PH4100 Major Project

Information regarding 4th year projects based on ATLFAST ntuples. See my Log Book 11, page 10, for useful notes for the project kick-off meetings.


In this project the student will be studying the feasibility of the Higgs search with the ATLAS detector at the Large Hadron Collider (LHC), in a given Higgs search channel or channels.

The student is advised to read about the LHC, its physics programme, and past and ongoing searches for the Higgs boson. Select some papers from this list of overview papers.

The fractions of signal and background events that will contribute to a particular final state (eg, tt-->bqq blv) should be calculated using this table of Branching Ratios (BR) (from PYTHIA 6.323). It contains useful data on the BRs of Standard Model particles such as W and Z bosons, tau leptons, and more. Higgs boson production cross-sections and decay branching fractions can be obtained from the ATLAS note

Higgs production cross-sections and branching ratios for the ATLAS Higgs working group, ATL-COM-PHYS-2007-024

ATLFAST ntuples

Information on the simulated samples can be found in my Log Book 11, page 23. All of the samples below include simulation of the underlying event. PYTHIA 6.323 was used to generate the events. The cross-sections quoted below are those provided by PYTHIA (except where explicitly stated otherwise). (See page 36 of Log Book 11 for more details.) The fast simulation of the detector response was carried out with ATLFAST 11.0.5, and the ATLFAST ntuples include Run No and Event No information.

More information: the ATLFAST simulation program; content of the ntuples.

Background samples

The following background samples can be found in linappserv1:/scratch0/ptd/ATLAS/EVTutorial/ReGenWithUE/

1 ls -al *ntp* | grep fastsim | grep _tt_ / total 80k events / PYTHIA sigma = 494.5 pb 
20k Jan  6  2007 fastsim_tt_r8050_ntp.root
20k Jan  7  2007 fastsim_tt_r8052_ntp.root
20k Jan  7  2007 fastsim_tt_r8054_ntp.root
20k Jan  7  2007 fastsim_tt_r8056_ntp.root
 1 ls -al *ntp* | grep fastsim | grep _WW_ / total 70k events / PYTHIA sigma = 70.9 pb 
30k Jan  6  2007 fastsim_WW_r8150_ntp.root
20k Jan  7  2007 fastsim_WW_r8152_ntp.root
20k Jan  7  2007 fastsim_WW_r8154_ntp.root
 1 ls -al *ntp* | grep fastsim | grep _ZW_ / total 50k events / PYTHIA sigma = 27.0 pb
30k Jan  7  2007 fastsim_ZW_r8250_ntp.root
20k Jan  8  2007 fastsim_ZW_r8252_ntp.root
 1 ls -al *ntp* | grep fastsim | grep _ZZ_ / total 50k events / PYTHIA sigma = 11.2 pb
30k Jan  5  2007 fastsim_ZZ_r8350_ntp.root
20k Jan  8  2007 fastsim_ZZ_r8352_ntp.root

Additional background samples (generated Mar 2009) can be found in

tt / total 660k
where NNNN (the run no.) is one of the following: 8051, 8053, 8055, 8057--8086 (33 runs in total). 
Each run has 20k events.                                                  
WW / total 60k                                                                                          
20k Mar 11 2009 fastsim_WW_r8156_ntp.root                                                 
20k Mar 11 2009 fastsim_WW_r8158_ntp.root                                                 
20k Mar 11 2009 fastsim_WW_r8160_ntp.root                                                 
ZW / total 40 k
20k Mar 11 2009 fastsim_ZW_r8254_ntp.root                                                 
20k Mar 11 2009 fastsim_ZW_r8256_ntp.root                                                 
ZZ / total 40 k 
20k Mar 11 2009 fastsim_ZZ_r8354_ntp.root                                                 
20k Mar 11 2009 fastsim_ZZ_r8356_ntp.root                                                 

Important Note: the PYTHIA cross-section for tt is LO only, and there are significant higher order corrections; to account for these, use a cross-section of 833 pb instead.

Signal samples

The following signal samples are available in linappserv1:/scratch2/ptd/ATLAS/MCsamples/2008/ATLFAST, with the exception of one sample generated in 2007 (*), which is available in linappserv1:/scratch0/ptd/ATLAS/EVTutorial/ReGenWithUE/ instead.

The following table gives details of all the signal samples

Process/details mh RunSorted descending Size EvGen σ x BR FastSim file Date completed
VBF; h-WW; W-all 180 4056 20k PYTHIA 2.54 pb fastsim_VBFhWW_m180_r4056_ntp.root 12/10/08
VBF; h-WW; W-all 160 4054 20k PYTHIA 2.83 pb fastsim_VBFhWW_m160_r4054_ntp.root 12/10/08
VBF; h-WW; W-all 140 4052 20k PYTHIA 1.81 pb fastsim_VBFhWW_m140_r4052_ntp.root 12/10/08
VBF; h-WW; W-all 120 4050 20k PYTHIA 0.591 pb fastsim_VBFhWW_m120_r4050_ntp.root 12/10/08
GF; h-WW; W-all 180 2056 20k PYTHIA 8.31 pb fastsim_GFhWW_m180_r2056_ntp.root 12/10/08
GF; h-WW; W-all 160 2054 20k PYTHIA 10.05 pb fastsim_GFhWW_m160_r2054_ntp.root 12/10/08
GF; h-WW; W-all 140 2052 20k PYTHIA 7.07 pb fastsim_GFhWW_m140_r2052_ntp.root 12/10/08
GF; h-WW; W-all 120 2050 20k PYTHIA 2.53 pb fastsim_GFhWW_m120_r2050_ntp.root (*) Jan 2007

Analysing the data

The simulated data ntuples can be analysed with the help of an object-oriented data analysis package provided by CERN, called ROOT. This tutorial covers the basic usage of ROOT for the purpose of running analysis tools on ATLAS data.

The actual data analysis code will be written by the student, in C++. I will provide you with template code to read in an ntuple, book some histograms, apply some event selection cuts, fill in the histograms and print them to file. (Files run_analysis.C, analysis.C and analysis.h)

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Topic revision: r11 - 19 Mar 2009 - PedroTD

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