Studies of Jet-Track Correlations in PbPb collisions with CMS

Transcription

1 Studies of Jet-Track Correlations in collisions with CMS Hard Probes 2015 Dragos Velicanu, MIT for the CMS Collaboration 6/30/2015 Dragos Velicanu 1

2 Questions this talk will address How are charged particles distributed around jets? What happens to these distributions when we compare leading and subleading jets? How many particles are there around these jets as a function of p T and centrality? What are effects of the QGP medium created in collisions that doesn t appear in pp? 6/30/2015 Dragos Velicanu - Hard Probes

3 Compact Muon Solenoid EM Calorimeter (ECAL) Hadron Calorimeter (HCAL) Beam Scintillator Counters (BSC) Forward Calorimeter (HF) TRACKER (Pixels and Strips) Muon System 6/30/2015 Dragos Velicanu - Hard Probes

4 Jets and tracks Tracks Inclusive Jets Standard CMS HI track selection η < > p T > 2.0 GeV/c 2.0 > p T > 3.0 GeV/c 3.0 > p T > 4.0 GeV/c 4.0 > p T > 8.0 GeV/c Standard CMS HI jet selection Anti k T jets with R = 0.3 η <1.6 Jet p T > 120 GeV/c Fully efficient from a triggered dataset corresponding to 166 ub -1 6/30/2015 Dragos Velicanu - Hard Probes

5 Jet-track correlations Signal pair distribution: Event 1 same event pairs 6/30/2015 Dragos Velicanu - Hard Probes

6 Jet-track correlations Signal pair distribution: same event pairs Event 1 Event 2 Mixed event pair distribution: mixed event pairs 6/30/2015 Dragos Velicanu - Hard Probes

7 Jet-track correlations Divide Signal by Mixed Event Associated hadron yield per trigger: Signal pair distribution: same event pairs Event 1 Event 2 Mixed event pair distribution: mixed event pairs 6/30/2015 Dragos Velicanu - Hard Probes

8 Jet-track correlations Associated hadron yield per trigger: Signal pair distribution: same event pairs Event 1 Event 2 Mixed event pair distribution: mixed event pairs 6/30/2015 Dragos Velicanu - Hard Probes

9 Jet track correlation topology 6/30/2015 Dragos Velicanu - Hard Probes

10 Jet track correlation topology Near-side (, ~ 0) correlations from particles around a jet 6/30/2015 Dragos Velicanu - Hard Probes

11 Jet track correlation topology Away-side ( ~ ) correlations from particles around the other jet Near-side (, ~ 0) correlations from particles around a jet 6/30/2015 Dragos Velicanu - Hard Probes

12 Jet track correlation topology Long range nearside jet correlations (weak in this example) Away-side ( ~ ) correlations from particles around the other jet Near-side (, ~ 0) correlations from particles around a jet 6/30/2015 Dragos Velicanu - Hard Probes

13 Study the jet peak Long range nearside jet correlations (weak in this example) Away-side ( ~ ) back-to-back jet correlations Near-side (, ~ 0) correlations from particles around a jet 6/30/2015 Dragos Velicanu - Hard Probes

14 Subtract combinatorial and long range bkg Construct the Δφ projection from the correlation region 1.5 < Δη < 3.0 6/30/2015 Dragos Velicanu - Hard Probes

15 Subtract combinatorial and long range bkg Subtract it from the original correlation function Fit a constant + the first 2 Fourier cosine terms and a Gaussian for the away side 6/30/2015 Dragos Velicanu - Hard Probes

16 Subtract combinatorial and long range bkg 6/30/2015 Dragos Velicanu - Hard Probes

17 Zoom in on the jet peak after subtracting 6/30/2015 Dragos Velicanu - Hard Probes

18 Project into Δη 6/30/2015 Dragos Velicanu - Hard Probes

19 Repeat for pp 6/30/2015 Dragos Velicanu - Hard Probes

20 Δη versus Centrality 6/30/2015 Dragos Velicanu - Hard Probes

21 Subtract pp from pp pp pp pp 6/30/2015 Dragos Velicanu - Hard Probes

22 Leading vs Subleading Look at leading and subleading in dijet events Standard CMS HI dijet selection Reconstruct all jets with η < 2.0 Leading and subleading reside η < 1.6 dijet Δφ > 5π/6 Leading jet p T > 120 GeV/c Subleading jet p T > 50 GeV/c 6/30/2015 Dragos Velicanu - Hard Probes

23 Vary centrality for Leading Jet Leading 6/30/2015 Dragos Velicanu - Hard Probes

24 Vary centrality for Leading & Subl Jet Leading Subleading 6/30/2015 Dragos Velicanu - Hard Probes

25 Subtract pp from for Lead and Subl Leading Subleading pp 6/30/2015 Dragos Velicanu - Hard Probes

26 Yield in Leading vs Subleading Jets Integrate to find excess yield pp 6/30/2015 Dragos Velicanu - Hard Probes

27 Yield in Leading vs Subleading Jets Integrate to find excess yield pp 6/30/2015 Dragos Velicanu - Hard Probes

28 Yield in Leading vs Subleading Jets Vary associate track p T : 1.0 > p T > 2.0 GeV/c 2.0 > p T > 3.0 GeV/c 3.0 > p T > 4.0 GeV/c 4.0 > p T > 8.0 GeV/c Less excess particles at higher p T 6/30/2015 Dragos Velicanu - Hard Probes

29 Width of the Leading vs Subleading Jet Fit the distribution with the sum of two Gaussians centered at zero Width Δη range that contains 67% of the total correlated yield 6/30/2015 Dragos Velicanu - Hard Probes

30 Δη Width Leading vs Subleading Jet 6/30/2015 Dragos Velicanu - Hard Probes

31 Summary Jet track correlations were measured for leading and subleading jets Inclusive jets are pp-like in peripheral collisions but have an excess yield in central collisions at low p T Subleading jets have greater excess yield compared to pp than leading jets Leading and subleading jets in are broader for low track p T compared to pp, effect goes away at high p T, no strong centrality dependence 6/30/2015 Dragos Velicanu - Hard Probes

32 Backup 6/30/2015 Dragos Velicanu - Hard Probes

33 Vary Centrality Δφ 6/30/2015 Dragos Velicanu - Hard Probes

34 Vary Centrality Leading & Subleading Δφ 6/30/2015 Dragos Velicanu - Hard Probes

35 Leading Δφ width 6/30/2015 Dragos Velicanu - Hard Probes

36 Subleading Δφ width 6/30/2015 Dragos Velicanu - Hard Probes

37 Missing p T comparison 6/30/2015 Dragos Velicanu - Hard Probes

38 ALICE Jet Broadening Statement PLB 712 (2012) 176 6/30/2015 Dragos Velicanu - Hard Probes