-
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
-
CERN-Project,
LEAR-Collaboration,
S Bossolasco,
M P Bussa,
L Busso,
L Fava,
L Ferrero,
A Grasso,
D Panzieri,
G Piragino, [......],
A Maggiora,
E Lodi Rizzini,
A Haatuft,
A Halsteinslid,
K Myklebost,
J M Olsen,
F O Breivik,
K M Danielsen,
T Jacobsen,
S O Sørensen
[show abstract]
[hide abstract]
ABSTRACT: The measured cross sections for K0s and Λ0 (Σ0) production in A reactions at 607 MeV/c incident momentum and the number of quark recombinations give the cross section σ(s) for strange particle production for target nuclei with A = 2, 4, 20 nucleons, respectively. The result favours the relation σ(s) A1/3. Scattering of an antiquark off a virtual s-pair, or gluon Bremsstrahlung emitted by scattering of an incident antiquark passing through nuclear matter, are possible processes consistent with this relation. Models inconsistent with this relation may be wrong.
Physica Scripta 09/2006; 42(3):263. · 1.20 Impact Factor
-
F Balestra,
G Bendiscioli,
V Filippini,
A Rotondi,
P Salvini,
A Zenoni,
S Bossolasco,
M P Bussa,
L Busso,
L Fava, [......],
G B Pontecorvo,
A M Rozhdestvensky,
M G Sapozhnikov, V I Tretyak,
A Haatuft,
A Halsteinslid,
K Myklebost,
J M Olsen,
K M Danielsen,
T Jacobsen
[show abstract]
[hide abstract]
ABSTRACT: Two narrow peaks at about 1500 and 1800 MeV/c2 are seen in the distributions of invariant mass of the assumed six-pion systems in the final states of Ne and He reactions at 607 MeV/c. In He-reactions the peaks are seen only in the forward direction, while in Ne-reactions they are also seen in the backward direction with momenta near the momentum of the incident antiproton. The peaks could possibly be due to glueballs.
Physica Scripta 09/2006; 44(4):323. · 1.20 Impact Factor
-
F Balestra,
S Bossolasco,
M P Bussa,
L Busso,
L Fava,
L Ferrero,
A Grasso,
A Maggiora,
D Panzieri,
G Piragino, [......],
C Guaraldo,
E Lodi Rizzini,
A Haatuft,
A Halsteinslid,
K Myklebost,
J M Olsen,
F O Breivik,
K M Danielsen,
T Jacobsen,
S O Sørensen
[show abstract]
[hide abstract]
ABSTRACT: Leading mesons are seen in 4He → neutral strange particles at 0.6 GeVc−1 incident momentum. These results differ somewhat from our previous results from Ne-reactions. The concept of an "effective target" is useless.
Physica Scripta 09/2006; 43(1):9. · 1.20 Impact Factor
-
K M Danielsen,
T Jacobsen,
A Haatuft,
A Halsteinslid,
K Myklebost,
J M Olsen,
F Balestra,
G Bendiscioli,
V Filippini,
A Rotondi, [......],
C Guaraldo,
E Lodi Rizzini,
Yu Batusov,
S A Bunyatov,
I V Falomkin,
F Nichitiu,
G B Pontecorvo,
A M Rozhdestvensky,
M G Sapozhnikov, V I Tretyak
[show abstract]
[hide abstract]
ABSTRACT: The ratio between the numbers of negative and positive leading pions in 20Ne reactions at 607 MeV/c can only be explained in terms of parton fragmentation.
Physica Scripta 08/2006; 48(6):653. · 1.20 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
-
A. Bianconi,
M. Corradini,
A. Donzella,
M. Leali,
E. Lodi Rizzini,
L. Venturelli,
N. Zurlo,
M. Bargiotti,
A. Bertin,
M. Bruschi, [......],
L. Ferrero,
R. Garfagnini,
A. Grasso,
A. Maggiora,
G. Piragino,
F. Tosello,
G. Zosi,
G. Margagliotti,
L. Santi,
S. Tessaro
[show abstract]
[hide abstract]
ABSTRACT: Data on p̅ slowing down and capture in helium at 1 and 0.2 mb at room temperature are presented and compared to the corresponding previously publicated data in molecular hydrogen and deuterium. A Monte Carlo simulation containing a low-energy extrapolation of measured p̅ electronic stopping power in helium gas, screened Rutherford collisions, and simple cascade mechanisms is able to reproduce the gross features of the data, but cannot explain some nontrivial details of the measured distributions.
Phys. Rev. A. 09/2004; 70(3).
-
E Lodi Rizzini,
A Bianconi,
M P Bussa,
M Corradini,
A Donzella,
L Venturelli,
M Bargiotti,
A Bertin,
M Bruschi,
M Capponi, [......],
L Ferrero,
R Garfagnini,
A Grasso,
A Maggiora,
G Piragino,
F Tosello,
G Zosi,
G Margagliotti,
L Santi,
S Tessaro
[show abstract]
[hide abstract]
ABSTRACT: We report the stopping power of molecular hydrogen for antiprotons of kinetic energy above the maximum (approximately 100 keV) with the purpose of comparing with the proton one. Our result is consistent with a positive difference in antiproton-proton stopping powers above approximately 250 keV and with a maximum difference between the stopping powers of 21%+/-3% at around 600 keV.
Physical Review Letters 11/2002; 89(18):183201. · 7.37 Impact Factor
-
M. Bargiotti,
A. Bertin,
M. Bruschi,
M. Capponi,
S. De Castro,
R. Donà,
L. Fabbri,
P. Faccioli,
D. Galli,
B. Giacobbe, [......],
M. Astrua,
E. Botta,
T. Bressani,
D. Calvo,
A. Feliciello,
A. Filippi,
N. Mirfakhrai,
S. Marcello,
M. Agnello,
F. Iazzi
[show abstract]
[hide abstract]
ABSTRACT: The annihilation frequency of the reaction p̅ p⃗π0π0 at rest in liquid hydrogen has been measured by the Obelix experiment by using different apparatus configurations and trigger conditions. The value obtained is f(π0π0, LH)=(2.8±0.1stat±0.4syst)×10-4. With the same data samples, the π0η annihilation frequency has been determined to be f(π0η, LH)=(0.9±0.2stat±0.1syst)×10-4. The results are discussed within the frame of the present experimental situation.
Phys. Rev. D. 12/2001; 65(1).
-
A. Bertin,
M. Bruschi,
M. Capponi,
A. Collamati,
S. de Castro,
R. Donà,
A. Ferretti,
D. Galli,
B. Giacobbe,
U. Marconi, [......],
D. Panzieri,
E. Rossetto,
F. Tosello,
L. Valacca,
M. Agnello,
F. Iazzi,
B. Minetti,
G. Pauli,
S. Tessaro,
L. Santi
[show abstract]
[hide abstract]
ABSTRACT: The spin-parity analysis of the
n¯p-->π+π+π- exclusive
reaction in flight is presented. The main aim is to study the
(π+π-) invariant mass spectrum in the region
around 1500 MeV. The analysis was performed with a Breit-Wigner
parametrization for all the resonant states and, for the scalar sector
in the mass region below 1.2 GeV, by means of a K-matrix-like treatment.
It clearly shows the need for two states, a scalar one (0++)
with mass and width (1522+/-25) MeV and (108+/-33) MeV, and a tensorial
one (2++) with mass (1575+/-18) MeV and width (119+/-24) MeV,
respectively. In addition, the analysis requires the presence of a
scalar state at (1280+/-55) MeV, (323+/-13) MeV broad, and of a second
vectorial one, in addition to the ρ0(770) signal, with
mass and width (1348+/-33) MeV and (275+/-10) MeV, respectively.
Physical review D: Particles and fields 12/1997; 57:55-66.
-
A. Bertin,
M. Bruschi,
I. D’Antone,
S. De Castro,
A. Ferretti,
D. Galli,
B. Giacobbe,
U. Marconi,
M. Piccinini,
N. Semprini Cesari, [......],
D. Panzieri,
D. Parena,
E. Rossetto,
F. Tosello,
G. V. Margagliotti,
G. Pauli,
C. Rizzo,
S. Tessaro,
E. Zavattini,
L. Santi
[show abstract]
[hide abstract]
ABSTRACT: A different type of analysis was performed to study the effect of contaminants on the temporal distribution of delayed annihilations
of antiprotons stopped in helium gas, with respect to some first results published in Ableevet. al. (Nuovo Cimento A,107 (1994) 1325). A more objective criterion was established to single out aslow part in the total delayed component, in order to deduce from this, for each case, the mean value of the product([`(vs)] )c, l(\overline {v\sigma } )_{c, l} of the quenching cross-section and the mean velocity of contaminant molecules, and the fraction of the slow componentη
c, l
. The fractionη
c, l
was found to be amazingly stable for each impurity, independent of the concentration: around 79% of the total delayed component
for all the atomic impurities (Ar, Ne, Xe) and 64% for the molecular ones (H2, N2).
Il Nuovo Cimento A 04/1997; 110(4):419-428.
-
The OBELIX Collaboration,
A. Bertin,
M. Bruschi,
M. Capponi,
S. De Castro,
A. Ferretti,
D. Galli,
B. Giacobbe,
U. Marconi,
M. Piccinini, [......],
S. Marcello,
D. Panzieri,
D. Parena,
E. Rossetto,
F. Tosello,
G. Margagliotti,
G. Pauli,
S. Tessaro,
E. Zavattini,
L. Santi
[show abstract]
[hide abstract]
ABSTRACT: The behaviour of the «delayed» component of the time distribution of the annihilation of
[`(p)]\bar p
at rest in4He is experimentally studied at various pressures of the gas target, in the range 3000 to 5 mbar at room temperature.
Il Nuovo Cimento A 01/1996; 109(10):1505-1516.
-
A. Bertin,
M. Bruschi,
B. Cereda,
S. de Castro,
A. Ferretti,
D. Galli,
B. Giacobbe,
U. Marconi,
M. Poli,
M. Piccinini, [......],
D. Parena,
E. Rossetto,
F. Tosello,
G. Zosi,
M. Agnello,
F. Iazzi,
B. Minetti,
G. Pauli,
S. Tessaro,
L. Santi
[show abstract]
[hide abstract]
ABSTRACT: The results of the analysis of 3940 (KKπ)ππ events from a
sample of 18 millions pp annihilations in the liquid hydrogen target of
the OBELIX spectrometer at LEAR (CERN) are presented. The presence of
two pseudoscalar states at 1.416 +/- 0.002 GeV/c2, with width
0.050 +/- 0.004 GeV/c2, and at 1.46 +/- 0.01
GeV/c2, with width 0.105 +/- 0.015 GeV/c2, is
established. The lighter mass resonance decays mainly to KKπ,
possibly with final state interactions and a small contribution coming
from a0π. The higher mass 0-+ state, which is
seen for the first time in pp annihilation at rest, decays only
toK*K . Masses, widths and decay modes are in agreement with
the analysis of J/ψ radiative decay performed by the Mark III
Collaboration. From the fit the G-parity was determined to be +1. The
dominant three-body decay mode of the lighter pseudoscalar is observed
for the first time in this measurement.
Physics Letters B 01/1995; 361:187-198. · 3.95 Impact Factor
-
The OBELIX Collaboration,
V. G. Ableev,
A. Adamo,
A. Andrighetto,
M. Angello,
F. Balestra,
G. Belli,
G. Bendiscioli,
A. Bertin,
P. Boccaccio, [......],
G. Usai,
L. Vannucci,
S. Vecchi,
G. Vedovato,
L. Venturelli,
M. Villa,
A. Vitale,
A. Zenoni,
A. Zoccoli,
G. Zosi
[show abstract]
[hide abstract]
ABSTRACT: We describe some results obtained by the OBELIX experiment at LEAR by exploiting the whole spectrometer, including the electromagnetic
calorimeter, to study the antiproton-proton annihilation at rest in an NTP hydrogen target. In particular, we give some information
on the calibration of the calorimeter, as obtained from the analysis of two-prong events, and we describe the status of the
analysis of the first sample of «all neutrals» events collected in gaseous hydrogen. A preliminary result on the branching
ratio of the annihilation reaction
[`(p)]p ® p0 p0\bar pp \to \pi ^0 \pi ^0
is reported.
Il Nuovo Cimento A 10/1994; 107(11):2287-2303.
-
The OBELIX Collaboration,
V. Ableev,
A. Adamo,
M. Agnello,
F. Balestra,
G. Belli,
G. Bendiscioli,
A. Bertin,
P. Boccaccio,
G. C. Bonazzola, [......],
G. Usai,
L. Vannucci,
S. Vecchi,
G. Vedovato,
L. Venturelli,
M. Villa,
A. Vitale,
A. Zenoni,
A. Zoccoli,
G. Zosi
[show abstract]
[hide abstract]
ABSTRACT: A study of
[`(n)]p\bar np
in-flight annihilations is presented. The 4π invariant mass spectrum resulting from the analysis of the five-prong exclusive
events, following the annihilation of ∼ (100–297) MeV/c
[`(n)]\bar n
, reveals, besides a large structure centred at ∼ 1500 MeV/c2, some evidences for a new state around 1660 MeV/c2.
Il Nuovo Cimento A 10/1994; 107(11):2243-2252.
