[Rivet] Validation & tuning phone meeting, Monday 29th Sept, 4pm (UK)

[Emily Nurse]

Hi Lars,

It doesn't look like the HERWIG plots are normalised to the data, is  
this right?
Could you do that? Otherwise its hard to see how well the shapes agree.

I'm surprised by how badly the MC is describing the low pT region.
For the HERWIG parameters you could try:

PTRMS = 1.6
VQCUT = 0.45
QCDLAM = 0.14

but these were tuned without Jimmy so may not be the best fit when  
you run with Jimmy.

I'm surprised that the ratio plot is still going in the opposite  
direction to the data even after scaling the Z pT by Mw/Mz.
The Z pT distribution peaks higher than the W pT because of the  
higher Z mass (more phase space available for gluon radiation at that  
energy). So without the scaling I would expect the W : Z ratio to  
decrease with pT. With the scaling it should go slightly the other  
way (I think because alpha_s is weaker at Q=Mz than at Q=Mw). This is  
what I saw when I did this study with HERWIG and what the data sees.  
So something funny is going on.

Could I take a quick look at your running parameters/switches and the  
routine?
>
> Concerning the overal normalisation there is an ambiguity:
> boson->tau->electron.
> I didn't switch this on, since the papers only talk about boson->e('s)
> without intermediate tau. This would increase the xsec roughly by  
> 1/3, but
> the pT spectrum of the electrons from taus is also a little bit  
> different.
> So if I would switch boson->tau on, it depends on how the  
> experiment has
> corrected (to boson->e('s) or to boson->e('s) + boson->tau('s)->e 
> ('s)).
>

You should run only Z->ee and W->enu, no tau final states. The number  
of Z->tautau and W->taunu events passing the cuts will be small (the  
electron pT spectrum is much softer) and the experiments will have  
(should have) included it as a background.

Cheers,
Emily.

>
>
> On Mon, 6 Oct 2008, Emily Nurse wrote:
>
>> Hi Lars,
>>
>> I think you will need to correct for the branching ratio  
>> difference as this is
>> a ratio of production cross sections , so your formula
>>> R_th = dsigma/dpt(W) / dsigma/[d(pt(Z)*Mw/Mz)] *
>>> B(Z->ee)/B(W->enu)
>>
>> looks correct - although its been a long time since I read the  
>> paper. If the
>> normalisation looks off lets re think it.
>>
>> Cheers,
>> Emily.
>>
>> On 6 Oct 2008, at 09:48, Lars Sonnenschein wrote:
>>
>>> Hello Emily
>>> thank you for your feedback.
>>> Indeed the paper has two formulas for the ratio:
>>> a theoretical one which corresponds to your formula below and an
>>> experimental one which looks like:
>>>
>>> R_exp(pT) = [dsigma/dpt(W) / dsigma/dpt(Z)] * Mw/Mz * B(Z->ee)/B 
>>> (W->enu)
>>>
>>> where Mw/Mz = 0.88 and B(Z->ee)/B(W->enu) = 0.3 roughly.
>>> The later formula I use for the ratio, i.e. scale the diff. xsec.  
>>> ratio
>>> by the constant factors given above.
>>>
>>> Now I could scale the Z pT before filling the histo according to the
>>> theoretical formula, but that would not alter the W pT spectrum.
>>>
>>> Though I will try to see the difference in the ratio.
>>>
>>> Now, since I select electrons (and  a neutrino in case of W)  
>>> should the
>>> formula look like R_th = dsigma/dpt(W) / dsigma/[d(pt(Z)*Mw/Mz)] *
>>> B(Z->ee)/B(W->enu)
>>> to take the branching ratio differences into account?
>>>
>>>      Lars
>>>
>>>
>>> On Mon, 6 Oct 2008, Emily Nurse wrote:
>>>
>>>> Hi Lars,
>>>>
>>>> Its hard to see how off the W pT plot is, can you compare it to  
>>>> the data
>>>> so we
>>>> can see?
>>>> As for the ratio, its more obvious that its going the wrong way  
>>>> compared
>>>> to
>>>> the data.
>>>> In the paper they are measuring dsigma/dpt(W) / dsigma/[dpt(Z) 
>>>> *Mw/Mz]
>>>> ie/ they scale the Z pT by the ratio of the W and Z masses, see  
>>>> page 20
>>>> and 21
>>>> of my 1st year PhD transfer report for more details, and  
>>>> comparisons of
>>>> the
>>>> data with Herwig:
>>>> http://www.hep.man.ac.uk/u/emily/1styear.ps
>>>>
>>>> It should also be explained in the paper. Are you doing this in the
>>>> routine?
>>>>
>>>> Cheers,
>>>> Emily.
>>>>
>>>>
>>>> On 6 Oct 2008, at 08:19, Lars Sonnenschein wrote:
>>>>
>>>>> Hi
>>>>> I have put some plots for the D0 2001 WpT <-> ZpT analysis at
>>>>> http://www-d0.fnal.gov/~sonne/D0_2001_S4674421/
>>>>>
>>>>>      Lars
>>>>>
>>>>>
>>>>> On Fri, 3 Oct 2008, Andy Buckley wrote:
>>>>>
>>>>>> Hi everyone,
>>>>>>
>>>>>> Our next Rivet etc. phone meeting will take place on Monday at  
>>>>>> 2pm (UK
>>>>>> time). Note that it's earlier than last week - this will be  
>>>>>> the normal
>>>>>> time from now on.
>>>>>>
>>>>>> Once again, we'll be using the DESY phone conference system:  
>>>>>> phone
>>>>>>
>>>>>> +49 40 8998 1390
>>>>>>
>>>>>> then enter conference code 74838 ("rivet") followed by #.
>>>>>>
>>>>>> From the UK, Telediscount can be useful if your office restricts
>>>>>> international dialling: 0844 861 3535.
>>>>>>
>>>>>> Have a good weekend!
>>>>>> Andy
>>>>>>
>>>>>> _______________________________________________
>>>>>> Rivet mailing list
>>>>>> Rivet at projects.hepforge.org
>>>>>> http://www.hepforge.org/lists/listinfo/rivet
>>>>>>
>>>>>
>>>>> -- 
>>>>>
>>>>>
>>>>> ________________________________
>>>>> Lars Sonnenschein
>>>>> ________________________________
>>>>> Home Institution:
>>>>> PH/TH 53/1-052
>>>>> CERN
>>>>> CH-1211 Geneve 23
>>>>> Switzerland
>>>>> Tel.:+41(22)767-2801
>>>>> --------------------------------
>>>>> ________________________________
>>>>> FNAL:
>>>>> D0, PK151
>>>>> Mailstop #352
>>>>> Fermilab, P.O.Box 500
>>>>> Batavia, IL 60510-500
>>>>> USA
>>>>> Tel.: +1(630)840-8740
>>>>> ________________________________
>>>>> _______________________________________________
>>>>> Rivet mailing list
>>>>> Rivet at projects.hepforge.org
>>>>> http://www.hepforge.org/lists/listinfo/rivet
>>>>
>>>>
>>>
>>> -- 
>>>
>>>
>>> ________________________________
>>> Lars Sonnenschein
>>> ________________________________
>>> Home Institution:
>>> PH/TH 53/1-052
>>> CERN
>>> CH-1211 Geneve 23
>>> Switzerland
>>> Tel.:+41(22)767-2801
>>> --------------------------------
>>> ________________________________
>>> FNAL:
>>> D0, PK151
>>> Mailstop #352
>>> Fermilab, P.O.Box 500
>>> Batavia, IL 60510-500
>>> USA
>>> Tel.: +1(630)840-8740
>>> ________________________________
>>
>>
>
> -- 
>
>
> ________________________________
> Lars Sonnenschein
> ________________________________
> Home Institution:
> PH/TH 53/1-052
> CERN
> CH-1211 Geneve 23
> Switzerland
> Tel.:+41(22)767-2801
> --------------------------------
> ________________________________
> FNAL:
> D0, PK151
> Mailstop #352
> Fermilab, P.O.Box 500
> Batavia, IL 60510-500
> USA
> Tel.: +1(630)840-8740
> ________________________________