The HERA polarimeter and the first observation of electron spin polarization at HERA

Barber, D. P.; Bremer, Hartmut; Böge, M.; Brinkmann, R.; Brückner, W.; Büscher, C.; Chapman, Michael; Coulter, K. P.; Delheij, P. P. J.; Düren, M.; Gianfelice-Wendt, E.; Green, P.E.W.; Gaul, H.G.; Gressmann, H.; Häusser, O.; Henderson, R.; Janke, T.; Kaiser, H.; Kaiser, R.; Kitching, P.; Klanner, R.; Levy, P.; Lewin, H. C.; Lomperski, M.; Lorenzon, W.; Losev, Leonid L; McKeown, R. D.; Meyners, N.; Micheel, B.; Milner, R.; Mücklich, A.; Neunreither, F.; Nowak, W.-D.; Patel, P. M.; Rith, Klaus; Scholz, C; Steffens, E.; Veltri, M.; Vetterli, M. C.; Vogel, W.; Wander, W.; Westphal, Douglas L.; Zapfe, K.; Zetsche, Frank

doi:10.1016/0168-9002(93)90924-7

Cited by 105 publications

(71 citation statements)

References 17 publications

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“…Starting from the year 2004, spin rotators on either side of the ZEUS detector changed the transverse polarisation of the beam into longitudinal polarisation and back again. The electron beam polarisation was measured using two independent polarimeters, the transverse polarimeter (TPOL) [36] and the longitudinal polarimeter (LPOL) [37]. Both devices exploited the spindependent cross section for Compton scattering of circularly polarised photons off electrons to measure the beam polarisation.…”

Section: Experimental Set-upmentioning

confidence: 99%

Inclusive dijet cross sections in neutral current deep inelastic scattering at HERA

Abramowicz¹,

Abt²,

Adamczyk³

et al. 2010

Eur. Phys. J. C

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Single-and double-differential inclusive dijet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector using an integrated luminosity of 374 pb −1 . The measurement was performed at large values of the photon virtuality, Q 2 , between 125 and 20 000 GeV 2 . The jets were reconstructed with the k T cluster algorithm in the Breit reference frame and selected by requiring their transverse energies in the Breit frame, E

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Section: Experimental Set-upmentioning

confidence: 99%

Inclusive dijet cross sections in neutral current deep inelastic scattering at HERA

Abramowicz¹,

Abt²,

Adamczyk³

et al. 2010

Eur. Phys. J. C

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“…The sign of the beam polarization was reversed every few months. The beam polarization was measured by two independent HERA polarimeters [22][23][24]. The average magnitude of the beam polarization was found to be 0.34 ± 0.01.…”

mentioning

confidence: 99%

Measurement of the virtual-photon asymmetry A 2 and the spin-structure function g 2 of the proton

et al. 2012

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“…The helicity of the beam was typically reversed every 2 months. The beam polarization was continuously measured by two Compton polarimeters [35,36]. The average value of the beam polarization for the events used in the analysis is about ±0.30 with a relative uncertainty of 2%.…”

Section: Methodsmentioning

confidence: 99%

Ratios of helicity amplitudes for exclusive $$\rho ^0$$ ρ 0 electroproduction on transversely polarized protons

et al. 2017

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Exclusive ρ 0 -meson electroproduction is studied by the HERMES experiment, using the 27.6 GeV longitudinally polarized electron/positron beam of HERA and a transversely polarized hydrogen target, in the kinematic region 1.0 GeV 2 < Q 2 < 7.0 GeV 2 , 3.0 GeV < W < 6.3 GeV, and −t < 0.4 GeV 2 . Using an unbinned maximum-likelihood method, 25 parameters are extracted. These determine the real and imaginary parts of the ratios of several helicity amplitudes describing ρ 0 -meson production by a virtual photon. The denominator of those ratios is the dominant amplitude, the nucleon-helicity-non-flip amplitude F 0 1 2 0 1 2 , which describes the production of a longitudinal ρ 0 -meson by a longitudinal virtual photon. The ratios of nucleon-helicity-nonflip amplitudes are found to be in good agreement with those from the previous HERMES analysis. The transverse target polarization allows for the first time the extraction of ratios of a number of nucleon-helicity-flip amplitudes to F 0 1 2 0 1 2 . Results obtained in a handbag approach based on generalized parton distributions taking into account the contribution from pion exchange are found to be in good agreement with these ratios. Within the model, the data favor a positive sign for the π − ρ transition form factor. By also exploiting the longitudinal beam polarization, a total of 71 ρ 0 spin-density matrix elements is determined from the extracted 25 parameters, in contrast to only 53 elements as directly determined in earlier analyses.

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The HERA polarimeter and the first observation of electron spin polarization at HERA

Cited by 105 publications

References 17 publications

Inclusive dijet cross sections in neutral current deep inelastic scattering at HERA

Inclusive dijet cross sections in neutral current deep inelastic scattering at HERA

Measurement of the virtual-photon asymmetry A 2 and the spin-structure function g 2 of the proton

Ratios of helicity amplitudes for exclusive $$\rho ^0$$ ρ 0 electroproduction on transversely polarized protons

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