Smearing of eta/phi in ATLAS card

[Jake]

Hi,

I'm trying to understand the functional form of the smearing of eta and phi for photons as a function of E and eta. I notice that there is a module called AngularSmearing but it doesn't look like it is called in the ATLAS card. Making plots of, for example, sigma(eta)/eta vs eta shows that there is certainly some sort of smearing that is performed. I'm wondering how (with which module) the angular smearing is performed in this case, and if there is a functional form for the angular resolution/where I could find such a function.

Thanks.

[Michele Selvaggi]

The smearing is performed via the calorimeter grid for photons.
See here:

​https://github.com/delphes/delphes/blob/master/cards/delphes_card_ATLAS.tcl#L226#L264

[Jake]

Hi,

Thanks for the response.

I'm still unsure how the smearing performed depends on the event kinematics. For phi is it taken to be a constant fraction of the bin size, where bin size depends on eta?

For eta resolution at least I find a functional form for the resolution of sqrt(a²+b²/eta²), similar to the energy resolution, but nothing like this appears in this block or in the analogous block in the card I use.

What about energy dependence of the eta/phi smearing?

Thanks.

[Michele Selvaggi]

Hi,

The bin size in (eta,phi) can be read directly from the card. For instance in the following block:

​https://github.com/delphes/delphes/blob/master/cards/delphes_card_ATLAS.tcl#L257#L264

the last bin in the forward region has deta = 0.3 and pi/18.0 in dphi.

Each photon with given eta,phi falls into a given rectangle of size deta,dphi in that grid. The smeared eta, phi values are obtained by randomly throwing eta,phi from a uniform distribution over that given rectangle.

The get a feeling for the calorimeter grids you can generate an image by doing:

./CaloGrid cards/delphes_card_ATLAS.tcl ECal
./CaloGrid cards/delphes_card_ATLAS.tcl HCal

Michele