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<center>HEP_01 : *ILC Top* </center>

_Summary_ :<br>
The ILC Physics Case can be summarized in two main domains:
precision measurements and discovery potential.
Whereas the principal aim of the precision measurements concerns the Higgs, 
a secondary but very important aim is to study the top: to determine accurately its mass
and to measure its couplings to the SM vector bosons.
The top mass will be obtained at 350 !GeV, by scanning the threshold of the top pair production.
The top couplings to the photon and the Z0 will be measured at about 500 !GeV.
<br>
For both measurements, a precise mastering of the !ElectroWeak loop corrections is essential since
it appears that they induce sizeable corrections to the leading mechanisms (typically 5-10%)
far larger than the precision achievable at the ILC.
<br>
The goals of the !TYL project “top-ILC” are twofold: strengthen further the 500 !GeV analysis that has been developed in the past years using semi-leptonic events [1], and design means to control theoretically and experimentally the !ElectroWeak loop corrections.
<br>
In that respect, following the first top-ILC workshop held in !KeK (2013) one of the approach that is pursued is to assess the potential of the 
double leptonic events, where both W’s decay leptonically.
<br>
Using Monte Carlo events provided by GRACE [2], it has been shown that experimentally one can cope with the two missing neutrinos and that a Matrix Element [3] analysis of the events 
using Leading Order expressions [4] should provide top-coupling measurements with an accuracy similar to the one attained using the semi-leptonic events, but with different systematical effects.

_French members_ :<br>
*F. Le Diberder*, S. Bilokin, P. Colas, E. Kou, R. Poeschl, F. Richard, V. Shavy, M. Titov, B. Tuchming

_Japanese members_ : <br>
*K. Fujii*, A. Ishikawa, D. Jeans, Y. Kiyo, M. Kurata, Y. Kurihara, T. Suehara, Y. Sato, Y. Sumino, T. Tanabe, H Yamamoto

_References_ :<br>
[1] M.S. Amjad et al. : arXiv:1307.8102 (2013) <br>
[2] Progress of Theoretical Physics, Vol. XX, No. X, October 1999 <br>
[3] H.J. Behrends et al., CELLO Collab. Z. Phys. C43 (1989)  <br>
[4] G. Kane, G. Ladinsky and C.P. Yuan, Phys. Rev. D 45 (1992) <br>


<center>------------------------------ </center>

<center>HEP_04 : *Cosmological tests of Fundamental Physics* </center>

_Summary_ :<br>

Several astrophysical or cosmological observations (evidences for dark matter, baryon asymmetry, inflation...) require an extension of the Standard Model of particle physics (so-called “beyond the standard model” (BSM) physics).  The links between cosmology and particle physics heavily rely on the understanding on the history of the universe, which is often based on standard assumptions. For instance: an inflationary epoch produces a quasi-power law spectrum of perturbations (seeds of current structures) and ends in a radiation dominated period, during which  conventional  electroweak symmetry and QCD breaking happen as crossovers, according to the SM.  Dark Matter is usually considered to be a particle relic, once in thermal contact with other SM species, etc. We are exploring possible departures from this simple picture. In the classically conformal extension of the SM, S. Iso, P. Serpico, and K. Shimada found that the chiral condensation in QCD can play an important role in the dynamics of the electroweak symmetry breaking. The phase transition becomes of the first order type and accordingly generates large gravitational waves that can be detected by future gravitational wave detectors [2]. Further consequences of this scenario, such as signatures of a late thermal inflationary phase and implications for dark matter, are being investigated. Always related to gravitational waves, it is well known that the LIGO interferometers have detected their first sources of gravitational waves, from coalescences of binary black holes (BHs). While such binaries have long been considered an attractive candidate, the mechanism to produce them is not established, yet, in particular for such high masses (about 30 times the mass of the sun). It has also been conjectured that such BH may be of primordial origin. Their formation requires a significant departure from the simplest inflationary models, and at the same time it would lead to non-standard cosmological signatures, which can be searched for. In [3], we studied the impact of accretion of primordial stellar mass black holes on  CMB anisotropies, finding stringent bounds. We are currently extending this study to massive and supermassive primordial black holes, which requires a careful treatment of the accretion in presence of a “dark matter” halo surrounding the black hole. 

_French members_ :<br>
*P. Serpico*, 
G. Bélanger, 
F. Boudjema

_Japanese members_ : <br>
*K. Kohri*,
T. Hasegawa,
N. Hiroshima,
S. Iso,
T. Mori  

_References_ :<br>
[1] S. Iso, K. Kohri and K. Shimada,
"Dynamical fine-tuning of initial conditions for small field inflation,"
  Phys. Rev. D  93, 084009 (2016)
  [arXiv:1511.05923]<br>
[2] S. Iso, P. D. Serpico and K. Shimada, "QCD-Electroweak first order phase transition in supercooled universe,''  
 Phys. Rev. Lett. 119, 141301 (2017)  [arXiv:1704.04955] <br>
[3]  V. Poulin, P. D. Serpico, F. Calore, S. Clesse and K. Kohri,
“CMB bounds on disk-accreting massive primordial black holes,''
  Phys. Rev. D  96,  083524 (2017)
  [arXiv:1707.04206]


<center>------------------------------ </center>


<center>HEP_06 : *Charged lepton flavour violation-searching for indirect signals of new physics* </center>

_Summary_ :<br>
 New particles and interactions beyond the Standard Model (SM) of particle physics are required to explain neutrino masses and mixing angles. The search for traces of this new physics (NP) is pursued on many fronts. One possibility is to look directly for the new particles implicated in neutrino mass generation, for instance at the LHC. A complementary approach seeks indirectly new interactions among rare processes, such as charged lepton flavour violation (CLFV). CLFV transitions can be induced by the observed massive neutrinos in the SM, at unobservable rates suppressed by 10 e-48. A detectable rate would point to the existence of new heavy particles, as may arise in models that generate neutrino masses, or that address other puzzles of the SM such as the hierarchy problem. Observations of CLFV are therefore crucial to identifying the NP of the lepton sector, providing information complementary to direct searches. The experimental sensitivity to a wide variety of CLFV processes is systematically improving. Current bounds on branching ratios of the muon to electron flavour changing processes are currently of order of 10 e-13. Future experimental sensitivities should improve by several orders of magnitude, in particular, the COMET and Mu2e experiments which aim to reach a sensitivity to &#956;-e conversion on nuclei of &#8764; 10 e-16. Given such rapid experimental progress in the future, our main area of research is to study in details physics opportunities for the CLFV processes, and explore new opportunities, by the joint collaboration of theorists and experimentalists between Japan and France. We have already made the first research achievement, on the study of spin-depended muon to electron conversion, which has been published in a scientific journal of Physics Letters in 2017 [1]. This physics case has never previously been considered. We will explore further unique physics cases in our research collaboration. To achieve this goal, we are planning to organize informal meetings and workshops between French and Japanese.

_French members_ :<br>
*S. Davidson*,
A. Saporta,
A. M.Teixeira 


_Japanese members_ : <br>
*Y. Kuno*,
J. Sato,
K. Tobe,
M. Yamanaka,
S. Kanemura

_References_ :<br>
[1] V. Cirigliano, S. Davidson and Y. Kuno, “Spin-dependent &#956;&#8594;e conversion“,  Phys. Lett. B771 (2017) 242-246
<br>
[2] S.  Davidson, Y. Kuno, A. Saporta, “Spin-dependent &#956;&#8594;e conversion on light nuclei”, Eur.Phys.J. C78 (2018) 109 
<br>

<center>------------------------------ </center>

<center>HEP_07 : *SiW ECAL* </center>

_Summary_ :<br>
A compact and highly granular electromagnetic calorimeter is one of the key requirements for PFA high precision jet reconstruction, and for full realization of ILC's physics potential.
The aim of this project is R&D of a silicon-tungsten calorimeter.
The main aim is to further develop the "technical prototype", in which different technical approaches to detector construction are tested and compared.
Aspects to be investigated include improvements in electrical design, thinner front-end boards, and silicon sensors of varying thickness.
Several beam tests of this prototype are foreseen during the year.
An important milestone is to develop a "long slab", chaining several unitary elements to make a large detector element, as will be needed in a full detector.
Physics analyses which make significant use of the ECAL will be further studied, with an emphasis on the reconstruction and use of tau lepton decays to probe for new physics.
An important aspect will be to quantify how different ECAL design choices (which may, for example, involve significantly different costs) impact such analyses.

_French members_ :<br>
*V. Boudry*, V. Balagura, J-C. Brient, R. Poeschl, F. Magniette

_Japanese members_ : <br>
*D. Jeans*, T. Suehara, K.Kawagoe, T. Yoshioka

_References_ :<br>
[1] T.H.Tran, "ILD !SiW ECAL and sDHCAL dimension-performance optimisation", report at LCWS'13, arXiv:1404.3173 [physics.ins-det]<br>
[2] Ch.Kozakai et al., "Robustness of a !SiECAL used in Particle Flow Reconstruction", report at LCWS'13, arXiv:1404.0124 [physics.ins-det]<br>
[3] T.Tomita et al., "A study of silicon sensor for ILD ECAL", report at LCWS'13, arXiv:1403.7953 [physics.ins-det]<br>
[4] Editors: T.Behnke et al., "The International Linear Collider Technical Design Report - Volume 4: Detectors", arXiv:1306.6329 [physics.ins-det]

_website_ :<br>
 https://twiki.cern.ch/twiki/bin/view/CALICE/SiWEcal
Topic revision: r16 - 2018-09-21 - 12:59:14 - IsabelleRippBaudot
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