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David Asner/LLNL

Resolved Photon Backgrounds to gg Processes. David Asner/LLNL. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. 4 th ECFA/DESY Workshop

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David Asner/LLNL

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  1. Resolved Photon Backgrounds to gg Processes David Asner/LLNL This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. 4th ECFA/DESY Workshop April 1-4, 2003, NIKHEP, Amsterdam

  2. Photons have Structure • Three types of gg collisions • Direct • Once resolved • Twice resolved “g”=0.99 g + .01 r Electroweak Electroweak (DIS) Strong (rr collider)

  3. Recent History • Since SNOWMASS 2001 we have predicted backgrounds due to resolved photons to be “too large” – Telnov • At St.Malo – de Roeck, Moenig, Schulte, Telnov – predict resolved photon background approximately an order of magnitude smaller • At Prague – Asner & de Roeck discovered • Order of magnitude  Factor of 6 • Not at all obvious why this large discrepancy exists • Recently resolved this problem!

  4. Procedure • Set Pythia parameters • Calculate cross sections • Generate Luminosity distributions - CAIN • Use above to generate stdhep output file • Overlay these events in gg physics studies

  5. Resolved Photon Backgrounds:#1 Concern gg collisions are NOT like e+e- 1.5x1010 Primary e-,1x1010 Compton g CAIN also includes e+e- from pair production and real g from beamstrahlung PYTHIA gamma/e- option simulates virtual g associated with e- beam • Approximately 83% of interactions are gg • Approximately 17% of interactions are eg • Approximately 0.4% of interactions are ee

  6. Luminosity: CAIN

  7. ggCross Section: Pythia vs Model

  8. Cross Section: Pythia gg,eg,ee Clearly eg cross section is NOT negligible, nor is luminosity  Must include in future studies

  9. Scenarios • Default Pythia parameters: Most similar to the study by de Roeck, Schulte, Telnov • Preliminary Butterworth parameters: Used in our earlier work. 6x larger background. • Updated Butterworth parameters: http://jetweb.hep.ucl.ac.uk/Fits/322/index.html http://jetweb.hep.ucl.ac.uk/Fits/757/index.html • PARP(67)=4.0 vs 1.0 PARP(91)=1.0 vs 0.0 • PARP(81)=1.8 vs 1.5 PARP(99)=1.0 vs 0.0 • MSTP(82)= 1 vs 4 c2/dof = 4.96 vs 4.97 • Newer fit use ~ ¼ LEP, HERA, Tevatron luminosity • Repeat analysis for Higgs Factory, 500 GeV, type-I&II

  10. # Overlay Events • Recall gg-NLC – rep. rate is 11.4kHz • 1.5e1010 e-/bunch • 95 bunches/train • 120 trains/second • Higgs factory • 6700 overlay events/second • 56 events/train • 0.6 events/crossing • 500 GeV Machine ~3x larger

  11. Occupancy: Tracks Plots correspond to 17000 bunch crossings Cos Q vs Energy (GeV) 3.7 tracks/crossing (|cos Q| < 0.9) Eavg = 0.7 GeV (p > 0.2 GeV)

  12. Occupancy: Showers Plots correspond to 17000 bunch crossings Cos Q vs Energy (GeV) 5.5 showers/crossing (|cos Q| < 0.9) Eavg = 0.4 GeV

  13. Impact on Higgs Reconstruction Higgs  bb (no n + resolved bkgd) Higgs  bb Higgs  bb (no n)

  14. Conclusions • Agreement with de Roeck, Moenig, Schulte, Telnov • Resolved photon backgrounds are weakly dependent on the choice of pythia settings • eg backgrounds are not negligble ~ 20% effect • 0.6 events/crossing at NLC Higgs Factory  1.2 at Tesla • 3.7 tracks/crossing at 0.7 GeV • 5.5 clusters/crossing at 0.4 GeV • Challenges of resolved photon backgrounds appear to be smaller than those due to n • This background to be included in the next iteration of our Higgs analysis – accepted Phys. Rev. D.

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