# Presentation: 193763

## Diboson Physics at the Tevatron

**    ****University of Illinois Chicago**
***...******on behalf of the CDF & DØ Collaborations***

**Diboson Physics at the Tevatron**

## Outline

**Tevatron Performance**
**DØ Detector**
**Diboson Production at the Tevatron**
**Cross Sections and Anomalous Couplings**
**WW**
**WZ**
**W******
**Z******
**Summary**

** ****See other related talks at this conference:**
**Tevatron W & Z Production & Asymmetries:  ****Dave Waters (Univ College London)**
**Higgs Searches at the Tevatron:  ****Lars Sonnenschein (LPNHE Paris)**

## Tevatron Collider with both DØ and CDF operating successfully
Tevatron delivered   L dt > 1.4 fb-1 
recorded  > 1 fb-1 per experiment
peak luminosities ~ 1.7  1032 cm-2 s-1
weekly integrated luminosity ~ 20 pb-1/week
Datasets used for results reported here range from ~ 0.2  to  0.8 fb-1

**Tevatron delivered  ******** ****L dt > 1.4 fb****-1**** **
**recorded  ****> ****1 fb****-1**** per experiment**
**peak luminosities ****~ 1.7 ******** 10****32**** cm****-2**** s****-1**
**weekly integrated luminosity ****~ ****20 pb****-1****/week**
**Datasets used for results reported here range from ****~**** 0.2  to  0.8 fb****-****1**

**Tevatron Performance**

**Zebra**
**mussels**

**1.72x10****32**

## DØ Detector

**Electroweak analyses make use of the full detector capabilities**

**Silicon detector and scintillating fiber tracker in 2.0 T solenoidal field**
**Coverage up to |********| ******** 2.5**
**Liquid Argon/Uranium calorimeters**
**Central and two forward calorimeters**
**Stable, uniform response, radiation hard**
**Hermetic with coverage up  to |****η****| = 4.2**
**Muon System**
**Coverage up to |********| ******** 2.0**
** ****Three layers of scintillators and drift tubes **
**Central and Forward **
**A layer – inside 1.8T toroid magnet**
**Shielding reduces backgrounds by 50-100x**
**Three Level Trigger**
**L1/L2/L3 ~ 1800/1000/50 Hz**

## Studying Dibosons at the Tevatron

**Measure cross sections and anomalous couplings**
**Probe non-Abelian nature of SU(2)****L********U(1)****Y ******** gauge boson self-interactions **
**Observation of events above Standard Model expectation would indicate new physics**
**Excursions from the SM can be described via effective Lagrangian:**

**where**

**In SM:**

**Determine deviation from SM values:**

## Studying Dibosons at the Tevatron

**Diboson production cross section is small**
**10****-2**** – 10****-4**** of single boson production cross section**
**Look for final states with W/Z decaying to e or ******
**Smaller branching ratio but cleaner signal**
**Diboson production is an important background to other high p****T**** processes**
**Top pair, Higgs, SUSY**

## Sensitive to WWZ / WW couplings
Dilepton channel provides cleanest signature: ee,  or e accompanied by missing ET
Main background processes: W+j/, dijet, Drell-Yan, top pairs, WZ, ZZ
Theory prediction for production cross section is 12.0-13.5 pb (J. Ohnemus, PRD 441403 (1991); PRD 50, 1931 (1994); J.M. Campbell and R.K. Ellis, PRD 60, 113006 (1999))  accessible at Tevatron Run II already with a couple of 100 pb-1.

**Dilepton channel provides cleanest signature: ee, ******** or e******** accompanied by missing E****T**
**Main background processes: W+j/********, dijet, Drell-Yan, top pairs, WZ, ZZ**
**Theory prediction for production cross section is ****12.0-13.5 pb**** *****(J. Ohnemus, PRD 441403 (1991); PRD 50, 1931 (1994); J.M. Campbell and R.K. Ellis, PRD 60, 113006 (1999))***** ******** ****accessible at Tevatron Run II already with a couple of 100 pb****-1****.**

**WW Production Cross Section**

## Event Selection
 2 opposite-signed leptons (e,) w/ pT>20 GeV
 Missing transverse energy (MET) > 25 GeV 
 If both leptons are same flavor and  76<Mll<106, then require MET/(ET) > 3.0
  (MET, nearest l) > 0.3 if MET < 50 GeV 
 0 jets (ET>15 GeV and |η|<2.5) 
Observe 95 events with an expected signal and background of 52.4±4.3 and 37.8±4.8 respectively

**Event Selection**
** ****2 opposite-signed leptons (e,********) w/ p****T****>20 GeV**
** ****Missing transverse energy (MET) > 25 GeV **
** ****If both leptons are same flavor and  76<M****ll****<106, then require MET/********(********E****T****) > 3.0**
** ******** ****(MET, nearest l) > 0.3 if MET < 50 GeV **
** ****0 jets (E****T****>15 GeV and |****η****|<2.5) **
**Observe ****95 events ****with an expected signal and background of ****52.4±4.3**** and ****37.8±4.8**** respectively**

**CDF: WW********ll+MET Cross Section**

****** ****L dt = 825 pb****-1**

******=13.6********2.3(stat)********1.6(sys)********1.2(lum) pb**

## DØ : WWll+MET Cross Section

**σ****(WW) = 13.8 ****+4.3**** ****-3.8****(stat) ****+1.2**** ****-0.9**** (sys) ± 0.9 (lumi) pb**

**Look for two oppositely charged leptons (e, ********) plus missing ET **
**DØ and CDF selection for WW signal are similar **
**Found ****25**** ****(6 ee, 4 ********, 15 e********) ****candidates in ~237pb****-1**
**Expected background ****8.1 ± 0.6 (stat) ± 0.6 (sys) ± 0.5 (lumi)**
**First 5.2******** observation of WW production at the Tevatron**

**PRL 94, 151801 (2005)**

**Both CDF and DØ measurements of WW cross section are consistent with the SM expectation  **

## WZ Production

** ****Sensitive to purely WWZ vertex**
**    ****(WW is sensitive to WWZ /WW********)**
** ****WZ production unavailable at e****+****e****-**** colliders**

** ****Search for WZ production in 3 leptons (eee,ee********, e********, ********) + missing E****T**
** ****Distinct, but rare signature: **
** ********(ppbar********WZ) = 3.7 ******** 0.1 pb *****(J.M. Cambell and R.K. Ellis, PRD 60, 113006 (1999))***
*** *****Branching fraction ~1.5%**
** ****Background processes: Z+jet(s), ZZ, Z********, ttbar production**

## CDF: W±Zol±l+l-+ MET Cross Section

****** ****L dt = 825 pb****-1 **
**Event Selection**
**- 3 leptons (e,********) w/ p****T****>20, 10, 10 GeV**
**- 76 < M****ll**** < 116 GeV**
**- MET > 25 GeV**
**Observe ****2 events**** with an expected signal and background of ****3.7±0.3 ****and**** 0.9±0.2**** respectively**

******(WZ) < 6.34 pb (95% C.L.)**

## DØ : W±Zol±l+l-+ MET Cross Section

-  channel

****** ****L dt = 300 pb****-1 **
**Observed ****3 events**** (1eee, 2********) with an expected signal and background of ****2.0±0.2 ****and**** 0.7±0.1**** respectively**
**Prob (3 events | 0.7 bkg) = 3.5%**

**PRL 95, 141802 (2005)**

******=1.5 TeV**

**2D limit at 95 % C.L.**

**1 D limits at 95% C.L. for ********=1 TeV:**
**           ****-0.53 < ********Z   ****<0.56**
**           ****-0.57 < ********g****Z ****< 0.76**
**           ****-2.0   < ********Z ****<2.4**

**Best limits if ********g****Z****, ********Z**** and ********Z**** from direct, model-independent measurement**

**Anomalous Couplings limits:**

****** ****< 13.3 pb at 95 % C.L.  **
****** ****= 4.5****+3.8****-2.6****(stat+sys) pb**

## CDF:  WW/WZ ljj Cross Section

**Higher branching fraction, but large W+jets background **
**Event Selection**
**Isolated Lepton p****T****>25 GeV**
****** ****2 jets w/ E****T****>15 GeV**
**MET > 25 GeV**
**Dijet mass 32-184 GeV**

******(WW+WZ) < 36 pb at 95% C.L.**

## CDF:  WW/WZ ljj Anomalous Couplings

**W transverse momentum most sensitive for AC limits**
**- formed from the lepton p****T**** and the MET (neutrino) **
**Full spectrum fitted for the AC hypothesis and used for setting the limits**

**Measured anomalous couplings limits, 1D,  95% C.L. **
**Assume equal TGC for          Z and ********, ********=1.5 TeV:**

**   ****-0.51 < Δ κ < 0.44**
**   ****-0.28 < λ < 0.28**

## W Production

**Sensitive to WW******** coupling**
**Study final states with W decaying to electron or muon    –    events with  e/******** + ******** + missing E****T****.**
**Main background from W+jets and Z+X (lepton from Z lost/mis-identified).**
**Efficient photon identification crucial**
**E****T  ****> 7 GeV (CDF),   E****T  ****> 8 (D0) GeV,**
**|********| < 1.0 (CDF),   |********| < 1.1 (D0) GeV  **
**Highest sensitivity to Anomalous Coupling at high photon E****T**** and M ****T****(W,******** )**

**Three diagrams at tree level**

**FSR photon in W******** is sort of “background” for studying AC  – apply ********R(lepton,********) > 0.7**** to suppress FSR contribution**
**Theoretical cross section ****~16-19 pb****      *****(U.Baur, E.L. Berger, PRD 41, 1476 (1990)) ***

## W Production

**Channel**          ee
****** ****L dt, pb****-1****         162                  134                       202                      192   **
**W********                      51.2 ******** 11.5       89.7 ********13.7          126.8 ******** 5.8          95.2 ******** 4.9**
**Total Bkgrd       60.8 ******** 4.5        71.3 ******** 5.2            67.3 ******** 18.1          47.3 ******** 7.6**
**# Observed        112                    161                     195                      128**** **
**A*********                     2.3%                 4.4%                  3.3%                  2.4%**
*******BR, pb         13.9********2.9********1.6   15.2********2.0********1.1         19.4********2.1********2.9      16.3********2.3********1.8**

**DØ**

**CDF**

** ****Cross section from combined electron and muon channels**

**DØ:**** **

**CDF:**

***PRD 71, 091108 (2005)***

***PRL 94, 041803 (2005)***

- SM expectation  : 16.0  0.4 pb

- SM expectation: 19.3  1.4 pb

## W: AC limits from DØ

******=2 TeV**

**2D limit at 95% CL**

** ****Photon E****T**** sensitive to presence of anomalous coupling **

**1D limits at 95% C.L. for ********= 2 TeV:**
**    ****-0.88 < ************<0.96**
**     ****-0.20 <************<0.20**

***PRD 71, 091108 (2005)***

** ****Important improvement with respect to Run I**

## Z Production

**Z******** Production**

**ISR and FSR contribution at tree level, ****but no ZZ******** or Z******** vertices in SM**

**Study final states with Z decaying to ee or ********  **
**events containing  ee/******** + ******
**Main background from Z+jet(s) where jet mis-identified as ********.**
**Theoretical cross section  ****~4-5 pb****      *****(U.Baur, T. Han****** and J. Ohnemus, PRD 57, 2823 (1998)) ***

## Z Production

**Channel                 ee********                 ********                   ee********                        ******** **
****** ****L dt, pb****-1       ****     324                   286                  202                        192 **
**SM Z********                109 ******** 7            128 ******** 8             31.3 ******** 1.6              33.6 ******** 1.5**
**Total Bkgd        23.6 ******** 2.3        22.4 ******** 3.0         2.8 ******** 0.9                2.1 ******** 0.7**
**# Observed        138                  152                    36                           35****  **
**A*********                     11.3%             11.7%               3.4%                      3.7%**
*******BR, pb                -                        -                   4.8********0.8********0.3           4.4********0.8********0.2**

**DØ**

**CDF**

** ****Cross section from combined electron and muon channels**

***PRL 94, 041803 (2005)***

***PRL 95, 051802 (2005)***

**DØ:**** **

**CDF:**

- SM expectation  : 3.9  0.2 pb

- SM expectation  : 4.5  0.3 pb

## Z: AC limits from DØ

**Z********: AC limits from DØ**

******=1 TeV**

**2D limit at 95% C.L.**

** ****Photon E****T**** sensitive to  presence of anomalous coupling **

** ****Most stringent limits to date**

***PRL 95, 051802 (2005)***

**Effective Lagrangian has 8 coupling parameters:**
**h****V****10****, h****V****20****, h****V****30****, h****V****40**** (V=Z,********)**
**All of these = 0 in SM**

## Summary

**Most of Run I measurements re-established; many improved and new Run II results:**
**Significant number of diboson candidate events**
**Good agreement with the SM**
**measured ****(WW) using the dilepton decay channel**
**first evidence of WZ production**
**Model independent limits on WWZ anomalous coupling using WZ events.**
**WWZ/WW******** anomalous coupling limits from WW/WZ********l********jj final states**
**Measured W******** and Z******** production cross sections and extracted corresponding anomalous coupling limits **
**More to come:**
**Lots of more data to come/analyze**
**Expect to observe Radiation Amplitude Zero in W******** production**
**Measure Quartic couplings**

## CDF: WW e Candidate

## CDF: WZ  eee Candidate