A Determination of a s (M Z 0 ) at LEP using Resummed QCD Calculations
Top/QCD program (b) Higher Order EW + QCD Fixed order vs resummed Normalization (and peak position)...
-
Upload
sherilyn-mclaughlin -
Category
Documents
-
view
216 -
download
0
description
Transcript of Top/QCD program (b) Higher Order EW + QCD Fixed order vs resummed Normalization (and peak position)...
Top/QCD program
(b)
Higher Order EW + QCD
Fixed order vs resummed
• Normalization (and peak position) stabilised by higher orders;– summation of leading logs important– N3LO improves NNLO considerably
Pineda
Instability Effects
• Experimental threshold complicated by beam effects
– Luminosity spectrum
– Absolute beam energy
• Machine parameters (interaction point beam sizes) change beamstrahlung component of luminosity spectrum
• Increase beamstrahlung reduces effective luminosity at threshold
– Small modification to shape
Threshold top quark production
€
σ obs s( ) = 1L0
L x( )0
1
∫ σ x s( )dx€
dLd s
€
s
Boogert, Gournaris
ILC accelerator parameters• Parameter group question
Is there any impact of decreasing (increasing) beamstrahlung by a factor of two relative to the standard parameters?
• Simulated 5 possible scenariosLow-Q, Nominal, Large-Y, Low-P, High-L
• Simulated using Guinea-Pig– Fitted using CIRCE-like
parameterization
• Total luminosity spectrum also includes– Intrinsic energy spread– Initial state radiation
• Bhabha acolinearity– Theoretical developments
• New 2 loop calculations• Monte Carlo generators
– Beamstrahlung extraction• Statistical error small• Systematic errors being evaluated
Boogert, Gournaris
Projected total top mass error
• Statistical error– Obtained directly from threshold fit
mt(stat-fit) = 100 to 15 MeV– Depends on parameter set
• Theory error (estimate)– From theoretical uncertainty in threshold
cross sectionmt(theory) = 35 MeV
• Absolute beam energy scale– Assumed precision of beam energy
diagnostics 1 part in 104
mt(e-beam) = 35 MeV
• Luminosity spectrum– Beamstrahlung component can be well
measured – K. Mönig & S. Boogert– Systematic error studies ongoing
mt(spectrum) = 2 MeV and 70 MeV
Boogert, Gournaris
At the ILC with , several hundred events are expected. Statistical error is less than 10 %. Therefore the effect of dim.6 couplings can be observed.
– We discuss the W-fusion with the non-SM Yt which are characterized by dim.6 operators.
– They are constrained by experimental data and unitarity.• Our calculations have been checked by ET.• The W-fusion has been analyzed by EWA and CalcHEP.
• Dim.6 couplings can enhance.
Dimension 6 top-Higgs coupling
Conclusion
Koji Tsumura