# Presentation: 529375

## Top & EW                  (Theory Introduction)

**Tim M.P. Tait**
**Argonne National Laboratory**

- Tevatron Connections
- Fermilab
- 6/25/2005

## Outline

- Introduction: Why are top & EW measurements so important today?
- EW Boson Production
- Top Production and Decay
- Outlook

- Tim Tait

- Tevatron Connections, 6/25/05

## Electroweak Symmetry Breaking

- The EW bosons (W, Z, and** ******) require gauge symmetries to be theoretically consistent.
- However, the gauge invariance would forbid masses for the W and Z, (and also for the fermions); thus the symmetry must be broken.
- We still have not identified the agent of the EW symmetry breaking, and thus we still don’t know what the responsible dynamics are.
- The SM has an ansatz based on a fundamental Higgs field.  Until we see it, the SM is still incomplete and unproven.
- We know the energy scale at which the symmetry breaking operates – it can’t be too far above the W and Z masses!  So whatever the theory is, it must be within grasp in the near future!
- Whatever the theory of EWSB, the most massive objects  (which felt the breaking most strongly) are the place to learn about it.
- Thus, it is natural to explore precision measurements of top and the Electroweak bosons, particularly in high energy processes.

- Tim Tait

- Tevatron Connections, 6/25/05

## Flavor Physics:

- Flavor Physics:

**Top & EW in the SM**

- EW Fit:

- Precision inputs from the top & EW sectors for precise SM predictions.

- Buchalla, Buras, Lautenbacher  RMP68,1125 (1996)

***i.e.*****:**

- Tim Tait

- Tevatron Connections, 6/25/05

## Most importantly, the MSSM only survives the LEP-II bound on mh because of the large yt:

(mt < 160 GeV rules out MSSM!)

- (**m****t** < 160 GeV rules out MSSM!)

- The large top Yukawa leads to the attractive scenario of radiative electroweak symmetry-breaking:
- This mechanism is also essential in many little Higgs theories.

**Top plays an important role in the minimal supersymmetric standard model.**

**Top Sector and SUSY**

- Tim Tait

- Tevatron Connections, 6/25/05

## EW Boson Production

**EW Boson Production**

- Production of EW bosons is a very important process at a hadron collider.
- Measurement of MW
- W kinematics (QCD)
- QED final state radiation
- EW Corrections
- PDFs
- Luminosity Measurement?
- Test of QCD / Resummation / MC

- Nadolsky HCP2004

- Anastasiou, Dixon,
- Melnikov, Petriello
- PRD69, 094008 (04)

- Brock, Landry, Nadolsky, Yuan
- PRD67, 073016 (2003)

- Tim Tait

- Tevatron Connections, 6/25/05

## Di-Boson Production

**Di-Boson Production**

- Even in the SM, diboson production is an important process to understand because it shares many characteristics (and is a background to) Higgs.
- Triple gauge vertices are difficult to access with any other process, and are expected to be sensitive to physics beyond the Standard Model.
- The current luminosity is just enough to observe several of these processes; Tevatron will explore radically new territory in the near future!

- M Kirby, HCP2004

**W ******

- New Physics generically parameterized as:

- Tim Tait

- Tevatron Connections, 6/25/05

## t t  Production

- At a hadron collider, the largest production mechanism is pairs of top quarks through the strong interaction.
- (Production through a virtual Z boson is much smaller).
- At leading order, there are gluon-gluon and quark-anti-quark initial states.
- At Tevatron, qq dominates (~85%).
- At LHC, gg is much more important.

- Tim Tait

- Tevatron Connections, 6/25/05

## t t  Production Rates

**t t  Production Rates**

- An impressive array of cross section measurements are performed across many top decay channels.
- Measurements help to test & tune the variety of cutting edge QCD predictions on the market.

- Tim Tait

- Tevatron Connections, 6/25/05

## New tt Resonances?

**New tt Resonances?**

- A neutral boson can contribute to tt production in the s-channel.
- Many theories predict such exotic bosons with preferential coupling to top:
- TC2, Top Seesaw: top gluons
- TC2, Topflavor: Z’
- Search strategy:  resonance in tt.
- Tevatron: up to ~ **850 GeV**

- Future EW Physics at the Tevatron, TeV-2000 Study Group

- Hill PLB345,483 (1995)
- Dobrescu, Hill PRL81, 2634 (1998)

- Hill PLB345,483 (1995)
- Chivukula, Simmons, Terning PRD53, 5258 (1996)
- Nandi, Muller PLB383, 345 (1996)
- Malkawi, Tait, Yuan PLB385, 304 (1996)

- Tim Tait

- Tevatron Connections, 6/25/05

## Top Decay

- SM: BR into W+b ~ 100%.
- Top decay represents our first glimpse into top’s weak interactions.
- In the SM, *W**-**t**-**b* is a left-handed interaction: ********** (**1** - ********5****)**.
- However, the decay does not offer a chance to measure the *magnitude* of the *W**-**t**-**b* coupling, but only its *structure*.
- This is because the top width is well below the experimental resolutions.
- Top is the only quark for which ******t** >> ******QCD**.  This makes top the only quark which we see “bare” (in some sense).
- Top spin “survives” non-perturbative QCD (soft gluons).

- CDF hep-ex/0505091
- Dø note 4833-CONF

-   ** ****V****tb** >> **V****ts**, **V****td**

- Tim Tait

- Tevatron Connections, 6/25/05

## Rare Decays

**Rare Decays**

- Many rare decays of top are possible.
- These can be searched for in large t t samples, using one standard decay to ‘tag’ and verifying the second decay as a rare one.
- One example is a FCNC: *Z**-**t**-**c*
- At LEP II, the same physics that results in t     Zq would lead to       e+e-      Z*      tq.
- More possibilities, such as t     c****,
-       t      cg, etc...

- Solid lines:     assume ****tc**** = 0.78
- Dashed lines: assume no *t**-**c**-*******

- Top Physics, hep-ph/0003033

- Tim Tait

- Tevatron Connections, 6/25/05

## Single Top Production

- Top’s EW interaction.
- Three modes:
- T-channel: q b     q’ t
- S-channel: q q’     t b
- Associated:  g b     t W-
**Coming soon to Run II!**

|  | Tevatron
Run I | Tevatron
Run II | LHC |
| --- | --- | --- | --- |
| t (NLO) | 1.45±0.08 pb | 1.98±0.13 pb | 247±12 pb |
| s (NLO) | 0.75±0.07 pb | 0.88±0.09 pb | 10.7±0.9 pb |
| tW (LL) | 0.06±0.01 pb | 0.09±0.02 pb | 56±8 pb |
| Total | 2.26±0.11 pb | 2.95±0.16 pb | 314±15 pb |

- Harris, Laenen, Phaf, Sullivan, Weinzierl, PRD 66 (02) 054024
- Tait, PRD 61 (00) 034001; Belyaev, Boos, PRD 63 (01) 034012

- Run II Limits

- < 6.4 pb

- < 5.0 pb

- DØ hep-ex/0505063
- CDF PRD71, 012005 (2005)

- Now in MCFM!

- Tim Tait

- Tevatron Connections, 6/25/05

## s- Versus t-Channels

- s-channel Mode
- Smaller rate
- Extra b quark final state
-  ******s** **** |**V****tb****|****2**
- Polarized along beam axis at Tevatron.
- Sensitive to resonances
- Possibility of on-shell production.
- Need final state b tag to discriminate from background.

- t-channel Mode
- Dominant rate
- Forward jet in final state
-  ******t**** ****** |**V****tb****|****2**
- Polarized along spectator jet axis.
- Sensitive to FCNCs
- New production modes.
- t-channel exchange of heavy states always suppressed.

- Mahlon, Parke PLB476 323 (2000); PRD55 7249 (1997)

- Tim Tait

- Tevatron Connections, 6/25/05

## s-t Plane

******s****-********t**** Plane**

**Run II**

**LHC**

- Since they are sensitive to different
- physics and have different, final
- states, ******s** and ******t** should be
- measured independently!

- Tait, Yuan PRD63, 014018 (2001)

**Theory + Stat errors only!**

- Modified  V-t-s

- Tim Tait

- Tevatron Connections, 6/25/05

## Outlook

- Top and EW bosons are unique as a laboratory for EWSB and fermion masses.  The Tevatron is currently the only place in the world which can study them at high energies.
- Ultimately, we would like to confirm the SM picture for EWSB, but most people believe that we are likely to find something more interesting and more profound.
- Di-boson production is a sensitive probe of physics  beyond the SM, allowing a test of the triple gauge couplings and is a background to Higgs searches.
- Direct measurements of mt and mW at Tevatron are essential for the EW fit, and contribute to our theoretical understanding of b physics.
- Single top production will most likely be observed within the next years.  This will be the first direct measurement of top’s weak interactions: Vtb.
- Systematics are coming under control and statistical samples have begun to over-shadow run I.  So it is exactly **NOW** that we should hope for our first glimpses of physics beyond the Standard Model!

- Tim Tait

- Tevatron Connections, 6/25/05

## Supplementary Slides

## Polarization

**W Polarization**
- SM: Depends on **m****t** & **m****W**:
- This is a direct test of the left-handed nature of the            *W*-*t*-*b* vertex.
* **********W*** correlated with               the direction of pe               compared with                     the direction of pW                  in the top rest frame.

**Top Polarization**
- t t production: no net** ********t**.
-  ******t** and ******t** are correlated by s-channel gluon (vector).
- Single t: ~100% polarization.
- t polarization correlates with pe

- Mahlon, Parke PLB411, 173 (1997)

- DØ:

-   CDF:

- CDF PRL84, 216 (2000)
- DØ hep-ex/0404040

- Tim Tait

- Tevatron Connections, 6/25/05

## The King of Fermions!

- In the SM, top is superficially much like other fermions.
- What really distinguishes it is the huge mass, roughly 40x larger than the next lighter quark, bottom.
- This may be a strong clue that top is special in some way.
- It also implies a special role for top within the Standard model itself.
- Top is only fermion for which the coupling to the Higgs is important: it is a laboratory in which we can study EWSB.

_**SM Fermions**_

- Tim Tait

- Tevatron Connections, 6/25/05

## tt Resonances

**tt Resonances**

- A neutral boson can contribute to tt production in the s-channel.
- Many theories predict such exotic bosons with preferential coupling to top:
- TC2, Top Seesaw: top gluons
- TC2, Topflavor: Z’
- Search strategy:  resonance in tt.
- Tevatron: up to ~ **850 GeV**.
- LHC: up to ~ **4.5 TeV**.

- Future EW Physics at the Tevatron, TeV-2000 Study Group

- Hill PLB345,483 (1995)
- Dobrescu, Hill PRL81, 2634 (1998)

- Hill PLB345,483 (1995)
- Chivukula, Simmons, Terning PRD53, 5258 (1996)
- Nandi, Muller PLB383, 345 (1996)
- Malkawi, Tait, Yuan PLB385, 304 (1996)

- Tim Tait

- Tevatron Connections, 6/25/05

## Phenomenology: H+

- Rare Top Decay: t      H+ b
- Tevatron Run II (2 fb-1) :
- LHC (100 fb-1):
-                 g b      t H- at LHC! (100 fb-1):
- Breakdown of MSSM Higgs mass relation:
- Testable through pp      A0 H+ at LHC (100 fb-1):

- Cao, Kanemura, Yuan hep-ph/0311083

- Marcela + ~ 1 billion friends, hep-ph/0010338

- CERN top Yellow Book, hep-ph/0003033

- NLO: Berger, Han, Jiang, Plehn hep-ph/0312286

- Les Houches Higgs Report, hep-ph/0203056

- Tim Tait

- Tevatron Connections, 6/25/05

## SU(2)2: Topflavor

*SU(2)**1* x *SU(2)**2* x *U(1)**Y*
- The usual *SU(2)**L* is the diagonal combination.
- The *SU(2)** x **SU(2)* breaking occurs through a Higgs which is a bi-doublet under both *SU(2)*’s.
- This model has been called “**Topflavor**”: a separate weak interaction for the 3rd family.

- Chivukula, Simmons, Terning PRD53, 5258 (1996)
- Muller, Nandi PLB383, 345 (1996)
- Malkawi, Tait, Yuan PLB385, 304 (1996)

- Recently proposed to increase
**m****h** in the MSSM!

- Batra, Delgado, Kaplan, Tait, JHEP 0402,043 (2004)

- Tim Tait

- Tevatron Connections, 6/25/05

## Measurements

- How well are these quantities known?
**g****S**, ***e***, and **s****2****W** are well known (**g****S**  at per cent level, EW couplings at per mil level) from other sectors.
**m****t** is reconstructed kinematically at the Tevatron:
- Run I: **m****t**** = ****178 ****±**** 4.3 GeV**
- Run IIb: prospects to a precision of **± 2**** GeV** (systematic).
**V****td**, **V****ts**, and **V****tb** are (currently) determined indirectly:
**V****td**: **0.004 – 0.014**       (< 0.09)
**V****ts**: **0.037 – 0.044**       (< 0.12)
**V****tb**: **0.9990 – 0.9993**   (0.08 – 0.9993)
- These limits assume the 3 (4+?) generation SM, reconstructing  the values using the unitarity of the CKM matrix.
**V****tb** can be measured directly from single top production.

- PDG: http://pdg.lbl.gov/pdg.html

- Tim Tait

- Tevatron Connections, 6/25/05

## Well, how well do we want to know them?

***need***

## Hints from b Couplings?

- Choudhury, TT, Wagner, PRD65, 053002 (2002)

- If top is special, b, its EW partner, must be as well.
- Right-handed b couplings measured at LEP deviate from the SM at the ~ 3 **** level.
- Left-handed at ~ 2 ****.
- It has been argued that this goes beyond the statistical significance, because of the role of AbFB in mH fit.
- The “beautiful mirror” solution requires an extra top-like quark with mass < 300 GeV.

- Chanowitz PRL87, 231802 (2001)

- Tim Tait

- Tevatron Connections, 6/25/05

## Top in the Standard Model

- In the SM, top is the marriage between a left-handed quark doublet and a right-handed quark singlet.
- This marriage is consummated by EWSB, with the mass (**m****t**) determined by the coupling to the Higgs (**y****t**).
- This structure fixes all of the renormalizable interactions of top, and determines what is needed for a complete description of top in the SM.
- Mass: linked to the Yukawa coupling (at tree level) through: **m****t**** = ****y****t**** ****v**.
- Couplings:  **g****S** and ***e*** are fixed by gauge invariance.  The weak interaction has NC couplings, fixed in addition by **s****2****W**.   CC couplings are described by **V****tb**, **V****ts**, and **V****td**.

- Tim Tait

- Tevatron Connections, 6/25/05

## Top Yukawa Coupling

**Top Yukawa Coupling**

- Maltoni, Rainwater, Willenbrock, PRD66, 034022 (2002)

- SM prediction for the t coupling to the Higgs:
- We’d like to directly verify the relation to roughly the same precision as **m****t** itself: a few %.
- Higgs radiated from tt pair is probably the best bet.
- LHC: **y****t**** **to about **10-15%** for **m****h** **< 200 GeV**.

**NLO: Dawson, Jackson, Orr, Reina, Wackeroth, PRD 68, 034022 (2003)**

- Tim Tait

- Tevatron Connections, 6/25/05

## Single Top + Higgs

**Single Top + Higgs**

- Very small in the SM because of an efficient cancellation between two Feynman graphs.
- Thus, a sensitive probe of new physics.
- Observable at LHC?

- Tim Tait

- Tevatron Connections, 6/25/05

## Charged Higgs H+, Top-pion +
RH coupling!

- Charged Higgs** H****+****,** Top-pion** ********+**
- RH coupling!

**Charged Resonance**

- Topflavor: **W’      t b**

- Sullivan hep-ph/0306266

- He, Yuan PRL83,28 (1999)

- Simmons, **PRD55, 5494 (1997)**

- Tim Tait

- Tevatron Connections, 6/25/05