ROOT Classes in Python

Newbie
1

Hey, all! I’ve been working in Python 3.x a lot and am in the process of reproducing many functions native to ROOT but in a numpy/pandas format. Most things I’m doing (going over StPico files for STAR analysis) are pretty straightforward, but one is eluding me: mass.

I’d like to get mass natively in Python, but I’m having trouble finding exactly how we get the mass parameter for a track in ROOT. Any idea where I can find this? I tried looking in the ROOT manual, but I was unsuccessful.

As an example, here’s how I get vertex positions for an event and then calculate v_r (where “data” is imported from a STAR pico file using upROOT):

    vX = np.hstack(np.asarray(data["Event"]["Event.mPrimaryVertexX"].array()))
    vY = np.hstack(np.asarray(data["Event"]["Event.mPrimaryVertexY"].array()))
    vZ = np.hstack(np.asarray(data["Event"]["Event.mPrimaryVertexZ"].array()))
    vR = np.power((np.power(vX, 2)+np.power(vY, 2)), (1/2))

Thanks!

ROOT Version: 6.14/02
Python Version: 3.7

2

Perhaps @Axel knows the answer (or knows who knows)?

3

I don’t understand the question. Are you asking “what is a lorentz vector”?

4

I’m asking where the code lives in ROOT that determines particle mass (or, even better, what that code is). I’m trying to duplicate its functionality in Python natively. Right now, I had something running like:

m_squared = np.divide(np.multiply(p_squared, g_squared), b_squared)

Where “p_squared” is the track momentum magnitude squared, “g_squared” is 1/gamma squared, and “b_squared” is beta squared.

It appears to be correct, but I’m trying to make sure I’m not doing something that’s different than what ROOT does to avoid inconsistencies.

5

There’s a module in upROOT called “vector” which works for these purposes; it’s new in uproot4 (running with awkward1.0). Anyone interested can check it out here. I’m marking this as solved.

Thanks!