# Presentation: 908723

## Exciting Run II opportunities in the Top Quark Sector 

**OUTLINE**
-  Motivation
-  Top Properties Tour
-  Conclusions

- Aurelio Juste
*Fermi National **Accelerator** Laboratory*

- TEV4LHC Workshop, Fermilab, Sept 16-18, 2004

## Why is Top Quark Physics Important?

- Existing indirect constraints on several of the top properties from low energy data are relatively poor and leave plenty of room for New Physics. Also true for Tevatron Run I measurements, largely limited by statistics.
- mt ~ 175 GeV ~ EW = 246 GeV         vs         mb~ 5GeV                                             Yukawa coupling t = 2 mt/v  1
- 	 likely that the generation of mass is closely related to EWSB (the top may even play a key role in the mechanism of EWSB)
- 	 effects from New Physics would be more apparent in the top sector (e.g. different models of EWSB can predict different interactions among the top quark and gauge bosons)
- Even if the top quark is just a normal quark
- most of the experimental measurements have no analogue  for the lighter quarks,
- will allow to make stringent tests of the SM.
- Will move at the Tevatron experiments from the discovery phase to a phase of precision measurements of top quark properties.

## Top Production and Decay at Tevatron

- Within the SM
-  t~1.4 GeV
- 	Top quark width acts as a cutoff  for non-perturbative QCD effects
- 	 Study decay of a “bare quark”
- B(tWb)~100%
- 	 (t Wd, Ws CKM suppressed)
- Final state fully determined by W  decay modes

- qq-annihilation
- (85%)

- gg fusion
- (15%)

- t-channel
- (W-g fusion)

- s-channel
- (Drell-Yan)

- associated

- Strong Interaction

- Electroweak Interaction

- ~6.7 pb

- ~2.0 pb

- ~0.9 pb

- ~0.09 pb

- BR(W  qq) ~ 67%
- BR(W  l)  ~ 11%, l=e,,

## Top Quark Yields

- Detector Improvements
- overall increase in  acceptance.
- 	D0, for instance:
- Electron sign detection
- e-ID improvement
- Better   pT resolution
- Better -ID
- Better soft lepton tagging
- Displaced vertex b-tagging

| Yields | Run II (*) |  |  |
| --- | --- | --- | --- |
| (CDF+D0) | (~0.40 fb-1) | (~8 fb-1) | S:B |
| Dilepton | ~16 | ~320 | ~3-4 |
| Lepton+4j | ~120 | ~2400 | ~0.4-0.7 |
| Lepton+4j / 1b | ~90 | ~1880 | ~3-4 |
| Lepton+4j /  2b | ~20 | ~400 | ~8 |
| Single top /  1b | ~28-11 | ~560-220 | ~0.05-0.13 |

- (*) tev_2000 Study Group estimates typically x2 larger

*Today’s*
*Performance*

## Experimental Limitations: B-Tagging

- B-tagging is extremely important in Top Physics:
- reduce backgrounds from light-quark/gluon jets
- reduce combinatoric effects
- tagging at the trigger level will reduce the trigger rate for interesting processes without loss of efficiency: tt  all jets, Z  bb
- A number of tagging algorithms are currently available with good performance:

**Lifetime tagging**: secondary vertex reconstruction
-                              impact parameter-based
- Example: D0 SVT
-    For a  taggable jet with 35<pT<55 GeV, |eta|<0.8:
-        b~46%, mistag~0.25%
-     P1tag(tt)~60%, P1tag(W+4 light jets)~1%

**Soft-lepton tagging**: P1tag(tt)~15%

- Improvements in tagging algorithms underway

## Experimental Limitations: Jet Energy Scale

- Dominant systematic uncertainty in most top quark measurements.
- _Jet Energy Scale Basics (D0)_:
- 	Jet corrections to compensate for detector and physics effects:
- 	 energy response ( R ) : use +jets events (non-zero missing ET estimates mismeasurement)
- 	 showering correction ( S ) : compensate for net energy flow through the cone boundaries during shower development
- 	 offset ( O ) : uranium noise, multiple interactions and pileup,  underlying event
- 	Some analysis further correct the jets to parton level (e.g. top mass).
- 	Corrections are flavor dependent.
- 	D0 Run I:
-           per-jet systematic ~2.5%+0.5 GeV
-            mt ~4 GeV in lepton+jet channel

## Outlining the Top Quark Profile

- Tevatron goal: outline the top  quark profile in a way as model -independent as possible .
- Could find significant deviations from the SM predictions which could indicate the presence of  New Physics:
- new particles
- new interactions
- Large top samples in Run II should allow us to be ambitious.
- _DISCLAIMER_
- Whenever possible, tried to extrapolate expected performance based on available Run II results. This will likely be conservative as improvements are expected.
- 	When that was not possible, typical references have been:

- The TeV-2000 Group Report, 1996, Fermilab-Pub-96/082.
- R. Frey *et al*, Fermilab-Conf-97/085 (1997), hep-ph/9704243

## Top Pair Production Cross Section

- Run I (L~120 pb-1) :
- 	tt/tt ~25% statistics dominated
- Run II (L~160-200 pb-1):
- 	Many preliminary measurements available in a variety of channels. No combined result available yet.
- 	Guess: tt/tt  < 20% with systematic              (b-tagging efficiency, background modeling, JES) starting to dominate stat uncertainty.
- Prospects for 4 fb-1:
- Statistical: ~4%
- Systematic:
- Background: ~2%
- JES: ~2%
- Radiation: 2-3%
- Acceptance (generator dependence): ~4%
- Luminosity: ~5%??
- Total: ~8-10% per experiment

- 1/N scaling

- Irreducible?

## Single Top Production Cross Section

-  t  |Vtb|2  the only direct measurement of |Vtb|
- Not  observed yet, despite the expected “large rate”  (s+t ~ 40% tt ).
- Event signature similar to ttl+jets but with lower jet multiplicity: large W+jets background.
- Existing upper limits (@ 95% CL):
- Accurate background predictions (W+jets: normalization and shape @ NLO) and efficient b-tagging extremely important. Use of sophisticated analysis techniques (NN, etc) mandatory for early observation and precise measurements.
- Prospects:
- Observation with ~1 fb-1
- Many systematics in common with tt. Many assumed to scale as 1/N.
- Possibility to use s-channel mode for smaller theoretical syst on |Vtb| to get final measurement at the Tevatron.

- Run I (~120 pb-1)

- Run II (~160 pb-1)

*CDF*:   s < 18 pb, t < 13 pb, s+t < 14 pb
*D**Ø*:     s < 17 pb, t < 22 pb

- Precision/experiment with 2 fb-1:
-   t ~ 13%(stat)  16%(syst) = 21%
-   |Vtb| ~ (21%(theory)  21%(exp))/2= 15%

## Top Quark Mass

- New D0 Run I measurement in lepton+jets
-     mt = 180.1  3.6 (stat)  3.9 (syst) GeV
- 	New Run I World Average:
- 	      mt = 178.0  2.7 (stat)  3.3 (syst) GeV
- Recent Run II preliminary results statistically competitive with Run I, although more work is needed to improve systematics.
- Dominant systematic uncertainty is JES.
- 	Improvements in Run II expected from:
- better constraints on MC modeling-related effects from large available dataset.
- In situ calibration from W jj in top events: early study claims 3% with 1fb-1
- Zbb selected using silicon track trigger to reduce systematic in energy scale for b-jets
- Run II goal is a total uncertainty on the top quark mass of 2.5 GeV (per experiment).

## Top Quark Width

- In general, there is no easy way to measure the _total top quark width_ in a model independent way.
- 	Single top cross-section gives strength of W-t-b vertex  (tWb).
- Large top width leads to interesting effects involving the interplay between the strong and weak interactions:
- 	Soft gluon (Eg~ t,)  radiation pattern can be affected by t.
- At high energy: production-decay interference dominates
- Near threshold: decay-decay interference dominates
- Still have to investigate in detail event rates, detector capabilities, etc.
- 	If possible at all, the Tevatron will likely be a better place than the LHC.

- Production

- Production
- +
- Decay

- Decay

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## Top Quark Charge

- The top quark charge, one of the most fundamental quantities characterizing a particle, has not been directly measured yet.
- A priori there is no guarantee that we are observing pair production of resonances with charge 2/3:
- A possible scenario (D. Chang et al, Phys Rev D59, 09153 (1999)):
- Introduce exotic 4th family of quarks and leptons + heavy Higgs triplet. In particular:
- This model accounts for all data, in particular Rb and AFBb (Z-bR-bR modified through mixing between b and Q1)
- The SM top quark is heavier (mt ~230 GeV) and has not been observed yet.
- The actual “discovered top-quark” is really Q4:
- Top quark charge measurement  b-quark charge measurement:
- Soft-lepton tagging: correlation between lepton and b charges, BUT small statistics and “background” from B0-B0 mixing,cl decays, etc.
- Secondary vertex tagging: b-jet charge distribution.
- This method doesn’t allow for a “direct measurement”, but mainly to rule out qt2/3 at some CL. It doesn’t tell us anything about the strength of the -t-t coupling...
- Performance of various analyses being evaluated.

- pp tt (W+b) (W-b)

- pp  Q4Q4  (W-b) (W+b)

- (Q1,Q4), qQ1 = -1/3, qQ4= -4/3 and mQ4=175 GeV.

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## Top Quark Spin

- The best evidence so far that the top quark has spin-1/2 comes from the agreement of tt with theoretical expectations.
- Spin 3/2 has not been ruled out and can be “natural” within composite models.
-  t ~ 1.4 GeV  top quark spin efficiently transferred to the final state
-  	  	             we can use polarization properties of the top quark as additional
-                                 observables for testing the SM (in particular the spin 1⁄2
-                                 hypothesis) and to probe for New Physics.
- Top quark decay products strongly correlated with the top quark spin:
- 	 can be directly observed in single top as the top quark is produced 100% polarized.
- Net polarization of top quark in pair production very small: N(t)=N(t) but large asymmetry between like- and unlike-spin configurations if proper spin quantization axes are chosen:
- 	  angular correlation between top and anti-top decay products
- D0 Run II dileptons: C>-0.25 @ 68% CL
- 	Prospects: C=0 ruled out at better than 2 with 2 fb-1

- i=1(-0.4)  for i=l(b)

## Discrete Symmetries: CP

- CP violation in the top sector is negligible within the SM                                            observation would be a clear indication of New Physics.
- b-quark very sensitive to the CKM phase
- top quark very sensitive to other kind of phases  CP studies at ~EW!!!
- A CP-violating phase (e.g. from extended Higgs sector or vertex corrections in  extended versions of SM) can endow the top quark with a large electric dipole moment:
- CP-sensitive observables may contain contributions from CP-violation in production AND decay (only relevant for pp  tt). Must disentangle between them.
- CP-even: e.g.                  ,
- CP-odd:
- Optimal observables usually improve over “naïve asymmetries”.
- Typical asymmetries from 2DHM or SUSY vertex corrections ~10-3- 10-2.
- Must understand detector systematics as well as ensure CP-blind selection.

- (dileptons)

- (lepton+jets)

- Top Pair

- Single Top

- (P0~100%)

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## Top Couplings to Gauge Bosons: g 

- Top Couplings to Gauge Bosons: g

- tt production is a direct test of the top coupling to gluons. Want to test not only effective coupling strength (total rate), but also the presence of a more complicated Lorentz structure:
- The above phenomenological form-factors can be expressed in terms of the coupling strengths (Ci) and  (New Physics scale) within EQFT.
- In order to disentangle the effects of the different operators, observables sensitive to different combinations need to be used: cross-section, tt invariant mass, polarization asymmetry, etc
- CP-conserving (2 limits)
- CP-violating

- _

- Within the SM:

- (chromo-magnetic dipole moment; CP conserving)

- (chromo-electric dipole moment; CP violating)

- (from top polarization asymmetry)

- (from tt; assume 5% syst)

- L=4 fb-1

- L=4 fb-1x 2 experiments

- (using single- or double-  leptonic transverse energy distributions)

## Top Couplings to Gauge Bosons: W

- 	In the SM:                          ; the rest = 0
- 	If                                                                 CP-violation

- Anomalous couplings can affect kinematic distributions  (e.g. lepton pT, lepton helicity angle, spin correlations,...) as well as inclusive observables (e.g. single top rate,...).

- In the SM:

## Top Couplings to Gauge Bosons: W (cont’d)

- L=4 fb-1x 2 experiments

- (using single- or double-  leptonic transverse energy distributions)

- W helicity measurements
- CP-violation:

- Run I (~120 pb-1):
-    CDF: F0 = 0.91  0.37(stat)  0.13 (syst)
-             F+ = 0.11  0.15(stat)
-    D0:   F0 = 0.56  0.31(stat+mt)  0.07 (syst)

- Run II (~160 pb-1)
-    CDF: F0 = 0.89  0.32(stat)  0.17 (syst)
-    D0:    F+< 0.24 @ 90% CL (topological)
-              F+< 0.24 @ 90% CL (b-tagging)

-  Prospects per experiment  for L=4 fb-1:  F0 ~ 6%, F+ ~ 3%

## Top Couplings to Gauge Bosons:  and Z

- Top Couplings to Gauge Bosons:  and Z

- -t-t
- Use pplvjjbb to measure (qt  x coupling strength) (U. Baur et al, Phys Rev D64, 094019, 2001)
- Z-t-t
- Use “Zstrahlung”: Z radiated off the top or anti-top quark line.
- Challenging, rate comparable to ttH (~few fb). Can look for anomalous couplings.

- Higher order process  low rate
- 	~60 selected double b-tagged events in 20fb-1
- Large contribution from ISR at the Tevatron dilutes sensitivity in total cross section.
- Decay-decay interference can lead to modifications in differential distributions.
- 20 fb-1:
- 	-0.21 qt -2/3 0.65 @ 95% CL
- 	(assuming tt(theo)=30%)
- My feeling: expected performance can likely be improved

## Top Couplings to Gauge Bosons: FCNC

- Tiny within the SM: BR(tcg)  10-10, BR(tc)  10-12                                                         		     BR(tcZ)  10-12, BR(tcH)  10-7
- Can be significantly enhanced in models beyond the SM (~103-104): 2HDM, SUSY, dynamical EWSB. In some models, the large Yukawa coupling makes BR(tcH)  1%.
- Implement effective lagrangian with FCNC interactions and set limits on coupling strengths, e.g.:
- Current bounds (LEP, HERA, CDF Run 1) are rather                                                                    weak and there is a lot of room for improvement in Run II.
- _Search strategy_:
- 	1) rare top decays (in tt or single top)
- 	2) anomalous single top production

- Assuming =0.1:
- (ugt)~230 pb
- (cgt)~9 pb
- (ggtc)~5 pb

- Observation is a signal
- of New Physics!

- _

- CDF Run I (@ 95% CL):
-   B(tc)+B(t u
-   B(tcZ)+B(t uZ

- 2 fb-1 (@ 95% CL):
-      B(tq)
-      B(t qZ

- Rather stringent limits should be possible

## New Particles in Top Production

- Many models of New Physics predict new particles preferentially coupled to the 3rd   family and in particular, the top quark:
- 	- Contamination in top sample: pptt, tt 0
- 	- Vector gauge bosons: qqgttt (Topcolor/Flavor, SU(3)C  SU(3)1,2  SU(3)3 )
- 	                                      qqZ’tt (Topcolor, U(1)Y  U(1)1,2  U(1)3 )
- 			            qqW’tb (Topflavor, separate SU(2) for t and b, extra-dim)
- 	- Charged scalars: e.g. cb+tb  (generic 2HDMs, MSSM, Topcolor...)
- 	- Neutral scalars:  ggTtt (Technicolor)
- 	- Exotic Quarks: qqW*tb’ (E6 GUT)
- Some of our tools:

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- Perform _model-independent searches_ for deviations in kinematic properties:                    e.g. tt, tb invariant masses and top pT distributions.

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- e.g. color-singlet vector resonance
-        with V= 0.2MV

- C. Hill et al, hep-ph/9312324

- Run I search of Z’ with =1.2%M:
-    CDF(D0): MZ’>480(560) GeV @ 95% CL
- 2 fb-1: limit extended to ~900 GeV (per experiment)

## New Particles in Top Production (cont’d)

- Make explicit use of polarization observables in different spin quantization bases:
- e.g. in cb+tb, + is a scalar and can be RH  tops appear RH (unpolarized) in the helicity (optimized) basis.
- Detect deviations in measured properties while not explicitly searching for these new particles (e.g. measure an effective axial coupling in g-t-t caused by contamination from a “wide” Z’)

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- T. Tait et al, hep-ph/0007298

- 3th

## Rare Top Quark Decays

- _Within the SM_
- tWb+Z, H: near or beyond threshold.
-  Tiny rates even with 15 fb-1. Its observation would signal New Physics.
- tWb+/g: potentially useful tools to learn about other top properties.
- tW+s/d:  constrain CKM matrix elements
-    From R and Vtb measurement
- _Beyond the SM_
- B(tWq)/B(tnon-W+X): model-independent measurement from
- Charged Higgs: if mH< mt–mb  t  H b (H  cs, , Wbb) competes with t  Wb
- Disappearance of SM ttWbWb signature (from R measuremnt)
- 	  sensitive only to region of large BR(t  H b) at low and large tan.
-  Anomalous  appearance at large tan
- Other: tt 0 (SUSY), tt b (TC2)

- Run II (~160 pb-1):
-   R=1.11+0.21–0.19 (CDF)
-   R=0.70+0.29-0.26 (D0)

- 2 fb-1: R~6% per experiment

- 2 fb-1: B(tHb)<11% (for tan>1)per experiment

- Significant extended reach in the tan -MH plane expected

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## Conclusions

- Tevatron Run II holds the promise of an exciting and comprehensive study of the Top Quark with the possibility of a surprise around every corner.
- Extremely rich spectrum of possible physics analyses: from canonical tests of QCD to searches for new particles, all with spectacular final states requiring to fully exploit the detector capabilities.
- Many measurements are expected to be limited by systematic uncertainties (both of experimental and theoretical origin):
- jet energy scale
- b-tagging
- energy flow in top events
- background modeling
- ...
- 	Tools and techniques developed at Tevatron to control systematic uncertainties to ~few % level will be invaluable at the LHC.