Particle Flow Jet Identification Criteria with CMS at 13 TeV

1. Magda Diamantopoulou, Niki Saoulidou,Eirini Tziaferi University of Athens,Greece Particle Flow Jet Identification Criteria with CMS at 13 TeV HEP 2016 - Conference on Recent Developments in High Energy Physics and Cosmology, 12-15 May 2015, Thessaloniki, Greece

2. Outline • The CMS detector and Jet reconstruction • Purpose of the studies • Documentation • Technical Details • Studies for JetID: - Clean back-to-back sample for efficiency - Noise sample for background rejection • Summary and Plans for 2016

3. 3.8 T Pixels σ/pT~ 1.5∙10-4pT(GeV)⊕0.005 Electromagnetic Calorimeter σE/E ≈ 2.9%/√E(GeV) ⊕ 0.5%⊕0.13GeV/E Hadronic Calorimeter σE/E ≈ 120%/√E(GeV) ⊕ 6.9% Muon Spectrometer σpT/pT ≈ 1% for low pT muons σpT/pT ≈ 5% for 1 TeV muons CMS detector

4. Jet Reconstuction

5. Purpose of the study Particle Flow (PF) JetID criteria is a set of cuts which was constructed in order to reject fake, badly reconstructed and noise jets while retaining 98-99% of real jets. PFJetID is used by all CMS analyses which make use of PF jets. The studies were done using: • Clean samples with back-to-back dijets to study efficiency • Pure noise sample to study background rejection

6. Documentation All CMS Analyses use JetID criteria The JETID Twiki with all important information: https://twiki.cern.ch/twiki/bin/viewauth/CMS/JetID AN-15-269 : A detailed note (68 pages) has been written and uploaded to iCMS: http://cms.cern.ch:80/iCMS/jsp/openfile.jsp?tp=draft&files=AN2015_269_v2.pdf • Current PFJetID criteria-

7. Technical details Data : 13 TeV stable beam collisions, 3.8 T ● Datasets /JetHT/Run2015C-PromptReco-v1/MINIAOD CMSSW_7_4_X /JetHT/Run2015D-PromptReco-v3/MINIAOD CMSSW_7_4_X /JetHT/Run2015D-PromptReco-v4/MINIAOD CMSSW_7_4_X /MinimumBias/Run2015C-PromptReco-v3/MINIAOD (Noise studies) ● MiniAODs centrally produced. ● Triggers : Used PFHT800, PFHT350 in order to be able to study lower and higher pT jets ● Simulation : QCD Spring15, Pythia8-Tune4C, bx50 : QCD Spring 15, Pythia8-TuneCUETP8M bx25

8. Back to back dijet sampleJet characteristics Selection cuts: Number of jets >=2 pT1 > 60GeV pT2 > 30GeV Δφ >2.7 The analysis was performed separately for seven eta bins from 0 to 5.0 with a step of 0.5.

9. Control check plot:MET/SumET The sample is clear of noise Nice aggrement between data and simulation

10. Charged hadron fractionmeasured from tracker The sample is clean of noise. Nice agreement between data and simulation Mean chf =0.6 as expected

11. Neutral hadron fraction (NHF) measured from hadronic calorimeter (HCAL) Noise from HCAL sits on high values of NHF The sample is clean of noise. Nice agreement between data and simulation Mean nhf =0.1 as expected

12. Neutral electromagnetic fraction (NEMF) measured from electromagnetic calorimeter (ECAL) Noise from ECAL sits on high values of NEMF The sample is clean of noise. Nice agreement between data and simulation Mean nemf =0.25 as expected

13. Multiplicities Charged Multiplicity Neutral Multiplicity Photon Multiplicity The sample is clean of noise. Nice agreement between data and simulation

14. Efficiency vs |η| We use tag-and-probe technique in dijet events to estimate efficiency for real and simulated events. For almost all eta bins, the effciency is ~100% which is expected since the sample is very clean. This indicates that the PFJetID criteria do not remove real physics jets. • We observe for |η| : 2.5-3.0 there is an inefficiency of 4% in simulation and 10% in data. For this we propose new improved criteria for the 2016 running (see back-up slides). • This inefficiency is due to the fact that we are close to the boundary of the forward region (|η| of 3) for which jet fractions are now (in Run II) defined differently.

15. Efficiency vs pT for several eta bins:data Use tag-and-probe techinque in dijet events to estimate the efficiency for real and simulated events. Observe that for |η| :2.5-3.0 ther is an inefficiency of 10% in data. For this we propose new improved criteria for the 2016 running.

16. Efficiency vs pT for several eta bins:simulation Use tag-and-probe techinque in dijet events to estimate the efficiency for real and simulated events. Observe that for |η| :2.5-3.0 there is an inefficiency of 4% in simulation. For this we propose new improved criteria for the 2016 running.

17. Noise rejection We use an enriched noise sample to check that the PFJetID does remove noise and to calculate the background rejection. • The analysis was performed separately for seven eta bins, with a step of 0.5. • Selection cuts: • Number of jets >= 1 • pt > 30 GeV

18. MET/SumETof a noise sample Background rejection efficiency is evident from the elimination of the high MET/SumET events which are all noise and/or mis-measurements.

19. Charged Hadron Fraction of a noise sample In the first bin of the charged hadron fraction distributions there are 103 - 105 jets PFJetID removes the vast majority of noisy jets in all eta bins.

20. Neutral Hadron Fractionof a noise sample Noise from HCAL sits on high values of NHF PFJetID removes the vast majority of noisy jets in all eta bins.

21. Neutral electromagnetic fractionof a noise sample Noise from ECAL sits on high values of NEMF PFJetID removes the vast majority of noisy jets in all eta bins.

22. Multiplicitiesof a noise sample Charged multiplicity Neutral multiplicity Photon multiplicity PFJetID removes the vast majority of noisy jets in all eta bins. In the first bin of the charged multipllicity distributions there are 103 - 105 jets

23. Performance of PF JetID on an inclusive sample Selection cuts: Number of jets>=1 pT>200 GeV

24. Background rejection vs |η|:MET/SumET MET/SumET no JetID Black : data Red : MC Use inclusive jet sample to test background rejection The long tails in the MET/SumET distribution indicate that we introduced plenty of noise in the sample

25. Background rejection vs |η|:MET/SumET MET/SumET with JetID Black : data Red : MC Use inclusive jet sample to test background rejection Background rejection efficiency is evident from elimination of the high MET/SumET events which are all noise and//or mis-measurements

26. Background rejection vs |η| Use enriched noise sample (Minimum Bias events) to estimate background rejection. • Background rejection efficiency is high for all eta bins. • PFJetID criteria are very efficient in noise removal while retaining the majority of physics jets.

27. Summary We demonstrated the performance of PFJetID criteria showing that works fine as it improves the agreement between data and MC in all PF jet variables and drastically removes the noise jets. We proposed an improvement in order to increase efficiency for the 2.7<|eta|<3.0 region. Plans • Study CMSSW 8_0_X in order to be prepared for the new Run. • Study and develop if needed JetID for PUPPI(PileUp per particle identification) Jets.

28. Back up

29. Proposed improvement for |η| : 2.5-3.0 • In order to increase efficiency for the 2.5-3.0 eta bin, we first located where the inefficiency is: • Found that up to an |η| of 2.7 there is no inefficiency • Inefficiency is introduced for |η| between 2.7 and 3.0, as expected, being closer to the forward region with different energy fraction definitions. • Considering the same JetID criteria up to an |η| of 2.7 and introducing the following for 2.7 < |η| < 3.0 alleviates the problem greatly: NEW for 2.7 < |η| < 3.0 : # of neutral particles > 2 & Neutral EM fraction <0.9

30. Efficiency vs pt for several eta bins • Use tag-and-probe technique in dijet events to estimate efficiency for the lowest prescaled (PFHT350) and the highest unprescaled trigger (PFHT800). • Inefficiency for 2.5<|η|<3.0 greatly reduced.