# Presentation: 404819

## Measurement of Diboson Production at the Tevatron

**Ivor Fleck**
- Universität Freiburg
- for the CDF and DØ collaborations

**Diboson production**
**- WW**
**- WZ/ZZ**
**- W******
**- Z******
**anomalous couplings**

- - all measurements in RunII, i.e. √s = 1.96 TeV
- - (nearly) all measurements use only leptonic final states of W and Z bosons

## Diboson Production

**test of non-ablelian component **
**of SM SU(2)****L**** x U(1)****Y**
**sensitive for anomalous couplings**
**background for searches, especially Higgs **
****** ****understanding important**

**t-channel**

**couplings:**        WW, WWZ,
- forbidden:         ZZ, Z

**u-channel**

**s-channel**

- W

- W

- W

- W

****

- Z

##     WW and WWZ anomalous couplings

- SM: 5 CP conserving parameters:              
-   	(
-     ggg
- in W production, only WW couplings
- in WZ production, only WWZ couplings
- in WW production, both couplings

-    PT(W) (GeV/c)

- # Events/20 GeV/c

- /\ : form factor to avoid unitarity violation at large s

**anomalous couplings lead to excess of events **
**for large E****T****  of gauge bosons**

- V = Z or 

## WW  Production

**two triple gauge couplings present:**** **WWZ and WW
- (same final state also in Higgs production)
- observed final states:  dilepton events (ee, e,) + missing E**T**

- event selection:
- - two leptons (e or ****) with p**T** > 20 (15) GeV
- - E**T,miss** > 20 - 40 GeV
- - Z boson veto

## WW cross section 

- NLO cross section: 12.4 ± 0.8 pb
**(Campbell,Ellis, Phys.Rev. D60 (1999) 113006)**
**D****Ø****:** L**int** = 240 pb**-1**
- observe 25 events with
- 8.1 ± 0.85 ± 0.5(lum) background events
- 5.2 σ significance
**CDF:** L**int** = 184 pb**-1**
- two analyses: dilepton and lepton plus track, i.e. second lepton identified by track and
- does not have to meet lepton ID criteria
- dilepton has better sensitivity
- observe 17 events with 5.0 background events

- PhysRevLett **94**, 041803

- PhysRevLett **94**, 151801

## WW in jets plus lepton final states

- first analysis with W/Z decaying in jets
- final state from Wl and W/Zqq
- advantage: much larger branching ratio
- disadvantage: much lager backgrounds
- main background: W + 2jets production
- fit background in sideband

- fit in signal region yields:
- observed 66  78  34 events
- with 91 events signal expectation
**** < 40 pb at 95% CL

## anomalous couplings limits from WW 

- most sensitive variable for anomalous couplings:  **p****T**** of W**
- formed using lepton and E**T,miss** ()
- anomalous couplings most visible at large
- pT of W
- figure shows signal with anomalous couplings **** =****** **= 0.5

## WZ Production

- NLO cross section: 3.7 ± 0.1 pb
- trilepton final states: eee, ee,e,
- very low background, very low BR~1,5%
**D****Ø****:** L**int** ≈ 300 pb**-1** , lepton p**T**>15 GeV, missing E**T**>20 GeV,
- lepton pair mass consistent with Z mass
- observe: 3 events with 0.71 ± 0.08 background events
- and 2.04 signal expectation
- main backgrounds:
- - Z+jets: 0.35±0.02, Z+: 0.15±0.02, ZZ: 0.20±0.07
****< 13.3 pb at 95%CL
- probability of fluctuation 0.71  3 is 3.5 %, less than 3 
**hep-ex/0504019, submitted to PRL**

- -only single triple gauge coupling **WWZ**
- -LEP did not measure this vertex
-  independently of WW vertex
- -Final state not observed elsewhere

## WZ Anomalous Couplings Limits

**- inner limit from analysis at 95%CL**
**for ******** = 1.5 TeV**
**- outer limit from S-matrix unitarity**

|  |  = 1 TeV  |  = 1.5 TeV |
| --- | --- | --- |
| g1Z = Z = 0 | -0.53<Z <0.56 | -0.48<Z <0.48 |
| Z = Z = 0 | -0.57< g1Z <0.76 | -0.49< g1Z <0.66 |
| Z = 0 | -0.49< g1Z = Z < 0.66 | -0.43< g1Z = Z < 0.57 |
| Z = g1Z  = 0 | -2.0< Z < 2.4 | - |

- As no deviation from the SM expectation observed:
- set limit on anomalous couplings

## WZ/ZZ Production

**CDF:** search for ZW and ZZ combined with L**int** = 194 pb**-1**
- final states: ll , ll ll, ll l
- observe 3 events withbackground expectation of 1.0 ± 0.2 events and signal expectation of 2.3 ± 0.3 events
- limit  < 15.2 pb at 95%CL  (PhysRev **D71**,091105)
- (SM:  = 5.0 ± 0.4 pb, (ZZ) = 1.39 ± 0.10pb, (ZW) = 3.65 ± 0.26 pb)
- sensitive to neutral triple-gauge-couplings and WWZ couplings

## W Produktion

- main background source:
- W+jet events: 87.1 of 114 background events
- jet   fake rate:
- 0.4% at 7 GeV, 0.1% at 18 GeV, 0.04% >40 GeV

- jet   fake rate

- 0.4% at 7 GeV

**CDF:**** **L**int** = 200 pb**-1**, W  e, 
- E**T**( > 7 GeV, |R(l,) > 0,7
- observe 323 events with
- 114 events background expectation
- Theory (NLO):  • BR (W l) = 19,3 ± 1,4 pb
- σ • BR (W l) = 18,1 ± 3,1 pb
- PhysRevLett **94**, 211801

- 0.1% at 18 GeV

## anomalous couplings limits from W

**D0:** limits for anomalous couplings:
- 1D limits at 95% CL

********

****

**D****Ø:** L**int** ≈ 150 pb**-1**, W  e, 
- E******T** > 8 GeV, R(l > 0.7
- Theory:  • BR (W l) = 16.0 ± 0.4 pb
-  • BR (W l) =
- 14.8 ± 1.6(stat) ± 1.0(syst) ± 1.0(lumi) pb
- PhysRev  D**71**, 091108

- limits on anomalous couplings using binned likelihood on photon E**T** spectrum
- limits calculated for M**T**(W,) > 90 GeV

- only single triple gauge coupling **WW******

## Z Produktion

- Initial State Radiation

- Final State Radiation

**Z bosons**

**Final state**
**radiation**

**Drell-Yan**
**leptons**

- neutral triple gauge couplings
- (ZZZ, ZZ, Z, )
- are forbidden in SM

- new couplings would show as high E**T** bosons

## Z Production Cross Sections

**D****Ø**:  Z ee,    L**int** ~ 300 pb**-1**
- M**ll**> 30 GeV/c**2**
- E**T**() > 8 GeV, R (l) > 0.7
- MC: σ x BR(Zl**+**l**-**) = 3.9 ± 0.15 pb
**(Baur and Berger)**
- 290 events with 45 events background
- σ = 4.2 ± 0.4 (stat +syst) ± 0.3 (lumi) pb
- hep-ex/0502036

**CDF**:  Z ee,    L**int** ~ 200 pb**-1**
- M**ll**> 40 GeV/c**2**
- E**T**() > 7 GeV, R (l) > 0.7
- MC: σ x BR(Zl**+**l**-**) = 4.5 ± 0.3 pb
**(Baur and Berger)**
- 71 events with 4.9 events background
- measurement: σ = 4.6 ± 0.6 pb
- PhysRevLett **94**, 211801

## Z Anomalous Coupling Limits

- ZZ limits 2D at 95%CL

- Z limits 2D at 95%CL

- Non-SM characterized by an effective Lagrangian with 8 form-factor coupling parameters called h1V, h2V, h3V, and h4V  where V stands for **** and Z.
- CP violating h1V and h2V
- CP conserving h3V and  h4V

- SM: all couplings equal to zero

- Limits on CP conserving and CP violating couplings found to be similar,
- same for real and imaginary part

- unitarity limits

## Comparison with LEP

**LEP: 2001 results**
**2005 results slightly different, but no limits calculated**
- 0.944 < g**1****Z** < 1.035
- 0.786 < ******** < 1.009
- -0.069 < ********** **< 0.026
- limits for couplings WWZ and WW from LEP much stronger than from Tevatron

- DØ has most restrictive limits in “h**2**” and  “h4”
- LEP has most restrictive limits in “h1” and  “h3”

##                    Summary

- - cross sections in diboson production of
**- WW**
**- WZ/ZZ**
**- W******
**- Z******
- have been measured in
- leptonic final states
- - first studies of lepton plus jets final states started
- - limits on anomalous couplings
- some better than results from LEP