Upload
ziazan
View
31
Download
0
Embed Size (px)
DESCRIPTION
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 - PowerPoint PPT Presentation
Citation preview
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.
David Asner/LLNL
4th ECFA/DESY WorkshopApril 1-4, 2003, NIKHEP, Amsterdam
Resolved Photon Backgroundsto Processes
Photons have Structure
• Three types of collisions
– Direct
– Once resolved
– Twice resolved
Electroweak
Electroweak(DIS)
Strong( collider)
“”=0.99 + .01
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 discovered1. Order of magnitude Factor of 6
2. Not at all obvious why this large discrepancy exists
• Recently resolved this problem!
Procedure
• Set Pythia parameters
• Calculate cross sections
• Generate Luminosity distributions - CAIN
• Use above to generate stdhep output file
• Overlay these events in physics studies
Resolved Photon Backgrounds:#1 Concern
collisions are NOT like e+e- 1.5x1010 Primary e-,1x1010 Compton
CAIN also includes e+e- from pair production and real from beamstrahlung
PYTHIA gamma/e- option simulates virtual associated with e- beam
• Approximately 83% of interactions are
• Approximately 17% of interactions are e
• Approximately 0.4% of interactions are ee
Luminosity: CAIN
Cross Section: Pythia vs Model
Cross Section: Pythia ,e,ee
Clearly e cross section is NOT negligible, nor is luminosity Must include in future studies
Scenarios1) Default Pythia parameters: Most similar to the study by de
Roeck, Schulte, Telnov2) Preliminary Butterworth parameters: Used in our earlier
work. 6x larger background.3) 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 2/dof = 4.96 vs 4.97– Newer fit use ~ ¼ LEP, HERA, Tevatron luminosity
4) Repeat analysis for Higgs Factory, 500 GeV, type-I&II
# Overlay Events
• Recall -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
Occupancy: Tracks
Cos vs Energy (GeV) 3.7 tracks/crossing (|cos | < 0.9)Eavg = 0.7 GeV (p > 0.2 GeV)
Plots correspond to 17000 bunch crossings
Occupancy: Showers
Cos vs Energy (GeV) 5.5 showers/crossing (|cos | < 0.9)Eavg = 0.4 GeV
Plots correspond to 17000 bunch crossings
Impact on Higgs Reconstruction
Higgs bb Higgs bb (no ) Higgs bb (no + resolved bkgd)
Conclusions
• Agreement with de Roeck, Moenig, Schulte, Telnov• Resolved photon backgrounds are weakly dependent on the
choice of pythia settings• e 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 • This background to be included in the next iteration of our
Higgs analysis – accepted Phys. Rev. D.