Bremsstrahlung spectra below 250 MeV have been measured colliding 500 MeV–electrons with Cu, Ag, and Au targets. The experimental intensity ratios relative to Cu are well described by an accurate analytical high-energy theory, which accounts both for Coulomb distortion and screening. This represents the first experimental verification of the discovery by Bethe-Maximon that leading-order quantum mechanical calculations, equivalent to quasiclassical approximations, become exact at high energies and small angles. It also shows that radiative QED effects play a minor role in the covered part of the spectral distribution within the accuracy (1.6%) of the present measurements.

Brazil

A. Mangiarotti

Germany

W. Lauth

D.H. Jakubassa-Amundsen

P. Klag

A.A. Malafronte

M.N. Martins

Denmark

C.F. Nielsen

U.I. Uggerhøj

Spectral distribution and Coulomb correction for nuclear bremsstrahlung induced by heavy targets

The Compact Linear Collider (CLIC) is an option for a future e+e- collider operating at centre-of-mass energies up to 3TeV , providing sensitivity to a wide range of new physics phenomena and precision physics measurements at the energy frontier. This paper is the first comprehensive presentation of the Higgs physics reach of CLIC operating at three energy stages: s=350GeV , 1.4 and 3TeV . The initial stage of operation allows the study of Higgs boson production in Higgsstrahlung ( e+e-→ZH ) and WW -fusion ( e+e-→Hνeν¯e ), resulting in precise measurements of the production cross sections, the Higgs total decay width ΓH , and model-independent determinations of the Higgs couplings. Operation at s&gt;1TeV provides high-statistics samples of Higgs bosons produced through WW -fusion, enabling tight constraints on the Higgs boson couplings. Studies of the rarer processes e+e-→tt¯H and e+e-→HHνeν¯e allow measurements of the top Yukawa coupling and the Higgs boson self-coupling. This paper presents detailed studies of the precision achievable with Higgs measurements at CLIC and describes the interpretation of these measurements in a global fit.

Israel

H. Abramowicz

Chile

A. Abusleme

Belarus

K. Afanaciev

CERN

N. Alipour Tehrani

Australia

C. Balázs

Y. Benhammou

Switzerland

M. Benoit

United States

B. Bilki

France

J.J. Blaising

M.J. Boland

Spain

M. Boronat

O. Borysov

Serbia

I. Božović-Jelisavčić

United Kingdom

M. Buckland

Poland

S. Bugiel

P.N. Burrows

T.K. Charles

W. Daniluk

D. Dannheim

R. Dasgupta

M. Demarteau

M.A. Díaz Gutierrez

Norway

G. Eigen

K. Elsener

U. Felzmann

M. Firlej

Romania

E. Firu

T. Fiutowski

J. Fuster

M. Gabriel

F. Gaede

I. García

V. Ghenescu

J. Goldstein

S. Green

C. Grefe

M. Hauschild

C. Hawkes

D. Hynds

M. Idzik

G. Kačarević

J. Kalinowski

S. Kananov

W. Klempt

M. Kopec

M. Krawczyk

B. Krupa

M. Kucharczyk

S. Kulis

Czechia

T. Laštovička

T. Lesiak

A. Levy

I. Levy

L. Linssen

S. Lukić

A.A. Maier

V. Makarenko

J.S. Marshall

V.J. Martin

K. Mei

G. Milutinović-Dumbelović

J. Moroń

A. Moszczyński

D. Moya

R.M. Münker

A. Münnich

A.T. Neagu

N. Nikiforou

K. Nikolopoulos

A. Nürnberg

M. Pandurović

B. Pawlik

E. Perez Codina

I. Peric

M. Petric

F. Pitters

S.G. Poss

T. Preda

D. Protopopescu

R. Rassool

S. Redford

J. Repond

A. Robson

P. Roloff

E. Ros

O. Rosenblat

A. Ruiz-Jimeno

A. Sailer

D. Schlatter

D. Schulte

N. Shumeiko

E. Sicking

F. Simon

R. Simoniello

P. Sopicki

S. Stapnes

R. Ström

J. Strube

K.P. Świentek

M. Szalay

Higgs physics at the CLIC electron–positron linear collider

We outline the opportunities to study the production of the Standard Model bosons, <math id="M4"><mrow><msup><mrow><mi>W</mi></mrow><mrow><mo>±</mo></mrow></msup></mrow></math>, <math id="M5"><mrow><msup><mrow><mi>Z</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math>, and <math id="M6"><mrow><msup><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math>, at “low” energies at fixed-target experiments based on possible future ultrahigh-energy proton colliders, that is, the High-Energy LHC, the Super proton-proton Collider, and the Future Circular Collider hadron-hadron. These can be indeed made in conjunction with the proposed future colliders designed to reach up to <math id="M7"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>100</mn></math> TeV by using bent crystals to extract part of the halo of the beam which would then impinge on a fixed target. Without disturbing the collider operation, this technique allows for the extraction of a substantial amount of particles in addition to serving for a beam-cleaning purpose. With this method, high-luminosity fixed-target studies at centre-of-mass energies above the <math id="M8"><mrow><msup><mrow><mi>W</mi></mrow><mrow><mo>±</mo></mrow></msup></mrow></math>, <math id="M9"><mrow><msup><mrow><mi>Z</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math>, and <math id="M10"><mrow><msup><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math> masses, <math id="M11"><msqrt><mi>s</mi></msqrt><mo>≃</mo><mn>170</mn></math>–300 GeV, are possible. We also discuss the possibility offered by an internal gas target, which can also be used as luminosity monitor by studying the beam transverse shape.

R. Mikkelsen

J.P. Lansberg

Near-Threshold Production of , , and at a Fixed-Target Experiment at the Future Ultrahigh-Energy Proton Colliders

When an ultrarelativistic electron traverses two closely spaced foils, a radiation spectrum ‘resonance’ appears, arising from the photon formation length extending from one foil, across the gap and into the second foil. Several theoretical approaches yield quite different answers to the spectral location of this ‘resonance’, and we have therefore in the CERN NA63 collaboration addressed the question experimentally with a 178 GeV electron beam. The experimental technique used – where a variable gap separates two thin gold foils – allows for a direct measurement of a length that is closely related to the distance over which the photon formation takes place. These are the first measurements to observe the gap dependence of the energy of the ‘resonance’ in the radiation spectrum from a structured target on a truly macroscopic scale up to 0.5 mm. The results are compared with the theory of Baier and Katkov, with both the modified and unmodified theories of Blankenbecler as well as with a naïve, straightforward expectation. Surprisingly, the experiment shows a clear preference for the two latter, comparatively unsophisticated, approaches.

K.K. Andersen

S.L. Andersen

H. Knudsen

R.E. Mikkelsen

H.D. Thomsen

T.N. Wistisen

J. Esberg

Italy

P. Sona

Netherlands

T.J. Ketel

Measurements of the spectral location of the structured target resonance for ultrarelativistic electrons