Clustering for VLE particles in CombinedTB

Carmen Iglesias

IFIC-University of Valencia

(Dpt. FAMN)

TileCal Analysis and Combined Test Beam, 14 February, TileCal Week

Ntuples

Energy #Run

1 GeV 2101077

2 GeV 2101078

3 GeV 2101079

4 GeV 2101080

5 GeV 2101047

Samples with electrons and pions from 1 to 9 GeV at eta=0.35, withCalo info (LAr+Tile) and the tracks info from TRT only (pixels have problems)

castor/cern.ch/atlas/ctb/test/real_data/reconstruction/Combined/

Energy #Run

6 GeV 2101084

7 GeV 2101085

8 GeV 2101048

9 GeV 2101049

They have been generated by Vincent using 9.1.1 Release with the default values of RecExTB. They can be located in:

Cut to separate particles • Selection of good tracks

• trk_nTracks==1Only 1 track• trk_nTrtHits[0]20 More than 20 hits per track

• for electrons• sADC_C2>650 Cherenkov2 counter cut • nHL>5 number of high-level hits

• for pions and muons• sADC_C2<650 Cherenkov2 counter cut • nHL≤2 number of high-level hits

• Pion- Muon separation• Pions: E<0.2 GeV in sample D (Pedestal in sample D,

we assume that only muons can reach D)• Muons: E> 0.2 GeV in sample D (signal in sample D)

Pion-electron separationCherenkov counter cut isn’t enough. We use the future of low-level hit and high-level trigger. A track has less than 5 high-level hits. The e- tracks have more than 2 high-level hits.

muons

pions

Clustering info in CBT ntuples• Emcluster: clusters from the sliding window algorithm

• Tbemclusters: clusters from an algorithm used in previous test beam. It has been added to allow comparison. It’s a window of 3x3 cells.– Emclusters and tbemclusters use only cells from the LAr calorimeter.

• Cmbclusters: sliding window clusters but they are done on towers (larg+tile) and not anymore on cells. It is not working for the moment because of a coordinate problem between LAr and Tile.

– LAr is shifted with respect to Tile by "half module" :• TileCal has just 3 modules -0.15 < eta < +0.15• LAr has -0.2 < eta < 0.2,

i.e. there are 3 slices with =0.1 in Tile and 4 slices in LAr, shifted by half of the slice

• Topo_EM cluster and Topo_Tile cluster: Finds a seed cell, then cluster expands by checking energy in neighboring cells. Thresholds for defining seed and including neighbors can be changed. The default values are:– seed threshold is E/σnoise>6– neighbor threshold is E/ σnoise>3

e- in Lar: Energy distributionFor electrons at 9 GeV

For electron it seems as the cuts on TRT works good

e- in LAr: Number of Clusters

# clusters

SW SW_TB TOPO_EM

9 GeV 31585 31607 31614

8 GeV 30475 30506 30514

7 GeV 27252 27303 27292

6 GeV 26878 26969 26961

5 GeV 21689 22446 22464

4 GeV 10994 13751 13670

3 GeV 2292 (*) 11869 11472

2 GeV --- (*) 5853 4574

1 GeV --- (*) 1093 482

#clusters is very similar between them for each ET value. #clusters defined increase with the energy.

(*) There is a cut (E>2 GeV) in this algorithm by definition

#clusters is very low

e- in LAr: Resolutions

SW SW_TB TOPO_EM

9 GeV 7.57 8.92 10.48

8 GeV 8.51 10.04 11.64

7 GeV 7.85 6.93 8.51

6 GeV 8.83 7.81 9.62

5 GeV 13.07 15.47 17.34

4 GeV 11.04 11.47 14.78

3 GeV 9.59 (*) 14.38 20.39

2 GeV ---(*) 20.51 34.99

1 GeV ---(*) 80.75 48.38

The best resolution is for SW, but all the algo present very similar results.TOPO obtain the worst resolutions

maybe it will be needed to change the thresholds for seed and neighbor cells.In my previous analysis of clustering in VLE in simulation: the best resolution with

seed threshold E/σnoise>4 and neighbor threshold E/ σnoise>2 (but they have been done without noise and pile-up)

In general, the E resolution is better when E increases

E resolution slightly better than it’s expected, WHY??

(*) There is a cut (E>2 GeV) in this algorithm by definition

Cone algorithm (I)Study in LAr the region =0.2 and =0.2

Select cells in LAr comes from electron E depositionssADC_C2>650 and nHL>5

Ecell >noise : Ecell > 100 MeV

Select the Cell with the longest E it will be the center of the cone

Define the radius of the cone:

where

R=2+2

=cellEmax-cell =cellEmax-cell

Strange results in DR distributions: it seemsas the most of the cells from electrons are farfrom the cell with Emax ???

Cone algorithm(II)Is due to the bad definition of or ??

Is due to the cell with Emax are in the wrong place?

If I repeat the analysis with an imaginary particle centred in =0.35 and =0.0:

The same distribution appears

Pions and Muons in Lar (I)The separationbetween pions and muons is not so easy.

total

electrons

muons

pions

muons

pions

There will be contamination on muon in the E distribution of Pions.

Pions

Muons

Pions and Muons in Lar (II)A part of the problem could be from PEDESTAL…

cellThresholdOnAbsEt = 0.*MeVneighborThresholdOnAbsEt = 100.*MeVseedThresholdOnEt = 200.*MeV

But, if we compare with the pedestal value per cell, the thresholds in TOPOto avoid the noise MUST be enough:

Pedestal in SW cluster id up to 1 GeV, and in TOPOcluster is up to 2 GeV maybe we must change the threshold for the min E inside cluster

Pions and Muons in Lar (III)

Very low muons don’t deposit in the last Tile sampling and are therefore taken as pions!

-Using TRT and Tile information it’s possible to distinguish between muons and pions only for E >3GeV, below it is difficult with this method

Improvement expected using the topological info in LAr and Tiles. - Based on the fact that the muons leave their energy uniformly (normalizing to the path length in a sampling) whereas pions should be giving most of their energy in this sampling.

muons

pions

muons

pions

muons

pions

Problem with muons with E ≤2GeV

Problems in Tile

there are electrons in Tile!!

In Tile, we expect that the most of the ET comes from PIONS, and also a contribution of muons. But the plots show that

Ecell > 25 MeV Ecell > 70 MeVThere are still electronsfor low energies

total

electrons

muons

pions

If we only select the E in Tile > 1000 MeV

total

electrons

muons

pions

Is possible to have electrons in Tile? Are they really pions?

estimation of the noise for cell in Tilefrom the pedestal for each cell

It is possible to have pions that pass the cherenkov cut. But in principle nHL>5 is a very efficient cut to select electrons only.

At 9 GeV there is no e- in Tile (even at higher energy it seems that e- cannot cross LAr)

Conclusions

• In Lar

– For electrons it seems as the cuts on TRT works good.

– Using TRT and Tile information it’s possible to distinguish between muons and pions only for E >3GeV. To improve:

• use topological information in LAr and Tiles• Compare VLE runs with MC

• In Tile– Pions are not well defined in Tile (some proportion of them are defined as e-)

TO GET PROGRESS IN CLUSTERING ANALYSIS, FIRST MUCH MORE WORK IS NEEDED TO DO IN THE SEPARATION OF PARTICLES AT VLE!!

About clustering algorithms:

About particles separation:

• For electrons, the best results in E resolution comes from SW algo•Anyway, it would be interesting to change the cut in Ecell>2 GeV to can study the VLE runs at 3, 2 and 1 GeV

• Results from TopoCluster can be improved• change the thresholds for seed and neighbor cells

• Needed to understand the behavior of Cone algorithm