[G12] Meeting today?

[Michael Paolone]

Hi Rafael,

Regarding TLorentzVector boosts:  I'm not sure what you mean when you
refer to "distributions" of a boost.  A boost is a one to one
transformation per event.  A quick look at the source code shows how the
boost is calculated:

void TLorentzVector::Boost(Double_t bx, Double_t by, Double_t bz)
{
   //Boost this Lorentz vector
   Double_t b2 = bx*bx + by*by + bz*bz;
   Double_t gamma = 1.0 / TMath::Sqrt(1.0 - b2);
   Double_t bp = bx*X() + by*Y() + bz*Z();
   Double_t gamma2 = b2 > 0 ? (gamma - 1.0)/b2 : 0.0;

   SetX(X() + gamma2*bp*bx + gamma*bx*T());
   SetY(Y() + gamma2*bp*by + gamma*by*T());
   SetZ(Z() + gamma2*bp*bz + gamma*bz*T());
   SetT(gamma*(T() + bp));
}

There could be some machine precision problems with the gamma calculation
when gamma gets very big or small compared to the boosted energy/momentum
of the 4vec you are looking at...  Again, I'm not exactly sure though what
you mean. Are you taking the same exact TLorentzVector and boosting it
multiple times and getting different results?!?  That would be bug, I
think.

-Michael


> My undergrad has something to show/ask in relation to the Boost method
> in the TLorentzVector class. When boosting to the rest frame of a
> particle and then looking at the components of the spatial momenta,
> they are Gaussian-like with a mean of order 10^(-4) but its standard
> deviation is of order 10^(-2). This does not seem very good. If it is
> the only thing to be presented today, we can resolve this issue on our
> own.
>
> Best regards,
>
> Rafael
>
>
> On Jun 4, 2014, at 10:29 AM, Michael Kunkel wrote:
>
>> Greetings,
>>
>> I have nothing to show today (guess that is reason enough to not
>> have a meeting :) )
>>
>> My vote is an abstain vote in regards to a meeting today.
>>
>> BR
>> MK
>>
>> Sent from my iPhone
>>
>>> On Jun 4, 2014, at 10:25 AM, Will Phelps <wphelps at jlab.org> wrote:
>>>
>>> Unless someone has something important to show we can cancel it.
>>> There's still a week before the collaboration meeting.
>>> -Will
>>>
>>> Sent from my iPhone
>>>
>>>> On Jun 4, 2014, at 9:54 AM, Michael Kunkel <mkunkel at jlab.org> wrote:
>>>>
>>>> Greetings
>>>>
>>>> With the users group meeting happening, are we having a G12 meeting?
>>>>
>>>> BR
>>>> MK
>>>>
>>>> Sent from my iPhone
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