# Presentation: 702669

## High PT Physics at Hadron Colliders

**                               ****Outline**
**1 - The Standard Model and EWSB**
**2 - Detector Basics**
**Tracking**
**Calorimetry**
**Muon Detection**
**3 - Collider Physics**

## High PT Physics at Hadron Colliders

**4 - Tevatron Physics**
**QCD**
**b and t Production**
**EW Production and D-Y**
**5 - Higgs Search Strategy at the LHC**
**6 - SUSY and Open Questions in HEP**

## 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-> 2,3,4 **
**2 ->2,3,4**
***x options**
**No 2 -> 1**

## COMPHEP –Simpson, BR

**Find simple 2->2. Graphs (with menu)**
**Results can be 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.**

## COMPHEP - Cuts

## COMPHEP - Vegas

**Full matrix element calculation - interference**

## 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.**

## 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**

## Gravity – Hail and farewell

**Ignore gravity until Chpt.6. 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 to be uncharged.**

## 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.**

## 1 - 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 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. How does this “spontaneous electroweak symmetry breaking” occur? (Higgs mechanism)**

## Field Theory

**Classical**
**Lagrangian density**
**Classical gauge replacement**
**Quantum gauge replacement**

## Gauge Couplings - EM, Weak, Strong

**Use EM as model for other gauge couplings**

**Covariant derivative  of fermions to vector fields (V) requires the gauge field and specifies the interaction. Color SU(3) has 8 colored gluons. Weak flavor SU(2) combined with EM U(1) of charge has 4 gauge bosons**

## 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.**

## 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 3 VVV couplings.**
**In COMPHEP play with the Breit-Wigner option as s dependence of the cross section depends crucially on the W width.**

## WW Cross Section at LEP

**COMPHEP point shown. Proof that the WWZ triple gauge boson coupling is needed.**

## WW at LEP

**Probe of quartic couplings.**
**LEP data confirms SM**

## ZZ at LEP

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

## e+e- Cross Sections

**WW and ZZ are seen at LEPII. At even higher C.M. energies WW********, WWZ and ZZZ are produced - indicating triple and quartic V couplings. New channels open up at the proposed ILC.**

## ILC Process - Example

**Cross section ~ 1 fb at 500 GeV in COMPHEP**

## Electro - Weak Unification

**The weak interactions are responsible for nuclear beta decay. The observed rates are slow, indicating weak effective coupling. The decays of the nuclei, n, and ******** are parameterized as an effective 4 fermion interaction with coupling, G ~ 10****-5**** GeV****-2****,************~ G****2****M********5****.**
**The weak SU(2) gauge bosons, W****+**** Z****o**** W****-**** , acquire a mass by interacting with the "vacuum expectation value" of the Higgs boson field, while the U(1) photon,********, remains massless.  M****W**** ~ g****W****<********>/********2.**
**The SU(2) and U(1) couplings are "unified" in that  e = g****W****sin(********W****). The parameter ********W**** can be measured by studying the scattering of  ********+ p,  since this is a purely weak interaction process.**
**The coupling g****W**** can be connected to G by noting that the 4 fermion Feynman diagram can be related to the effective 4 fermion interaction by the Feynman "propagator",  G ~ g****W****2****/M****W****2****. Thus, from G, e and sin(********W****) one can predict M****W****. The result, M****W**** ~ 80 GeV was confirmed at CERN in the pp collider. The vacuum Higgs field has <********> ~ 174 GeV.**

## The Higgs Boson Postulated

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

## 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 beat 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. (Chpt 5)**

## Higgs Coupling to Fermions

**The fermions are left handed weak doublets and right handed singlets. A mass term in the Lagrangian, mff = m(f****L****f****R**** + f****R****f****L****) is then not a weak singlet as is required.**
**A Higgs weak doublet is needed, with Yukawa coupling, L ~ g****f****[(f****L********)f****R**** + h.c.]. **

**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 ff.**
** ****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.**

## 12 Unresolved Fundamental Questions

**How do the Z and W acquire mass and not the photon? (Chpt. 1)**
**What is M****H**** and how do we measure it? (Chpt.4,5)**
**Why are there 3 and only 3 light “generations”?**
**What explains the pattern of quark and lepton masses and mixing?**
**Why are the known mass scales so different? ********QCD**** ~ 0.2 GeV << EW vev ~ 246 GeV << M****GUT**** ~ 10****16**** GeV << M****PL**** ~ 10****19**** GeV **
**Why is charge quantized?**
**Why do neutrinos have such small masses**
**Why is matter (protons) ~ stable?**
**Why is the Universe made of matter? (CP violation)**
**What is “dark matter” made of?**
**Why is the cosmological constant small?**
**How does gravity fit in with the strong, electromagnetic and weak forces?**

**There are many unresolved questions implicit in the SM**

## The Weinberg EW Mixing Angle

**The neutral physical particle mass eigenstates need not be the SU(2) and U(1) eigenstates. Write the covarient derivative in terms of electro-weak eigenstates. The coupling to charge is fixed as Qe.**

## The Gauge Coupling of the Z

**Universal gauge couplings of the bosons are defined by a single coupling constant for each gauge group****.**

## Graphical EW Mixing

**A**
**B****o**

**Z         W****o**

**e**

**g****2**

**g****1**

******W**

******W**

******g****1****2****+g****2****2**

**Neutral gauge bosons have mass eigenstates different from the EW eigenstates.**

## Gauge Couplings of V to l,q

****** ****, W, Z, g coupling to leptons and quarks is specified by gauge principle. EM is V, weak is V-A. The quark weak eigenstates are mixed strong eigenstates [V****qq’****].**
**Couplings specified by ********, ********s****, and ********W****.**