# Presentation: 867035

## Revisiting EW Constraints at a Linear Collider

- Work done by
- S. Heinemeyer	P. Rowson	U. Baer
- G. Weiglein	M. Woods	+ many others
- K. Moenig	B. Schumm
- R. Hawkings	D. Gerdes
- G. Wilson	L. Orr

- Lawrence Gibbons
- Cornell University

## Why improve EW parameters?

- Dominant theory limitations
-  Mt
-   = QED(MZ)-QED(0)
- Three key measurements
- tt threshold:        Mt
- Z pole:                  sin2 eff
- W+W- threshold:  MW

- Chicago LC Workshop

- 7 Jan 2002

## Why improve EW parameters?

**Why improve EW parameters?**

- Dominant theory limitations
-  Mt
-   = QED(MZ)-QED(0)
- Three key measurements
- tt threshold:        Mt
- Z pole:                  sin2 eff
- W+W- threshold:  MW
- Indirect prediction power
- MW to 4 MeV
- MH to +- 8%
- Caveat: must improve 

- Chicago LC Workshop

- 7 Jan 2002

## tt threshold: Mt

- Kinematic reconstruction
- Hadronic machines systematics limited
- Mt to ~ 2-3 GeV
- Measures ~ pole mass
- Pole mass ill-defined in QCD
- Nonperturbative ambiguity of (QCD) in definition

- Eg., poorly-behaved perturbation series for threshold cross-section
- Want short-distance mass, eg. Mt(Mt)
- EW constraints, MB, ...

- Chicago LC Workshop

- 7 Jan 2002

## tt threshold: Mt

- Large t (~1.4 GeV) a boon
-  t >> QCD  no narrow resonances, smooth line shape
- Allows calc. in pert. QCD
- infrared cutoff, smearing

- A few short-distance mass def’s near threshold
- 1S peak position stable to ~200-300 MeV
- Masses related to MS mass via pert. QCD series
- Modest luminosity required
- 10 fb-1  40 MeV stat. uncertainty

**M****t**** to ********200 MeV **

- Chicago LC Workshop

- 7 Jan 2002

## Other top measurements

- Threshold
- Total top width
- Peak  ~ 1/t
- 100 fb-1  ~2% uncertainty
- Yukawa coupling
- 115 GeV Higgs  5-8% increase in threshold  
- 2-3% uncertainty in predicted cross section
- 14-20% on Yukawa coupling
- Sensitivity drops for increasing Higgs mass

- High energy
- Yukawa coupling
- e+e-  tth  W+W-bbbb
- 800 GeV (1000 fb-1): ~5.5%
- 500 GeV: ~4x worse
- All neutral and charged current couplings
- Measure/limit mostform factors at 1% level
- 500 GeV, 100-200 fb-1
- ttZ couplings unique to LC
- production polarization asymm.
- Test QCD, EW radiative corr.
- (e+e-  tt  ljjbb) to < 1%

- Chicago LC Workshop

- 7 Jan 2002

## sin2W status

- At Z pole: dominated by
- LEP b quark AbFB
- SLD ALR
- AbFB: not in best agreement w/ SM
- Lower energy scales
- Recent NUTEV result
- “3 high”
- atomic parity violation
- ~2  low

- Chicago LC Workshop

- 7 Jan 2002

## Giga-Z

- Revisit Z pole with a linear collider
- Expect  ~ 5 x 1033 cm-2s-1 
- 109 Z decays in ~ 107 s
- Could contemplate interruption of high energy program
- 1010 Z decays:  3-5 year program
- Would need simultaneous low energy/high energy running
- Mainly heavy flavor program benefits
- Polarization
- 80% electron polarization a given
- positron polarization an enormous boon: achievable?
- 60% polarization desirable

- Chicago LC Workshop

- 7 Jan 2002

## Z pole scan

- Current measurements systematics limited
- 2x improvement on eff. syst. (no th’y improvement for )
- 4x Rl, 30% 0 improvements
- Ebeam/ Ebeam: potentially 10-5 w/ Moller spectrometer?
- 2x Z improvement
- Energy spread: beamstrahlung to (2%): further study needed
- Z, l limited otherwise
- monitor with Bhabha acolinearity? 5 point scan?

- Chicago LC Workshop

- 7 Jan 2002

## ALR  sin2W

- ALR the most sensitive variable to sin2W
- GigaZ = 2000x SLD
- SLD: ALR=0.15140.0022

- e+ polarization:
- None: P-/P-  dominates uncertainty: 0.25% (optimistically) feasible
-  ALR to 4x10-4
- With: use Blondel scheme (combine NLL,NRR,NLR,NRL)
- 60% P+  effective 95% polarization, don’t need absolute polarization
-  ALR to 10-4

- Chicago LC Workshop

- 7 Jan 2002

## ALR  sin2W: experimental issues

- polarization
- Blondel scheme: need *relative* L,R polarizations to 10^-4
- Appears feasible
- Systematics: polarimeters after IP?
- Difficult w/o crossing angle
- Can positron helicity be switched rapidly enough relative to beam stability?
- What is the relevant time scale?

- Chicago LC Workshop

- 7 Jan 2002

## ALR  sin2W: experimental issues

- Z- interference: ALR changes rapidly away from pole
- Control E/E to 10-5
- Control of beamstrahlung (effective s shift)
- Ignore: ALR shift of 9x10-4 at TESLA, much worse at NLC
- E scale from Z pole scan + LEP MZ.  Same beam parameters?
- Trade  for reduced beamstrahlung
- NLC:12518 MeV E shift for factor 5  penalty
- If beam issues controlled:

**sin****2********W**** to ********0.000013 **

- Chicago LC Workshop

- 7 Jan 2002

## Zbb vertex

- Ab: 2.5–3.5  discrepancy w/ SM persists
- Stat’s dominated measurement
- Complementary sensitivity to “new physics” than S,T,U
- Rb=bb/  had
- Measure corrections to Zbb vtx
- EW prop., QCD corr. cancel
-  5x improvement from b-tagging
- Ab(=3/4 AFB,LR)
- P+ =60%: 15x improvement
- P+ =0: 6x improvement

- Chicago LC Workshop

- 7 Jan 2002

## b physics at Giga-Z?

- Great potential
- Production flavor tagging
- D2~0.6 vs 0.1-0.25
- D=1-2P(mistag)
- Large boost
- b’s well-separated
- Excellent b tagging
- Well-defined initial state:
- ”-reconstruction”
- Stiff competition
- Mainly cross checks others on “standards”
- CKM unitarity angles
- ms

- Chicago LC Workshop

- 7 Jan 2002

## Some unique b physics

- Bs Xlrate
- Constrain uncontrolled uncertainty in OPE from quark-hadron duality violations
- Polarized b decays (G. Hiller)
- Probe bRqL (SM) vs bLqR (new physics)
- 109 Z’s gives interesting reach in (spin,p) asymmetry
- BXs
- Emiss constraints + well-separated b decays allow access
- Non-SM physics affects Xs, Xsl+l- differently
- reach?  B bkg?
- Production flavor tagged B00

- Chicago LC Workshop

- 7 Jan 2002

## W+W- threshold: MW

- Potential indirect precision: MW ~ 4 MeV
- Tevatron/LHC: expect 15-20 MeV precision (syst. limited)
- EW constraints: can LC approach indirect precision?
- Ebeam, beamstrahlung appear to be most serious issues
- high energies: direct reconstruction needs Ebeam constraint
- E scale likely to be pinned via MZ
- Beamstrahlung scales as (Ebeam) 2
- Threshold needs:
- Ebeam to 10-5: potentially e+e-  Z, Z  ,ee?
- Stat’s for s vs time?
- Beamstrahlung: control shape distortion to 0.12%2 MeV
- Bhabha acolinearity?
- Theory: cross section shape to 0.12%

-  explore threshold region

- Chicago LC Workshop

- 7 Jan 2002

## W+W- threshold: MW

- 100 fb-1  5 MeV (stat)
- 60% e+ polarization
- ~107 sec
- Strategy: t-channel dominates
- 75% e+Re-L
- 15% e+Le-R  (~ no W+W-)
- 10% other
- Polarization
- 0.25% absolute or e+e-  Z + Blondel scheme
- P+=0: doubles  required

**M****W**** to ********7 MeV **

- Chicago LC Workshop

- 7 Jan 2002

## EW reach summary  (U. Baer et al, hep-ph/0111314)

**EW reach summary****  **(U. Baer *et al*, hep-ph/0111314)

- Run IIB: 15 fb-1
- Run IIB*: 30 fb-1

- LC improvement in sin2eff:
- dedicated fixed target Moller scattering exp.
- GigaZ improvement in Mt:
- from improved s (Z pole scan)

- Chicago LC Workshop

- 7 Jan 2002

## Constraint potential: S,T,U

- S,T,U
- Parameterize effect of new physics on W, Z vacuum pol.
- EW variables linear fcn’s of STU
- Sensitivity (nowLC/GigaZ)
- S: 0.11  0.05 (0.02 w/ U=0)
- T: 0.14  0.06 (0.02 w/ U=0)
- U: 0.15  0.04
- Peskin,Wells (PRD 64, 093003)
- Survey models w/ heavy Higgs:
- Significant dev’s in S,T from SM observable w/ GigaZ

- M. Peskin, J. Wells

- eg. technicolor
- S, T > ~0.1
- 5 deviation from SM

- Chicago LC Workshop

- 7 Jan 2002

## Constraint potential: SUSY

- MSSM Higgs, light scalar top seen at Tevatron/LHC/LC
-                    at LC yields
-    mass, stop-sector mixing to 1%
- Various MSSM constraints
- sin2W vs MW predicted vs. measured
- Mh predicted vs measured
- Constraint on mass of heavy scalar top

- S. Heinemeyer, G. Weiglein

- Chicago LC Workshop

- 7 Jan 2002

## Conclusion

- Low energy program adds great value to the overall LC and general HEP program
- Powerful constraints provide
- Self-consistency checks for interpretation of new particles
- Extension of effective mass reach
- Unique flavor physics contributions a bonus
- Beam energy and polarization issues need further study
- Solutions will involve monitoring instrumentation that must be allowed for in baseline designs

- Chicago LC Workshop

- 7 Jan 2002