Multi boson production Paolo Mastrandrea PIC 2009 Kobe 8/31/ /2/2009

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 2 Diboson production Associated production of 2 vector bosons (, W, Z) can occur via: –particle-antiparticle annihilation (t-channel) –boson self-interactions or Triple Gauge Coupling (TGC) (s-channel) t-channel s-channel

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 3 Why is diboson interesting? Measure coupling between W,Z and  to test SM prediction; unique probe for Triple Gauge Coupling (TGC); observing TGCs not permitted in the SM or anomalous TGCs would be a sign of new physics; signature similar to Higgs (not in this presentation). All presented analysis from Tevatron: –most updated; –highest q 2 available; –techniques in LHC perspective.

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 4 Triple Gauge Couplings anomalous Triple Gauge Couplings (aTGCs): –can affect cross-section and kinematics observables (i.e. lepton or boson p T distributions); –can depend on q 2. CouplingDecay VWW (V = Z,) WWWW Not present at LEP WWZ WW Lep and Tevatron ZWW Z * and ZZ * ZZ Absent in SM ZZZZ ZZ * and ZZZ * ZZ ZZZ

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 5 Triple Gauge Couplings VWW: 14 independent couplings (7 each for ZWW and WW); can be reduced to 5 assuming C and P conservation and electromagnetic gauge invariance. –Common set ( ,  Z, , Z, g Z 1 ); –gauge invariance:  Z = g Z 1 - (  - 1)tan 2  W and Z =  ; –in SM at the tree level   =  Z = g Z 1 = 1 and  = Z = 0; –  =  - 1 ; g = g - 1. [ LEP2 arXiv:hep-ex/ v2 ]arXiv:hep-ex/ v2

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 6 Triple Gauge Couplings Z * and ZZ * : deviations from SM couplings may be described by 8 parameters h V i ( i = 1,..4; V = , Z) ZZ * and ZZZ * : deviations from SM couplings may be described by 4 parameters f V i ( i = 4, 5; V = , Z) [ LEP2 arXiv:hep-ex/ v2 ]arXiv:hep-ex/ v2

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 7 Analysis techniques Leptons for clear signatures; now start using jets; increasing statistics is pushing close/beyond LEP limits on aTCGs parameters. WlWjjZl+l-Zl+l- ZZjj Wl WW Wjj WW-- Zl+l-Zl+l- WZ ZZ Z WZ ZZ-- Zjj WZ--ZZ --  Wg--Zg --

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 8 ZZZZ Z Copious non-collision background: –a pointing alghoritm which exploits the transverse and longitudinal energy distributions in the EM calorimeter and central preshower detector is used to evaluate z EM ; –reject events with |z EM - z V | > 10 cm. 5.1 s.d. significance - First Tevatron observation D0 3.6fb -1 (ppZ)Br(Z), E T  >90GeV, Missing E T > 70 GeV [fb] data 32 ± 9 (stat.+syst.) ± 2 (lumi.) SM prediction 39 ± 4 fb Events selection Triggerhigh-E T single EM cluster Photon E T >90 GeV, ||<1.1, n  =1 NeutrinoMissing E T >70 GeV

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 9 Z - aTGC Photon E T spectrum in data compared to MC signal + background expectation for a grid of pairs of anomalous coupling parameters; 1 and 2-dimensional bounds obtained setting all other parameters to SM prediction; limits on Z * and ZZ * aTGC. Parameter95% C.L. |h  30 | [-0.033, ] |h  40 | [ , ] |h Z 30 | [-0.033, ] |h Z 40 | [ , ] (h  30 = 0.09 and h  40 = 0.005) World's best

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 10 WWWW Wl Sensitive to WW aTGC CDF 1fb -1 Selection criteria WeWW Lepton E T >25GeV, ||<1.1p T >20GeV/c, ||<1.1 NeutrinoMissing E T >25 GeVMissing E T >20 GeV Transverse mass30 < M T < 120 GeV/c 2 Photon E T > 7 GeV, ||<1.1 (ppW)Br(Wl), (l=e,), E T  >7GeV [pb] data ± 0.65 (stat.) ± 2.55 (syst.) ± 1.05 (lumi.) SM prediction 19.3 ± 1.4

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 11 WWWW W+Xl+X, (l=e,) Limits on WW aTGC Selection criteria WeWW LeptonE T >25GeVp T >20GeV/c NeutrinoMissing E T >25 GeVMissing E T >20 GeV Transverse massM T > 40 GeV/c 2 Photon E T > 8 GeV, R l >0.7 (ppW+X)Br(Wl), E T  >8GeV, R l >0.7 [pb] data ± 1.6 (stat.) ± 1.0 (syst.) ± 1.0 (lumi.) SM prediction 16.0 ± 0.4 D0 162pb -1 Parameter95% C.L.   [-0.88, +0.96]  [-0.20, +0.20]

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 12 WW W + W - l +l' - l', events selection: –high-p T e and  trigger paths; –2 opposite charge leptons (e, ). Background reduction: –no jets with E T >15GeV and ||<2.5; –missing E T not alligned with leptons or jets - reduces DY background; –M ll > 16 GeV to suppress h.f. contribution. Event-by-event matrix element probability density functions are used to build a likelihood ratio discriminant. Binned likelihood fit to extract (ppWW). CDF 3.6fb -1

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 13 WW Matrix element probability density functions pdf: – x obs - This represents the observed lepton momenta vectors as well as the two transverse components of the missing E T. –1/ - This is a normalization factor based on the total leading order cross section and detector acceptances. –  - This refers to the leading-order cross section. – y - The true lepton 4-momenta which are integrated over. –  - Detector efficiencies and acceptances. – G - A generalized detector resolution function. Likelihood ratio: –where i are the background processes modeled and k i is the relative fraction of the i-th mode such that the sum over all k i equals 1. [All distributons in backup]

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 14 WW Cross section extracted using a binned likelihood fit which includes gaussian constraints for systematics. Correlation between systematics taken into account. (ppWW) [pb] data 12.1 ± 0.9 (stat.) (syst.+lumi.) SM prediction ± 0.70

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 15 WW - aTGC The efficiency at a given leading lepton p T is similar for any given coupling - allow to avoid full simulation for every possible coupling The resulting efficiency curve is then applied to MCFM NLO matrix element simulations for a grid of values of the couplings parameters The measured leading lepton pT distribution is fitted to extract limits on Z, g Z 1 and  

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 16 WW W + W - l +l' - l' aTGC limits extracted comparing the lepton p T distributions with MC simulations for different sets of ( , , g Z 1 ) D0 1.0 fb -1 (ppWW) [pb] data 11.5 ± 2.1 (stat.+syst.) ± 0.7 (stat.) SM prediction [13.0, 13.5] Parameter95% C.L.   [-0.54, +0.83]  [-0.14, +0.18] gZ1gZ1 [-0.14, +0.30]

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 17 WZ WZl' l' l + l - extended categories of charged leptons to increase acceptance (ppWZ) [pb] data (stat.) ± 0.2 (sysy.) ± 0.3 (lumi.) NLO prediction 3.7 ± 0.3 CDF 1.9fb -1

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 18 WZ - aTGC Z p T distribution is sensitive to aTGC Efficiency independent from aTGC couplings Z pT distribution fitted to for every combination of simulated parameters to extract limits 95% C.L. Z gZ1gZ1  Z =1.5 TeV [-0.14, 0.15][-0.14, 0.25][-0.81, 1.29] =2.0 TeV [-0.13, 0.14][-0.13, 0.23][-0.76, 1.18] Expected limit [-0.15, 0.16][-0.18, 0.28][-0.68, 1.00]

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 19 ZZ Zl + l - l' + l - '; extended categories of charged leptons to increase acceptance. CDF 4.8fb -1 (ppZZ) [pb] data (stat.) ± 0.25 (sysy. + lumi.) NLO prediction 1.4 ± 0.1

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 20 ZZ ZZl + l - l' + l' s.d. significance (ppZZ) [pb] data (stat.) ± 0.08 (sysy.) ± 0.10 (lumi.) NLO prediction 1.6 ± 0.1 D0 1.7 fb -1

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 21 ZW, ZZ ZW/ZZl + l - jj; extended categories of charged leptons to increase acceptance; signal fraction extracted by an unbinned fit to dijet mass distribution. CDF 1.9fb -1 95% CL limit (ppZZ) [pb] (ppZW) [pb] 140<p T (Z)<210 GeV/c p T (Z)>210 GeV/c control region aTGC SM p T (Zl + l - ) GeV/c

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 22 ZW, ZZ - aTGC ZW/ZZl + l - jj. aTGC limits extracted comparing M jj distribution to MC simulation. 95% C.L.Limit gg =1.5 TeV Expected[-0.16, 0.26][-0.88, 1.16][-0.14, 0.15] Measured[-0.22, 0.32][-1.09, 1.40][-0.18, 0.18] =2.0 TeV Expected[-0.15, 0.24][-0.81, 1.07][-0.13, 0.13] Measured[-0.20, 0.29][-1.01, 1.27][-0.16, 0.17] 95% C.L.Limitf4Zf4Z f5Zf5Z f4f4 f5f5 =1.2 TeV Expected[-0.11, 0.11][-0.12, 0.11][-0.11, 0.11][-0.12, 0.11] Measured[-0.12, 0.12][-0.13, 0.12][-0.10, 0.10][-0.11, 0.11]

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 23 WZ, WW WW/WZljj, l = e,. Event selection: –1 lepton with E T >20GeV and ||<1.2; –missing E T >25GeV; –≥ 2 jet with E T >20GeV, ||<2.4, <2.5; –M T W >30GeV/c 2 ; –p T (jj)>40GeV/c. Diboson fraction extracted by a binned fit to Mjj distribution. 4.6 s.d. significance (expected 4.9 s.d.) CDF 3.9fb -1 (ppWV), V=W,Z [pb] data 14.4 ± 3.1 (stat.) ± 2.2 (sysy. + lumi.)

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 24 WZ, WW WW/WZljj, l = e,. Matrix element technique to maximize the use of collected information in signal- background discrimination. 5.4 s.d. significance (expected 5.1 s.d.). CDF 2.7fb -1 (ppWV), V=W,Z [pb] data 17.7 ± 3.1 (stat.) ± 2.4 (sysy. + lumi.)

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 25 VV->Missing E T +jj Search for and l final states. Acceptance for WW, WZ and ZZ events. Event selection: –Missing E T > 60 GeV; –2 jets E T > 25 GeV, || < 2.0; –Missing E T significance > 4; –Missing E T -jet  > 0.4. Missing E T model to enanche QCD rejection. Sysytematic uncertaintiy on V+jj background shape checked with +jj events. (ppVV), V=W,Z, with one Vjj [pb] data 18.0 ± 2.8 (stat.) ± 2.4 (sysy.) ± 1.1 (lumi.) NLO prediction 16.8 ± 0.5 j j, lep CDF 3.5fb -1

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 26 … and what about LHC ? … and what about LHC ? Tevatron: –proton-antiproton –s = 1.96 TeV – L = 310 32 cm -2 s -1 [arXiv: ; CERN-OPEN ] LHC: –proton-proton –s = 14 TeV – L = cm -2 s -1

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 27 … and what about LHC ? … and what about LHC ? Example on WW, =2TeV [arXiv: ; CERN-OPEN ] Experiment s [TeV] L [fb -1 ]    gZ1gZ1 D [-0.54, +0.83][-0.14, +0.18][-0.14, +0.30] CDF3.6 [-0.57, +0.65][-0.14, +0.15][-0.22, +0.30] ATLAS [-0.476, ][-0.564, ][-0.741, ] 1 [-0.240, ][-0.259, ][-0.355, ] 10 [-0.088, ][-0.074, ][-0.149, ] 30 [-0.056, ][-0.052, ][-0.149, ]

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 28 Conclusions Diboson program is wide and exciting Tevatron is producing mature results … even more in the next LHC era!

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 29 Backup

PIC Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 30 WW Matrix element probability density functions pdf: