First measurement of EWK Z2 j production cross

First measurement of EWK Z+2 j production cross section and hadronic activity in rapidity gap in CMS A. Nikitenko (IC) for 7 Te. V Analysis Team March, 2013

Public PAS. Paper is under CWR

EWK Z + 2 jet production Bremsstrahlung VBF multiperipheral Large, negative interference between VBF and others two processes s EWK mmjj = 255 fb, mll > 50 Ge. V, p. Tj > 10 Ge. V, |hj|< 7. 0, mjj > 120 Ge. V s VBF H->tt = 80 fb for m. H=125 Ge. V

Backgrounds 1. Dominant: high order as corrections to DY production: “QCD Z+jets” 2. Small: tt~ production 3. Small: diboson production:

Analysis strategy • Signal is very small (S/B ~ 0. 1 after optimized selections), therefore • Use different methods to extract signal • Confirm signal in mm and ee modes • Use different methods of jet reconstruction • JPT jets • PF jets

Event selection cut flow table Uncertainty on the dominant background QCD Z+jets due to JES , +13%, -9% is comparable with the signal. The signal must be extracted from the distributions, most sensitive to the presence of the signal

• Signal is extracted by two methods • from fit of mjj • from fit of BDT output

mjj fit; mm mode S +/- stat B +/- stat JPT jets 1. 14+/-0. 28 0. 869+/-0. 008 PF jets 1. 14+/-0. 30 0. 897+/-0. 008

Signal extraction from fit of BDTD output Variables for BDTD 1. p. TJ 1 2. p. TJ 2 3. |h. J 1 -h. J 2| 4. mjj 5. p. TZ 6. y* = y. Z – (y. J 1 + y. J 2)/2 7. h. J 1+h. J 2 8. y. Z 9. |f. J 1 -f. Z| 10. |f. J 2 -f. Z| 11. |f. J 1 -f. J 2| Pre-selections for BDTD: |hj| < 3. 6 9

BDTD output fit; mm and ee modes mm mode ee mode S +/- stat B +/- stat JPT jets 0. 90+/-0. 19 0. 905+/-0. 006 PF jets 0. 85+/-0. 18 0. 937+/-0. 007 PF jets 1. 17+/-0. 27 0. 957+/-0. 010

measured cross sections agrees with NLO prediction (VBFNLO): 166 fb at mll > 50 Ge. V, p. Tj > 25 Ge. V, |hj|< 4. 0, mjj > 120 Ge. V

Section: Hadronic activity in rapidity gap

Check theory expectations with data • Jet activity in rapidity gap for QCD Z/W+jets: • the larger Dhj 1 j 2, the bigger probability to have additional jet in h region between j 1 and j 2 • the larger p. T of tagging jets, the bigger probability to have additional jet in h region between j 1 and j 2

<Njets> vs Dhjj

Conclusions • First measurement of EWK Z+2 j process demonstrates the CMS detector and analysis capability to extract a process which is topologically similar to VBF Higgs production and has a cross section comparable to that in the standard model. • First analysis of hadronic activity in the rapidity interval between forward and backward jets in Z+jets process shows good agreement with Mad. Graph predictions

Difference in kinematics for EWK Z+jets, VBF H and QCD Z+jets

• Expected Feature 1 • the larger p. T of tagging jets, the bigger probability to have additional jet(s) between them • data confirms simulation predictions

Expected feature 2 The larger rapidity separation between tagging jets, the bigger probability to have additional jet(s). data confirms simulation predictions