Select the minimal supersymmetric standard model
model = MSSM
and consider a decay cascade of up-squarks into neutralinos and selectrons
process dec_su_q = su1 => u, neu2 process dec_neu_sl2 = neu2 => SE12, e1
where the up-squark pairs are generated from up quarks
process susybg = u,U => SU1, su1
We will compare the results with the full process including all irreducible backgrounds
process full = u, U => SU1, u, e1, SE12
Call O'Mega and compile the matrix elements
compile
We use the SLHA convention to choose the SPS1a parameter point
?slha_read_decays = true read_slha("sps1ap_decays.slha")
Obtain the total widths (simple integration, no singularities, not too many points required)
integrate (dec_su_q, dec_neu_sl2) { iterations = 1:1000 }
We're at the full energy LHC
sqrts = 14000 beams = p, p => lhapdf
Obtain the up-squark production cross section and the cross section for full process
integrate (susybg) { iterations = 5:10000, 2:10000 } integrate (full)
Simulate 10K events
n_events = 10000
Allocate histograms
$title = "Full process" $description = "$p + p \to u+ \bar u \to \bar{\tilde u}_1 + u + \tilde e_{12}^+ + e^-$" $xlabel = "$M_{\rm inv}(ue^-)$" histogram inv_mass1_full (0,600,20)
$title = "Factorized process with complete spin correlations" $description = "$p + p \to u\bar u \to \bar{\tilde u}_1 + (\tilde u_1 \to u + (\tilde\chi_2^0 \to \tilde e_{12}^+ + e^-))$" histogram inv_mass1 (0,600,20)
$title = "Factorized process with classical spin correlations" histogram inv_mass1_dia (0,600,20)
$title = "Factorized process with isotropic decay" histogram inv_mass1_iso (0,600,20)
Simulate the full process
simulate (full) { $sample = "casc_dec_full" analysis = record inv_mass1_full (eval M / 1 GeV [combine[u,e1]]) }
Simulate the cascade decay, including all off-diagonal spin correlations
unstable neu2 (dec_neu_sl2) unstable su1 (dec_su_q) unstable neu2 (dec_neu_sl2) simulate (susybg) { $sample = "casc_dec" analysis = record inv_mass1 (eval M / 1 GeV [combine[u,e1]]) }
Simulate the cascade decay, keeing only the classical (diagonal) spin correlations
?diagonal_decay = true unstable su1 (dec_su_q) unstable neu2 (dec_neu_sl2) simulate (susybg) { $sample = "casc_dec_dia" analysis = record inv_mass1_dia (eval M / 1 GeV [combine[u,e1]]) }
Simulate the cascade decay, dropping all spin correlations (i.e. assume isotropic decays)
?isotropic_decay = true unstable su1 (dec_su_q) unstable neu2 (dec_neu_sl2) simulate (susybg) { $sample = "casc_dec_iso" analysis = record inv_mass1_iso (eval M / 1 GeV [combine[u,e1]]) }
Write the results to file
write_analysis compile_analysis { $out_file = "casc_dec.dat" }
Running this script, we obtain terminal output and PDF/PS files displaying separate histograms.
NB: since there's also the histogram data, one can use gamelan magick (or ROOT etc.) to produce a plot with combined histograms.
Attachments (6)
- casc_dec.dat (11.9 KB) - added by ohl 7 years ago.
- whizard.log (31.7 KB) - added by ohl 7 years ago.
- casc_dec1.tex (1.9 KB) - added by ohl 7 years ago.
- casc_dec1.pdf (15.6 KB) - added by ohl 7 years ago.
- casc_dec.sin (2.9 KB) - added by jr_reuter 6 years ago.
- casc_dec.pdf (24.9 KB) - added by jr_reuter 6 years ago.
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