Boson Production at Hadron Colliders

02-12-2003 Beate Heinemann - MIT seminar 1

Boson Production at Hadron Colliders

• The Standard Model and Beyond

• Hadron-Colliders: TeVatron and LHC

• Di-Boson Production

• Exclusive Higgs Production

• Conclusions

Beate Heinemann, University of Liverpool/UK


Di-Boson Production: What’s that?

Associated production of ≥ 2 gauge bosons of electroweak interaction

?

Something happens

pp-> , W, Z, WW, WZ, ZZ

+ X


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

-Standard Model survived all experimental challenges in past 30 years

Particle Mass (GeV/c2)

Force

Photon (γ) 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


The Higgs Boson: the missing piece?

• Precision measurements of – MW =80.450 +- 0.034 GeV/c2

– Mtop=174.3 +- 5.1 GeV/c2

• Prediction of higgs boson mass within SM due to loop corrections

If higgs boson is found at predicted values the Standard Model will have succeeded again

TeVatron

Mtop (GeV)

MW

(G

eV)

193 GeV


What if there is no Higgs?

-WW cross section would violate unitarity since amplitude perturbative expansion in s: σ~s2/v2 + s4/v4…

-Need either a SM Higgs with M<1 TeV or some other new physics (e.g. SUSY, Technicolor)

-TeVatron and LHC probe relevant scale of 1 TeV!

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


• Supersymmetry (SUSY):– Each SM particle has a

“super”-partner with same quantum numbers apart from spin (top <-> stop, photon <-> photino, etc.)

– Masses are O(1 TeV)– Unification of forces at

GUT scale (1016 GeV)• Extra Dimensions

– String theory: links gravity to other forces

– Could be large (0.1mm): probed at TeV scale

• The unexpected…

What could be Beyond the SM?


Main Injectorand Recycler

p source

Booster

The TeVatron: Run IICDF

D0

p-p collisions at sqrt(s) = 2.0 TeV

bunch crossing rate 396 ns

525 people

13 countries

580 people

17 countries

-


Run II at the Tevatron• Run I: 100 pb-1 until 1996• Run II:

– Started March 2001– 2 fb-1 by 2004->2006– 6.5 fb-1 by 2008

• Disappointing startup but have about run I luminosity now!

• Performance continuously improving:– Peak luminosities:

• Run I best: 2.8x1031 cm-2s-1

• Run II best: 3.5x1031 cm-2s-1

• Run II goal: 20 x1031 cm-2s-1

Run I

CDF Trigger fully working

Factor 20-65 increased statistics compared to Run I


The Upgraded CDF Detector

New

Old

Partially new

Forward muonEndplugcalorimeter Silicon and drift

chamber trackers

Central muonCentral calorimeters

Solenoid

Front endTriggerDAQOffline

TOF


02-12-2003 11

All detectors inside the solenoid are new

wire drift chamber (96 layers) TOF System

A new 3d tracking system and vertex detector covering ||out to 2.0.

A new scintillating tile plug calorimeter covering || out to 3.6.

COT

0

.5

1.0

1.5

2.0

0 .5 1.0 1.5 2.0 2.5 3.0

END WALL HADRON CAL.

Inner silicon 6 layers

30

300

SOLENOID

Intermediate silicon 1 or 2 layers

= 1.0

= 2.0n

EN

D P

LUG

EM

CA

LOR

IMETER

EN

D P

LUG

HA

DR

ON

CA

LOR

IMETER

= 3.0n

n

m

m


First Physics with CDF in Run II

B-Physics: 1st lifetimes and masses

Z->μμ: 1st search for new high mass particles

W->ev: cross-section measurement

A lot more in upcoming Spring Conferences (LaThuile, Moriond)

ct=458±10 stat. ±11 syst. mm

(PDG: 469±4 mm)


Beyond the TeVatron: LHC

• 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


Di-Boson Production: Why?

?

Something happens

-SM precision tests

-SUSY

-Large Extra Dimensions

-Higgs

-Run I anomalies


Di-Photon Production at the Tevatron

• SM couplings small (αem)

• New Physics Scenarios:– Large Extra Dimensions:

• Graviton exchange contributes

• Present sensitivity about 900 GeV

• Run II: sensitivity about 2 TeV

– Generic “bump” search– Extraodinary events with 2 photons and transverse momentum imbalance(?)


Di-Bosons: W/Z + Photon

• Sensitive to coupling of gauge boson to each other: WW vertex

• Gauge structure of SU(2)xU(1) gives precise prediction

• Construct effective Lagrangian: introduce “anomalous couplings” and – vanish in SM – E.g. sizeable if W not point-like

• Z+γ don’t couple to another (diagram C non existent):– Test this experimentally!

• Signatures:– W : charged lepton, photon and

Et (neutrino) – Z : 2 charged leptons, photon

• Typical cuts: lepton and neutrino Et >20 GeV, photon Et>7 GeV


W/Z + Photon as Standard Model test

• Limits on Δκ and λ:– Test SM at level of about

10(30)% in Run II– Similar precision achieved

in measurements at LEP

• “Radiation Zero” unique to TeVatron: – suppressed w.g. for W-

cosΘ*=-(1+2Qi)=-1/3 – Observable in angular

separation of lepton and photon: ηγ-ηlepton

CDF II


W + Photon as Search

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)


• Run I:

– found 1 event with 2 photons, 2 electrons and large imbalance in transverse momentum

– SM expectation 10-6 (!!!)

• Run II:

– Any such new event would be exciting!

– Key problem: misidentification of jets as photons (hard pi0’s)

– Other exclusive channels: lepton+photon+Met+X (high Pt)

W/Z+gamma+X: more exclusive channels

SUSY?


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 WWγ

-Experimental signature similar to SUSY “trilepton” channel:

Associated production of chargino and neutralino: disentangle on basis

of imbalance in transverse momentum, angular distributions

SM

SUSY


Di-Boson Production: Run I vs Run II

“Leptonic” channelsN(Data) N(BG) σ(exp.)* σ(th.)* N(RunII)

Wγ 109 26.4 20.7±3.0 18.6 2400

Zγ 31 1.4 5.7±1.4 4.8 1100

WW 5 1.2 10.2±5.9 9.5 150

WZ 1 0.3 3.2+5.0 2.5 50

ZZ 1 ? ? 1.0 5-3.2

* All cross sections in pb

- Run I cross section measurements slightly higher than SM prediction

- Run II: huge increase due to luminosity and higher acceptance in

forward region (new calorimeter, Si tracking)


WW,WZ: hadronic channels

RunI:0.5-1%

• Large backgrounds from QCD processes: W+jets, Z+jets

• Use bbbar channel (QCD BG suppressed)• WW & WZ have to be seen in hadronic

channel before seeing the higgs=> excellent calibration channel

• Exercises mass resolution: combiningcalorimeter and tracking => 30% improvement in energy resolution

(B.H. et al.)


Di-Boson Production via Higgs-decay

Dominant Production: gg-> H Decay: Di-bosons (γγ, WW or ZZ)

Main Higgs discovery channels at LHC:

two bosons in final state

one year


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


Hgap gap

b

b -jet

-jet

Exclusive HiggsA recent development: search for exclusive Higgs production pp p H p

p p

beam

p’

p’

dipoleroman potsCross sections somewhat uncertain ~ 2 fb at LHC

roman pots

dipole

exclusive


Exclusive Higgs Production

Reconstruct mass from protons only:

=>Mass resolution of O(1 GeV/c2) independent of decay mode

Access all Higgs decay modes: =>verify coupling to mass

Measure ξ in Roman Pots


Exclusive Higgs: Competitive channel at LHC

DeRoeck, Khoze, Martin, Orava, Ryskin Eur.Phys.J.C25:391-

403,2002

30 fb-1 at LHC


Exclusive Higgs: Status of Theory

• (fb) MH=120 GeV: Tevatron LHC Normalisation

• Cudell, Hernandez (1994) - exclusive 30 200-400 elastic and soft pp

• Cox, Forshaw, Heinemann: Phys.Lett.B540:263-268,2002

– inelastic 0.03-0.1 2-4 HERA x gap survival

• Khoze, Martin, Ryskin: Eur.Phys.J. C23 (2002) 311-327

– inelastic ~0.05 ~3 – exclusive 0.02 3.0 “absolute”

• Enberg et al. (2002) – inelastic 1.2-2.4.10-4 0.19 P(soft gluon exchange)– exclusive < 10-4

- Predictions difficult due to soft gluon contributions

-Two predictions agree but need experimental testing!


Diffractive Higgs: Experimental Status

All predictions tested by just one run I measurement of dijet-production:

(inel.)=44±20 nb

(excl.)<3.7 nb at 95% C.L.

exclusive

CDF Run I data

- Higgs mass reconstruction only possible in exclusive

channel but never observed experimentally

- Prediction (KMR): σ≈1nb => Run II


Diffractive Higgs: Measurements at the Tevatron

Should see bb, di-photon and Xb at TeVatron if predictions correct

1000 events/pb-1

100 events/fb-1

-Should observe exclusive production: Xb and very clean

-Test theoretical predictions => build such detectors at LHC?

Excl. Xb->Yγ: σ≈120 pb


γγ

Process Physics

Inclusive Higgs

Exclusive Higgs

Non-SM Higgs

Large Extra DimensionsSM precision tests

WW

W/Zγ

Run I anomalies

SUSY

WZ

ZZ

b

Mostly relevant for TeVatron and LHC

Conclusions


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 )


Signatures for Diffraction

Elastic protons

Single Diffraction

Double Diffraction

DPE

Non-Diffractive


Exclusive central diffraction is experimentally distinctive - inclusive has higher rate...

In exclusive process: pp p + X + p:• only Jz = 0, P=+1 contribute1 • signature: forward-backward pair of protons separated by two rapidity gaps from the central pair of jets

In inclusive process: pp p X p extra particles emitted in the central region.

(see:Ch. Royon)

1 Amplitude averaged over the two transverse polarisations of the incoming gluons

Khoze, Martin, RyskinBoonekamp, Peschanski, RoyonCox, Lonnblad,...


Double Pomeron Exchange: exclusive channels with leading protons and rapidity gaps.The Pomeron has the internal quantum numbers of vacuum.

PP: C = +, I=0,...

P: JPC = 0++, 2++, 4++,... (not 1++ etc.)

gg vs. uu, dd, ss, cc, bb ?- - - - -

Gap GapJet+Jet

p1

p2p2’

p1’

P

P

diffractive systemproton:p2’proton:p1’

rapidity gaprapidity gap

min max

min max

Rapidity Gap Survival Probability1

Tevatron LHCCD 5-14% 2-11%

Two types of signatures

1 Khoze, Martin, Ryskin/Levin/Block et al

compare to: V-mesons, elastic scatt....

But there is a price to be paid for exclusivity!


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 (B. Heinemann et al.):– Jet fake rate about 0.1-0.01% for

developed cutsP

(jet

->

phot

on)


Going to High Energy

LEPSLC

100 GeV

1000 GeV

Tevatron: 1000 GeV protons

LHC: 7000 GeV protons


The Success of the Standard Model

The Standard Model survived all experimental challenges of the last 30 years:

• Discovery of 2nd and 3rd family of leptons

• Discovery of W- and Z-bosons

• Precision measurements of various SM parameters (MW, Mtop, sin2θW, etc.): e.g. indirect prediction of top mass (LEP) agrees with direct measurements (TeVatron)

LEP

CDFD0

Tevatron (CDF+D0)

lower limits


Di-Boson Production: What’s that?

Associated production of ≥ 2 gauge bosons of electroweak interaction

pp-> γγ, Wγ, Zγ, WW, WZ, ZZ

+ X?

Something happens


The Standard Model of Particle Physics

- 6 quarks and 6 leptons interact via exchange of gauge bosons:

-Electroweak: W, Z, γ-Strong: gluon (g)

-All particles apart form gluon and photon are massive

-All particles have been observed apart from Higgs boson

-Particle mass is consequence of electroweak symmetry breaking due to Higgs field

Mass (GeV/c2)

Particle


The Success of the Standard Model

The Standard Model survived all experimental challenges of the last 30 years:

LEP

CDFD0

TeVatron (CDF+D0)

lower limits

• E.g. LEP precision measurements (MW,MZ):

– Predicted top quark mass agrees with direct measurement at TeVatron

• No physics found beyond the Standard Model despite trying very hard…

But most crucial higgs-boson

Not seen yet!


Double Diffractive Dijets

CDF Phys. Rev. Lett 85 4215 (2000)

Appleby & Forshaw, Phys.Lett.B451:108-114,2002


Double Diffractive Higgs

IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS

1 E+ -11 101 0 0 4 5 0.00 0.00 980.0 980.0 0.00

2 E- 11 102 0 0 6 7 0.00 0.00 -980.0 980.0 0.00

3 CMF 0 103 4 6 0 0 0.01 -1.05 -31.1 163.0 160.02

4 GAMMA 22 3 1 0 0 0 0.07 -0.81 65.9 65.9 -0.84

5 E+ -11 1 1 0 0 0 -0.07 0.81 914.1 914.1 0.00

6 GAMMA 22 3 2 0 0 0 -0.06 -0.24 -97.1 97.1 -0.27

7 E- 11 1 2 0 0 0 0.06 0.24 -882.9 882.9 0.00

---HARD SUBPROCESS---


8 GLUON 21 121 10 9 11 9 0.05 -0.62 50.8 50.9 0.75

9 GLUON 21 122 10 8 15 8 -0.04 -0.16 -65.0 65.0 0.75

10 HIGGS 25 120 8 9 67 67 14.85 -6.11 -14.4 117.0 115.01

---H/W/Z BOSON DECAYS---


79 BQRK 5 123 67 80 81 80 25.96 -26.45 -57.1 68.2 4.95

80 BBAR -5 124 67 79 86 79 -11.11 20.34 42.6 48.8 4.95


Double Diffractive Dijets and Higgs Production

POMWIG : “Central-inelastic” process

p+p p + gap + H + X + gap + p

Khoze, Martin & Ryskin, hep-ph/0207313, Eur.Phys.J. C23 (2002) 311-327Cox, Forshaw & Heinemann, Phys.Lett.B540:263-268,2002 De Rouke, Khoze, Martin, Orava & Ryskin hep-ph/0207042Albrow and Rostovtsev, hep-ph/0009336 …

“exclusive”

• Is this really a contender for a light Higgs discovery channel ?

• We won’t see DD Higgs at Tevatron, BUT we do see DD dijets

•Question : Can we see the exclusive contributions in the DD dijets ?

•Answer: Not yet, but we should (if it exists) in RunII.


QCD Hard scattering factorisation :

conditional proton parton densities for particular xIP, t

Regge factorisation :


WHAT IS POMWIG ?

• No doubt that Ingelman – Schlein (Regge factorisation) works at HERA

• Pomwig uses measured structure functions and flux from H1 OR user defined structure functions / flux


Why not the Standard Model?

• Electroweak scale (100 GeV) much much lower than Planck Scale (1019 GeV)… (hierarchy problem)

• No unification of forces • No explanation for matter/

anti-matter asymmetry in universe (CP-violation)

• Many free parameters, e.g. masses of all particles => unsatisfactory

Documents

Boson Production at Hadron Colliders