[Rivet] Jets in DIS

[Andy Buckley]

Hi Roman,

Thanks for the feedback. What do you suggest as an alternative scheme: 
highest-energy electron (in what frame)? What is done experimentally? 
Apologies for the DIS-unawareness!

Cheers,
Andy


On 17/10/11 22:51, Roman Kogler wrote:
> Dear Andy,
>
> I checked out the new Rivet version, thanks for including the boost of
> the final state to the Breit frame. I'm happy to see that working.
>
> However, there is a bug in Rivet when looking for the scattered electron
> in DIS. The algorithm (DISLepton.cc) looks for the electron (or
> positron) in the event with the highest value of pz. This works at low
> Q2 rather well, but at high Q2 this algorithm fails. Here is why:
> At HERA the +pz direction is defined to be the proton beam direction. So
> the electron beam has pz=-27.6. At low Q2, where the electron is
> scattered under small angles, the 'signed value' of the scattered
> electron is then +pz'. However, at high Q2 the electron can be scattered
> perpendicular to the beam (pz'=0) or in the forward direction (-pz'). So
> if there is any other electron in the event present, which goes in the
> -pz direction, it will be misidentified as the scattered electron. Below
> is an example for an event generated with Q2~17000, where the scattered
> electron has been misidentified and the calculated value of Q2 in Rivet
> is 72.8.
>
> Cheers,
> Roman
>
>
> DISLepton: searching for ID -11 with pz > -1e+09
> part 0 id = -11 px = -55.7936 py = 67.9235 pz = 73.3469 E = 114.483
> part 0 id = -11 signed_pz = -73.3469
> ---> taking 0 as outgoing lepton
> part 1 id = 211 px = 4.3922 py = -5.36174 pz = 21.1347 E = 22.2426
> part 2 id = 2212 px = 19.1258 py = -22.3493 pz = 85.5571 E = 90.4775
> part 3 id = -2212 px = 7.27322 py = -8.24468 pz = 32.7272 E = 34.5373
> part 4 id = 2112 px = -0.258489 py = 0.0192201 pz = 140.113 E = 140.116
> part 5 id = 22 px = 0.0752175 py = -0.0810541 pz = 0.527222 E = 0.538693
> part 6 id = -211 px = 2.95982 py = -3.164 pz = 14.1068 E = 14.7578
> part 7 id = 130 px = 0.251775 py = -0.163703 pz = 183.251 E = 183.252
> part 8 id = 211 px = 6.86782 py = -8.30335 pz = 33.2207 E = 34.9249
> part 9 id = -211 px = 2.33043 py = -2.5695 pz = 10.0595 E = 10.6417
> part 10 id = 22 px = 0.693957 py = -0.670989 pz = 3.14172 E = 3.28667
> part 11 id = 22 px = 1.11994 py = -1.31727 pz = 5.41137 E = 5.68088
> part 12 id = 130 px = -0.151476 py = -0.389603 pz = 18.067 E = 18.0787
> part 13 id = -321 px = -0.516672 py = -0.553757 pz = 19.2324 E = 19.2536
> part 14 id = 211 px = 0.0829556 py = 0.0993597 pz = 4.24924 E = 4.2535
> part 15 id = 130 px = 0.375512 py = -0.621349 pz = 14.7582 E = 14.7844
> part 16 id = 22 px = -0.0301481 py = -0.00922794 pz = 0.33583 E = 0.337307
> part 17 id = 22 px = 0.340224 py = -0.445809 pz = 1.41281 E = 1.52004
> part 18 id = 11 px = 0.075713 py = -0.141711 pz = 0.556192 E = 0.578934
> part 19 id = -11 px = 0.124663 py = -0.154993 pz = 0.645015 E = 0.674987
> part 19 id = -11 signed_pz = -0.645015
> ---> taking 19 as outgoing lepton
> part 20 id = 22 px = 0.04499 py = -0.12844 pz = 0.397113 E = 0.419785
> part 21 id = 22 px = 0.827752 py = -1.19367 pz = 4.91671 E = 5.1268
> part 22 id = 22 px = 0.748384 py = -1.12375 pz = 4.89815 E = 5.08082
> part 23 id = 22 px = -0.00267821 py = -0.00925982 pz = 0.0143985 E =
> 0.0173273
> part 24 id = 130 px = 0.287098 py = 0.19742 pz = 17.3042 E = 17.3149
> part 25 id = 130 px = 0.122298 py = -0.0634414 pz = 25.2863 E = 25.2916
> part 26 id = 22 px = 0.0347235 py = 0.144282 pz = 1.65602 E = 1.66266
> part 27 id = 22 px = -0.0248541 py = 0.146226 pz = 3.67157 E = 3.67456
> part 28 id = 211 px = 0.954048 py = -0.963005 pz = 3.13684 E = 3.42006
> part 29 id = 211 px = 0.235199 py = -0.343671 pz = 1.4502 E = 1.51525
> part 30 id = -12 px = 1.57995 py = -1.37946 pz = 7.29499 E = 7.59052
> part 31 id = 11 px = 0.471629 py = -0.856397 pz = 2.71535 E = 2.88599
> part 32 id = 211 px = -0.0294085 py = -0.547087 pz = 0.758253 E = 0.94583
> part 33 id = -211 px = 0.0861909 py = -0.0196154 pz = 0.452828 E = 0.482023
> part 34 id = 211 px = 0.225543 py = -0.161993 pz = 0.915438 E = 0.966756
> part 35 id = -211 px = 0.571015 py = -0.738361 pz = 5.30456 E = 5.38786
> part 36 id = 211 px = 0.129393 py = -0.267621 pz = 1.02406 E = 1.07542
> part 37 id = -211 px = 1.77415 py = -1.73558 pz = 7.05777 E = 7.48274
> part 38 id = 22 px = 0.205595 py = -0.0964995 pz = 1.00644 E = 1.03175
> part 39 id = 22 px = -0.00465838 py = -0.055959 pz = 0.356084 E = 0.360484
> part 40 id = 22 px = 0.567172 py = -0.788086 pz = 3.53189 E = 3.66293
> part 41 id = 22 px = 0.406857 py = -0.734593 pz = 2.77624 E = 2.90046
> part 42 id = 211 px = 0.374462 py = -0.325563 pz = 2.74971 E = 2.7976
> part 43 id = -211 px = 0.206282 py = -0.339635 pz = 0.964825 E = 1.05274
> part 44 id = -211 px = 1.22403 py = -0.939285 pz = 24.7002 E = 24.7488
> part 45 id = 211 px = -0.401421 py = 0.084246 pz = 17.7685 E = 17.7737
> part 46 id = 22 px = 0.657991 py = -0.669357 pz = 29.0299 E = 29.0451
> part 47 id = 22 px = 0.30748 py = 0.0117005 pz = 5.16715 E = 5.17631
> part 48 id = 22 px = -0.0346924 py = -0.117068 pz = 6.57012 E = 6.57125
> part 49 id = 321 px = -0.74251 py = -0.217304 pz = 43.1924 E = 43.2021
> part 50 id = -321 px = -0.140918 py = -0.269146 pz = 4.47808 E = 4.51544
> fulfilled phase space cuts, Q2 = 72.8641 y = 0.999457 weight = 51.0074
> scat. elec: E = 0.674987 theta = 0.299122
>
> Here is the code that I used the generate this output. It's the code of
> DISLepton.cc with some output statements added.
>
> cout << "DISLepton: searching for ID " << id << " with pz > " << pzMax
> << endl;
> const FinalState& fs = applyProjection<FinalState>(e, "FS");
> int ipart = 0;
> foreach (const Particle& p, fs.particles()) {
>
> cout << "part " << ipart << " id = " << p.pdgId()
> << " px = " << p.momentum().px()
> << " py = " << p.momentum().py()
> << " pz = " << p.momentum().pz()
> << " E = " << p.momentum().E() << endl;
> double pz = _sign * p.momentum().pz();
> if(p.pdgId() == id && pz > pzMax){
> cout << "part " << ipart << " id = " << p.pdgId() << " signed_pz = " <<
> _sign * p.momentum().pz() << endl;
> cout << " ---> taking " << ipart << " as outgoing lepton " << endl;
> _outgoing = p;
> pzMax = pz;
> }
> ++ipart;
> }
>
>
>
>
> On 8/15/11 10:17, Andy Buckley wrote:
>> Hi Roman,
>>
>> I'm no DIS expert, but I think that the FinalStateHCM should do
>> something like that -- is it not acceptable?
>>
>> If that is not appropriate, you don't absolutely need to use the
>> "central registry" aspect of the projection system: you can make your
>> list of particles, boosted and filtered however you want, in the
>> analyze() method, and then use the calc() method of a local JetAlg
>> object to make the jets. Let us know if you need more help with this
>> direction: we've only recently started providing this sort of access
>> to projection features without having to register the projections --
>> sometimes it's necessary, but the normal docs don't describe it!
>>
>> Cheers,
>> Andy
>>
>>
>> On 15/08/11 18:08, Roman Kogler wrote:
>>> Dear Rivet authors and developers,
>>>
>>> I'm trying to implement a new jet analysis in Rivet. The data come from
>>> H1. The analysis is not published yet, but we are close to the
>>> publication. It's a measurement of inclusive jet, dijet and trijet cross
>>> sections in DIS at high Q^2 (for more information have a look at
>>> H1prelim-11-032).
>>>
>>> In this jet analysis jets are found in the Breit frame and I could not
>>> find a way in Rivet how to do this. What I need is to boost the full
>>> event to the Breit frame before the jet finding is performed. FastJet
>>> should then be applied to all final state particles in the Breit frame.
>>>
>>> Is there an elegant solution to do this in Rivet?
>>>
>>> Thanks,
>>> Roman
>>>
>>>
>>
>>
>


-- 
Dr Andy Buckley
SUPA Advanced Research Fellow
Particle Physics Experiment Group, University of Edinburgh

The University of Edinburgh is a charitable body, registered in
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