Scaling Lorentz Vector

ROOT
1

Is there is implementation of a way to scale a lorentz vector’s magnitude and keeping its angles the same?

Thanks
MK

2

If Root decides to implement this, note that they should do it “both” ways:

(1) Assuming the mass stays the same (e.g., scaling a reconstructed muon)

(2) Assuming mass is scaled by same factor (e.g., composite objects like jets)

Cheers,
Charles

3

If Root decides to implement this, note that they should do it “both” ways:

(1) Assuming the mass stays the same (e.g., scaling a reconstructed muon)

(2) Assuming mass is scaled by same factor (e.g., composite objects like jets)

Cheers,
Charles[/quote]
Yes I agree, and should have stated such. Thank you for the add-on.

Regards
MK

4

Hi,
for both TLorentzVector and ROOT::Math::LorentzVector you can use the operator * to scale the vector. It will scale all the 4 components.

ROOT::Math::XYZTVector v(1,2,3,4);
v *= 10;  // scale by a factor 10

If you want to scale only the momentum and keep the mass constant just get the spatial components using Vect()
and scale those.

Best Regards

Lorenzo

5

[quote=“moneta”]for both TLorentzVector and ROOT::Math::LorentzVector you can use the operator * to scale the vector. It will scale all the 4 components.

ROOT::Math::XYZTVector v(1,2,3,4);
v *= 10;  // scale by a factor 10

[/quote]

Ahh… Didn’t know that. Good! :slight_smile:

This is something that almost everybody who plays with four vectors eventually does. It would be a nice thing to add as a member function (named ‘constMassScale()’ or something like that). :smiley:

Cheers,
Charles

6

Hi,

we could add this function, however this can be done easly like in the code below and this avoid mis-interpretation of the function:

TLorentzVector v(.....);
v.SetZYZM(scale * v.X(). scale * v.Y(), scale * v.Z(), v.M() );

or if using the ROOT::Math::LorentzVector classes

ROOT::Math::XYZTVector  v(....);
v = ROOT::Math::PxPyPzMVector(scale * v.X(), scale * v.Y(), scale * v.Z(), v.M() );

Lorenzo