010 Contribution to high_pT Report for CMS-HI Annual Meeting at CERN 1

V0 Version July 15 at 11:35 PM CERN

A template version for Ben to use

Goals of the π0 Analysis: For the long term, and for July

•  Show that the ECAL calibration works well for HI events   Supports the photon jet studies

•  Excellent first PR plot for the HI program, as it was for pp   The π0 is prolifically produced in HI events,; just a few days running

will be sufficient to demonstrate the mass peak

•  The RAA of the π0 at the LHC would be a certain PRL   Can CMS take advantage of its acceptance coverage over ALICE in a

wide enough pT range over a wide enough centrality range?

•  Deliverables planned for the July exercise   Show that a π0 mass peak can be reconstructed

  Show the mass peak over a wide enough pT range, and a wide enough centrality range

  Use the accepted pp reconstruction software (Cal-Tech and Rome)


What Was Done In 2-3 Days (While Otherwise Busy for CMS-HI)

•  Ben Snook   Ported Cal Tech 3x3 cluster finder software to CMSSW_3_7_0

  Showed a reconstructed mass peak in peripheral events with this Cal Tech software

  Worked with Shahram of the Rome group to start the porting their software to HI analysis; will complete this work next week

  The Cal Tech and the Rome pp software have the (to-be-certified) procedures for doing acceptance and mass corrections in CMS

  What works in pp should work similarly in peripheral HI events

•  Charles Maguire   Private 3x3 cluster finding software, based on Cal Tech software

Adapted to include MC matching (will be applied to JEX results)

  Showed a mass peak in three centrality bins: 20-30, 30-50, 50-100 Over a wide enough pT range: 3.0-8.0, 2.5-8.0, 2.0-8.0 GeV/c



Results from Ben Snook


Confirming Results from Charles Maguire


Mass peak from 30K NZS Events in 50-100% Centrality Range pT Range is 2.0 to 8.0 GeV/c

This would be our “Day 1” PR plot showing good HI data taking



A good mass peak is still visible, but occupancy corrections are needed



The mass peak is at the visibility limit; strong occupancy corrections will be needed

Summary

•  A π0 mass peak is observed in the JEX NZS data

•  While the most central (0-15%) events will be difficult to obtain in Week 1, the 20-30% and higher are will in reach

•  The pT range is acceptably wide



Backup slides from last efficiency presentation

Motivation


•  π0 reconstruction efficiency is seen to be η-dependent

π0 pT integrated yield spectrum shown at ECal February 23 meeting

Distribution in η for reco π0 at fixed pT from MC with uniform η-generation

Reco efficiency for the π0 is seen to be strongly η-dependent in both studies

pp study will likely choose some ηmax, and select a few η bins < ηmax

How do the photon energy and η cuts affect the reco efficiency as function of pT?

•  A cut is placed on both photon energies   Choose initial photon energy cut at 0.75 GeV (pp study at 0.50 GeV)

•  This cut number will be studied for signal/background optimization   Minimum Bias heavy ion running in 2010 will study ECAL in HLT

•  Different η-cuts on the parent π0 are then compared   Used a first MC generator which has a uniform pT and

a uniform η distribution of the parent π0, 1.2M single π0 events

  Second examples are from the standard HI MC generator HYDJET •  This generator has a realistic pT spectrum and a realistic η distribution

•  9,000 minimum bias 2.76 TeV events generated at MIT (test production sample)

•  Last set of comparisons looked at reconstructed π0

  These comparisons quantify the effect of the photon conversions, and other sources of reconstruction losses




Above histogram has no photon energy cuts, only |η| < 1.2

|η| < 1.2

|η| < 0.95

|η| < 0.50

|η| < 0.70

Histograms below all have photon energy cuts: γ > 0.75 GeV



Above histogram has no photon energy cuts, only |η| < 1.2

|η| < 1.2

|η| < 0.95

|η| < 0.50

|η| < 0.70

Histograms below all have photon energy cuts: γ > 1.25 GeV

Using a larger minimum photon energy cut


η-cut Sum pT 2-3 GeV Sum pT 7-8 GeV Ratio

|η| < 1.2, No energy cuts 85,952 85,898 1.0

|η| < 1.2, Eγ > 0.75 GeV 43,034 71,780 0.60

|η| < 0.95, Eγ > 0.75 GeV 31,814 56,149 0.57

|η| < 0.70, Eγ > 0.75 GeV 21,896 40,970 0.53

|η| < 0.50, Eγ > 0.75 GeV 15,010 29,006 0.52


The combination of cuts in the photon energies and the η-value of the parent π0 leads to dependencies in the pT efficiencies.

The raw pT distribution will have to be corrected for this dependency.

The above results are only from a simple generator level study. They do not include other efficiency losses such as photon conversion


η-cut Sum pT 2-3 GeV Sum pT 7-8 GeV Ratio

|η| < 1.2, No energy cuts 85,952 85,898 1.0

|η| < 1.2, Eγ > 1.25 GeV 15,930 62,448 0.26

|η| < 0.95, Eγ > 1.25 GeV 9,116 48,158 0.19

|η| < 0.70, Eγ > 1.25 GeV 4,512 34,756 0.13

|η| < 0.50, Eγ > 1.25 GeV 2,424 24,396 0.10


The combination of cuts in the photon energies and the η-value of the parent π0 leads to dependencies in the pT efficiencies.

The raw pT distribution will have to be corrected for this dependency.

The above results are only from a simple generator level study. They do not include other efficiency losses such as photon conversion

Results with HI HYDJET Generator 9000 Minimum Bias Events


Imposition of photon energy cuts, with |η| < 1.2, changes the shape of the pT spectrum

Centrality > 34%

16% < Centrality < 34%

6% < Centrality < 16% Centrality < 6%

Results with HI HYDJET Generator


Cut of |η| < 0.7, leads to greater changes the shape of the pT spectrum One can compare correction factors according to different MC generators



Imposition of higher photon energy cuts, with |η| < 1.2, changes pT much more



Imposition of higher photon energy cuts, with |η| < 0.7, changes pT hugely

Quality of the Reconstructed Mass and pT Spectrum


Cuts in |η| < 1.2 and photon energies are using the reconstructed values

544 counts after reco (29%) compared to 1853 counts before reco

Centrality > 34%

Quality of the Reconstructed pT Spectrum


Cuts in |η| < 1.2 and photon energies are using the true values

633 counts after reco (34%) 1853 counts before reco

Quality of the Reconstructed Mass and pT Spectrum


Cuts in |η | < 0.7 and photon energies are using the reconstructed values


Quality of the Reconstructed pT Spectrum


Cuts in |η| < 0.7 and photon energies are using the true values


Summary

•  Initial, learning study of pT dependent correction factors   These correction factors show a coupling between the choice

of the η window and the choices for the photon energy cuts

•  Similar work being done by people at CalTech and at Rome for pp analysis Plan is to get a unified set of correction factors based on η and π0 energy

  This coupling can be studied first at the generator level, using different generators, with a goal to quantifying the systematic effects

  Second phase of the study looked at the correction factors after the reconstruction step (photon conversion losses, cluster losses, ...)

•  Future Work   Depends on the guidance from the pp analyzers

  Will repeat the studies using the pp reconstruction code, with Ben

•  Personal Schedule (planning to be at CERN for June CMS week)

  Major review of CMS-HI computing plan by DOE-NP on June 2

•  It is critical to get a good review in order to get first funds in the summer

•  Assuming a 50% occupancy level preparing for this review (Off-Line coordinator)


Ben Snook and Charles Maguire Vanderbilt Universitymaguirc/CMS-HI/pizeroInJEX_16July2010V0.pdf ·...

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