Allow for inDet Brem recovery in UPC mode

For what "Brem Recovery in InDet"

Short: We need the electron tracks to be recovered and survive (not be killed as bad pions) until we reach the GSF . So we try some "fast approximations".

Long : https://arxiv.org/pdf/1902.04655.pdf 5.2

The pattern-recognition algorithm uses the pion hypothesis for the model of energy loss from interactions of the particle with the detector material. However, if a track seed with pT > 1 GeV cannot be successfully extended to a full track of at least seven silicon hits per candidate track and the EM cluster satisfies requirements on the shower width and depth, a second attempt with modified pattern recognition, one which allows up to 30% energy loss for bremsstrahlung at each intersection of the track with the detector material, is made. Track candidates with pT > 400 MeV are fit, according to the hypothesis used in the pattern recognition, using the ATLAS Global χ2 Track Fitter [30]. Any ambiguity resulting from track candidates sharing hits is resolved at the same stage. In order to avoid inefficiencies for electron tracks with significant bremsstrahlung, if the fit fails under the pion hypothesis and its polar and azimuthal separation to the EM cluster is below a value, a second fit is attempted under an electron hypothesis (an extra degree of freedom, in the form of an additional Gaussian term, is added to the χ2 to compensate for the additional bremsstrahlung losses coming from electrons; such an energy-loss term is neglected in the pion-hypothesis fit).

Now :

• This seems not to be enabled by default in minbias but prb we want to have it in UPC. At least if we want to be able to do electrons (and also photon conversion as electron legs ... ) as best as we can wrt to pp.

• The way the info is passed to the Pattern/ambi is by checking the primary pass extension (c'est la vie I guess))

• After discussion with @tstreble prb the more clean is to have a UPC pass with its own extension (so we touch nothing else)

• Note that the track seed with pT > 1 GeV cannot be successfully extended is left as is. In principle since we have lowered the E of the clusters to 400 MeV and of the tracking is 100 MeV we could lower it. But this is for another day

Anyhow, basically

• We introduce doUPC which also enables doMinBias so we get this/existing behaviour but we can add
• We also have UPCPass which starts as MinBias pass but also can change some of the flags .
• For now this is the "extension" and could be the 1 GeV (but not done here).
• The "extension" allows us to say to the pattern and the ambi "please do brem recovery"

Running the test under Reconstruction/RecExample/RecJobTransformTests/test/test_data22_upc.sh

Now (before Brem attempted / recovered were 0 )

"""RAWtoALL 01:55:00 ******************* Tracking reconstruction Config *******************
RAWtoALL 01:55:00                      Active Config is  UPC
RAWtoALL 01:55:00 Flag Name                                : Value

RAWtoALL 01:59:16   number of normal fits           :     3974     1024     1213     1673       64
RAWtoALL 01:59:16   + 2nd brem fit for failed fit   :        0        0        0        0        0
RAWtoALL 01:59:16   normal brem fits for electrons  :      302       34       77      186        5
RAWtoALL 01:59:16 ------------------------------------------------------------------------------------
RAWtoALL 01:59:16   sum of succesful fits           :     4151     1037     1269     1775       70
RAWtoALL 01:59:16   sum of failed fits              :      132       22       31       79        0
RAWtoALL 01:59:16 ------------------------------------------------------------------------------------
RAWtoALL 01:59:16   Number of subtracks created     :     1325      285      396      629       15
RAWtoALL 01:59:16   Number of candidates excluded   :     3012      659     1035     1259       59
RAWtoALL 01:59:16 ------------------------------------------------------------------------------------
RAWtoALL 01:59:16   Number of tracks accepted       :     2405      701      789      878       37
RAWtoALL 01:59:16   including number of brem fits   :       90       16       30       42        2
RAWtoALL 01:59:16 ------------------------------------------------------------------------------------

ping @pbalek , @stapiaar , @igrabows , @tstreble , @slawlor