[Rivet] W finder and PartonJet question

[kristin Lohwasser]

Hi Andy,

thanks for the quick answer. Let me iterate a bit.

1) hm, but then the questions is: What is with analyses, that should be 
implemented in Rivet, that actually are Born level (there are at least 
some I believe) and for those, as well as for the dijet cross section 
measurements, you'd never be able to make the data/comparisons plots 
using rivet, no? (this is a general question)

3) ok, this is not so urgent, and for my application it can be achieve 
in a different way.

2) ok, thanks this explains it. I started from the non-weighted events, 
since I have a truth (unfolding) code, where I cross check against.

Cheers
kristin


On 05/15/2014 12:55 PM, Andy Buckley wrote:
> Hi Kristin,
>
> There is no mechanism in Rivet to find Born-level W/Z or parton jets --
> in fact the whole design of Rivet is explicitly to discourage such
> approaches because they are not portable between generators, and their
> exact physical meaning is also rather vague.
>
> 1) If you want to construct these, then turn off QED FSR and any other
> EW corrections in your MC: the bare leptons will then be "Born".
>
> 3) For parton jets you would need to turn off QCD FSR, hadronization,
> and decays in the generator.
>
> At this point you pretty much just have parton level events of the sort
> that would appear in an LHE file... and to my mind you might as well
> just use an LHE parser and analyse the parton events directly rather
> than fight against a system which is explicitly designed to encourage
> more "final-state type" analyses!
>
> 2) When you say that you reapply the MET cut, do you mean the cut on
> nu.pT()? This isn't quite the same as MET: the MET cut that we apply
> also includes any other neutrinos in the event (including those from
> hadron and tau decays) as well as ET imbalance due to acceptance
> limitations. This is something where we might add more options in future
> if there is demand, e.g. in response to the ATLAS (& wider) truth
> definition workshops. Would this difference explain the change in
> numbers that you are seeing? (By the way, it's a good idea to not just
> use raw int cut-passed counters but to add the event weights instead --
> that way you still get a physical answer if you use weighted generators.)
>
> Andy
>
>
> On 15/05/14 11:30, kristin Lohwasser wrote:
>> Dear all,
>>
>> I have a (couple of) question(s) concerning the WFinder implementation
>> in Rivet and how to get Parton Jets in Rivet (is this possible at all?).
>>
>> Essentially I want to get BORN level electrons, for this I am using the
>> WFinder (since as I understand, this is the recommended way to
>> reconstruct W's in Rivet -- please correct me, if I am wrong)
>>
>> 1) CLUSTERING DEFINITION
>> --> For Born level I am not sure, what setting for the Photon clustering
>> to use, essentially for the below settings, the WFinder::NOCLUSTER and
>> WFinder::CLUSTERNODECAY yield the same results (but these are different
>> from my cross check numbers for Born level)
>>        WFinder wfinder_born_el(fs, -2.5, 2.5, 20*GeV, PID::ELECTRON,
>> 0*GeV, 8000*GeV, 25*GeV, 0.2, WFinder::NOCLUSTER    );
>> so I am not sure, whether any of the ENUMS will actually selec W-Born
>> level.
>>
>> 2) Difference for MET
>> I understand, you set the MET cut in the WFinder Declaration (25*GeV in
>> the above case).
>> However, I apply a MT cut afterwards as well and there I also doublely
>> applied the MET cut -- however when I *REMOVED* it, the number of
>> selected events *CHANGED*, which should not happen (code follows now):
>>
>>
>>        if (!wfinder_born_mu.particles().empty()) {
>>          const FourMomentum& nu =
>> wfinder_born_el.constituentNeutrinos()[0].momentum();
>>          if ( calcMT(nu,
>> wfinder_born_el.constituentLeptons()[0].momentum())  > 40*GeV &&
>> nu.pT()>25*GeV) {
>>            keepevent=true;
>> }}
>>
>>        if (!keepevent) {
>>          MSG_DEBUG("event does not pass mT and MET cuts");
>>          vetoEvent;
>>        }
>> COUNT_PASS_W++;
>>
>> 3) How can want one get Parton Jets in Rivet? I tried to find some other
>> analysis using this, e.g. ATLAS jets, but it seems, they are not
>> implemented. It would be great, if you could suggest me something.
>>
>> Thanks & Best
>> Kristin
>>
>>
>>
>>
>>
>


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Dr. Kristin Lohwasser

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