Strategies ��� for 2 jet analysis

Keisuke YOSHIHARA Tatsuya Masubuchi, Junichi Tanaka

University of Tokyo ( ICEPP )

11/10/17

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Outline

¤  Analysis Overview

¤  Optimization

¤  Discussion of Pt (tot) selection

¤  Top Control Region

¤  WW background and Signal Region

¤  Summary of baseline strategies

¤  Next step

¤ Backup (Other topics w.r.t 2 jet analysis)

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1. Analysis Overview ��� ~ Review of current selections ~

¤ Preselections

Cut J0 : At least 2 jets

Cut J1 : η1*η2 < 0

Cut J2 : Δη > 3.8

Cut J3 : Mjj > 500 GeV

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Cut J4 : Central Jet Veto |η| < 3.2

Cut J5 : b-jet veto

Cut J6 : Pt(tot) < 30 GeV

Cut J7 : Ztautau Veto

¤ Topological Selections

•  Requiring 2 forward jets in the opposite hemisphere. (Cut J1) •  Rapidity gap can be observed in VBF process. (Cut J2 / J3 ) •  Additional jet in the gap should be vetoed. (Cut J4 )

VBF Selections ( topological requirement )

1. Analysis Overview ��� ~ Conditions of my studies

¤ Rel. 16 full samples are used for my studies.

¤ MC-based optimization is performed with scaling up to 5 fb-1 in the step of normalization.

¤  A mass point, mH = 130 GeV, is chosen for optimization.

¤ Optimization is based on a Poisson significance defined as the formula below.

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Significance with Poisson probability

b : background s : signal

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2. Optimization��� ~ Matrix scan of Mjj VS Δη

After requiring η１＊η２< 0, Mjj VS Δη was scanned.

0.481 0.4675 0.442 0.4326 0.4315 0.4341 0.4255 0.4236 0.4196 0.4158 0.4165 0.4133 0.416 0.4219 0.4268 0.4044

0.4494 0.4433 0.4308 0.4272 0.4292 0.4327 0.4245 0.4236 0.4194 0.4159 0.4165 0.4133 0.416 0.4219 0.4268 0.4044

0.3824 0.3872 0.3871 0.3901 0.3997 0.4084 0.4065 0.4151 0.4144 0.4139 0.4162 0.4132 0.4162 0.4222 0.4269 0.4045

0.3607 0.3649 0.3686 0.3742 0.3805 0.3898 0.3952 0.4052 0.4106 0.4149 0.4182 0.414 0.4153 0.4222 0.4269 0.4045

0.354 0.3569 0.3603 0.3651 0.369 0.3767 0.3837 0.3922 0.4039 0.4081 0.4146 0.4158 0.4188 0.4242 0.4275 0.4047

0.3576 0.3601 0.3641 0.3688 0.3709 0.3757 0.3811 0.3899 0.4 0.4034 0.4068 0.4123 0.4138 0.4184 0.428 0.4047

0.3568 0.3592 0.3624 0.3659 0.3682 0.3733 0.378 0.3859 0.3942 0.4019 0.404 0.411 0.4108 0.4197 0.4267 0.4053

0.3648 0.367 0.3703 0.3729 0.3735 0.3768 0.3815 0.3885 0.3938 0.4015 0.4033 0.4072 0.4091 0.4167 0.4258 0.4056

0.3698 0.3713 0.3732 0.3756 0.376 0.3779 0.3828 0.3901 0.3954 0.3998 0.4026 0.4085 0.4093 0.4157 0.4303 0.4059

0.3734 0.3745 0.3751 0.3764 0.3767 0.3793 0.3827 0.3887 0.3936 0.3987 0.4024 0.4112 0.4116 0.4156 0.4275 0.4123

0.3701 0.3708 0.3715 0.373 0.3733 0.3755 0.3782 0.3817 0.3855 0.3904 0.3954 0.4042 0.4033 0.4075 0.4212 0.406

0.3679 0.3685 0.3687 0.3699 0.3694 0.3697 0.3713 0.3733 0.3783 0.3817 0.3885 0.3971 0.3977 0.3981 0.4149 0.3952

0.3597 0.3602 0.3604 0.3607 0.3608 0.3626 0.3643 0.3653 0.3691 0.3714 0.3748 0.3833 0.3847 0.3874 0.4053 0.388

0.3493 0.35 0.3501 0.3502 0.3508 0.3515 0.3528 0.3531 0.3561 0.3583 0.3597 0.3672 0.3682 0.3685 0.3872 0.3699

0.3401 0.341 0.341 0.3411 0.3409 0.3417 0.3422 0.3428 0.3454 0.3465 0.3469 0.3539 0.354 0.3526 0.3648 0.3539

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Mjj

GeV

0

100

200

300

400

500

600

700

0.36

0.38

0.4

0.42

0.44

0.46

0.48

mH=130GeV with ggF

Optimization doesn’t work well due to ggF and WH/ZH signals !! There is still a large non-VBF signal contribution in this level.

Z : significance

mH = 130 GeV with ggF/VBF/WH/ZH

2. Optimization��� ~ Baseline strategies

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At least 2 jets

b- jet veto / (Pt (tot) ) / Z tautau veto

VBF selection

Topological selection Topological selection

2jet analysis can be divided in 2 categories of VBF and no-VBF analyses to maximize sensitivity.

Pass VBF selection ( VBF dominant )

Fail VBF selection (ggF/WH/ZH dominant )

No-VBF channel is also treated as a new channel.

2. Optimization��� ~Matrix scan of Mjj VS Δη again

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0.1419 0.1468 0.1527 0.1617 0.1739 0.1876 0.2005 0.2157 0.2306 0.2376 0.2502 0.264 0.2679 0.283 0.2942 0.2903

0.1464 0.1508 0.1553 0.1635 0.1747 0.1879 0.2007 0.2158 0.2307 0.2377 0.2503 0.264 0.2679 0.283 0.2942 0.2903

0.1638 0.1682 0.1714 0.1766 0.1861 0.1958 0.205 0.2177 0.2318 0.2382 0.2506 0.2641 0.2681 0.2832 0.2942 0.2904

0.1903 0.1938 0.1968 0.2007 0.2074 0.2155 0.2217 0.2303 0.2416 0.2462 0.2552 0.2654 0.2681 0.2832 0.2942 0.2904

0.2121 0.2145 0.217 0.2204 0.2257 0.2317 0.2374 0.2445 0.2541 0.2568 0.2644 0.2735 0.2742 0.2859 0.2947 0.2905

0.2355 0.2378 0.2405 0.2437 0.2475 0.2514 0.2551 0.261 0.269 0.2706 0.2737 0.2821 0.2811 0.2877 0.2968 0.2905

0.2512 0.253 0.2552 0.2579 0.261 0.2643 0.2684 0.2744 0.281 0.2868 0.2864 0.2929 0.2911 0.2965 0.303 0.2928

0.2676 0.2693 0.2717 0.2738 0.2755 0.2778 0.2813 0.2868 0.2901 0.2961 0.296 0.2986 0.2984 0.3021 0.309 0.2968

0.2789 0.2801 0.2816 0.2836 0.2853 0.2865 0.2902 0.2958 0.2997 0.3038 0.3048 0.3095 0.31 0.3135 0.3217 0.3052

0.2933 0.2942 0.2947 0.296 0.2972 0.2989 0.3016 0.3063 0.3099 0.3145 0.3167 0.3236 0.3242 0.3261 0.3329 0.3189

0.299 0.2996 0.3002 0.3014 0.3024 0.3039 0.3061 0.3089 0.3118 0.3154 0.3186 0.326 0.3252 0.3276 0.3354 0.3221

0.3033 0.3039 0.304 0.305 0.3055 0.3055 0.3068 0.3084 0.3127 0.3151 0.3206 0.3276 0.3265 0.3243 0.3367 0.3206

0.3033 0.3038 0.3039 0.3042 0.3046 0.306 0.3075 0.3082 0.3116 0.3131 0.3165 0.3232 0.3231 0.3234 0.3379 0.3231

0.2977 0.2984 0.2985 0.2985 0.2993 0.2999 0.3011 0.3011 0.3039 0.3055 0.307 0.3132 0.3129 0.3117 0.326 0.3105

0.2904 0.2913 0.2913 0.2914 0.2914 0.2922 0.2926 0.2931 0.2955 0.2962 0.2968 0.303 0.3022 0.2999 0.3089 0.298

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Mjj

GeV

0

100

200

300

400

500

600

700

0.16

0.18

0.2

0.22

0.24

0.26

0.28

0.3

0.32

mH=130GeV only VBF

•  An optimal point is satisfied with the conditions, Δη > 4.2 and Mjj > 550 GeV.

•  It seems that our current selections, Δη > 3.8 and Mjj > 500 GeV, is pretty reasonable as VBF selections.

Z : significance

2.Optimization��� ~Cutflow tables

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signal WW ttbar Tot bkg significance

At least 2 jet 20.47 202.89 6698.39 7486.35 - b - Veto 18.94 191.16 980.64 1446.64 -

Pt (tot) < 30 GeV 12.92 123.90 485.50 745.79 - Ztautau Veto 12.83 120.38 470.63 698.70 - η1*η2 < 0 6.89 58.64 200.20 302.21 - Δη > 3.8 3.14 10.98 28.63 43.81 -

Mjj > 500 GeV 2.17 4.71 13.84 18.83 - CJV |η| < 3.2 1.96 3.93 7.82 12.40 0.54

VBF signal like

signal WW ttbar Tot bkg significance

No VBF selection 10.87 116.39 462.81 686.37 0.41

ggF/WH/ZH signal like

•  No-VBF channel is also not negligible !! •  Systematics are not considered in this step.

3. Discussion of Pt (tot) selection 11/10/17

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Pt (tot) selection This selection can be well performed in 1jet analysis. In case of 2 jet analysis, however, it seems that there is not only a large signal loss ( ~ 30 % ) but also significance loss. Thus the selection should be removed at all.

signal WW ttbar Tot bkg significance

b - Veto 18.94 191.16 980.64 1446.64 0.50 Pt (tot) < 30 GeV 12.92 123.90 485.50 745.79 0.47

Ztautau Veto 12.83 120.38 470.63 698.70 0.48

signal WW ttbar Tot bkg significance

b - Veto 18.94 191.16 980.64 1446.64 0.50 Ztautau Veto 18.80 185.43 983.76 1396.54 0.50

With Pt(tot) selection

Without Pt(tot) selection

4. Top Control Region��� ~ Definition of Top CR

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Top CR is defined after VBF selection ( with b-tagging )

b- jet tagging / Z tautau veto

VBF selection

Top CR for VBF like Top CR for No VBF like

VBF like events No VBF like events

Top CR Definition

Cutflow of Top CR for VBF selection

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4. Top Control Region��� ~Top CR distribution for VBF channel

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•  Very pure CR is defined. •  VBF channel should be defined

as a 1 channel ( flavour combined ) due to small statistics. (~ 20 events)

5. WW background and Signal Region 11/10/17

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Signal Region plots after Mll < 80 GeV selection

•  There is a small statistics and is also a large contribution of Top background in higher Mll Region. It is thus difficult to define WW CR.

•  WW background is estimated based on MC prediction ( ? ) •  In the No VBF channel, there is also a large Z+jets background. •  How to estimate Z+ jets background ? •  Any new ideas ?

VBF channel SR No VBF channel SR

Significance after Mt cut : 0.98

Significance after Mt cut : 0.50

Summary of baseline strategies 11/10/17

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•  2 jet analysis could be divided into 2 categories, VBF channel and No VBF channel. (non-negligible contribution!)

•  Pt (tot) cut could be removed for increasing signal statistics (and sensitivity).

•  Top CR could be also divided into 2 categories after VBF selections.

•  WW CR cannot be defined, thus we need to consider another method to estimate WW background.

•  Z+jets background study for 2 jet analysis is important.

Next step 11/10/17

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•  WW and Z+jets contributions will be re-estimated in Rel. 17. •  Cross check of VBF optimization with new MC samples. •  Optimization of topological selection for 2 jet analysis specific. •  In case that lower lepton Pt will be available, it is also

necessary to estimate fake background contribution in 2 jet analysis as well. (W+jets etc)

•  Systematic studies for 2jet analysis, especially for No-VBF channel. (VBF channel is almost free from background)

I’ll also be responsible to study 2 jet analysis.

Backup

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•  Cutflows of 2 jet analysis with 2.05 fb -1 •  Comparison of WW samples •  Signal Region and Limit Setting •  Other discussions

Prospective cutflows of ��� 2 jet analysis with 5 fb-1

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VBF channel cutflow ��� with / without Pt(tot) selection

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Including pt(tot) cut

Not including pt(tot) cut

No VBF channel cutflow ��� with / without Pt (tot) selection

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Including pt(tot) cut

Not including pt(tot) cut

Comparison of WW samples

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WW background sample Studies 1 11/10/17

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McAtNlo VS Alpgen (VBF channel SR plots)

McAtNlo

Alpgen Alpgen Alpgen

McAtNlo McAtNlo

WW background sample Studies 2 11/10/17

McAtNlo VS Alpgen (jet bin and jet Pt / Eta) Alpgen

McAtNlo

Alpgen Alpgen

McAtNlo

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McAtNlo

Cutflow comparison ( Alpgen VS McAtNlo ) 11/10/17

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Alpgen

McAtNlo

Cutflow comparison ( Alpgen VS McAtNlo ) 11/10/17

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•  McAtNlo doesn’t have ElectroWeak process actually. Thus we need to add this kind of process using sherpa.

•  It seems that there is a large discrepancies between Alpgen and McAtNlo in jet bin. At least I can say that McAtNlo cannot be modeled 2 jet bin and more than 3 jet bin.

•  But Alpgen sample has a small statistics. •  jet η distribution might be also different between 2

generators. (?)

Signal Region and Limit setting

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Signal Region for VBF channel 1 11/10/17

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After Mll < 80 GeV selection

After ΔΦll < 1.3 selection

Signal Region for VBF channel 2 11/10/17

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After Mll < 80 GeV selection After Mt window selection

Signal Region for No VBF channel 11/10/17

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After Mll < 80 GeV selection

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Mjj distribution

η* distribution

Δηjj distribution

η* = η3 – (η1 + η2) / 2

η* is defined as the formula below,

Distributions before any VBF selections

Two jet kinematic distributions

Ref : arXiv : hep-ph / 9908378 v1

Limit Setting Procedure 11/10/17

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Try to fit ΔΦll distribution after Mll selection for limit calculation. There are 4 channels in 2 jet analysis,

Dominant systematics for shape fitting in 2 jet analysis

•  B-tagging efficiency ? •  JES/JER ?

1. ee channel for No-VBF channel 2. mumu channel for No-VBF channel 3. emu channel for No-VBF channel 4. Combined flavour channel for VBF channel

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GeVHm110 120 130 140 150 160 170

SM/

95%

C.L

. lim

it on

1

10

210

310 Prospected plot

=7TeVs, -1 Ldt = 5 fb

l l (*) WWH

Expected 1±

2±

* Systematic inputs like shape systematics, are not validated in this plot.

Combined Limit for 2 jet Analysis 11/10/17

Very Preliminary ...

Other discussions 11/10/17

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CVJ selection There is still a room for discussion how to veto the event with Central Jet. Several possibilities below should be studied, 0. Current selection should be kept ? 1. Can we use η* for veto CJ events ? η＊ = η３ – ( η１＋η ２ ) / 2

2. Exactly 2 jet ?

WW sample It seems that McAtNlo doesn’t model well for WW background with more than 2 jet. Thus, we should consider to use another samples like Alpgen (or PowHeg (?) or Sherpa (?) ) . See Tatsuya’s slide. Comparison table and plots of Alpgen VS McAtNlo are put on the backup.