Study of Dihadron Fragmentation Function Correlations in p-p collisions at 7 TeV. Derek Everett Dr. Claude Pruneau, Dr.

Transcription

1 Study of Dihadron Fragmentation Function Correlations in p-p collisions at 7 TeV Derek Everett Dr. Claude Pruneau, Dr. Sidharth Prasad

2 Outline Physics Motivation Definitions of Observables PYTHIA Monte Carlo Simulation Data from ALICE Detector Results: Jet spectrum and fragmentation function Dihadron fragmentation functions and correlation functions

3 Jets Highly collimated spray of particles Result of fragmentation of hard-scattered partons Used to test predictions of pqcd

4 Understanding Jet Structure Studies of correlation have led to better understanding of hot and dense medium. Studying intra-jet correlations may lead to better understanding of jet structure and behavior. Studying how jet structure evolves with energy (DGLAP)

5 Observables

6 Correlation (1)

7 Simulation Details PYTHIA 6.4, Tune : Perugia 0 (320) Proton - Proton collisions CMS energy: 7 TeV Generated in ten hard bins: 5-11, 11-21, 21-36, 36-57, 57-84, ,117156, , , >249 (GeV/c)

8 Hard Bin Generation For Jets, the p.d.f. of pt decreases in the form of a power law, so a jet with high pt is very unlikely. Minimum Bias generation resembles reality, but requires significant computing resources. To have significant statistics, we fix the momentum transfer Q2 to be on a certain scale. These scales are referred to has hard bins.

9 ALICE Detector Effects Time-Projection Chamber (TPC) Detector Resolution of pt Efficiency Simulated with GEANT 3 Package

10 Jet Reconstruction FastJet Anti-kT algorithm Resolution Parameter = < Jet pt < 100 (GeV/c) Jet η < 0.5 Track pt >.150 GeV/c Track η < 0.9

11 Results Results

12 Jet pt Spectrum Jet Spectrum Normalization: i: hard bin index

13 Fragmentation Function (Particle Level) *Probability of high momentum fraction is very unlikely. *D.F.F. is also steeply falling

14 z1, z2 dependence Kinematic Constraint: z1 and z2 are necessarily dependent:

15 Dihadron Fragmentation Jet pt 20 to 30 (GeV/c) Data Detector Level *Steeply decreasing as z1, z2 increase *Symmetric about z1 = z2

16 Correlation (z1, z2) Jet pt 20 to 30 (GeV/c) Data Detector Level *Good agreement between simulation and data. *Finding particle with high z2 decreases as z1 increases

17 Correlation (z1, z2) Jet pt 30 to 40 (GeV/c) Data Detector Level *Most likely to find another particle with low mom. fraction z when we have a particle with low z.

18 Correlation (z1, z2) Jet pt 40 to 60 (GeV/c) Data Detector Level *Statistical fluctuations in data set. *Magnitude / shape of correlation function is very similar from different pt bins, despite increase in track multiplicity.

19 Efficiency If particle detection is independent:

20 Efficiency

21 Robustness δr/r ~ 7% δr/r ~ 22% δr/r ~ 13% δr/r ~ 2% δr/r ~ 3%

22 Summary and Outlook Dihadron Fragmentation Function Correlations (C2) are studied in pp collisions at 7 TeV using ALICE C2 are very similar across pt bins Robustness of C2 Compare with theoretical predictions Examine Correlation Plots of xi and pt Analysis including neutral particles Use other event generators

23 Results Backup Slides

24 References Elnimr, Muhammad, Dihadron Fragmentation Functions In Proton-Proton Collisions At The Relativistic Heavy Ion Collider (rhic) (2010). Wayne State University Dissertations. Paper 66. ALICE Collaboration, Study of charged jet production cross sections and properties in proton-proton collisions at s = 7 TeV (2013) Majumder, Abhijit, The dihadron fragmentation function and its evolution (2008).

25 Hard Bin Normalization p: Jet pt bin i: hard bin

26 Normalized Fragmentation Function

27 Anti-kT Algorithm for each particle pair ( i, j ), we find the distance kt : transverse momentum y : rapidity Φ : azimuth R : Resolution parameter

28 Anti-kT Algorithm For each particle, also find the beam distance Find the minimum, dmin, of all dij, dib If dmin is a dij, merge particles i and j (add four-momenta) If it is a dib, declare particle i to be a final jet, and remove it from list Repeat until there are no particles left.

29 D.F.F 20 to 30 GeV/c Data Detector Level

30 D.F.F. 30 to 40 GeV/c Data Detector Level

31 D.F.F. 40 to 60 GeV/c Data Detector Level

32 D.F.F. 60 to 80 GeV/c Data Detector Level

33 D.F.F. 80 to 100 GeV/c Data Detector Level

34 Convolution 20 to 30 GeV/c Data Detector Level

35 Convolution 30 to 40 GeV/c Data Detector Level

36 Convolution 40 to 60 GeV/c Data Detector Level

37 Convolution 60 to 80 GeV/c Data Detector Level

38 Convolution 80 to 100 GeV/c Data Detector Level