-
M. Alekseev,
V.Yu. Alexakhin,
Yu. Alexandrov,
G.D. Alexeev,
A. Amoroso,
A. Arbuzov,
B. Badełek,
F. Balestra,
J. Ball,
G. Baum, [......],
R. Windmolders,
S. Wirth,
W. Wiślicki,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
J. Zhao,
R. Ziegler,
A. Zvyagin,
The COMPASS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The longitudinal double spin asymmetry A1
ρ for exclusive leptoproduction of ρ0 mesons, μ+N→μ+N+ρ, is studied using the COMPASS 2002 and 2003 data. The measured reaction is incoherent exclusive ρ0 production on polarised deuterons. The Q2 and x dependence of A1
ρ is presented in a wide kinematical range, 3×10-3<Q2< 7(GeV/c)2 and 5×10-5<x<0.05. The results presented are the first measurements of A1
ρ at small Q2 (Q2< 0.1(GeV/c)2) and small x (x<3×10-3). The asymmetry is in general compatible with zero in the whole kinematical range.
European Physical Journal C 09/2007; 52(2):255-265. · 3.63 Impact Factor
-
E S Ageev,
V Yu Alexakhin,
Y. Alexandrov,
G D Alexeev,
A Amoroso,
B Badelek,
F Balestra,
J Ball,
G Baum,
Y Bedfer, [......],
U Wiedner,
M Wiesmann,
R Windmolders,
S Wirth,
W Wilicki,
A M Zanetti,
K Zaremba,
J Zhao,
R Ziegler,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: We present a precise measurement of the deuteron longitudinal spin asymmetry $A_1^d$ and of the deuteron spin-dependent structure function $g_1^d$ at $Q^2 < $ 1~(GeV/$c$)$^2$ and $4\cdot$10$^{-5} < x < $~2.5$\cdot$10$^{-2}$ based on the data collected by the COMPASS experiment at CERN during the years 2002 and 2003. The statistical precision is tenfold better than that of the previous measurement in this region. The measured $A_1^d$ and $g_1^d$ are found to be consistent with zero in the whole range of $x$.
Physics Letters B 04/2007; 647(5-6):330-340. · 3.95 Impact Factor
-
E S Ageev,
V Yu Alexakhin,
Yu A Alexandrov,
G D Alexeev,
A Amoroso,
B Badelek,
F Balestra,
J Ball,
G Baum,
Y Bedfer, [......],
U Wiedner,
M Wiesmann,
R Windmolders,
S Wirth,
W Wislicki,
A M Zanetti,
K Zaremba,
J Zhao,
R Ziegler,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: We present a determination of the gluon polarization Delta G/G in the nucleon, based on the helicity asymmetry of quasi-real photoproduction events, Q^2<1(GeV/c)^2, with a pair of large transverse-momentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6-LiD target. The helicity asymmetry for the selected events is <A_||/D> = 0.002 +- 0.019(stat.) +- 0.003(syst.). From this value, we obtain in a leading-order QCD analysis Delta G/G=0.024 +- 0.089(stat.) +- 0.057(syst.) at x_g = 0.095 and mu^2 =~ 3 (GeV}/c)^2.
Physics Letters B 02/2006; 633(1):25-32. · 3.95 Impact Factor
-
E.S. Ageev,
V.Yu. Alexakhin,
Yu. Alexandrov,
G.D. Alexeev,
A. Amoroso,
B. Badelek,
F. Balestra,
J. Ball,
G. Baum,
Y. Bedfer, [......],
U. Wiedner,
M. Wiesmann,
R. Windmolders,
S. Wirth,
W. Wiślicki,
A.M. Zanetti,
K. Zaremba,
J. Zhao,
R. Ziegler,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: We present a determination of the gluon polarization ΔG/G in the nucleon, based on the helicity asymmetry of quasi-real photoproduction events, Q2<1 2(GeV/c), with a pair of large transverse-momentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6LiD target. The helicity asymmetry for the selected events is 〈A∥/D〉=0.002±0.019(stat)±0.003(syst). From this value, we obtain in a leading-order QCD analysis ΔG/G=0.024±0.089(stat)±0.057(syst) at xg=0.095 and μ2≃3 2(GeV/c).
Physics Letters B. 02/2006; 633(1):25-32.
-
V Yu Alexakhin,
Yu Alexandrov,
G D Alexeev,
A Amoroso,
B Badełek,
F Balestra,
J Ball,
G Baum,
Y Bedfer,
P Berglund, [......],
E Weise,
M Wiesmann,
R Windmolders,
S Wirth,
W Wiślicki,
A M Zanetti,
K Zaremba,
J Zhao,
R Ziegler,
A Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: First measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarized 6LiD target are presented. The data were taken in 2002 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. The Collins asymmetry turns out to be compatible with zero, as does the measured Sivers asymmetry within the present statistical errors.
Physical Review Letters 06/2005; 94(20):202002. · 7.37 Impact Factor
-
E S Ageev,
V Yu Alexakhin,
Yu A Alexandrov,
G D Alexeev,
A Amoroso,
B Badeek,
F Balestra,
J Ball,
G Baum,
Y Bedfer, [......],
Q. Weitzel,
M Wiesmann,
R Windmolders,
S Wirth,
W Wislicki,
A M Zanetti,
K Zaremba,
J Zhao,
R Ziegler,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: Narrow Xi-pi+- and Xi-bar+pi+- resonances produced by quasi-real photons have been searched for by the COMPASS experiment at CERN. The study was stimulated by the recent observation of an exotic baryonic state decaying into Xi-pi-, at a mass of 1862 MeV, interpreted as a pentaquark. While the ordinary hyperon states Xi(1530)^0 and Xi-bar(1530)^0 are clearly seen, no exotic baryon is observed in the data taken in 2002 and 2003.
European Physical Journal C 05/2005; 41(4):469-474. · 3.63 Impact Factor
-
E S Ageev,
V Yu Alexakhin,
Yu A Alexandrov,
G D Alexeev,
A Amoroso,
B Badeek,
F Balestra,
J Ball,
G Baum,
Y Bedfer, [......],
Q. Weitzel,
M Wiesmann,
R Windmolders,
S Wirth,
W Wislicki,
A M Zanetti,
K Zaremba,
J Zhao,
R Ziegler,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: We present a new measurement of the longitudinal spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron in the range 1 GeV^2 < Q^2 < 100 GeV^2 and 0.004< x <0.7. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarised muon beam and a large polarised 6-LiD target. The results are in agreement with those from previous experiments and improve considerably the statistical accuracy in the region 0.004 < x < 0.03.
Physics Letters B 04/2005; 612(3-4):154-164. · 3.95 Impact Factor
-
V Yu Alexakhin,
Yu A Alexandrov,
G D Alexeev,
A Amoroso,
B Badeek,
F Balestra,
J Ball,
G Baum,
Y Bedfer,
P Berglund, [......],
E Weise,
M Wiesmann,
R Windmolders,
S Wirth,
W Wislicki,
A M Zanetti,
K Zaremba,
J Zhao,
R Ziegler,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: First measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarized 6-LiD target are presented. The data were taken in 2002 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. The Collins asymmetry turns out to be compatible with zero, as does the measured Sivers asymmetry within the present statistical errors.
Physical Review Letters 02/2005; 94(20). · 7.37 Impact Factor
-
S Horikawa,
I Daito,
A Gorin,
T Hasegawa,
N Horikawa,
T Iwata,
K Kuroda,
I Manuilov,
T Matsuda,
Y Miyachi,
A Riazantsev,
A Sidorov, N Takabayashi,
T Toeda
[show abstract]
[hide abstract]
ABSTRACT: An extensive study was performed on the development of fast and precise scintillating-fibre detectors with position-sensitive photomultipliers (PSPM) for application in high-rate experiments. Several detector prototypes with Kuraray multi-cladding fibres of 0:5 mm diameter and Hamamatsu 16-channel H6568 PSPMs were constructed and tested under different beam conditions at the CERN PS and SPS beam lines. High time resolution of the order of 300 ps (r.m.s.) was obtained with spatial resolution of about 125 mm (r.m.s.) and with detection efficiency in excess of 98%. The detector prototype equipped with a 3-m-long light guide was also tested and showed a time resolution of about 540 ps (r.m.s.). Results of tests using a high-intensity muon beam show excellent stability of the detector performances in time and spatial resolutions as well as in detection efficiency under beam fluxes of up to 1:4 Â 10 8 muons per 2.4-second spill.
Nuclear Instruments and Methods in Physics Research A. 01/2004; 5164060(85).
-
The GDH and Collaborations,
J. Ahrens,
S. Altieri,
J.R.M. Annand,
G. Anton,
H.-J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri, [......],
T. Speckner, N. Takabayashi,
G. Tamas,
A. Thomas,
R. van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka,
G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the γ
p↦pη reaction has been measured for the first time at a center-of-mass angle θ*
η = 70° in the photon energy range from 780 MeV to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector
system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. The helicity 3/2 cross-section
is found to be small and the results for helicity 1/2 agree with predictions from the MAID analysis.
European Physical Journal A 05/2003; 17(2):241-244. · 2.19 Impact Factor
-
J Ahrens,
S Altieri,
J R M Annand,
G Anton,
H-J Arends,
K Aulenbacher,
R Beck,
C Bradtke,
A Braghieri,
N Degrande, [......], N Takabayashi,
G Tamas,
A Thomas,
L Tiator,
R Van Vyver,
A Wakai,
W Weihofen,
F Wissmann,
F Zapadtka,
G Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the gamma-->p-->-->ppi(0) reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D13(1520) resonance and are used to determine its helicity amplitudes.
Physical Review Letters 07/2002; 88(23):232002. · 7.37 Impact Factor
-
S. Horikawa,
I. Daito,
N. Doshita,
A. Gorin,
T. Hasegawa,
N. Horikawa,
T. Iwata,
K. Kondo,
K. Kuroda,
I. Manuilov,
T. Matsuda,
Y. Miyachi,
A. Riazantsev, N. Takabayashi,
T. Toeda,
S. Torimitsu
[show abstract]
[hide abstract]
ABSTRACT: A fast and precise scintillating fiber (SciFi) tracker, using 0.5-mm-diameter fibers (Kuraray SCSF-78MJ) and position-sensitive photomultiplier tubes (Hamamatsu H6568), has been developed for the COMPASS (NA58) experiment at CERN. Tests of a 16-channel prototype showed an excellent stability in time resolution, in spatial resolution, as well as in detection efficiency under different beam flux of up to 1.4 × 10<sup>8</sup> muons/spill. Four SciFi tracker stations have been constructed and all of them are presently under operation in the experiment with high performances as expected from the prototype.
IEEE Transactions on Nuclear Science 07/2002; · 1.45 Impact Factor
-
S Horikawa,
I. Daito,
N Doshita,
N Horikawa,
T Iwata,
K Kondo,
Y Miyachi, N Takabayashi,
T Toeda,
S. Torimitsu,
A. Gorin,
I. Manuilov,
A. Riazantsev,
T Hasegawa,
T Matsuda,
K. I. Kuroda
[show abstract]
[hide abstract]
ABSTRACT: Fast and precise scintillating fiber tracker (SciFi), using 0.5 mm diameter fibers (Kuraray SCSF-78MJ) and position-sensitive photomultiplier tubes (Hamamatsu H6568), has been developed for COMPASS (NA58) experiment at CERN. Tests of a 16-channel prototype showed an excellent stability in time resolution, in spatial resolution as well as in detection efficiency under different beam flux of up to 1.4×10<sup>8</sup> muons/spill. Four SciFi stations have been constructed and all of them are presently under operation in the experiment with high performances as expected from the prototype.
Nuclear Science Symposium Conference Record, 2001 IEEE; 12/2001
-
J Ahrens,
S Altieri,
J.R.M Annand,
G Anton,
H.-J Arends,
K Aulenbacher,
R Beck,
C Bradtke,
A Braghieri,
N Degrande, [......],
T Speckner, N Takabayashi,
G Tamas,
A Thomas,
R van de Vyver,
A Wakai,
W Weihofen,
F Wissmann,
F Zapadtka,
G Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the total cross section for the reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D13 resonance.
Physics Letters B.
-
J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N D'Hose, [......],
T. Speckner, N Takabayashi,
G. Tamas,
A Thomas,
R. Van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka,
G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the gamma p to p eta reaction has been measured for the first time at a center-of-mass angle theta /sub eta //sup */=70 degrees in the photon energy range from 780 MeV to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4 pi -detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. The helicity 3/2 cross-section is found to be small and the results for helicity 1/2 agree with predictions from the MAID analysis.
-
J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......], N Takabayashi,
G. Tamas,
A Thomas,
L. Tiator,
R. Van Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka,
G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the (γ) over right arrow(p) over right arrow →ppi(0) reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi - detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D-13(1520) resonance and are used to determine its helicity amplitudes.
-
J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......],
M. Steigerwald, N Takabayashi,
G. Tamas,
A Thomas,
R. Van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka,
G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the single pion photoproduction on the proton has been measured in the energy range from 200 to 450 MeV for the first time. The experiment, performed at the Mainz microtron MAMI, used a 4 pi-detector system, a circularly polarized, tagged photon beam, and a frozen-spin target. The data obtained provide new information for multipole analyses of pion photoproduction and determine the main contributions to the Gerasimov-Drell-Hearn sum rule and the forward spin polarizability gamma(0).
-
J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......],
M. Steigerwald, N Takabayashi,
G. Tamas,
A Thomas,
R. Van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka,
G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: A direct measurement of the helicity dependence of the total photoabsorption cross section an the proton was carried out at MAMI (Mainz) in the energy range 200 lt E-[gamma] lt 800 MeV. The experiment used a 4[pi] detection system, a circularly polarized. tagged photon beam, and a frozen spin target. The contributions to the Gerasimov-Drell-Hearn sum rule and to the forward spin polarizability gamma (0) determined from the data are 226 +/- 5(stat) +/- 12(syst) mub and -187 +/- 8(stat) +/- 10(syst) x 10(-6) fm(4), respectively, for 200 lt E-[gamma] lt 800 MeV.
-
J. Ahrens,
S Altieri,
J. R. M. Annand,
G. Anton,
H.J. Arends,
K. Aulenbacher,
R. Beck,
C. Bradtke,
A. Braghieri,
N. Degrande, [......],
T. Speckner, N Takabayashi,
G. Tamas,
A Thomas,
R. Van de Vyver,
A. Wakai,
W. Weihofen,
F. Wissmann,
F. Zapadtka,
G. Zeitler
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the total cross section for the gamma p to n pi /sup +/ pi /sup 0/ reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D/sub 13/ resonance.
-
J Ball,
G Baum,
P Berglund,
I Daito,
N Doshita,
F Gautheron,
St Goertz,
J Harmsen,
T Hasegawa,
J Heckmann, [......],
Yu Kisselev,
J Koivuniemi,
K Kondo,
J.M Le Goff,
A Magnon,
A Meier,
W Meyer,
E Radtke,
G Reicherz, N Takabayashi
[show abstract]
[hide abstract]
ABSTRACT: The COMPASS (NA58) experiment at CERN operates with a large solid polarized target (PT) to study the spin structure of the nucleon. The COMPASS PT system started its operation with the target material in 2001. Deuteron polarizations of +54.2% and −47.1% were achieved in a dilution refrigerator at a magnetic field of . The equal spin temperature (EST) concept was found to hold among the deuteron, the and the nuclei during the dynamic nuclear polarization (DNP) process. The agreement with the EST concept allows the permanent monitoring of only one nuclear species by the nuclear magnetic resonance (NMR) method.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
