# Presentation: 239048

## Di-Boson Production at Hadron Colliders 

- Beate Heinemann, University of Liverpool

- The Standard Model and Beyond
- Tevatron and the LHC
- 
- W and Z
- WW, WZ, ZZ
- Wh
- Summary and Outlook

- Northwestern University - Seminar Oct. 4th 2004

## ?

- Di-Boson Production: What’s that?

- Associated production of ≥ 2 gauge bosons of electroweak interaction

- Something happens

- pp->	, W, Z, 	WW, WZ, ZZ
- 	+ X

- Beate Heinemann - Northwestern University

- 10-04-2004

## The Standard Model of Particle Physics

- 3 generations of quarks and leptons interact via exchange of gauge bosons:
- Electroweak SU(2)xU(1): W, Z, 
- Strong SU(3):                  g
- Symmetry breaking caused by Higgs field
- Generates Goldstone bosons
- Longitudinal degrees of freedom for W and Z
-  3 massive and one massless gauge bosons

| Particle | Mass (GeV/c2) | Force |
| --- | --- | --- |
| Photon () | 0 | Electroweak |
| W± | 80.450 | Electroweak |
| Z0 | 91.187 | Electroweak |
| Gluons (g) | 0 | Strong |

- Gauge Bosons

- Higgs Boson

- Vacuum quantum numbers (0++)
- Couples to mass

- Beate Heinemann - Northwestern University

- 10-04-2004

## Precision measurements of 
MW  =80.412 ± 0.042 GeV/c2
Mtop=178.0   +- 4.3    GeV/c2
Prediction of higgs boson mass within SM due to loop corrections
Most likely value: 114 GeV
Direct limit (LEP): mh>114.4 GeV 

- The Higgs boson: what do we know?

- Precision measurements of
- MW  =80.412 ± 0.042 GeV/c2
- Mtop=178.0   +- 4.3    GeV/c2
- Prediction of higgs boson mass within SM due to loop corrections
- Most likely value: 114 GeV
- Direct limit (LEP): mh>114.4 GeV

- mW depends on mt and mh

- Beate Heinemann - Northwestern University

- 10-04-2004

## Precision measurements of 
MW  =80.412 ± 0.042 GeV/c2
Mtop=178.0   +- 4.3    GeV/c2
Prediction of higgs boson mass within SM due to loop corrections
Most likely value: 114 GeV
Direct limit (LEP): mh>114.4 GeV 

- Precision measurements of
- MW  =80.412 ± 0.042 GeV/c2
- Mtop=178.0   +- 4.3    GeV/c2
- Prediction of higgs boson mass within SM due to loop corrections
- Most likely value: 114 GeV
- Direct limit (LEP): mh>114.4 GeV

- The Higgs boson: what do we know?

- Better prediction with expected
- improvements on W and top
- mass precision

- Beate Heinemann - Northwestern University

- 10-04-2004

## Higgs Production: Tevatron and LHC

- Dominant Production: gg-> H, subdominant: HW, Hqq

- LHC

- Tevatron

- Beate Heinemann - Northwestern University

- 10-04-2004

## Higgs boson decay

- Depends on Mass
- M<130 GeV:
- bb dominant
-  subdominant
-  used at LHC
- M>130 GeV
- WW dominant
- ZZ cleanest

- => di-boson decays most promising!

- Beate Heinemann - Northwestern University

- 10-04-2004

## What if there is no Higgs?

- WLWL cross section would violate unitarity since amplitude perturbative expansion in energy (s): ~s2/v2 + s4/v4...
- Need either a Higgs boson with mh<1 TeV or some new physics (e.g. SUSY, Technicolor)
- Tevatron and LHC probe relevant scale of 100 GeV - 1 TeV!

- => We will find something (higgs or more extraodinary) in the next 10 years!

- Beate Heinemann - Northwestern University

- 10-04-2004

## Beyond the Standard Model

- Why not the Standard Model?
- Hierarchy problem: mh<<mPl  new physics at TeV scale
- Most Dark Matter in our universe unaccounted for
- No unification of forces ...+ many more
- What is beyond the Standard Model?
- Supersymmetry (SUSY):
- rather complex (>100 parameters)
- Extra Dimensions
- Techni- and Topcolor
- Little Higgs
- Extended Gauge Groups or Compositeness:
- Z’, excited fermions, leptoquarks, ...

- New particles heavy 
- At high energy colliders
-  Direct production
-  Indirect contributions

- Beate Heinemann - Northwestern University

- 10-04-2004

## Tevatron Run II

- Upgrade completed in 2001
- Accelerator:
- Experiments CDF and D0:
- New tracking systems
- New RO electronics+trigger
- Many other substantial new components and upgrades
- Data taking efficiency>85%
- Will mostly focus on CDF but show also some D0 results

|  | √s(TeV) | t(ns) | L(cm-2 s-1) |
| --- | --- | --- | --- |
| Run I | 1.8 | 3500 | 2.5x1031 |
| Run II | 1.96 | 396 | 1.0x1032 |

- Beate Heinemann - Northwestern University

- 10-04-2004

## Tevatron Performance

**∫ ****Ldt= 680 pb****-1**

**Max. L=1.03x10****32**** cm****-2**** s****-1**

- Beate Heinemann - Northwestern University

- 10-04-2004

## Tevatron Performance

**∫ ****Ldt= 680 pb****-1**

**Max. L=1.03x10****32**** cm****-2**** s****-1**

- Beate Heinemann - Northwestern University

- 10-04-2004

## Tevatron: Expected Performance

- Beate Heinemann - Northwestern University

- 10-04-2004

## pp-collider at CERN
Center-of-mass energy: 
		14 TeV
Starts operation in 2008
3 years “low” luminosity: 	10 fb-1 /yr
High luminosity: 		100 fb-1 /yr

- pp-collider at CERN
- Center-of-mass energy:
- 		14 TeV
- Starts operation in 2008
- 3 years “low” luminosity: 	10 fb-1 /yr
- High luminosity: 		100 fb-1 /yr

- Beate Heinemann - Northwestern University

- 10-04-2004

## ?

- Di-Boson Production: Why?

- Something happens

- SM precision tests
- SUSY
- Large Extra Dimensions
- Higgs
- Run I anomalies

- Precision of Run I measurements
- limited

- Beate Heinemann - Northwestern University

- 10-04-2004

## SM couplings small
Ideal for New Physics Searches:
Large Extra Dimensions:
Graviton exchange?
Present sensitivity about 900 GeV
Run II: sensitivity about 2 TeV
Higgs ->
BR small in SM 9but discovery channel at LHC)
Enhancements predicted in some BSM theories (“bosophilic Higgs”)
Extraodinary events with 2 
    photons and transverse 
    momentum imbalance(?)

- SM couplings small
- Ideal for New Physics Searches:
- Large Extra Dimensions:
- Graviton exchange?
- Present sensitivity about 900 GeV
- Run II: sensitivity about 2 TeV
- Higgs ->
- BR small in SM 9but discovery channel at LHC)
- Enhancements predicted in some BSM theories (“bosophilic Higgs”)
- Extraodinary events with 2
-     photons and transverse
-     momentum imbalance(?)

- G

- G, h

- Example LHC signal (CMS: 3 yrs)

- Beate Heinemann - Northwestern University

- 10-04-2004

## Di-Photon Cross Section

- Select 2 photons with Et>13 (14) GeV
- Statistical subtraction of BG (mostly 0)
- Data agree well with NLO
- PYTHIA describes shape (normalisatio off by factor 2)

- M (GeV)

- 

- Beate Heinemann - Northwestern University

- 10-04-2004

## Randall-Sundrum Graviton

- Analysis:
- D0: combined ee and 
- CDF: separate ee,  and 
- Data consistent with background
- Relevant parameters:
- Coupling: k/MPl
- Mass of 1st KK-mode
- World’s best limit:
- M>785 GeV for k/MPl=0.1

- 345 pb-1

- Beate Heinemann - Northwestern University

- 10-04-2004

## D0: Non-SM Light H

- D0: Non-SM Light H

- Some extensions of SM contain Higgs w/ large B(H)
- Fermiophobic Higgs : does not couple to fermions
- Topcolor Higgs : couples to only to top (i.e. no other fermions)
- Important discovery channel at LHC

- Event selection
-  2 Isolated ’s with
- pT > 25 GeV
- ||<1.05 (CC) or 1.5<||<2.4 (EC)
-  pT () > 35 GeV (optimised)
- BG: mostly jets faking photons
- Syst. error about 30% per photon!
- Estimated from Data

- ∫Ldt=191 pb-1

- Central-Central

- Central-Forward

- Beate Heinemann - Northwestern University

- 10-04-2004

## Non-SM Light Higgs H

- Perform counting experiments on optimized sliding mass window to set limit on B(H) as function of M(H)

- Non-SM Light Higgs H

- Beate Heinemann - Northwestern University

- 10-04-2004

## Run I: 
found 1 event with 2 photons, 2 electrons and large missing Et
SM expectation 10-6 (!!!)
Inspired SUSY model where SUSY is broken at low energies: “Gauge Mediated Symmetry Breaking” 
Run II:
Any new such event would be exciting! 

- Run I:
- found 1 event with 2 photons, 2 electrons and large missing Et
- SM expectation 10-6 (!!!)
- Inspired SUSY model where SUSY is broken at low energies: “Gauge Mediated Symmetry Breaking”
- Run II:
- Any new such event would be exciting!

- +X: more exclusive channels

- Beate Heinemann - Northwestern University

- 10-04-2004

## GMSB: +Et

- Assume 01 is NLSP:
- Decay to G+
- G light M~O(1 keV)
- Inspired by CDF ee+Et
-     event
- D0 (CDF) Inclusive search:
- 2 photons: Et > 20 (13) GeV
- Et > 40 (45) GeV

|  | Exp. | Obs. | M(+1) |
| --- | --- | --- | --- |
| D0 | 2.5±0.5 | 1 | >192 GeV |
| CDF | 0.3±0.1 | 0 | >168 GeV |

- ~

- ~

- Beate Heinemann - Northwestern University

- 10-04-2004

## SM Theory of W/Z+ Production

- SM Theory of W/Z+ Production

- Tree-level diagram of

- Tree-level diagram of

- These diagrams interfere and decay products are detected in the detector

- Beate Heinemann - Northwestern University

- 10-04-2004

**Notes:**
Indicate W->lnu

## Anomalous Couplings

- LEP results hard to beat but complementary:
- higher energy
- WW vs WWZ

- Existence of WW vertex indirectly seen at LEP

- Beate Heinemann - Northwestern University

- 10-04-2004

- W, Z: beyond the Standard Model

- Any anomalous couplings:
- Increase in cross-section
- Excess of events in high Et region
- Physics beyond SM (e.g. excited W/Z,excited e*):*
- Increase in cross-section
- Excess of events in high Et region
- Excess of events in high 3 body Mass region

- Beate Heinemann - Northwestern University

- 10-04-2004

**Notes:**
DEFINE DR!

## W+ Results

|  | Electron  | Muon |
| --- | --- | --- |
| W+  MC  | 126.8 ± 5.8  | 95.2 ± 4.9 |
| W+jet BG | 59.5 ± 18.1 | 27.6 ± 7.5 |
| W+  (tau) | 1.5 ± 0.2 | 2.3 ± 0.2  |
| Z+  | 6.3 ± 0.3 | 17.4 ± 1.0 |
| Total SM  | 194.1 ± 19.1 | 142.4 ± 9.5 |
| data | 195 | 128 |
| *BR | 19.4 ± 2.1 ± 2.9 | 16.3 ± 2.3 ± 1.8 |

- Combined: *BR=18.1  1.6(stat)  2.4(sys)  1.2(lumi) pb

- SM: 19.3±1.4 pb

- Beate Heinemann - Northwestern University

- 10-04-2004

**Notes:**
Update numbers

## Z Results

|  | Electron (±sys) | Muon (± sys) |
| --- | --- | --- |
| Z+ MC  | 30.9 ± 1.6 | 33.2 ± 1.5 |
| Z+jet BG | 2.8 ± 0.9 | 2.1 ± 0.7 |
| Total SM  | 33.7 ± 1.8 | 35.3 ± 1.6 |
| data | 35 | 35 |
| *BR | 4.7 ± 0.8 ± 0.3 | 4.5 ± 0.8 ± 0.2  |

- Combined: *BR=4.6 ± 0.5(stat) ± 0.2(sys) ± 0.3(lumi) pb

- SM: 4.5±0.3 pb

- Beate Heinemann - Northwestern University

- 10-04-2004

**Notes:**
Upper cut of 120 GeV

## Ratio of Cross Sections

- Inclusive W and Z production:
- Recent CDF result (hep-ex/0406078)
- (Z)xBR(Z->ll) / (W)xBR(W->lv)                    =10.150.21%
- Wg and Zg Production for Et>7 GeV:
- (Z)xBR(Z->ll) / (W)xBR(W->lv) = 4.6/18.1 = 25+-5 %
-  =>  Expected due to
- interference of t-, u-, and s-channel diagrams in W
- No s-channel diagram in Z=> no interference

- =>Indirect Evidence for WWg vertex!

- Beate Heinemann - Northwestern University

- 10-04-2004

## Photon Et

- Data agree well with SM
- Will be used to extract WW and ZZ couplings

- Beate Heinemann - Northwestern University

- 10-04-2004

## Mass

- Data agree well with prediction: no sign of any signal of high mass
- Can be used to constrain e.g. W* and Z*

- Beate Heinemann - Northwestern University

- 10-04-2004

## WW: Why?

- Never observed at hadron colliders with any significance (run 1: 5 observed / 1.2+-0.3 BG)
- SM test
- Higgs -> WW

- Beate Heinemann - Northwestern University

- 10-04-2004

## WW Cross Section

- Beate Heinemann - Northwestern University

- 10-04-2004

## WW: Decay Channels

- Beate Heinemann - Northwestern University

- 10-04-2004

## WW: Cross Section Results

- 2 independent analysis (high purity vs high acceptance) =>Consistent results
- First significant signal: significance>3
- Agree with theor. prediction: NLO = 12.5+-0.8 pb

- Beate Heinemann - Northwestern University

- 10-04-2004

## WW Candidate Event

- Beate Heinemann - Northwestern University

- 10-04-2004

## WW kinematic distributions

- Kinematic properties as expected from SM WW production
- => use the data to constrain new physics

- Beate Heinemann - Northwestern University

- 10-04-2004

## H  WW(*)  l+l- 

- Higgs mass reconstruction not possible due to two neutrions:
- Dilepton mass lower for h->WW: mass dependent cut
- Employ spin correlations to suppress WW background:
- leptons from h ****** **WW(*)  l+l- tend to be collinear

- H  WW(*)  l+l-

**Higgs of 160 GeV**

**Higgs of 160 GeV**

- Beate Heinemann - Northwestern University

- 10-04-2004

## H  WW(*)  l+l-

- Similar analysis by D0
- Neither CDF nor D0 see any evidence for h production => set upper limit on cross section

- H  WW(*)  l+l-

- Expect 0.11 events for 160 GeV SM Higgs with 200/pb

| D0 | ee | e |  |
| --- | --- | --- | --- |
| Observed | 2 | 2 | 5 |
| Expected | 2.7±0.4 | 3.1±0.3 | 5.3±0.6 |

- Excluded cross section times
- Branching Ratio at 95% C.L.

- Beate Heinemann - Northwestern University

- 10-04-2004

## WZ and ZZ

- Select 2 leptons with M(ll) in Z mass range and
- 2 leptons (ZZ->llll)
- 1 lepton and Et (WZ->lll)
- Significant Et (ZZ->ll)

- Expect 5.0+-0.6 events
- Observe 4 events 
- <13.9 pb @ 95% C.L.
- NLO: =5.2±0.4pb

- Beate Heinemann - Northwestern University

- 10-04-2004

## WZ/ZZ: kinematics 

- Consistent with expectation
- More data needed!

- Beate Heinemann - Northwestern University

- 10-04-2004

## Large backgrounds from QCD processes: W+jets, Z+jets
Use h->bb channel for Higgs search
WZ->Wbb will be observable  before seeing the higgs=> excellent calibration channel
Exercises mass resolution: combining
	calorimeter and tracking => 30% improvement in energy resolution 

- RunI:0.5-1%

- Large backgrounds from QCD processes: W+jets, Z+jets
- Use h->bb channel for Higgs search
- WZ->Wbb will be observable  before seeing the higgs=> excellent calibration channel
- Exercises mass resolution: combining
- 	calorimeter and tracking => 30% improvement in energy resolution

- Beate Heinemann - Northwestern University

- 10-04-2004

## Wh Production: Run 2 data

- Selection:
- W(or e)
- 2 jets: 1 b-tagged
- Search for peak in dijet invariant mass distribution
- No evidence yet for WZ or Wh

- mbb (GeV/c2)

- Beate Heinemann - Northwestern University

- 10-04-2004

## Summary of CDF Higgs Searches

- Beate Heinemann - Northwestern University

- 10-04-2004

## Higgs Discovery at Tevatron?

- 2009

- 2006

- NOW

- Beate Heinemann - Northwestern University

- 10-04-2004

## Higgs Discovery at the LHC?

- fb-1

- 1 year
- @1033

- 1 month
- @1033

- 1 year
- @1034

- LHC: ATLAS

- Values for single experiment

- time

- Beate Heinemann - Northwestern University

- 10-04-2004

## Summary and Outlook

- Diboson Production excellent probe for New Physics
- Higgs production
- SUSY
- Large Extra Dimensions
- Precision test of SU(2)xU(1) gauge structure
- Many new results from Tevatron
- Machine and experiments running great!
- Have got 2x more data on tape!
- Anticipate 1.5-2 fb-1 by 2007 and
-                   4.4-8.6 fb-1 by 2009
- Crucial for Higgs discovery at both Tevatron and LHC

**Cross Section (pb)**

- Beate Heinemann - Northwestern University

- 10-04-2004

## Backup Slides

## CDF: COT Aging Problem Solved!

- Beate Heinemann - Northwestern University

- 10-04-2004

## Silicon Performance

- See talk by R. Wallny

- Beate Heinemann - Northwestern University

- 10-04-2004

## CDF: B-tagging and tracking

- Beate Heinemann - Northwestern University

- 10-04-2004

## “Radiation Zero” unique to TeVatron: 
suppressed w.g. for W- 
cosΘ*=-(1+2Qi)=-1/3 
Observable in angular separation of lepton and photon

- Radiation Zero

- “Radiation Zero” unique to TeVatron:
- suppressed w.g. for W-
- cosΘ*=-(1+2Qi)=-1/3
- Observable in angular separation of lepton and photon

- Beate Heinemann - Northwestern University

- 10-04-2004

## Run II:
Repeat run I analysis (20 x more data)
Extend to forward region (silicon tracker, new Plug calorimeter, new forward muon system)

- Run I: Et>25 GeV, lepton Et>25 GeV, photon Et>25 GeV

| lepton | Data | SM exp |
| --- | --- | --- |
| muon | 11 | 4.2 |
| electron | 5 | 3.4 |
| both | 16 | 7.6 |

- Run II:
- Repeat run I analysis (20 x more data)
- Extend to forward region (silicon tracker, new Plug calorimeter, new forward muon system)

- Phys. Rev. Lett. 89, 041802 (2002)

- Beate Heinemann - Northwestern University

- 10-04-2004

## WZ Production: leptonic channel

- -Leptonic channel (Z->ll, W->lv) background rather low (S/B=3) but
- 	cross section also low (=2.5 pb)
- Anomalous couplings: WWZ may be different to WW
- Experimental signature similar to SUSY “trilepton” channel:
- Associated production of chargino and neutralino: disentangle on basis
- of imbalance in transverse momentum, masses

- SM

- SUSY

- Beate Heinemann - Northwestern University

- 10-04-2004

## Di-Boson Production 

**- ****Di-Photon Production: **
**	****discovery channel at LHC for mh<130 GeV**

**WW and ZZ Production: **
**discovery channels at LHC for 500>mh>130 GeV**

- Beate Heinemann - Northwestern University

- 10-04-2004

## Why WW scattering?

- Without the Higgs, WL WL        WL WL violates perturbative unitarity at 1.2 TeV

- (WT WT         WT WT doesn’t)

- In the high energy limit, the WL ARE the 3 goldstone bosons associated with electroweak symmetry breaking

- Using all we know about electroweak symmetry breaking, (v = 246 GeV, 3 goldstone bosons, W Z (residual global SU(2) symmetry)), can write quite generally, to 1 loop (from the EWChL):

- a4 and a5 parameterise our ignorance of the new physics (they come from the only dimension-4 terms we could add to the EWChL )

- Beate Heinemann - Northwestern University

- 10-04-2004

## Backgrounds:
 jet fragmenting into single hard pi0
Use high granularity strip and wire chambers in central calorimeter to separate pi0 from photon
New strip and wire chambers in forward calorimeter

Electrons where track is not found
Difficult in forward region where only Silicon (no drift chamber)
Developing robust and efficient algorithms
Develop generic methods to estimate backgrounds:
Jet fake rate about 0.1-0.01% for developed cuts

**Experimental Aspects: Photons**

- Backgrounds:
-  jet fragmenting into single hard pi0
- Use high granularity strip and wire chambers in central calorimeter to separate pi0 from photon
- New strip and wire chambers in forward calorimeter
- Electrons where track is not found
- Difficult in forward region where only Silicon (no drift chamber)
- Developing robust and efficient algorithms
- Develop generic methods to estimate backgrounds:
- Jet fake rate about 0.1-0.01% for developed cuts

- P(jet->photon)

- Beate Heinemann - Northwestern University

- 10-04-2004