Triple Gauge Couplings in diboson production at LHC

1. Triple Gauge Couplings in diboson production at LHC • Introduction • Theoretical framework • Form Factor considerations • Diboson production: WZ, W, ZZ and Z • Analysis strategies • Channel and selections • Expected sensitivity • Summary Samira Hassani CEA/DAPNIA/Saclay France (On behalf of the ATLAS Collaboration)

2. Charged Triple Gauge Couplings (TGC) non-abelian SU(2)LxU(1)Y  W W Z ,W W  vertices Open window to EW symmetry breaking mechanism Probe tool: sensitive to low energy remnants of new physics Compliment to direct searches for new physics Motivation for TGC’s  Probe W W V vertex with W Z, W , W W Under general assumptions (Gauge, C,  P invariance) 5 parameters specify the anomalous W W V vertex g1z,  Z, Operators of dimension 4 grow like √ŝ Z,  Operators of dimension 6 grow like ŝ g1z,  Z, , Z,  = zero in S.M. LEPMoriond 2003 TeVatron expected Run II 95  C.L. limits are O (0.02-0.10)

3. Neutral Triple Gauge Couplings (NTGC) Physics beyond the S.M. Standard Model NTGC / / / The SM has no interaction between (Z,) Higher order corrections through virtual loop contribute at the level of 10-4 Virtual effects from new heavy fermions and supersymetric models In Model independent, the Z V* and ZZV* (V*=Z, ) vertex are described by 12 parameters requiring Lorentz + EM gauge invariance, Bose symmetry hiZ ,(i=1,…,4) : Z V* vertex (8 parameters) in Z final state fi Z (i= 4, 5) : Z Z V* vertex (4 parameters) in ZZ final state f4, f5, h1, h3 operators of dimension 6 grow like (ŝ)3/2 h2, h4 operators of dimension 8 grow like (ŝ)5/2

4. Form Factors • Constant non-standard TGC (NTGC) would lead to a unitarity violation of the s-matrix  Form Factor req’d for TGC • Many valid choices (and interpretation) of FF • Ideally the limit should be given as function of the scale • At high Λ there is a asymptotic limit, because of machine/energy/luminosity limitations convoluted with analysis sensitivity  For LHC this gives Λ=8 to10 TeV

5. Diboson production at the LHC • At LHC energies, higher order QCD corrections (NLO) becomes dominant (a factor 1.4 to 3 on total cross section) • At high PT(V) (V=Z, W,  ), the NLO corrections are largest. Qualitatively, this is precisely what one expects for TGC and NTGC Lowering TGC and NTGC sensitivity However • Dominant channel, qg, does not contain TGC and NTGC • A jet veto is very efficient in recovering the qualitative shape of the LO distribution Restore TGC and NTGC sensitivity WZ Z 

6. Experimental sensitivity to TGC and NTGC comes from three different types of information : cross section energy dependence polarization Cross section : Parabolic increase of cross section with TGC and NTGC due to the linear Lagrangian : σ ~ (TGC)2 Analysis strategies

7. TGC (NTGC) lead to a broad increase in the differential cross section at large invariant mass M WV, ZV (V=Z, ) and transverse momentum PT(V) (V= W, Z, ) Energy dependence ZZ ZZ

8. Polarization • Production angular information of the bosons for TGC: • A Born~ cos Θ ± 1/3 “ Radiation Zero ” • Since different TGCs contribute to different helicity configuration, and NTGC lead to primarily longitudinally polarized Z •  boson angular information can be used as “ projectors” W

9. WZ and W production at LHC Consider leptonic channels only :  ± / e ± Number of events for 30 fb-1 W±Z → l ±l± l±ν ( l = , e) W±  →  l±ν ( l = , e) • Expected number of events : ~ 2000 • almost background free • Expected number of events :~ 4300 • Jets faking photons is large background • (signal/backgrounds = 1.62)

10. ZZ and Z production at LHC Number of events for 100 fb-1 • Z Z → l ±l± l ±l± ( l = , e) : ~780 events ( almost background free) Z  →  l± l± ( l = , e) • Z Z→ l ±l±νν ( l = , e) • Expected number of events for • PT(Z) > 150 GeV : ~ 580with 6 % background • Expected number of events : • ~ 2050 with 5 % background

11. Extracting the confidence intervalsfor TGC • Binned maximum likelihood fit to PT(V) distribution • Sensitivity lies mainly in high-end PT(Z/ ) spectrum • Investigated: • Optimal observables • Multi-variant fits • Other 1-D distributions • 95 % Confidence Intervals are derived by averaging over large “mock” ATLAS experiments -0.0035 <  < +0.0035 -0.0073 < Z < +0.0073 -0.075 <  < +0.076 0.0086 < g1Z < 0.011 -0.11 <  Z < +0.12 For 30 fb-1, systematics included.

12. Extracting the confidence intervalsfor NTGC ZZ • Multi-parameter show a large correlation (50 %) between fZ5 (fZ4) and f5 (f4) • Sensitivity for 10 fb-1 are of the order Ο(0.001)

13. Extracting the confidence intervals for NTGC • The limitsobtained for h Z,2,4 and h Z,2,4 are different because their ŝ dependence • Theoretical errors dominate the systematics • (PDF, scale) Z

14. What can we do if we observe anomalous couplings?? • Structure and scale of form-factor must be determined to have • meaningful results • This can be done at LHC by measuring bare-couplings in ŝ bin and fit to form factor parameterization

15. Summary • The study of boson pair productions at LHC provides an opportunity to probe gauge boson self-interaction in direct way • At LHC, the luminosity will allow fits using multi-dimensional distribution • NLO effects increase cross sections and tend to reduce sensitivity to TGC and NTGC, however a jet veto restores cross section to a fair approximation to born level • In case TGC or NTGC are observed, the scale and the functional behavior of the form factor can be assessed • The Triple Gauge-boson couplings can be measured at LHC at the level of 10-2 to 10-3 (order of magnitude improvement over LEP  TeVatron) • The Neutral Triple Gauge-boson couplings can be measured very accurately at LHC at the level of 10-4 to 10-7( 3 to 5 orders of magnitude improvement over LEP  TeVatron)  Become almost sensitive to radiative corrections and contributions from supersymetric models