1. In situ Hadronic E/p Calibration of the ATLAS barrel calorimeters using Minimum Bias Events N.Huseynov 1,2, Y.Kulchitsky 1,3, P.Tereshko 1,3,V.Vinogradov 1 1.JINR, Dubna, Russia 2.IP ANAS, Baki, Azerbaijan 3.IP NAS, Minsk, Belarus

2. 11.05.2015 2:26N.Huseynov The Xth International School-Seminar, Gomel The ATLAS experiment at the LHC will have the huge physics discovery potential, in particular in the detection of a heavy Higgs boson. Calorimeters will play a crucial role in it. The key question of calorimetry is the absolute energy calibration. The precise measurement of the momentum of hadrons in the tracking detectors ( ), compared to the energy E measured in the calorimeters ( ) can provide a calibration of the response of the calorimeter to pions at the percent level. The tracking system can be used to verify the hadronic calorimeter calibration in the energies rage between 400 MeV to about 200 GeV. The E/p ratio allows to check the absolute energy scale calibration over the pseudo-rapidity range of the tracking detectors which covers the barrel part of LAr and Tile Calorimeter ( |η| <1). The single hadron E/p performances are studied in two data samples: the minimum bias sample (within energy range from 400 MeV to 12 GeV, may be more) and in tau single prong decay, with tau from W and Z decays (which covers the energy range between 10 to 150 GeV). It was used MonteCarlo data: mc08.105001.pythia_minbias.recon.ESD.e357_s462_r541 - (dataset name) containing 250K events, ( ≈ 6 mil. tracks). Motivation

3. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel ATLAS DETECTOR R

4. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Analysis of Minimum Bias Events Event Selection: Rejection of events with energy deposition E LAr0 > 3σ noise_cell (150 MeV)‏ Selection of events with energy depositions (E > 2σ noise_cell ) in the LAr2 and LAr3 layers Shower isolation: η -P track selection: |η track | < 0.6 1< P track < 8 GeV/c by step of 1 GeV/c. Quality of tracks:  At least one hit in the B layer of the pixel detector  No more than one hole in the other pixel and SCT layers  χ 2 /ndof < 2. The ID tracking performance group doesn't recommend to use cut on the χ 2. We will not use this cut in our future analysis. Energy reconstruction by the Local Hadronic Calibration method for cells with E cell > 2σ noise (σ noise are different for each sampling). Tracks isolation: no other tracks within ∆R distance < 0.4 (η,φ coordinates) ‏

5. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Results: E/P distributions for P=1 - 5 GeV/c with LAr cuts: E LAr0 2σ noise_cell =0.99±0.02 σ =0.51±0.02 2-3 GeV 1 - 2 GeV =0.966±0.025 σ =0.525±0.025 1-2 GeV =0.96±0.03 σ =0.50±0.03 4-5 GeV =1.05±0.02 σ =0.40±0.03 σ =0.46±0.01 =1.03±0.01 3-4 GeV

6. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Results: E/P distributions for P=5 - 8 GeV/c with LAr cuts: E LAr0 2σ noise_cell 5 - 6 GeV =1.11±0.02 σ =0.36±0.02 7 - 8 GeV =1.10±0.05 σ =0.39±0.05 6 - 7 GeV =1.10±0.03 σ =0.36±0.03

7. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Results of the analysis: linearity There is linearity for E>3 GeV : the points are within ±1% within the errors. Nonlinearity is observed. This is an effect of the noise cuts: selection of cells with E cell > 2σ noise that leads to energy losses especially at low energies (E<3 GeV).

8. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel General agreement between the obtained minbias events resolution and the extrapolation of the CTB04 resolution is observed. (ATL-TILECAL-PUB-2008-009)‏ E.Abat et al. "Study of the response of the ATLAS central calorimeter to pions of energies from 3 to 9 GeV"; ATL-COM-GEN-2009-009 Our energy resolution (hadronic scale ) about 1.1-1.5 times better than result from this work (EM scale)‏ Comparison with CTB-2004 results Comparison with CTB-2004 results ATL-TILECAL-PUB-2008-009 ATL-COM-GEN-2009-009 given study

9. 25.07.2009N.Huseynov The Xth International School-Seminar, GomelConclusions We have investigated the possibility in situ E/p Calibration of the ATLAS barrel calorimeters on the basis of Minimum Bias Events (250K events, 6 million tracks, ATHENA release 14.2.20) and the Local Hadronic Calibration Method for particles with |η| 1 GeV/c with 1 GeV/c step. It is shown that such calibration is possible. However, nonlinearity is observed especially at low energies (E<3 GeV/c) due to effect of the noise cuts: selection of cells with E cell > 2σ noise that leads to energy losses. There is linearity for P>3 GeV: the points are within ±1% within the errors. Agreement between the minimum bias energy calorimeter resolution and the CTB04 testbeam one (Y.Kulchitsky et al. ATL-TILECAL-PUB-2008-009) is observed. The used simulated data in this work, 250K minbias events, will be registered by ATLAS during about 5 days at the integrated luminosity of 5 pb -1 (ATL-COM-PHYS-2008-074, ATL-COM-PHYS-2009-081).

10. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel  We should reject background from egamma and neutral hadrons (K 0 and π 0 ).  We should reject fake traks.  We are going to use low energy hadrons without showering in Lar calorimeter from minbias events for calibration of TILE calorimeter.  We should use more statistic of the Minimum bias events to E/P study in the energy range between 8 to 12 GeV, may be more.PLANS

11. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel

12. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel

13. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Why should we measure minimum bias at ATLAS? – dNch/dη at η = 0: compare to NSD data from SppS and Tevatron. – Pile-up studies: calorimeter & physics analyses. – Overlap with underlying event studies: jets studies, VBF, … – Expected to improve modeling of soft hadronic interactions – Inter-calibration of detector elements: uniform events. – Baseline for heavy-ion studies. pp collisions at the LHC Essentially all physics at LHC are connected to the interactions of quarks and gluons (small & large transferred momentum). Hard processes (high-pT): well described by perturbative QCD Soft interactions (low-pT): require nonperturbative phenomenological models Minimum-bias and the underlying event are dominated by “soft” partonic interactions.

14. 14 Measuring the minimum bias events at ATLAS First, you need to select minimum bias events… σ NSD ~ 65 - 73mb σ tot ~ 102 - 118 mb (PYTHIA) (PHOJET) (PYTHIA) (PHOJET) Minimum bias trigger scintillators (MBTS) ‏

15. 15 Experimental definition: depends on the experiment’s trigger! “Minimum bias” is usually associated to non-single- diffractive events (NSD), e.g. ISR, UA5, E735, CDF,… σ NSD ~ 65 - 73mb σ tot ~ 102 - 118 mb (PYTHIA) (PHOJET) (PYTHIA) (PHOJET) At the LHC, studies on minimum bias should be done early on, both for collisions at √s=900 GeV and √s=14 TeV at low luminosity to remove the effect of overlapping proton-proton collisions! A minimum-bias event is what one would see with a totally inclusive trigger. On average, it has low transverse energy, low multiplicity. Many can be diffractive (single and double).UA5CDF Minimum bias events

16. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel In this method the reconstructed energy in a calorimeter is Longitudinal samplings – LAr1, LAr2, LAr3, Tile0, Tile1, Tile2 ─ weights, Monte Carlo simulation ─ Energy density in cell ─ cell energy deposition in electromagnetic (hadronic) scale Local Hadronic Calibration Method

17. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel We have used our own created weights.Weights were packed to TProfile2D(E,ρ,w), containing for 6 samplings of 43 logarithmically equidistant incident particle energies in the range 0.8 – 500 GeV and 20 bins of logarithm of cell energy density. Before we have used similar weights for the analysis of the Combined Test Beam 2004 data. Good results have been obtained! (Y. Kulchitsky et al. ATL- TILECAL-PUB-2008-009)‏ Local Hadronic Calibration Method log(ρ), log(GeV/L)‏ log(E) w

18. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Oxford-Stockholm group: Local Hadronic Calibration (w≥0.6 ( ATL-LARG-PUB_2009-001 ), η =0.45 )‏ Our energy resolution about 1.5 times better than the O-S group results Comparison with the results of ATL-CAL-PUB-2007-001 Energy linearity with our weights are mostly within ±1% Linearity of the O-S group results is within ±8%

19. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Momentum distribution =3.5 GeV Without η selection Results of the analysis | η |< 0.6 Momentum distribution =3.5 GeV after η cut about 2K tracks with P>10GeV =27 tracks / event Number track distribution Without η selection Mean momentum in barell part of Calorimeter =3.5GeV. We have 2K particles with energy greater than 10 GeV which go to Barrel LAr and Tile Calorimeter.

20. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Results of the analysis Most particles go to Extended Barrel Tile Calorimeter and LAr Hadronic End-Cap Calorimeter About 15% of particles go to barell part of calorimeter (|η|<0.6) η -distribution after η - P selection |η |<0.6 891128 η -distribution before η - P selection 5915378

21. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Tracks quality cuts At least one hit in the B layer of the pixel detector No more than one hole in the other pixel and SCT layers χ 2 / ndof < 2 Track isolation: no other tracks within ΔR < 0.4 ΔR is the distance between impact point in the beginning of the calorimeter for given track and ones of other tracks Rejected tracks The ID tracking performance group doesn't recommend to use cut on the χ 2. We will not use this cut in our future analysis. Rejected ≈ 10% tracks

22. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel For selection of “shower cells” related with extrapolated track all cells of the calorimeter are considered and the cells satisfying to the following criteria are taken : |φ ext,i - φ i,k | < ∆φ i |η ext,i - η i,k | < ∆ η i E i,k > 2σ noise,i, where φ i,k, η i,k are coordinates of the centre of the i,k cell, φ ext,i, η ext,i are coordinates of track extrapolation in i-layer, i=0,…,6. The values of ∆φ i and ∆η i have been determined from the lateral profiles in each longitudinal layer obtained in given work. Analysis of Minimum Bias Events

23. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel LAr showers ∆η Lateral profiles for 4-5 GeV Energy depositions of showers in the LAr cells as a function of ∆η=η cell -η track,extr E cell /∆ η

24. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Tile showers ∆η  Lateral profiles for 4-5 GeV Energy depositions of showers in the Tile cells as a function of ∆η=η cell -η track,extr E cell /∆ η

25. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel LAr showers ∆φ Lateral profiles for 4-5 GeV Energy depositions of showers in the LAr cells as a function of ∆φ= φ cell - φ extr.track E cell / ∆ φ ∆ φ E cell / ∆ φ ∆ φ E cell / ∆ φ ∆ φ E cell / ∆ φ ∆ φ

26. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Tile showers ∆φ Lateral profiles for 4-5 GeV Energy depositions of showers to the Tile cells as a function of ∆φ= φ cell_centre - φ extr.track E cell / ∆ φ ∆ φ E cell / ∆ φ ∆ φ E cell / ∆ φ ∆ φ

27. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Lateral η-region of showers 0.4 0.2 2.3 m 0 LAr TileCal 0 ∆η =η cell center - η track extr coordinate difference 1 longitudinal coordinate along the shower axis -0.2 -0.4 0 1 2 0 1 2 3 INNER DETECTOR Track extrapolation

28. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Lateral φ-region of showers 0.4 0.2 2.3 m 0 LAr TileCal 0 ∆φ=φ cell,centre ̶ φ track,extr coordinate difference 1 longitudinal coordinate along the shower axis -0.2 -0.4 INNER DETECTOR Track extrapolation 102 0 123

29. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Cuts in the LAr0 energy deposition and shower isolation Rejection of events with energy deposition E LAr0 > 3σ noise_cell (150 MeV)‏ for elimination of events with considerable energy loss before the calorimeter. In other words we have rejected most of hadrons created showers before calorimeter. The K isol is a shower isolation coefficient. Energy deposition in LAr0 1-2 GeV Shower isolation Distribution of K isol 1-2 GeV

30. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Effect of the LAr cuts on E/p distributions Events selection with energy depositions in LAr2 and LAr3 layers: E LAr2 and E LAr3 >2σ noise_cell. These cuts are empirically founded ones. Due to these cuts the E/P distributions closer to 1 and smaller widths have been obtained. 1-2 GeV without the LAr2 and LAr3 selection with the LAr2 and LAr3 selection

31. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Comparison with CTB04 Data E/P ratio measured (open points) and predicted by Monte Carlo simulation (full points) as a function of E beam for η beam =0.35. test-beam data, em scale minimum-bias, had scale E.Abat et al. "Stmudy of the response of the ATLAS central calorimeter to pions of energies from 3 to 9 GeV" ATL-COM-GEN-2009-009 ATL-TILECAL-PUB-2008-009 ATL-COM-GEN-2009-009

32. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Results of the analysis 0.36±0.021.11±0.023605 - 6 0.40±0.031.05±0.021K4 - 5 0.36±0.031.10±0.031806 - 7 0.45±0.011.03±0.012K3 – 4 7 - 8 2 – 3 1 - 2 Energy range, GeV/c 0.39±0.051.10±0.05106 0.51±0.020.99±0.0210K 0.52±0.030.97±0.0370K σ(E/P)‏

33. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Charged Hadron Track Isolation ATL-COM-PHYS-2008-074 ΔR between cone center and closest neutral particle from Monte-Carlo truth. ΔR between cone center and closest reconstructed non-candidate track In minimum bias events, extra particles within the ΔR cone of the track considerably bias the measured pion energies. The main source of background was found to be photons from π 0 decay closely spaced in ΔR to the track. Almost all pions in the range 1-10 GeV in minimum bias events are accompanied by another particle within ΔR < 1. ΔR=sqrt((Δφ) 2 +(Δη) 2 ) ‏

34. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Cut-away view of the ATLAS Inner Detector CERN-OPEN-2008-020 Momentum resolution [P T ]=GeV/c 0.25<|η|<0.5 σ(P T )/P T = 2% for 1-2 GeV/c σ(P T )/P T = 4% for 100 GeV/c

35. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Calorimeters in ATLAS EM LAr |η| < 3 : Pb/LAr 24-26 X 0 3 longitudinal sections; 1.2 λ; Δη×Δφ=0.025×0.025 Central Hadronic |η|<1.7: Fe(82%)/scintillator (18%) 3 longitudinal sections; 7.2 λ; Δη×Δφ=0.1×0.1 End Cap Hadronic 1.7 <|η|<3.2: Cu/LAr – 4 longitudinal sections; Δη×Δφ<0.2×0.2 Forward calorimeter 3<|η|<4.9 : EM Cu/LAr – HAD W/Lar; 3 longitudinal sections (ATL-TILECAL-PUB-2008-009)‏ Linearity within ±1% (10-350 GeV)‏ LAr + TileCal resolution (obtained at 2004 Combined TestBeam) Tile Calorimeter EM barrel and EndCap Hadronic EndCap Forward Calorimeter

36. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Table 1. ∆φ i and ∆η i values used for cell shower selection 0.1×0.2 0.1×0.1 0.025×0.05 0.025×0.025 0.1×0.003 0.1×0.025 cell size ∆φ×∆η 0.480.36Tile2 0.320.29Tile1 0.230.21Tile0 0.150.12LAr3 0.0770.082LAr2 0.0290.086LAr1 0.0740.112LAr0 ∆ η i ∆φ i layer

37. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Comparison with recent E/p studies Talk «Pion E/p Studies» given by N.Davidson, ATLAS TILECAL meeting 20 th April 2009 |η|<1.5 p T =1- 3 GeV =0.572±0.003 |η|<0.6 E=2- 3 GeV/c <E/P>=0.99±0.02 Our result of the E/P study The result of =0.99±0.02 obtained in our work (hadronic scale) is considerably better the result of =0.572±0.003 obtained in N.Davidson talk (EM scale)‏.

38. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel given work Talk «Pion E/p Studies» given by N.Davidson, ATLAS TILECAL meeting 20 th April 2009 Comparison of linearity with recent E/p studies

39. 25.07.2009N.Huseynov The Xth International School-Seminar, Gomel Weights for 0.8-500 GeV