Jet Radiation in SUSY events

People

1. Johan Alwall
2. Simon de Visscher
3. Fabio Maltoni

Aim of the project

We study QCD radiation in SUSY events, such as gluino-gluino, stop-stop, stop-gluino processes. We use the MLM matching and verify/improve the results of ​Tilman, David and Peter, and in particular we investigate whether the extra hard jets in SUSY events are well described by the parton-shower, as it is usually claimed, or if matching gives a better description. We also study the matching in heavy tops events as a reference and the SM background needed in these kind of analysis. The SM samples will be used also for other applications.

Tools

• Madgraph/MadEvent v4 : SUSY and matching
• ​MadMatchChecker

Work

We have identified two phases:

1. MC samples generation and validation
2. Physics results and paper writeup

MC samples generation and validation

The strategy here is to first generate samples at the after-showering level to perform the validation. Once all samples are validated, we'll do the full Pythia-PGS simulation.

Generation

Standard Model Samples (Simon)

To get a faster generation we:

• define a new model (smzerobmass), where the bmass is set to "Zero" in the particles.dat. This optimizes the flavor sum
• We don't decay the Z, W+,W-, and tops. We'll let these particles be decayed by Pythia. In doing this we loose spin correlations, which, however are irrelevant for the multi-jet samples for this type of studies.
• Not to generate the single particle samples for Z and W. These have a negligible impact on the multi-jet

configurations we are interested in.

• In Pythia, we consider only decays of W into leptons (e, mu and tau) and also into neutrinos for Z.

SUSY and SM Samples

Process	Webpage	section(s)	LHE (on disks)	Pythia	MC	PGS
1. gogo at 607 GeV (sps1a)	n/a	all	ok	ok	ok
1a. SC 1	n/a	4	ok	ok	n/a
1b. SC 2	n/a	4	ok	n/a
1c. SC 3	n/a	4	ok	n/a
1d. SC 4	n/a	4	ok	n/a
1e. QCUT x 2	n/a	3.1	ok	n/a
2. gogo at 607 GeV with xqcut and QCUT / 2	​here	3.1				n/a
3. gogo at 607 GeV with scales divided by 2	​here	3	ok			n/a
4. gogo at 607 GeV with scales multiplied by 2	​here	3	ok			n/a
5. gogo at 300 GeV		4	ok	ok	ok	n/a
6. gogo at 1200 GeV		4	ok	ok	ok	n/a
7. sqsq at sps1a	n/a	4,5	ok
8. sqgo at sps1a	n/a	4,5	ok
9. ulul at 607 GeV	​here	3,4	ok	ok		n/a
10. ulul at 607 GeV with scales divided by 2	​here	3	ok	ok	ok	n/a
11. ulul at 607 GeV with scales multiplied by 2	​here	3	ok	ok	ok	n/a
12. ululbar at 607 GeV	​here	3,4	ok	ok	ok	n/a
13. ululbar at 607 GeV with scales divided by 2	​here	3	ok	ok	ok	n/a
14. ululbar at 607 GeV with scales multiplied by 2	​here	3	ok	ok	ok	n/a
15. ttbar	n/a	3,5	ok	ok	ok
15a. QCUT x 2	n/a	3,5	ok			n/a
16. ttbar with xqcut and QCUT / 2	n/a	3.1				n/a
17. ttbar with scales divided by 2	​here	3	ok	ok	ok	n/a
18. ttbar with scales multiplied by 2	​here	3	ok	ok	ok	n/a
19. W+4 jets biaised	n/a	5	ok
20. W+3 jets biaised	​here	5	ok
21. Z+4 jets biaised	n/a	5	ok

Physics results and paper writeup

Plots for the paper

Explanation of notation:

• 4x2 runs means 4 unmatched, 4 matched runs with the different shower params
• 4 params means with the 4 different shower params
• decay jet #s means number of jets from decays
• jet numbers means plot of number of jets above (say) 50 GeV in the events

Figure	section	Process(es)	Description	Done (plan)	plot
1	2	n/a	Feynman diagrams illustrating resonance double counting (3 plots)	done
2	3.1	1,1e,2,15,15a,16	Standard validation plots: diff. jet rates 0,1,2 with QCUT, x2, /2 for pT- and Q2-ordered showers, for gogo and ttbar (4x3x3 plots)	?
3a	3.2	15 (4x2 runs),16,17	pT of 1st and 2nd extra jet in ttbar, unmatched and matched dep on shower params, scale dep. for matched (4 plots)	6-7/08	Pt_ttbar.eps​
3b	3.2	1 (4x2 runs),3,4	pT of 1st and 2nd extra jet in gogo, unmatched and matched dep on shower params, scale dep. for matched (4 plots)	8/08?	Pt_gogo.eps​
4(7)	3.3	1,9,12	HTred and pTs, matched for gogo, ulul and ulul* 600 GeV (3 plots)	11/08	Htred.eps​
5(6)	3.3	1,5,6	pT of 1st-2nd extra jet and HTred, matched for gogo at 300, 600, 1200 GeV (2x3 plots)	11/08	pt_300_600_1200.eps​
6a(8)	4	1a (4x2 runs)	HT(n),n=3,4,5(?) matched for gogo with decay jet #s, ETmiss unmatched and matched for sc. 1 (4 plots)	6-7/08	htcontrib-mockup.eps​
6b(9)	4	1b (4x2 runs)	HT(n),n=3,4,5(?) matched for gogo with decay jet #s, ETmiss unmatched and matched for sc. 2 (4 plots)		htcontrib-sc2.eps​
7(10)	4.1	1a (4 unm runs),12	HT(n),n=2,3,4 and jet numbers for unmatched gogo sc. 1 (4 params) and matched ululbar sc. 3 (2x4 plots)	12/08
8(11)	4.2	1d (4x2 runs)	ETmiss unmatched and matched (1 plot)	12/08

For sec. 5 we should plot the most important quantities used in typical experimental analyses, such as ETmiss, HT(4), and what else? All after PGS.

-- Main.JohanAlwall - 05 Aug 2008

• Pt_ulul.eps​: Pt of 1rst and 2nd jet for ulul

• Pt_ululbar.eps​: Pt of 1rst and 2nd jet for ululbar

• Htred.eps​: Ht red for gogo, ulul and ululbar, as well as Pt of 1rst and second, all with and without matching

• htcontrib-mockup.eps​: contrib of jets to Ht scenario 1

• Pt_ttbar.eps​: pt for ttbar

• pt_300_600_1200.eps​: characteristic of jets for in gogo for go mass=300, 600 and 1200 GeV

• Pt_gogo.eps​: pt of the 1rst and 2nd jet for gogo (with ME and PS)

• Pt_ulul.eps​: Pt of two leading jets for ulul

• Pt_ululbar.eps​: pt of leading jets for ululbar

• Htred.eps​: Htred and Pt for gogo, ulul and ululbar, Pythia vs ME

• Pt_ttbar.eps​: Pt_ttbar.eps

• Pt_ulul.eps​: Pt_ulul.eps

• Pt_ululbar.eps​: Pt_ululbar.eps

• Pt_ulul.eps​: Pt_ulul.eps

• pt_300_600_1200.eps​: pt_300_600_1200.eps

• htcontrib-sc2.eps​: preliminary plot showing the contribution of decay jets to Ht and MET for scenario2

• Htred.eps​: Htred.eps