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.