1 1/5/2007Beijing, Zhengguo Zhao Studies of Diboson Production and Triple Gauge Boson Couplings Zhengguo Zhao University of Michigan, Ann Arbor, USA 9 th ACFA Physics and Detector Workshop& ILC GDE Meeting Feb. 4-7, 2007, Beijing

2 1/5/2007Beijing, Zhengguo Zhao Introduction Recent Tevatron results Effort from ATLAS/CMS Summary Outline

3 1/5/2007Beijing, Zhengguo Zhao Introduction

4 1/5/2007Beijing, Zhengguo Zhao Diboson Production at Hadron Collider V3V3 V1V1 V2V2 q q q’ V2V2 V1V1 q q V2V2 V1V1 LO Feynman diagram, V 1, V 2, V 3 = Z, W,   WW, ZW, ZZ, W  Production cross section predictable Only s channel has three boson vertex, which manifest the gauge boson coupling SM: Pure neutral vertexes ZZZ, ZZ  are forbidden (Z/  carry no charge and weak isospin that needed for gauge bosons couple) Only charged couplings WW , WWZ are allowed

5 1/5/2007Beijing, Zhengguo Zhao Triple Gauge Boson Couplings Characterized by an effective Lagrangian, parameterized in terms of coupling parameters for new physics C, P and CP symmetry conservation, 5 free parameters: - , Z : grow with s, big advantage for LHC -     ,  g 1 Z = g 1 Z -1,  Z =  Z -1: grow with  s Tree level SM:  = Z =    g 1 Z =  Z = 0

6 1/5/2007Beijing, Zhengguo Zhao Production of WZ, WW s-channel dominates, Sensitive only to WWZ coupling Clean signal eee, ee ,  e,  3 isolated high p T leptons with large E T (miss) q q’ W W Z l+l-l+l- l l l Sensitive to WWZ and WW  Clean signal ee, , e  2 isolated high p T leptons with opposite charge and large missing E T s-channel t-channel

7 1/5/2007Beijing, Zhengguo Zhao Production of W , ZZ l+l-l+l- l’ + l’ - q qbar q’ s channel suppressed by O(10 -4 ) Only t-channel at tree level, 4 isolated high p T leptons from the Z pair decays Clean signal eeee, ee , , almost bkg free Isolated high p T lepton (e,  ) large missing E T Isolated  Main bkg: W+jet, Z+  z z

8 1/5/2007Beijing, Zhengguo Zhao Diboson as background for searches ZZ H

9 1/5/2007Beijing, Zhengguo Zhao Motivations Measure diboson production  and TGCs Explore none-Abelian SU(2)  U(1) gauge structure of SM Probe new physics if production cross section, or TGCs deviate from SM prediction  complementary to direct search for new physics Understand the backgrounds of many important physics analyses Search for Higgs, SUSY, graviton and study of ttbar

10 1/5/2007Beijing, Zhengguo Zhao Recent Results from Tevatron

11 1/5/2007Beijing, Zhengguo Zhao Experiments at Tevatron

12 1/5/2007Beijing, Zhengguo Zhao CDF & D0 Detectors CDF Run II Upgrades: New Silicon Vertex Detector (SVX) and faster tracking drift chamber (COT) New scinitllating-tile end-plug calorimeters Increased ηφ coverage for muon detectors New Scintillator Time-Of-Flight system D0 Run II Upgrades: New silicon (SMT) and Fiber (CFT) trackers, placed in new 2T Solenoid Calorimeters supplemented with Preshower detectors Significantly improved Muon System

13 1/5/2007Beijing, Zhengguo Zhao

14 1/5/2007Beijing, Zhengguo Zhao WW Production at Tevatron L(pb -1 )N obs /N b  (pb) D /9.8 CDF82595/ ±2.3(stat) ±1.6(sys) ±0.9(lum ) NLO12±0.8

15 1/5/2007Beijing, Zhengguo Zhao WW+WZ  l jj 1 lepton with p T >25GeV, E T >25 GeV ≥2 jets with p T > 15 GeV  (WW+WZ) < 36 95% CL

16 1/5/2007Beijing, Zhengguo Zhao WW+WZ  l jj anomalous coupling from CDF Select 56 < m jj < 112 peak region Minimize likelihood for p T of W(l,E T ) <  < 0.44, < < 0.28

17 1/5/2007Beijing, Zhengguo Zhao WZ  l ll 3 leptons (e,  ) - CDF: p T (leading) >20 GeV, p T (others) > 10 GeV - D0: p T (all) > 15 GeV m(l + l - ) within m Z window E T is used to suppress the bkg of Z+jet/  q q’ W W Z l+l-l+l- l

18 1/5/2007Beijing, Zhengguo Zhao WZ  l ll results L(pb -1 )N obs  (pb) D ± ± 0.2 CDF ± ± 0.2< 6.3 (95% CL) NLO3.7 ± 0.1

19 1/5/2007Beijing, Zhengguo Zhao For L = 300 pb -1 data, expect 2 signal and 1 background events. Observed 3 events. TGCs are determined to be WWZ Anomalous Coupling

20 1/5/2007Beijing, Zhengguo Zhao  (W  l ) from D0 ChannelL(pb -1 )  (pb) W  e ± 0.49 ± 0.19 W  ± 0.49 ± 0.2 SM3.21±0.08

21 1/5/2007Beijing, Zhengguo Zhao Tevatron Results on Dibson Studies Tevatron results consistent with SM prediction

22 1/5/2007Beijing, Zhengguo Zhao Diboson Studies from ATLAS and CMS

23 1/5/2007Beijing, Zhengguo Zhao The LHC Experiments 4.5 km

24 1/5/2007Beijing, Zhengguo Zhao Collisions at the LHC N = L ×  (pp) = 10 9 Mostly low p t events (soft) events Interesting high p t events are rare New physics rate ~ Hz  event selection: 1 in 10,000,000,000, bunch/beam TeV separation: 7.5 m (25 ns) 40 MHz crossing rate proton / bunch 10 9 pp collision/s (superposition of 23 pp interactions per bunch crossing: pile-up)

25 1/5/2007Beijing, Zhengguo Zhao Inner detector Si pixels and strips Transition Radiation Detector (e/  separation)  /p T ~ 0.05% p T (GeV)  0.1%; |  | < 2.5, B=2 T(central solenoid) Hadron Calorimeter Fe/scintillator (central), Cu/W-LAr (fwd)  /E ~ 50%/√E(GeV)  3% |  |<3 Muon spectrometer air-core toroids, MDT+RPC+TGC  /p T ~ 2-7 % |  | < 2.7, |  |<2.5 ( precision phys.) EM Calorimetry Pb-LAr  /E ~ 10%/√E(GeV)  1% |  |<3.2, |  | < 2.5 (fine granularity) Length: ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons Channels: ~ 10 8 L cable : ~ 3000 km

26 1/5/2007Beijing, Zhengguo Zhao EM calorimeter: Lead tungstate  /E = 5% / √E (GeV)  2% Magnet solenoid 4 T Hadron Calorimeters Barrel & Endcap: Cu/Scintillating sheets s/E = 65% /√E (GeV)  5% Inner Detector: Silicon pixels and strips Muon spectrometer DT+CSA+RPC

27 1/5/2007Beijing, Zhengguo Zhao LHC Expectations for the TGCs LHC High CM energy  larger  High luminosity  high statistics High sensitivity Expected to be ~10 improvement on LEP/Tevatron <  < < Z < <   < <  Z < <  g 1 Z < Predictions for TGCs at 95% C.L. for L=30 fb -1 (inc syst)

28 1/5/2007Beijing, Zhengguo Zhao MC Data for Diboson Studies(ATLAS) ProcessMC dataProcessMC data ZW +  2e/2  + X ttbar  l +x 1.96  10 5 ZW -  2e/2  + X  ee/   2.30  10 6 ZZ  4e, 4 , 2e2  W  e/  t  10 6 WW  l  x W+jets  l  x 1.59  10 6 ZZ(pythia)  4 l ( e,  4.66  10 4 Z+jet  ee/  5.80  10 6 Zbb  4 l 4.99  10 4 DY Z /   l + l - (e,  ) 1.67  10 7 Z   ll ( e,  2.50  10 4 Data produced in ATLAS GRID, and Michigan ATLAS computer cluster Background (pythia 6.2), 10 6 ~ 10 7 for Z+jet, W+jet, DY, W+jet and W  lepton Signal events produced by (v2.3)–Jimmy, W/Z width effect is not included (v3.1 has included width)

29 1/5/2007Beijing, Zhengguo Zhao P t (l + l - ) WW ZZ ZZ Zjet cut P t (l + l - ) cut to reject fate events Vector∑E t (jet) tt WW cut Vector∑E t (jet) to reject jet M Z(ee) M Z(  ) -M W(e ) WZWW

30 1/5/2007Beijing, Zhengguo Zhao N eee N ee  N  e N  N total (1fb -1 ) N signal N bkg S/B ZW Signal and Backgrounds(ATLAS) (for 1 fb -1 data) 47.4% 42.9% 7.7% 2.1%

31 1/5/2007Beijing, Zhengguo Zhao WW Signal and Background (ATLAS) (for 1 fb -1 data) ProcessN ee N  NeNe N total WW  l +X ( l =e,  ) Total background S/B % 38.4% 8.3% 3.4% 2.6%

32 1/5/2007Beijing, Zhengguo Zhao M(e + e - ) M(  +  - ) P t (e + e - ) Pt(+-)Pt(+-) Invariant Mass and Pt Distributions for ZZ 13 events candidates Background free with current statistics For 1 fb -1 data at ATLAS

33 1/5/2007Beijing, Zhengguo Zhao Comparison of the efficiencies of BDT/ANN ANN BDT Background efficiency Signal efficiency

34 1/5/2007Beijing, Zhengguo Zhao Signal and Background Samples (CMS) tt(2l) generated with TopReX, Zbb with CompHEP, all others with Pythia  ×Brk-factor ZZ(4e)18.7 fb1.3 WZ(3l, l=e, ,  )1.6 pb1.92 ttbar(2l)62.3 pb1.6 Z(ee)bb60.3 pb2.4 Z(  )bb60.3 pb2.4 ttbar(4e)194 fb1.6 ZZ(2e2  )32.3 fb1.35 Signal Main bkg

35 1/5/2007Beijing, Zhengguo Zhao WZ → 3l Expected Signal & Background M(l + l - ) after all cuts 4 channels combined (3e,2e1 ,2  1e,3  ) Presence of peaking backgrounds - Zbb - ZZ (irreducible) High significance in the first 1 fb -1 L = 1 fb -1 Expected signal and background yields for 1 fb -1

36 1/5/2007Beijing, Zhengguo Zhao ZZ → 4e Expected Signal & Background M(e + e - ) after all cuts (2 entries per event) L = 10 fb -1 Nearly background free! Expected signal and background yields for 1 and 10 fb -1

37 1/5/2007Beijing, Zhengguo Zhao 0 WZ and ZZ Discovery Potential (CMS) ZZ → 4e signal significance WZ → 3l signal significance 5  discovery ZZ: ~1 fb -1 WZ: ~150 pb -1 Ideal simulation miscalibration Systematic effects Ideal simulation miscalibration Systematic effects

38 1/5/2007Beijing, Zhengguo Zhao Summary D0 and CDF have been actively studies diboson production and the corresponding TGCs. The results so far are consistent with SM predictions. WZ, WW and ZZ signals are expected to be established at CMS and ATLAS with 100pb -1 ~1fb -1 Anomalous gauge boson coupling can be probed with a few fb -1 data Advanced techniques (BDT, ANN) can significantly improve the S/B. To improve the TGCs with LHC data, it’s crucial to correctly build the TGCs into event generators

39 1/5/2007Beijing, Zhengguo Zhao Anomalous Coupling and Form Factor TGCs manifest in - cross section enhancement - high p T (V=Z,W,  ) - production angle Cross section increase for coupling with non-SM values, yielding large cross section at high energies that violating tree level unitarity  form factor scale s: subprocess CM energy.  : form factor scale

40 1/5/2007Beijing, Zhengguo Zhao Diboson Production Cross Section Tevatron LHC

41 1/5/2007Beijing, Zhengguo Zhao Boosted Decision Trees (BDT) and Artificial Neural Network (ANN) e-boost ANN ATLAS