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Searches for double partons

Study on transverse track activity in jet events to investigate double parton hard scattering. Analyzing jet data, vertex requirements, angular correlations, and trigger effects. Results suggest potential for finding multiple parton interactions.

jenniferglass
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Searches for double partons

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  1. Searches for double partons Lee Pondrom University of Wisconsin July 23, 2012

  2. Rick Field’s definition of the ‘underlying event’

  3. Single vertex dijet or Z+jet event

  4. Charged tracks in the transverse region • R Field studied the underlying event and tuned Pythia to match the charged track activity observed in the transverse region. • (PRD 82, 034001,(2010). • Track pT > .5 GeV, track |η|<1 • Parameters track multiplicity, scalar sum track pT. • He looked at Z D-Y data to define the transverse region.

  5. RField’s Z transverse data X X X X X =jet20,50,70, and 100 data

  6. Use jets to define the axis and check Field’s Z results

  7. Transverse track activity depends slowly on pTZ or jet1 ET • About 90% of the ∑pT and track number plots are energy independent. • Underlying event activity is the same for pTZ ≈ jet1ET • If double parton hard scattering exists, a good place to look for it would be in the transverse region. • Try scalar ∑transverse track pT>15 GeV as a ‘trigger’

  8. To see if it works, try jet events with two vertices • Use jet100 jet50, and jet20 data • Require jets one and two to be on the first vertex. Exactly two vertices per event. • Extra jets three and four can be anywhere • Separate the two vertices by at least 10 cm. • Require vtx2 to have at least 3 charged tracks, with pT>.5 GeV and |η|<1. • Second vtx σ≈ 6 mb.

  9. Two vertex event with 2 jets on primary vtx and 2 jets on 2nd vtx

  10. Second vertex is ‘minbias’ • CDF minbias defined by the CLC σ≈ 36 mb • Track requirements here are different, in particular |η|<1, so σ is smaller, although 6 mb is a soft number – it depends on instantaneous luminosity taken to be 2E32. • For the jet stntuples analyzed, the avge probability of two vertices is 30%.

  11. Transverse tracks on primary and secondary vertices

  12. Transverse track activity • The first vertex transverse tracks are defined with respect to the azimuth φ of the highest ET jet: /3<Δφ(jet-track)<2/3 • second vertex transverse tracks are defined in the same way with respect to the same jet – highest ET jet on vtx1, track on vtx2. • Jet activity ‘triggered’ by ∑transtrackpT>15 GeV is similar in jet20 and on 2nd vtx. • ~90% of all ‘triggers’ have a third jet ET>5 GeV

  13. Fraction of ∑transtrackpT>15GeV vs ET jet1

  14. ∑transtrackpT>15 GeV • Note that the fraction increases from .001 to .015 going from minbias (plotted as ET=5GeV) to jet20. Using σ≈6 mb for the 2nd vertex, the cross section for the ∑pT>15 GeV ‘trigger’ is σ≈ 6 b. about 5 times larger than the effective cross section for jet20.

  15. Jet activity ‘triggered’ by ∑pT>15 GeV – 2nd vtx and jet20

  16. Jet activity ‘triggered’ by ∑pT>15 GeV 2nd vtx compared to jet20 • Jet4 is similar 2nd vtx compared to jet20 • Δφ12 is the azimuthal angular correlation for the two leading jets. For the 2nd vtx the ‘trigger’ has no effect on Δφ12, which is on the other vertex. But with transverse tracks on the same vertex, Δφ12 is totally wiped out for jet20. Effect for jet100 is less traumatic.

  17. Δφ dijet angular correlations-main jet on vtx 1, jets 3&4 on vtx 2

  18. Δφ jet-jet angular correlations after transtrack ∑pT>15 GeV • Δφ23 is shifted into the transverse region. The third jet appears near 90 degrees to the second one. Jet 2 and jet 3 are on different vertices. • Δφ14 shows a similar shift. Relative to the primary axis, jets 3 and 4, on the second vertex, are in the ‘transverse’ region.

  19. Δφ for jets 3&4 on 2nd vtx, selected by ∑transtrackpT>15GeV

  20. Δφ34 with transtrack∑pT>15 GeV • For the 2nd vtx Δφ34 has a distinct peak near . (Sum 2.4<φ<)/all events=3.5E-4 • Jets 3&4 are not required to be on vtx2. Events with Δφ<1 are probably on vtx1 • Δφ12 for jet20 data without the ∑pT>15 GeV requirement is shown for comparison of the jet-jet angular correlation. Jet20 is sharper – the average jet ET’s are higher.

  21. Jet ET on 2nd vertex with ∑trackpT>15 GeV ‘trigger’

  22. Jet20 Data Stntuple gjt1bk & gjt1bj 3E6 events • Require only one vertex • Require at least two jets with |η|<1. ET1>20 GeV. Other jet ET>5 GeV • Apply level 5 jet energy corrections • Events • Jet1&2 Jet3 Jet4 Lum(live) • 110203 61769 21174 151694/nb • 56% 19% • Prescaled σ ≈ 0.7 nb; unprescaled σ≈1.2b

  23. Jet20 data Jet ET

  24. Jet20 data Δφ distributions

  25. Following Rick Field, define the transverse region relative to jet1φ • Look at charged tracks with |η|<1, pT>.5 GeV, and with /3<Δφ<2/3, where Δφ is the azimuthal angle between the track and the highest ET (trigger) jet. • These tracks are sensitive to the underlying event, and hence at least in part depend on multiparton interactions.

  26. Jet20 data properties of the transverse tracks

  27. Jet20 transverse track pT cut • Based on the idea that the transverse region has some sensitivity to what is going on in the event other than the two primary jets, we make a cut on the scalar sum of track pT>15 GeV. • This cut leaves 1611events – 1.5% of all dijets. The fraction increases with jet energy. • The cut moves jet3 into the Δφ region of the tracks.

  28. Effect of the ∑transtrackpT>15GeV on the jet φ distributions

  29. Effect of the ∑transtrack pT>15 GeV cut on jet φ • Of the 1611events, 1495, or 93%, have jet3ET >5 GeV, and these jets are clustered around /2 relative to the trigger jet. • 15 GeV is too high relative to the main jet activity, so the correlation Δφ12 is strongly perturbed.

  30. Δφ34 and the high pT transverse tracks • The idea is that jets 3 and 4 could be result of independent scattering of two other partons. • If that is true, a good place to look is in the Δφ region of the underlying event. • The ∑transtrack pT>15 GeV serves as a ‘trigger’. • Δφ34 should peak near .

  31. Δφ34 and jet3ET before and after track∑pT>15 GeV cut

  32. Enhancement near Δφ=? • Normalizing the two distributions to Δφ<1.5 gives a difference 2.4<Δφ<3.2 of • -8±17 events. • Transverse jet energies for jets3 and 4 are increased by the track pT cut

  33. Look at jet100 data 1E6 events gjt4bk & Pythia bt0stb • Same requirements: only one good vertex, trigger jet ET>100 GeV, level5 jetECorr • Yields for 1E6 events • Jet1&2 jet3 jet4 pT>15GeV Lum • 170710 101231 35034 10247 126342/nb • Jet3 and jet4 fractions same as jet20 • pT>15 GeV fraction 4x larger than jet20 • σ ≈ 1.3 nb no prescale

  34. Jet100 data and Pythia ET

  35. Jet100 & Pythia transtrack pT and Δφ12

  36. Jet100 data effect of the transverse tracks on Δφ12 and Δφ13

  37. Jet100 effect of transverse tracks on jetET3 and Δφ34

  38. Jet100 & Pythia effect of ∑pT>15 GeV cut on transverse tracks

  39. Jet100 effect of transverse tracks Jet100 similar to jet20. Pythia & data agree. Perturbation of Δφ12 considerably less than for jet20. Δφ13 shifts so that jet3 is /2 away from jet1 Jet3 ET shifts to larger values

  40. Compare jet100 and Pythia Δφ34 before and after ∑pT>15GeV cut

  41. Jet100 data and Pythia Δφ34 • The data and Pythia agree qualitatively in the shapes of the Δφ34 angular distributions before and after the ∑pT>15 GeV cut on the scalar sum of transverse tracks. • Near Δφ34≈ Pythia has a smaller excess than the data.

  42. Now compare Δφ34 before and after ∑pT>15 GeV cut

  43. Excess near Δφ34≈ • Normalize the plots to .5<Δφ34<1.5 • Subtract (after cut)-(before cut) 2.4<Δφ34<3.2. • Jet100 data difference = 295±50 events • Pythia difference = 54±30 events

  44. Does this excess mean anything? • There are 170710 jet100 good dijet events • So the excess 2.4<Δφ34< is 0.0017±0.0003. • Pythia excess is smaller: 0.0007±0.0004. • If the number of MPI’s per hard scatter is 5, which comes from Field’s analysis of Drell Yan (PRD 82,034001(2010)), the probability of a second hard scatter is 0.00034±0.00005, or about 3.5E-4 for the jet100 data.

  45. Compare to the 2nd vertex Δφ34 • The 2.4<Δφ< fraction for 2nd vtx =3.5E-4, which agrees with the peak fraction observed in the jet100 data (but not in Pythia). • The dip in Δφ34 near 1.7 radians for the ‘trigger’ events in jet100 is of unknown origin, but is reproduced by Pythia. • Subtract (after ∑pT –before ∑pT) and compare to 2nd vertex peak.

  46. Compare jet100 excess with 2nd vertex

  47. Look at Jet50 data and Pythia • Jet20 data are too low ET relative to the ∑transtrackpT>15 GeV cut. • Jet50 data are higher, and the Pythia file bt0srb has 4.5E6 events, while bt0stb (jet100) has only 1E6 events, so we have better statistics for the monte carlo. • Same procedure as jet20 and jet100

  48. Jet transverse energies after level5 jet energy corrections

  49. Jet-jet Δφ correlations jet50 and Pythia

  50. Jet50 data and Pythia

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