1. Filimon Gournaris - 15/4/051 Luminosity Spectrum & Top Quark Threshold Studies at the ILC Filimon Gournaris 4C00 Project

2. Filimon Gournaris - 15/4/052 Particle Physics needs… The ILC  Precision physics needs e + e - machine with CoM energies of 0.5 – 1 TeV to complement the LHC…  Cannot build synchrotron, LEPII was the limit that e + e - circular machines can reach, at higher energies energy loss due to synchrotron radiation is prohibiting. Thus need something LINEAR!  The ILC will be a high energy high luminosity linear collider, and is expected to do the precision physics of all the discoveries of the LHC, and new discoveries of its own..  Based on superconducting (“cold”) technology (TESLA) for the accelerating cavities.  ~35 km long linear accelerator.  Due to the high energy and high luminosity however, complications are introduced to the Luminosity Spectrum of the machine.  And to do precision physics, we need to understand it well…

3. Filimon Gournaris - 15/4/053 Luminosity Spectrum  Three main energy loses: Initial state radiation Beamspread Beamstrahlung  ISR calculable in QED  Beamspread assumed Gaussian for TESLA design  Beamstrahlung is the problem… Can be modelled microscopically with Guinea-Pig Parameterized into a function (Κιρκη)

4. Filimon Gournaris - 15/4/054 Guinea-Pig Microscopic Simulation  550 bunch-bunch collisions including full accelerator effects (ground motion etc) using FONT @ 0.5 TeV  This includes beamspread  Cannot be used for fitting/reading spectra  Provides the basis for testing parameterizations

5. Filimon Gournaris - 15/4/055 Beamstrahlung Parameterization  Κιρκη Function: With parameters  However, this is not flexible enough…+ we want to parameterize beamstrahlung together with beamspread  Naturally, this means convoluting κιρκη with a Gaussian (assuming beamspread is Gaussian), but the β-function in κιρκη does not allow for this to be done analytically… Thus, we need a new parameterization

6. Filimon Gournaris - 15/4/056 New Parameterization  The proposed parameterization has the form:  The sum with n = 4 (4 exponential terms) is used in this study.  10 parameters describing the spectrum, 8 are used for the exponentials (describing different regions of the spectrum), and σ is the spread of the Gaussian (beamspread).  Leads to a 10-11 parameter fit (using MINUIT) ! ! !

7. Filimon Gournaris - 15/4/057 Fitting the Guinea-Pig Spectrum

8. Filimon Gournaris - 15/4/058 Numerical Convolution  Can use numerical methods to convolute κιρκη with beamspread.  Two techniques available: Standard Trapezium/Simpson Crude Monte-Carlo  Only managed to do MC: Results look OK… However, did not manage to fit with this algorithm…  Still useful! Provides a simple data set to test the new parameterization…

9. Filimon Gournaris - 15/4/059 Fitting the Monte Carlo LumiSpectrum  Standard beamspread 0.1% used in convolution…  The Fit Looks GOOD!!  Next step is to make the algorithm work for fitting..  And Develop a proper numerical technique as well..

10. Filimon Gournaris - 15/4/0510 Top Quark @ the ILC  Top quark measurement is one of the first tasks of the ILC..  Current measurement 5GeV, we think ILC can deliver 100MeV  Top quarks are produced @ = 2M t (~350GeV)via channel: Clear detector signatures However, precision depends on knowledge of the luminosity spectrum.  With luminosity spectrum formalism developed, we can simulate the effects of the lumiSpectrum at the top threshold…

11. Filimon Gournaris - 15/4/0511 Effects of LumiSpectrum at the Top Threshold  Top cross-section does not have clear toponium resonance.  Vulnerable to LumiSpectrum uncertainties  Simulation based on applying luminosity spectra with different parameters at cross-section and comparing the results…

12. Filimon Gournaris - 15/4/0512 Fitting Method  Top Cross-section calculated to NNLO through TOPPIK Interpolated Parameter space f(M t,Γ τ,α s ; )  Then smear cross-section with lumiSpectrum.  Smear again another dataset with different lumiSpectrum.  Treat one as data, other as theory…  Fit theory to data, minimize the Chi 2 and see shift introduced in the top parameters by difference in the lumiSpectrum  Can check how uncertainty in lumiSpectrum parameters influences top measurement.

13. Filimon Gournaris - 15/4/0513 Varying Beamspread Data 0.3% Fit 0.1% Large effect -> Keep it small, or measure it well !!

14. Filimon Gournaris - 15/4/0514 Varying Beamstrahlung This is done in two ways:  Can use uncertainties introduced (K.Monig) by measuring the lumiSpectrum using the Bhabha acolinearity method (D.Miller): Κιρκη parameters: Does NOT include detector effects, just acolinearity method. o Or can introduce larger random uncertainties o ->Wait for two slides

15. Filimon Gournaris - 15/4/0515 Bhabha Acolinearity Uncertainties Acolinearity method OK. N.B. Does not include detector effects ! ! !

16. Filimon Gournaris - 15/4/0516 More Variation: Random Uncertainties…  Since Acolinearity uncertainties have no effect, we can introduce larger uncertainties to see an effect.  We choose 5% and 10%.  The cross-section becomes :

17. Filimon Gournaris - 15/4/0517 More Variation: Random Uncertainties… Data: Circe+10% Fit: Circe

18. Filimon Gournaris - 15/4/0518 Effective LumiSpectrum for Top production  What is the fraction of the lumiSpectrum effective for Top production?  Can check by truncating the spectrum and using our fitting strategy to see how it influences the top measurement.  LumiSpectrum still described using standard κιρκη… 20% used5% used

19. Filimon Gournaris - 15/4/0519 Effective LumiSpectrum for Top production II ~3-4% @ peak produces t-tbar AS EXPECTED! Does not mean that all previous analysis is useless.. Due to detector efficiencies etc. need a good description of ~20%

20. Filimon Gournaris - 15/4/0520 Outlook and the Future…  Examined luminosity spectrum and devised a more flexible parameterization of it.  Developed MC numerical convolution method Needs to be tested by fitting.. Also need to do a proper numerical convolution  Examined behaviour of top threshold under variations of the luminosity spectrum: Beamspread effect determined. Bhabha acolinearity method OK! Beamstrahlung (κιρκη) behaviour determined.  Determined Percentage of Lumi Spectrum effective for top production at threshold.  NEED to develop a scan strategy…  Also should redo the Bhabha acolinearity simulation based on the new parameterization, and examine the effects to the top.  Include/Determine detector efficiencies for both beam spectrometry and top reconstruction ->Have a conclusive (??) study for top precision..!!!

21. Filimon Gournaris - 15/4/0521 THE END! MANY INTERESTING THINGS TO BE DONE…

22. Filimon Gournaris - 15/4/0522 Back-Up: The Function.