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

Public PAS. Paper is under CWR

EWK Z + 2 jet production  EWK  jj = 255 fb, m ll > 50 GeV, p T j > 10 GeV, |  j | 120 GeV  VBF H->  = 80 fb for m H =125 GeV Bremsstrahlung VBF multiperipheral Large, negative interference between VBF and others two processes

Backgrounds 1.Dominant: high order  s 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  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 m jj from fit of BDT output

m jj fit;  mode S +/- stat B +/- stat JPT jets 1.14+/ / PF jets 1.14+/ /-0.008

9 Signal extraction from fit of BDTD output Variables for BDTD Pre-selections for 1. p T J1 BDTD: 2. p T J2 3. |  J1 -  J2 | 4. m jj 5. p T Z 6. y* = y Z – (y J1 + y J2 )/2 7.  J1 +  J2 8. y Z 9. |  J1 -  Z | 10. |  J2 -  Z | 11. |  J1 -  J2 | |  j | < 3.6

BDTD output fit;  and ee modes S +/- stat B +/- stat  mode JPT jets 0.90+/ / PF jets 0.85+/ / ee mode PF jets 1.17+/ /-0.010

measured cross sections agrees with NLO prediction (VBFNLO): 166 fb at m ll > 50 GeV, p T j > 25 GeV, |  j | 120 GeV

Section: Hadronic activity in rapidity gap

Check theory expectations with data Jet activity in rapidity gap for QCD Z/W+jets: the larger  j1j2, the bigger probability to have additional jet in  region between j1 and j2 the larger p T of tagging jets, the bigger probability to have additional jet in  region between j1 and j2

vs  jj

Conclusions First measurement of EWK Z+2j 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 MadGraph 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