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

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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…

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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)

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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

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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

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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) ! ! !

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

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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…

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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..

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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…

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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…

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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.

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

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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

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

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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 :

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

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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

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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%

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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..!!!

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

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

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