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SNOWMASS-EF  August 2013

SNOWMASS-EF August 2013

Subject:

list of bulletin points from the EW WG

From:

Doreen Wackeroth <[log in to unmask]>

Reply-To:

snowmass-ef Snowmass 2013 Energy Frontier conveners <[log in to unmask]>

Date:

Sat, 3 Aug 2013 02:05:13 -0400

Content-Type:

MULTIPART/MIXED

Parts/Attachments:

Parts/Attachments

TEXT/PLAIN (29 lines) , EWWGlistofbulletinpoints.txt (1 lines)

Dear Chip and Michael,
Please find attached a text file with the bulletin points from the
Electroweak WG.
Cheers,
Doreen and Ashutosh

--
----------------------------------------------------------
  Doreen Wackeroth
  Professor of Physics

  Department of Physics
  239 Fronczak Hall
  University at Buffalo - The State University of New York
  Buffalo, NY 14260-1500, USA

  Phone: (716) 645-5445
  Fax: (716) 645-2507
  Homepage: http://ubpheno.physics.buffalo.edu/~dow
  E-mail: [log in to unmask]

----------------------------------------------------------

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Study of Electroweak Interactions at the Energy Frontier
=========================================================

* The knowledge of the Higgs mass has sharpened the predictions of
these EWPOs such that the predictions are a factor of 2-4 more
precise than the experimental measurements.

* In extensions of the SM, which are associated with the
electroweak symmetry-breaking sector, these EWPOs usually receive corrections
due to quantum loops (due to e.g. supersymmetric particles or
techni-fermions), or due to effective operators (induced for example in
strongly-interacting light Higgs models), or due to Kaluza-Klein
modes in extra-dimensional models.

* $M_W$ and $\sin^2\theta_\eff^l$ typically have different sensitivities
to the sources of new physics. This may be demonstrated by the
parametrisation of new physics in the gauge boson self-energies in
terms of the $S$, $T$ and $U$ "oblique" corrections. Fixed values of
$M_W$ and $\sin^2\theta_\eff^l$ correspond to lines in the $S-T$ plane
with different slopes. Thus, improved measurements of both EWPOs can
constrain all of the above sources of new physics in a relatively
model-independent fashion.

* The current world average $M_W$ has a precision of 15 MeV,
dominated by the combined Tevatron measurement, which has a precision
of 16 MeV based on the analysis of partial datasets. CDF and D\O\
have projected that analyses of the full Tevatron statistics can
yield a 10 MeV measurement, assuming a factor of two improvement in
the uncertainty due to parton distribution functions,
improvement in the calculation of radiative corrections and improved
understanding of the trackers and calorimeters.

* Studies based on pseudo-data have demonstrated that measurements
of boson distributions with the 2011-2012 LHC data may be able to
improve the PDFs relevant for the $M_W$ measurement by a factor of
two in the near future, enabling the Tevatron potential for $M_W$ to
be realized.

* Enormous statistics of $W$ bosons and control samples at the LHC
offer the prospect of higher $M_W$ precision. Studies based on
pseudo-data have shown that the PDF uncertainty in $M_W$ is about
twice as big at the LHC as the Tevatron, due mainly to the larger
fraction of sea quark-initiated production. Thus, further
improvement by a factor of 2-3 in the PDFs will be required, beyond
what is needed for the Tevatron. Furthermore, additional
improvements in the QED radiative correction calculations and
NNLO+NNLL generators for $W$ and $Z$ bosons will likely also be
required. However, considering the 15-year time scale for the
ultimate $M_W$ measurement from the LHC, we consider a target
precision of 5 MeV to be appropriate for the LHC.

* Studies of the M_W measurement at the ILC using the threshold scan
and final state reconstruction have been updated. The ILC TDR
assuming 100 fb-1 quotes an uncertainty of 6-7 MeV for MW measured
at the WW threshold. The updated study projects that the ILC will
be able to perform the M_W measurement with a precision of 4.5 and
2.5 MeV for 100 fb-1 and 480 fb-1 respectively. These estimates
assume an electron(positron) polarization of 90%(60%) and beam
energy calibration using final state reconstruction of Z->mu mu and
J/Psi etc.

* The circular electron-positron TLEP machine, running at the $WW$
threshold, can produce very high statistics for the $M_W$
measurement, and is likely to achieve energy calibration at the
level of 0.1 MeV using teh resonant depolarization technique. This
potential motivates further studies of other systematics achievable
at TLEP. Given an integrated luminosity that can enable a
statistical precision of $\sim 0.3$ MeV with four detectors, further
investigations of related issues are clearly warranted. Assuming a 1
MeV error in the threshold shape calculation the target uncertainty
is 1.2 MeV.

* The measurement of $\sin^2 \theta_\eff$ from LEP and SLC have
averaged to a precision of $16 \times 10^{-5}$, albeit with a $\sim
3 \sigma$ difference between them. Additional, especially improved,
measurements will be valuable to shed light on this difference.

* A measurement of $\sin^2\theta_\eff^l$ using the full Tevatron dataset
is projected with a precision of $41 \times 10^{-5}$. This
measurement will be interesting to compare with LEP and SLC.

* Compared to the Tevatron, measurement of $\sin^2 \theta_\eff^l$ at the
LHC is handicapped by a larger sensitivity to PDFs due to the
dilution of the quark and antiquark directions. As with the $M_W$
measurement, considerable control of the experimental and production
model uncertainties will be required. Under the condition that a
factor of 6-7 improvement on PDFs is achieved (a condition also
required for the $M_W$ target for the LHC), a projected uncertainty
on $\sin^2\theta_\eff^l$ of $21 \times 10^{-5}$ is obtained. This
precision is similar to the current LEP and SLC measurements and is
valuable before the advent of future lepton colliders.

* Considerably more precise measurements of $\sin^2 \theta_\eff^l$ are
highly desirable for taking the stringency of the SM tests to the
next order of magnitude. Such measurements are possible at future
lepton colliders running on the $Z-$pole such as ILC/GigaZ and TLEP.

* The ILC/GigaZ projection for the precision on $\sin^2 \theta_\eff^l$ is
$1.3 \times 10^{-5}$ without including beam energy and theory systematics.
This is a factor of 10 improvement on the current
world average. The corresponding TLEP target uncertainty is $0.3 \times 10^{-5}$
when extracted from A_LR at the Z peak.

* TLEP may have the potential to go beyond ILC/GigaZ in the precision
on $\sin^2\theta_\eff^l$, which also warrants a detailed study. The
target precision on $\sin^2 \theta_\eff^l$ is $0.3 \times 10^{-5}$
when extracted from A_LR at the Z peak without including beam energy
and theory systematics. In principle, the precision at TLEP could
be high enough that all aspects of EWPOs, both theoretical and
experimental, need to be revisited.

* These improved measurements and predictions of EWPOs will enable
stringent tests of the SM and of BSM scenarios. Once a discovery is made EWPOs
will help to test and predict other aspects of the BSM model.

* Measurements of $M_W$ at the few MeV level, and $\sin^2 \theta_\eff^l$
at the level of $10^{-5}$, require that the parametric uncertainties
from $m_{top}, M_Z$ and $\alpha_{had}$ (the contribution to the running
of $\alpha_{EM}$ from hadronic loops) as well as the missing higher
order calculations be addressed. It is anticipated that calculations
in the coming years will reduce the effect of missing higher-order
calculations to a sub-dominant level. Parametric uncertainties from
$m_{top}$ and $\alpha_{had}$, if reduced by a factor of two compared
to current uncertainties, will prevent them from exceeding the total
precision on $M_W$ and $\sin^2\theta_\eff^l$. A factor of 3-4 improvement
would be desirable, to $\delta m_{top} \sim 0.3$ GeV and $\delta
\alpha_{had} \sim 0.3 \times 10^{-5}$. The LHC may be able to
achieve $\delta m_{top} \sim 0.5$ GeV but further progress at the LHC
will likely be limited by theoretical uncertainties in the
non-perturbative QCD effects associated with translating the
kinematically-reconstructed $m_{top}$ to the pole mass.
Further considerable improvement in parametric and theory uncertainties is needed
for the target uncertainties at ILC and TLEP.

* The EFT formulation is not limited to specific models; any high
energy theory can be reduced to a low-energy EFT and the former will
specify the values of operator coefficients in the latter. Therefore,
EFT operators provide a general method of parametrizing the effects
of new physics at a high scale.

* Studies of vector boson scattering and triboson production have
become possible, for the first time, at the LHC.

* For the next decade, the LHC will continue to be the facility to
explore these processes at higher levels of precision.

* The HL-LHC is needed to demonstrate that the Higgs couplings to the
electroweak vector bosons is an essential component of the
unitarization mechanism for vector boson scattering. The definite
proof of unitarization via teh Higgs will be difficult at an
integrated luminosity of 300 fb$^{-1}$.

* The sensitivity to higher-dimension operators improves by a
factor of 2-3 with the HL-LHC, in comparison with the 300 fb$^{-1}$
at the LHC.

* Triboson production is also sensitive probe of higher
dimension operators, complementary to vector boson scattering.
This process becomes rapidly more sensitive with increasing beam energy.

* We expect anomalous quartic couplings induced by dimension eight operators
to be probed with rapidly increasing sensitivity for higher energy colliders.

* Comparison to a 1 TeV ILC sensitivity shows that the LHC is more
sensitive to quartic anomalous couplings by an order of magnitude.


Conclusions:

A) The W mass measurement at the LHC is competitive with the ILC at 100 fb-1.

B) For all other EWPOs lepton colliders will make significantly more precise measurements of EWPOs than the LHC.
This is especially the case for sin^2theta_eff^l where ILC will improve upon LEP/SLC by an order of magnitude.
Prelimary estimates of the TLEP potential find that the current LEP measurement of MZ improves by a factor of 10,
the projected ILC accuracy of MW and sin^2theta_eff^l by a factor of about 3 and 4 respectively.

C) Comparison to a 1 TeV ILC sensitivity shows that the LHC is more
sensitive to quartic anomalous couplings by an order of magnitude.

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