The Underlying Event at s = 500 GeV at STAR

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1 The Underlying Event at s = 500 GeV at STAR Grant Webb MPI Trieste November,

2 Outline RHIC/STAR review Event SelecOon Method to determine the Underlying Event Data/MC Comparisons Pythia Tune Study Spin Dependence of Underlying Event 2

3 The RelaOvisOc Heavy Ion Collider Siberian Snakes Hydrogen Jet Polarimeter Carbon Polarimeters PHENIX STAR Spin Flipper Spin Rotators Siberian Snakes Polarized Source Tune Jump Quads Helical ParOal Snake 200 MeV Polarimeter LINAC BOOSTER AGS Strong Snake AGS pc Polarimeter 3

4 The Solenoid Tracker At RHIC 4

5 Jet ReconstrucOon PARTON PARTICLE DETECTOR π + e - e + π 0 Κ 0 π GEANT JETS PYTHIA JETS DATA JETS AnO- K T algorithm ([arxiv: ]) Successive CombinaOon Radius R = 0.6 d ij = min 1 d ib = 1 2 k Ti ( 2, 1 )!R 2 ij 2 k Ti k Tj R 2 Use PYTHIA + GEANT to quanofy detector response 5

6 STAR Dijet Cross SecOon at 500 GeV x 1 = 1 s p T 3 e! 3 + p T 4 e! 4 ( ) x 2 = 1 s p T 3 e!! 3 + p T 4 e!! 4 ( ) M = x 1 x 2 s! cos! * = tanh " +" $ 3 4 # & " 2 % ReconstrucOng Di- jets provide access to the inioal partonic kinemaocs at LO 6

7 Defining the Regions to Access the UE Trans Toward Track p T and Tower E T > 200 MeV Detector jet η < 0.5 JP Trigger (JP2) with threshold > 13 GeV Leading Jet matches fired JP Trigger Away Trans L.A. Cruz, Using Max/Min transverse regions to study the underlying event in run2 at the Tevatron UMI , MPI Trieste φ = φ jet φ track/tower Toward: φ < 60 Away: φ > 120 Transverse: 60 < φ < 120 7

8 SeparaOng the Transverse Regions Toward TransMax TransMin Away Trans Plus: 60 < φ < 120 Trans Minus: - 60 > φ > Trans Max and Min: Find Σ track p T for TranP and TranM The region with higher Σ track p T is trans Max and the other is trans Min 8

9 Data/MC Comparison: Σ Track p T STAR preliminary Perugia0 MC sample STAR preliminary embedded into zerobias data Uncorrected detector- level quanooes Excellent agreement seen in all 3 regions 9

10 Data/MC Comparison: Track MulOplicity STAR preliminary STAR preliminary 10

11 Data/MC Comparison: Σ Tower E T STAR preliminary STAR preliminary 11

12 Data/MC Comparison: Tower MulOplicity STAR preliminary STAR preliminary 12

13 Data/MC Comparison: Track p T and Tower E T STAR preliminary STAR preliminary 13

14 Pythia Tune Analysis Produced 1 M events of Perugia0 and 1M events of TuneA The tune was the only parameter changed in the analysis Performed the Underlying Event analysis on both tunes and compared. 14

15 Pythia Tune Comparison 15

16 Pythia Tune Comparison 16

17 The Double Spin Asymmetry STAR ements! 4 ++!!! +! #fa #fb "g = ALL " a LL ++ +!! +! fa fb "q Δf: polarized parton distribuoon funcoons!!ij/!tot Inclusive Jet production (200GeV: Solid line / 500GeV: Dashed line) 0.7-1<"<1 0.6 gg qg qq ments!ij/!tot 0 STAR pt 0.7-1<"<1 0.6 gg qg qq 1 N ++! N +! ALL = PY PB N ++ + N +! 0.5 "g "q 0.2! 0.1 ij/!tot pt / s MPI Trieste 0.45 XT line) Inclusive Jet production (200GeV: Solid line / 500GeV: Dashed ! <"<1 gg qg qq Bernd Surrow Observables: Inclusive Jets Dijet Inclusive π0 s 17

18 High Precision 2009 RHIC DATAà Δg(x) A LL STAR 2009 p+p Jet+X s=200 GeV η < STAR BB10 DSSV LSS10p LSS10 NNPDF A LL < η < ±6.5% scale uncertainty from polarization not shown Parton Jet p (GeV/c) T A LL =! ++!! +!! ++ +! +! " #f a #f b f a f b â LL 18

19 Spin Dependent UE Analysis: Σ Track p T Spin!!+"" Spin!"+"! STAR preliminary STAR preliminary 19

20 Spin Dependent UE Analysis: Track MulOplicity Spin!!+"" Spin!"+"! STAR preliminary STAR preliminary 20

21 Conclusions Data/MC Comparisons agree extremely well for all 3 Regions Slight discrepancies in the track and tower muloplicioes and sum p T and sum E T The UE analysis can also be used to determine the agreement of different pythia tunes. Spin Dependence of the Underlying Event can be determined for the first Ome at STAR! 21

22 Back Up 22

23 Data/MC Comparisons: Track <pt> 23

24 Data/MC Comparison: Tower <E T > 24

25 Spin Dependent UE Analysis: Track <p T > 25

26 Spin Dependent UE Analysis: Tower <E T > 26

27 Pythia Tune Comparison 27

28 Spin Dependent UE Analysis: Max Track p T 28

29 Spin Dependent UE Analysis: Max Tower E T 29

30 Spin Dependent UE Analysis: Σ Tower E T 30

31 Spin Dependent UE Analysis: Tower MulOplicity 31