# Presentation: 244331

## High PT  Hadron Collider Physics

**                               ****Outline**
**1 - The Standard Model and EWSB**
**2 - Collider Physics**
**3 - Tevatron Physics**
**QCD**
**b and t Production**
**EW Production and D-Y**

## Backup Text

## Units

## Tools Needed

**(will use both during lecture demonstrations)**

**( Google them all – also Ghostview and Acrobat reader )**

## COMPHEP – Models and Particles

**Can edit the couplings – e.g. ggH**
**Use SM Feynman gauge**
**Watch for LOCK**

## COMPHEP - Process

**1-> 2,3**
**1-> 2,3,4 **
**1,2 ->3,4**
**1,2 ->3,4,5**
**1,2-> 3,4,5,6 (slow)**
***x options**
**No 2 -> 1**

## COMPHEP –Simpson, BR

**Find simple 2->2. Graphs (with menu)**
**Results can be written in .txt files**
**Several PDF, p and pbar,**
**Check stability of results**

## COMPHEP - Cuts

**May be needed to avoid poles or to simulate experimental cuts, e.g. rapidtiy or mass or Pt.**

## COMPHEP - Cuts

## COMPHEP - Vegas

**Full matrix element calculation – interference. Watch chisq approach 1. Setup plots, draw them and write them.**

## COMPHEP - Decays

**Strictly tree level. Does not do “loops” or “box” diagrams. **
**Explore this very useful tool. If there are problems bring them to the class and we’ll try to fix them.**

## 1 - The SM and EWSB

**1.1 The Energy Frontier**
**1.2 The Particles of the SM**
**1.3 Gauge Boson Masses and Couplings**
**1.4 Electroweak Unification**
**1.5 The Higgs Mechanism for Bosons and Fermions**
**1.6 Higgs Interactions and Decays**

## The Energy Frontier

**Historically HEP has advanced with machines that increase the available C.M. energy. The LHC is designed to cover the allowed Higgs mass range. Colliders give maximum C.M. energy.**

**The Energy Frontier**

## The Standard Model of Elementary Particle Physics

**Matter consists of half integral spin fermions. The strongly interacting fermions are called quarks. The fermions with electroweak interactions are  called leptons. The uncharged leptons are called neutrinos.**
**The forces are carried by integral spin bosons. The strong force is carried by 8 gluons (g), the electromagnetic force by the photon (********), and the weak interaction by the W****+**** Z****o**** and W****-****. The g and ******** are massless, while the W and Z have ~ 80 and 91 GeV mass respectively.**

**J = 1**

**g,********, W****+****,Z****o****,W****-**

**Force Carriers**

**J = 1/2**

**u**
**d**

**c**
**s**

**t**
**b**

**e**
******e**

****
********

****
********

**Q/e=**

**2/3**
**-1/3**

**1**
**0**

**Quarks**

**Leptons**

**J = 0**

**H**

## Gravity – Hail and Farewell

**Ignore gravity. However, gravity is a precursor gauge theory which is non-Abelian. The gauge quanta are “charged” ******** non-linearity. The gravity field carries energy, or mass. Therefore, “gravity gravitates”. This is also true of the strong force (gluons are colored) and the weak force (W,Z carry weak charge). The photon is the only gauge boson which is uncharged.**

##  How do the Z and W acquire mass and not the photon?

**Gravity - Physics is the same in any local general coordinate system --> metric tensor or spin 2 massless graviton coupled universally to mass = G****N****.**
**Electromagnetism - Physics is the same regardless of wave function phase assigned at each local point --> massless, spin = 1,  photon field with universal coupling = e**
**These are “gauge theories” where local invariance implies massless quanta and specifies a universal ( G****N****, e ) coupling of the field to matter.**
**Strong interactions are mediated by massless “gluons” universally coupled to the “color charge” of quarks = g****s****.**
**Weak interactions are mediated by massive W****+****,Z,W****- ****universally coupled to quarks and leptons. g****W****sin********W**** = e. How does this “spontaneous electroweak symmetry breaking” occur? (Higgs mechanism)**

## Lepton Colliders - LEP

**Z peak**
**L and R leptons have different couplings to the Z. There is Z-photon interference which leads to a F/B asymmetry. A way to measure the Weinberg angle. g****W**** measured from muon decay.**

## Field Theory

**Classical Special Relativity**
**Lagrangian density, P is an operator**
**Classical gauge replacement**
**Quantum gauge replacement**

## WW in e+e- Collisions

**Test of self-coupling of vector bosons. There are s channel Z and photon diagrams, and t channel neutrino exchange. Test of VVV couplings.**
**In COMPHEP play with the Breit-Wigner option as s dependence of the cross section depends crucially on the W width – i.e. technique to measure W width.. **

## Simpson –Angular Dist

**Cross section without neutrino exchange in the t channel. Note divergent C.M. energy dependence – voilates unitarity.**

## WW Cross Section at LEP

**COMPHEP point shown. Proof that the WWZ triple gauge boson coupling is needed and that there are interfering amplitudes that themselves violate initarity.**

## WW at LEP

**Probe of quartic couplings.**
**LEP data confirms SM**
**WWAA, WWZA**

**Cross section in COMPHEP with all final state bosons having Pt > 5 GeV is 0.36 pb**

## ZZ at LEP

**SM has only the single Feynman diagram. There are no relevant triple or quartic couplings – in the SM. Use the data to set limits on couplings beyond the SM.**

## e+e- Cross Sections

**WW, ZZ, and WW******** are seen at LEPII. At even higher C.M. energies, WWZ and ZZZ are produced - indicating triple and quartic V couplings. New channels open up at the proposed ILC.**
**Try a few (red dots) processes yourself.....**

## ILC Process - Example

**Cross section ~ 1 fb at 500 GeV in COMPHEP. Approximate agreement with full calculation.**

## The Higgs Boson Postulated

**Potential                                                              Lagrangian density**
**Minimum at a non-zero  vev                          “cosmological term”**

**This is Landau-Ginzberg superconductivity – much too simple?**

## How the W and Z get their Mass

**Covariant derivative contains gauge fields W,Z. Suppose an additional scaler field ******** exists and has a vacuum expectation value. Quartic couplings give mass to the W and Z, as required by the data [ V(r) ~e(exp(-r/********)/r)  - weak at large r, strength e at small r].**

## Numerical W, Z Mass Prediction

**The masses for the W and Z are specified by the coupling constants. G comes from beta decays or muon decay.**

## Higgs Decays to Bosons

**Field excitations ==> interactions with  gauge bosons  VVH, VVHH, VVV, VVVV**

**Higgs couples to mass. Photons and gluons are massless to preserve gauge symmetry unbroken. Thus there is no direct gluon or photon coupling. **

## ZZH Coupling and ILC Production

**ILC at 500 GeV C.M. Higgs production by off shell Z production followed by H radiation, Z* ->Z+H.**

## Higgs Coupling to Fermions

**The fermions are left handed weak doublets and right handed singlets. A mass term in the Lagrangian,                                is then not a weak singlet as is required.**
**A Higgs weak doublet is needed, with Yukawa coupling,  **

**Yukawa**
**Mass from Dirac Lagrangian density**
**Fermion weak coupling constant**

## Higgs Decay to Fermions

**The threshold factor is for P wave, ********2l+1 ****since scalar decay into fermion pairs occurs in P wave due to the intrinsic parity of fermion pairs.**
** ****The Higgs is poorly coupled to normal (light) matter**
**  ****g****t**** ~ g****W ****(m****t****/ M****W****)/********2 ~ 1.0, so top is strongly coupled to the Higgs****.**

## The Higgs Decay Width

**The Higgs decay width, ******** scales as M****H****3. ****Thus at low mass, the detector defines the effective resonant width and hence  the time needed to discover a resonant enhancement. At high masses, the weak interactions become strong and ********/M ~ 1.**

## Higgs Width - WW + ZZ

**Higgs decays to V V have widths ******** ~ M****3**
**Try this as a **
**COMPHEP example**

## Higgs Width Below ZZ Threshold

**Below ZZ threshold, decays can occur in the tails of the Breit Wigner Z resonance, with ******** ~ 2.5 GeV, M ~ 91 GeV. This compares to the width to the heaviest quark, b at a Higgs mass of ~ 150 GeV. Means  that W*W is an LHC strategy.**

## Early LHC Data Taking

**We have seen that the Higgs couples to mass. Thus, the cross section for production from gluons or u, d quarks is expected to be small.**
**Therefore, it is a good strategy to prepare for LHC discoveries by establishing credibility. The SM predictions , extrapolated from the Tevatron, should first be validated by the LHC experimenters.**

## Vector Bosons and Forces 

**The 4 forces appear to be of much different strength and range. We will see that this view is largely a  misperception.**