1. TESLA - The TEV-Energy Superconducting Linear Accelerator Light Higgs Production at the Tesla Photon Collider Aura Rosca DESY Zeuthen Amsterdam, Netherlands, 1-4 April 2003

2. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen2 Motivation Measure the two-photon partial width: –Contribution to the two photon decay width from any kind of massive charged particles. Any deviation of the partial width from SM prediction: Evidence for new physics; Can be directly compared to predictions of alternative models (MSSM, NMSSM, general 2HDM).

3. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen3 How to Get Widths? The Higgs mass peak gives Taking and from LHC or LC, This is proposed as the way to get the total width. This would be a model- independent result.

4. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen4 Realistic Luminosity Spectra and Polarization for the Photon Beams Luminosity spectra for J=0,2 with Total luminosity for Circe 2.0

5. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen5 Higgs boson has spin-0 –It is produced from J=0 Adjust beam polarization to increase the signal cross section; If know, adjust photon energies to have. The Signal

6. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen6 Higgs Decay Light Higgs Signature –2-jet events Background –large cross sections, can be suppressed exploiting the polarization dependence of the cross section.

7. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen7 The Background Suppression removed for Need to take into account the NLO corrections! Need b-tag to reduce bkg. Photons of the same helicity suppress continuum

8. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen8 Background Cross Sections NLO cross sections include: –Exact one-loop QCD corrections (Jikia, Tkabladze) –Non-Sudakov form factors (Melles, Stirling, Khoze)

9. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen9 Simulation Results include realistic photon spectrum for ++ and +- helicities simulated with Circe 2.0; Signal MC generated with Pythia and passed through the TESLA fast simulation, Simdet 4.02; Background MC generated with Pythia and passed through the TESLA fast simulation: – –Convolution with the realistic photon spectrum for ++ and +- helicities –Events weighted by the NLO Xsec for ++ and +- helicities B-tagging

10. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen10 Cross Sections Cross section (pb) Number of expected ev. Number of generated ev. Signal process 0.25 ~20 00050 000 Background J=0 (from Pythia) 0.7544 175.0600 000 J=2 4.79102 314.4600 000 J=0 13.4789 260.0600 000 J=2 85.11 817 734.0600 000

11. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen11 Selection Requirements Isotropic angular distributions for signal and forward peaked for the background: Jet clustering using Durham with y=0.02; Other cuts on

12. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen12 B-tagging Performance Events containing at least one jet with two reconstructed vertices:

13. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen13 Invariant Mass Spectrum It is possible to isolate the signal from the background.

14. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen14 Partial Width Uncertainty This is one of the main justifications for a Photon Collider.

15. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen15 Summary Measure with a precision of 1.9% by: –Taking into account the QCD radiative corrections to the background process (Pythia + NLO Xsec.) through a reweighting procedure; –Adopting a b-quark tagging algorithm based on a neural network.

16. TESLA - The TEV-Energy Superconducting Linear Accelerator April 2003Aura Rosca DESY-Zeuthen16 Summary Measure with a precision of 1.9% by: –Taking into account the QCD radiative corrections to the background process (Pythia + NLO Xsec.) through a reweighting procedure; –Adopting a b-quark tagging algorithm based on a neural network.