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

Transcription

1 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 Bell 1

2 Relativistic Heavy Ion Collider (RHIC) 1km STAR Collides heavy ions like Au, Cu, and U. Also, protons and deuterium. Experiments are conducted at energies around Long Island, New York 2

3 STAR experiment The Barrel Electromagnetic Calorimeter (BEMC) detects neutral particles such as a π 0 pion. The Time Projection Chamber (TPC) detects charged particles such as π +, π -, as well as protons. 3

4 Au+Au head-on collision at the Relativistic Heavy Ion Collider (RHIC) 4

5 pt per grid cell [GeV] η ϕ Dijet well explain by pqcd in p+p collisions. There is low probability that a high p T scattering will occur in a collision. 5

6 How do we define a jet event? To fire the online trigger of a BEMC tower, a particle must have E T > 5.4 GeV. This particle must be detected in a tower with Δφ x Δη = 0.05 x

7 Method ROOT is used with the Anti-k T jet clustering algorithm [1] and the cone radius parameter set at R=0.4 Events are read in Clustered into jets Integrated over η space Set in relative ( Δφ = φ Jet φ Bkg ) vs. p T space Projected onto the p T axis Divided for ratio analysis The area of study is Δφ = π/2 +/- 0.6 Using this area minimizes dijet affects. [1] M. Cacciari, G. P. Salam, and G. Soyez, Journal of High Energy Physics 2008, 063 (2008). 7

8 pt per grid cell [GeV] Au+Au 0-20% Δφ = φ Jet φ Bkg η ϕ In collisions, theoretically a Quark-Gluon Plasma (QGP) is formed. The QGP hadronizes into particles. 8

9 What I am trying to find Is there a distinctive flow pattern in background Δφ = Jet - Bkgspace governed by this equation? Can elliptic (v 2 ) and triangular (v 3 ) flow be quantified? How do elliptic and triangular flow affect the p T distribution? Is there a p T dependence on the coefficients? 9

10 pt per grid cell [GeV] First study Only particles with p T > 200 MeV were counted. η ϕ 10

11 p T Cluster (GeV/c) Area of study π/2-0.6 π/2 π/ Spatial coordinates in relative Δφ space. Background clusters relative to jets are studied. 11

12 p T projections Both bins projected onto the p T axis Now divide the left projection by the right projection p T Cluster (GeV/c) 12

13 The p T projection π/2-0.6 < Δφ < π/2 divided by the p T projection π/2 < Δφ < π/ Now comes the hard part: What does this ratio mean? p T Cluster (GeV/c) 13

14 Qualitative effects of elliptic and triangular flow π/2-0.6 π/2+0.6 π/2 v 2 =6% v 3 =2% Only elliptic flow: Symmetry around π/2 in Δφ space. 2% triangular flow: Shifts the mean. Alters the distribution. Destroys the symmetry. 14

15 p T Cluster (GeV/c) Can we convince ourselves the distribution is due to triangular flow? π/2-0.6 π/2 π/ Distribution could be due to a v 3 mimic by: Detector affects The jet finding algorithm. 2 tests conducted: 1) Particles in the Δφ area of study were randomized with a uniform Δφ distribution. 2) Particles in the Δφ area of study were modulated with v 2 =6% & v 3 =0%. 15

16 p T Cluster (GeV/c) For both tests, the pt division resulted in a uniform symmetry around π/2. 16

17 Does v 3 do what we expect? Background modulated with 6% v 2 & 1% v 3. The addition of the triangular flow coefficient indeed causes the p T distribution to reflect closer to what the data shows. p T Cluster (GeV/c) 17

18 Can we make a quantitative conclusion? More tests were conducted with modulating the background. Then the ratios are divided by the data ratio. If the equation of modulation matches with the data, there will be uniformity. Furthermore, fitting this ratio with a linear function should result in a slope of 0. The closest achieved was with a modulation of 6% v 2 & 1% v 3 More study is needed to make a definitive conclusion. Results are consistent with a v 3 modulation of 1%. 18

19 Is there a p T dependence? Since this analysis integrates over all η values, that dependence can be discounted. However, thus far all analysis has been conducted with a p T cut of 0.2 GeV. A. Adare (PHENIX Collaboration), Phys. Rev. Lett. 107, (2011). p T Particle (GeV/c) 19

20 p T cut 0.2 GeV 1.0 GeV 2.0 GeV p T Cluster (GeV/c) p T Cluster (GeV/c) Linearly decreasing trend. Increasing p T cut seems to have an effect on the distribution of energy among clusters. p T Cluster (GeV/c) 20

21 Conclusion It seems as though there is a p T dependence, which is consistent with expectations. More study needed on if the clusters follow a similar trend as single particles. A. Adare (PHENIX Collaboration), Phys. Rev. Lett. 107, (2011). 21

22 Next Study Dijet Asymmetry A J characterizes the balance or imbalance of the trigger and recoil jets. The asymmetry ratio is interesting, since it measures if the jet is altered due to partonic energy loss in the QGP. 22

23 Pb+Pb CMS data 23

24 Au+Au collisions 0-20% centrality Increasing nucleons: Shifts peak Peaks distribution Changes overall trend A J 24

25 p+p collisions Pythia does NOT match data Why is this? Detector affects? Analysis? More study needed. A J 25

26 Summary We observed a finite triangular flow (v 3 ) modulation consistent with 1%. More study needed on how increasing the p T cut affects triangular flow. More study needed on why p+p collision data doesn t match with pythia simulation. 26