Kalanand's March 2012 Log

   February 2012   
March 2012
   April 2012   

March 2nd

How do we actually improve the WW mass resolution ?

Here is the email I wrote to Dmytro Kovalskyi
Here are the two steps we use to improve the W(lnu)W(jj) mass resolution:

1.) Compute the neutrino pz by requiring the nominal W mass (i.e., 80.4 GeV)
    for the leptonic W.

   M_W^2 = (E_lepton + p_neutrino)^2  - (px_lepton + px_neutrino)^2
                     - (py_lepton + py_neutrino)^2 
                     - (pz_lepton + pz_neutrino)^2       ------- Eq.[1]
   MET = sqrt(px_neutrino^2 + py_neutrino^2)             ------- Eq.[2]

   If there are two acceptable physical solutions for neutrino pz
   then we take the one which is closest to the lepton pz.
   If the solutions are imaginary (which happens some small fraction
   of the time), then we take the real part. This means assuming
   the discriminator of the quadratic equation to be 0, which in
   turn gives another quadratic equation involving MET. We then
   redefine the MET to be the solution of this Eq.

   The code for this step in (cvs HEAD version)

   ElectroWeakAnalysis/VPlusJets/src/METzCalculator.cc (.h)

2.) Now we perform a kinematic fit constraining
    the hadronic W mass to the nominal W mass
    and leptonic W mass also to the nominal W mass.      
    We take the netrino pz from step 1 to form the starting
    4-vectors for neutrino. This kinematic fit gives us the
    m_WW which has better resolution than the simple
    addition of 4-vectors of the final state particles.

    The code can be found in lines 793--803, i.e.,  just
    below the comment "Do kinematic fit" in

    ElectroWeakAnalysis/VPlusJets/test/kanamuon.C (or kanaelectron.C)

    You also need to check out HEAD version of PhysicsTools/KinFitter.

March 30th

More AFS user space at Cern

Since recently, Cern-IT offers to all lxplus/AFS users a possibility to extend their AFS disk space allocation by creating a "workspace" (max 20 GB):

Login to the "account" web page https://account.cern.ch/account/

Go to "Applications and Resources" and to the "Manage"-link next to "Linux and AFS".

There you can ask for "workspace" in AFS, as well as extend the quota for your $home (still up to 2 GB).

Please note the new style AFS path to your workspace:
So, the new workspace is not hanging from your $home but on a different path which contains the first letter of your loginname and then your loginname.

March 31th

Recovering deleted files on uscms/home

Look in /uscms/home/.snapshot/< date>/< username>

There you will find 4 directories with snapshots from the last 4 days. In addition we do have tape backups of the home area and you can request a restore from tape if the file you need is from more than 4 days ago.

Go to February's log

Last modified: Sat Mar 31 23:44:20 CST 2012