Missing ET performance on random triggers. UNAPPROVED, FOR INTERNAL DISCUSSIONS ONLY

This wiki is meant for preparation of plots and text to be approved for studies of Missing ET performance on random triggers. For internal iteration within working group only, final version will be made available in proper public place.

Introduction

Contact the Jet/EtMiss combined performance coordinators (Tancredi.Carli@cernNOSPAMPLEASE.ch, proudfoot@anlNOSPAMPLEASE.gov) in case of questions and/or suggestions.

The ATLAS calorimeters have recorded millions of cosmic ray and random trigger. Detailed understanding and improvement of the signal reconstruction has made it possible to study the performance on these events of higher level quantities such as missing ET. Data taken with close to full detector readout in September and October 2008 has been reprocessed at the end of 2008. The performance of standard calorimeter MissingET algorithms, as planned to be used for the analysis of the collision data, on random trigger is shown here.

The missing vectorial and scalar transverse energies in the calorimeters are reconstructed using two methods:

  • The cell based method uses all cells above a noise threshold of two standard deviations (|E|>2*$\sigma_{noise}$). This method is a simple one that characterises the basic detector performance.

  • The topo-cluster based method uses topological clusters measured in the calorimeter. Clusters are derived from calorimeter cells by adding the energy in neighbouring cells with a dynamical topological cluster algorithm. All the cells in the neighbourhood of the cluster are included, if they have an energy larger than a predefined threshold (neighbour threshold). The procedure is repeated until no cells in the neighbourhood of the cluster are found. As a last step all cells surrounding the cluster are merged to the cluster. The default configuration uses a seed threshold of 4 standard deviations and a neighbour threshold of 2 standard deviations

The width of the energy distribution in each cell, $\sigma$noise, has been estimated previously on a cell by cell basis for both LAr and Tile calorimeters as the RMS of the energy distribution in one early calibration run, and recorded in the database used at reconstruction level (known in Atlas as CaloNoiseToolDB). Cells with very high noise are masked early in calorimeter reconstruction.

Different missing ET variables are being looked at:

  • EXmiss = - $\Sigma$E sin$\theta$cos$\varphi$
  • EYmiss = - $\Sigma$E sin$\theta$sin$\varphi$
  • $\Sigma$ET = $\Sigma$E sin$\theta$
  • ETmiss = √((EXmiss)2+(EYmiss)2)

Since random triggers are used, no real energy is expected to be deposited in the calorimeters. So the only contribution to missing ET is electronic noise. Hence EXmiss, EYmiss and $\Sigma$ET are expected to follow Gaussian distributions centered on 0.

MissingET variables with random triggers

Detailed analysis has been made with 50292 random events from run 91639, taken the 14th of October 2008.

The cell based algorithm is a simple one that is used to assess the basic calorimeter performances. The topological clustering algorithm provides a better noise suppression and therefore a better ETmiss resolution. This algorithm is close to the default ETmiss reconstruction algorithm that will be used for the analysis of collision data since it provides more refined results. However it requires a more accurate description of the noise in the calorimeter.

The Gaussian noise model parametrises the cell energy distribution, based on values derived from a simple Gaussian distribution. For each cell, energy values are picked by this Gaussian distribution which is centered at 0 and has an standard deviation which is equal to the respective $\sigma$noise value derived from the CaloNoiseToolDB.

Cell and topo cluster based EXmiss showing a good control of the energy reconstruction in the 187000 cells of the Calorimeter. The topo cluster based missing energy has better noise suppression. eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch
EXmiss<br />
EYmiss is very similar to EXmiss as expected. eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch

EYmiss<br />
$\Sigma$ET also has the expected Gaussian shape, with similar improvement of topocluster based missing ET w.r.t cell based. A small shift (w.r.t.) RMS of the cell based $\Sigma$ET is being scrutinised. eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch
sumET<br />
Inclusive distributions of ETmiss for both methods are shown, showing again the better noise suppression of the topocluster method. Tails in the distribution (beyond 8 GeV for topo clusters based and 16 GeV for cell based) contributing to less than 0.1% of events have been understood to come from coherent noise in a specific region of LAr presampler (reference to LAr approved plots needed there when available). eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch
MET_data<br />
The expected ETmiss distribution obtained by a randomisation of the cell energy with a Gaussian noise of width $\sigma$noise is superimposed to the measured one, showing a good agreement. Similar studies for the topocluster based missing ET requires an accurate description of the noise up to and beyond 4 $\sigma$, which is being worked on.

eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch

MET_CellBased<br />

Evolution of topocluster-based missingET variables with time

Use of 35 runs taken between the 10th of September and the 23th of October. Thus run 91639 corresponds to day 36.
For each run, reconstruct missing ET variables computed with standard topocluster algorithm, and fit with Gaussian distribution to extract mean ($\mu$) and standard deviation ($\sigma$).

Deviation of the mean of the EXmiss distribution ($\mu$) from its average value <$\mu$> (0.103 ± 0.005 GeV).
Great stability over one month and a half.

eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch

EXmiss_mean<br />

Deviation of the width of the EXmiss distribution ($\sigma$) from its average value <$\sigma$> (1.000 ± 0.005 GeV).
Great stability over one month and a half. No significant change in resolution with time.

eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch

EXmiss_width<br />

Deviation of the mean of the EYmiss distribution ($\mu$) from its average value <$\mu$> (0.023 ± 0.004 GeV).
Great stability over one month and a half.

eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch

EYmiss_mean<br />

Deviation of the width of the EYmiss distribution ($\sigma$) from its average value <$\sigma$> (0.932 ± 0.003 GeV).
Great stability over one month and a half. No significant change in resolution with time.

eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch

EYmiss_width<br />

Deviation of the mean of the sumET distribution ($\mu$); from its average value <$\mu$> (0.780 ± 0.014 GeV).
Good stability over one month and a half: variations are small compared to absolute value of Gaussian width.

eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch

sumET_mean<br />

Deviation of the width of the sumET distribution ($\sigma$) from its average value <$\sigma$> (1.372 ± 0.006 GeV).
Great stability over one month and a half. No significant change in resolution with time.

eps version
Contact: Tancredi.Carli@cernNOSPAMPLEASE.ch

sumET_width<br />



Major updates:
-- DimitrisVarouchas - 27 Mar 2009 -- ElisabethPetit - 29 Mar 2009

Tancredi Carli and Jimmy Proudfoot Last reviewed by: Never reviewed

Topic attachments
I Attachment History Action Size Date Who Comment
Unknown file formateps EXmiss_METtopo_mean_time.eps r1 manage 8.0 K 2009-03-27 - 14:24 DimitrisVarouchas  
GIFgif EXmiss_METtopo_mean_time.gif r1 manage 8.8 K 2009-03-27 - 13:35 DimitrisVarouchas  
Unknown file formateps EXmiss_METtopo_width_time.eps r1 manage 8.0 K 2009-03-27 - 14:25 DimitrisVarouchas  
GIFgif EXmiss_METtopo_width_time.gif r1 manage 8.9 K 2009-03-27 - 11:46 DimitrisVarouchas  
Unknown file formateps EYmiss_METtopo_mean_time.eps r1 manage 8.0 K 2009-03-27 - 14:25 DimitrisVarouchas  
GIFgif EYmiss_METtopo_mean_time.gif r1 manage 8.9 K 2009-03-27 - 11:46 DimitrisVarouchas  
Unknown file formateps EYmiss_METtopo_width_time.eps r1 manage 8.0 K 2009-03-27 - 14:26 DimitrisVarouchas  
GIFgif EYmiss_METtopo_width_time.gif r1 manage 8.8 K 2009-03-27 - 11:47 DimitrisVarouchas  
PNGpng Image_1.png r1 manage 571.5 K 2009-03-27 - 09:43 DavidRousseau  
Unknown file formateps MET_CellBased.eps r1 manage 15.3 K 2009-03-30 - 11:48 DimitrisVarouchas  
GIFgif MET_CellBased.gif r1 manage 15.0 K 2009-03-27 - 14:14 DimitrisVarouchas  
Unknown file formateps MET_data.eps r1 manage 18.7 K 2009-03-30 - 11:48 DimitrisVarouchas  
GIFgif MET_data.gif r1 manage 17.0 K 2009-03-27 - 13:43 DimitrisVarouchas  
Unknown file formateps Px_data.eps r1 manage 13.3 K 2009-03-30 - 11:49 DimitrisVarouchas  
GIFgif Px_data.gif r1 manage 10.4 K 2009-03-27 - 12:07 DimitrisVarouchas  
Unknown file formateps Py_data.eps r1 manage 13.3 K 2009-03-30 - 11:48 DimitrisVarouchas  
GIFgif Py_data.gif r1 manage 10.6 K 2009-03-27 - 12:08 DimitrisVarouchas  
Unknown file formateps SumEt_data.eps r1 manage 13.2 K 2009-03-30 - 11:49 DimitrisVarouchas  
GIFgif SumEt_data.gif r1 manage 10.2 K 2009-03-27 - 12:09 DimitrisVarouchas  
Unknown file formateps sumET_METtopo_mean_time.eps r1 manage 7.9 K 2009-03-27 - 14:27 DimitrisVarouchas  
GIFgif sumET_METtopo_mean_time.gif r1 manage 8.8 K 2009-03-27 - 11:47 DimitrisVarouchas  
Unknown file formateps sumET_METtopo_width_time.eps r1 manage 7.9 K 2009-03-27 - 14:24 DimitrisVarouchas  
GIFgif sumET_METtopo_width_time.gif r1 manage 8.9 K 2009-03-27 - 11:48 DimitrisVarouchas  
Edit | Attach | Watch | Print version | History: r22 | r17 < r16 < r15 < r14 | Backlinks | Raw View | Raw edit | More topic actions...
Topic revision: r15 - 2009-04-06 - ElisabethPetit
 
    • Cern Search Icon Cern Search
    • TWiki Search Icon TWiki Search
    • Google Search Icon Google Search

    Atlas All webs login

  • Edit
  • Attach
This site is powered by the TWiki collaboration platform Powered by PerlCopyright & 2008-2021 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
or Ideas, requests, problems regarding TWiki? use Discourse or Send feedback