Dijet Asymmetry in Pb+Pb Collisions at S NN = 2.76 TeV Using the ALICE Experiment

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Osborne Simmons
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1 Dijet Asymmetry in Pb+Pb Collisions at S NN = 2.76 TeV Using the ALICE Experiment { Isaac Mooney Advisors: Joern Putschke, Rosi Reed Wayne State University National Science Foundation Friday, August 8, 24

the physics of strongly interacting matter at extreme energy densities, where the formation of

2 A Large Ion Collider Experiment Experiment at LHC 8 subdetectors in total I focused on the EMCal (Electromagnetic Calorimeter) and the TPC (Time Projection Chamber) Our aim is to study the physics of strongly interacting matter at extreme energy densities, where the formation of a new phase of matter, the quark-gluon plasma [QGP], is expected. * About ALICE *aliceinfo.cern.ch

3 Covers almost the full TPC in η, but not φ Detects neutral particles Tracks only charged particles EMCal TPC

4 FastJet 2.4. Longitudinally invariant Kt, anti-kt, and inclusive Cambridge/Aachen clustering using fast geometric algorithms, with area measures and optional external jet-finder plugins * PYTHIA 8.3 a program for the generation of high-energy physics events contains theory and models for a number of physics aspects, including hard and soft interactions, parton distributions, initial- and final-state parton showers, multiple interactions, fragmentation and decay. ** ktroot (ROOT ktjet libraries) The ROOT system provides a set of OO [Object- Oriented] frameworks with all the functionality needed to handle and analyze large amounts of data in a very efficient way *** Software Environment * ** ***

5 Learning some basic Linux commands Brushing up on my C++ Learning ktroot Debugging Challenges

6 Hard scatter of colored partons Jet - cone of hadrons produced by hadronization of these partons Jets tell us about properties (kinematics and topology) of original partons Final state is color neutral Jet production well described by QCD/MC generators like Pythia Jets

QCD QGP Jets Confinement quarks bound as hadrons Asymptotic Freedom at high energies, quarks and gluons interact weakly to produce QGP Hot, dense soup which cools instantly Back-to-back scatter Fast,

7 QCD QGP Jets Confinement quarks bound as hadrons Asymptotic Freedom at high energies, quarks and gluons interact weakly to produce QGP Hot, dense soup which cools instantly Back-to-back scatter Fast, high energy shower of particles Strongly interacting, but not fully absorbed Jet Quenching jets transfer energy/momentum to the medium while traversing (gluon bremsstrahlung) Without this background, QCD works well, and our Pythia simulation is a good model. Jets offer an internal x-ray of the medium, similar to a Rutherford scattering. Why Jets?

8 AJ = pt, - pt, 2 pt, + pt, 2 Comparing Full-Full dijets to Full-Charged ones (useful since EMCal does not have full φ coverage) Making this comparison, after adding a background Reducing background effects on A J My Focus

9 Compared the effects of different cuts Cuts included: ΔΦ (to obtain a true pair), η (because of detector limitations), p T (to model true kinematics), R cone (balance of background exclusion, and jet inclusion) R cone = R cone = Process *at RHIC energies Effect: larger R cone, more balanced jets at higher p T

10 v. v. Charged Pt v. v. Charged Pt FC A j j FF A.. FC A Aj j FF Pythia only event Pythia + background 3D plots contain quickly accessible information, obtained by taking projections Results I. Constituent pt cut: 2 GeV Leading jet pt range: 8 GeV Full-Full AJ v. Full-Charged AJ v. Subleading Charged pt

11 4-2 GeV GeV GeV *best p T range GeV 2 4 GeV 4 6 GeV* 6-8 GeV GeV GeV **reflects leading jet kinematics GeV 8 GeV** GeV Results II. Constituent p T cut: 2 GeV Leading jet p T range: 8 GeV Full-Charged A J v. Full-Full A J for varying subleading charged jet p T

12 2-2 GeV GeV GeV.. 2 GeV 2 4 GeV 4 6 GeV GeV GeV GeV Because of more energetic constituents, background effects are reduced, so plots correspond well to Pythia-only ones Constituent p T cut: 2 GeV Leading jet p T range: 8 GeV GeV 8 GeV GeV Results II. with background Full-Charged A J v. Full-Full A J for varying subleading charged jet p T with background

13 Fraction of Jets Fraction of Jets 5 3 GeV Pt cut 4 GeV Pt cut 5 GeV Pt cut 5 GeV charged Pt cut 2 GeV charged Pt cut 3 GeV charged Pt cut Full-Full A J Full-Charged A J Results III. Constituent p T cut: 2 GeV Leading jet p T range: 8 GeV A J for various p T cuts

14 Fraction of Jets 5 no background with background 5. A J without background, compared to A J with background.5. Results IV. Constituent p T cut: 2 GeV Leading jet p T range: 8 GeV

15 Fraction of Jets Constituent p T cut: 2 GeV Leading jet p T range: 8 GeV with background (4 GeV cut) with background (3 GeV charged cut) Further study will be required to fully map these two onto each other. Conclusion: It is feasible to use the charged away side (TPC only) jet, applying a background suppression constituent p T cut to measure the dijet imbalance, A J in PbPb collisions in ALICE w.r.t. the full-full dijet case.. Aj Results V. *2/3 of particles are charged, so 4 GeV subleading p T cut is comparable to 3 GeV subleading charged p T cut Full-Full A J with Full-Charged A J with background

16 References

Assessment of triangular flow in jet background fluctuations for Au+Au collisions First look at dijet imbalance (A J )

Assessment of triangular flow in jet background fluctuations for Au+Au collisions First look at dijet imbalance (A J ) Wayne State REU 2012 Research Advisor: Joern Putschke Research Undergraduate: Joshua