-
A. Airapetian,
N. Akopov,
Z. Akopov,
E. C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian,
E. Avetisyan,
S. Belostotski,
H. P. Blok, [......],
C. Vogel,
S. Wang,
S. Yaschenko,
Z. Ye,
S. Yen,
W. Yu,
V. Zagrebelnyy,
D. Zeiler,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: Multiplicities in semi-inclusive deep-inelastic scattering are presented for
each charge state of \pi^\pm and K^\pm mesons. The data were collected by the
HERMES experiment at the HERA storage ring using 27.6 GeV electron and positron
beams incident on a hydrogen or deuterium gas target. The results are presented
as a function of the kinematic quantities x_B, Q^2, z, and P_h\perp. They
represent a unique data set for identified hadrons that will significantly
enhance our understanding of the fragmentation of quarks into final-state
hadrons in deep-inelastic scattering.
Physical Review D 04/2013; 87(7):14. · 4.56 Impact Factor
-
K. Ackerstaff,
A. Airapetian,
I. Akushevich,
N. Akopov,
M. Amarian,
E.C. Aschenauer,
R. Avakian,
H. Avakian,
A. Avetisian,
B. Bains, [......],
M.C. Vetterli,
E. Volk,
W. Wander,
T.P. Welch,
S.E. Williamson,
T. Wise,
T. Wolfel,
K. Zapfe-Duren,
G. Zograbian,
R. Zurmuhle
[show abstract]
[hide abstract]
ABSTRACT: Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function g1 n(x,Q 2) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3He internal gas target. The data cover the kinematic range 0.023<x<0.6 and 1(GeV/c) 2<Q 2<15(GeV/c) 2. The integral ∫0.023 0.6g1 n(x)dx evaluated at a fixed Q 2 of 2.5(GeV/c) 2 is −0.034±0.013(stat.)±0.005(syst.). Assuming Regge behavior at low x, the first moment Γ1 n=∫0 1g1 n(x)dx is −0.037±0.013(stat.)±0.005(syst.)±0.006(extrapol.).
Physics Letters B 02/2013; 404(3-4):383-389. · 3.95 Impact Factor
-
K. Ackerstaff,
A. Airapetian,
N. Akopov,
I. Akushevich,
M. Amarian,
E.C. Aschenauer,
H. Avakian,
R. Avakian,
A. Avetisian,
B. Bains, [......],
M.G. Vincter,
J. Visser,
E. Volk,
W. Wander,
J. Wendland,
S.E. Williamson,
T. Wise,
K. Woller,
S. Yoneyama,
H. Zohrabian
[show abstract]
[hide abstract]
ABSTRACT: Cross section ratios for deep-inelastic scattering from 14N and 3He with respect to 2H have been measured by the HERMES experiment at DESY using a 27.5 GeV positron beam. The data cover a range in the Bjorken scaling variable x between 0.013 and 0.65, while the negative squared four-momentum transfer Q^2 varies from 0.5 to 15 GeV^2. The data are compared to measurements performed by NMC, E665, and SLAC on 4He and 12C, and are found to be different for x < 0.06 and Q^2 < 1.5 GeV^2. The observed difference is attributed to an A-dependence of the ratio R = sigma_L / sigma_T of longitudinal to transverse deep-inelastic scattering cross sections at low x and low Q^2.
Physics Letters B 02/2013; 475:386-394. · 3.95 Impact Factor
-
A. Airapetian,
N. Akopov,
Z. Akopov,
E.C. Aschenauer,
W. Augustyniak,
A. Avetissian,
E. Avetisyan,
B. Ball,
N. Bianchi,
H.P. Blok, [......],
C. Vogel,
S. Wang,
S. Yaschenko,
H. Ye,
Z. Ye,
S. Yen,
W. Yu,
D. Zeiler,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: The exclusive electroproduction of rho-0 mesons was studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target. Spin density matrix elements for this process were determined from the measured production- and decay-angle distributions of the produced rho-0 mesons. These matrix elements embody information on helicity transfer and the validity of s-channel helicity conservation in the case of a transversely polarized target. From the spin density matrix elements, the leading-twist term in the single-spin asymmetry was calculated separately for longitudinally and transversely polarized rho-0 mesons. Neglecting s-channel helicity changing matrix elements, results for the former can be compared to calculations based on generalized parton distributions, which are sensitive to the contribution of the total angular momentum of the quarks to the proton spin.
Physics Letters B 02/2013; 679:100-105. · 3.95 Impact Factor
-
A. Airapetian,
N. Akopov,
Z. Akopov,
M Amarian,
V.V. Ammosov,
A Andrus,
E.C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian, [......],
J Volmer,
C. Weiskopf,
J Wendland,
J. Wilbert,
G. Smit,
Y Ye,
Z Ye,
S. Yen,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: Hard exclusive electroproduction of pi(+) pi(-) pairs off hydrogen and deuterium targets has been studied by the HERMES experiment at DESY Legendre moments (P-1) and (P-3) of the angular distributions of pi(+) mesons in the center-of-mass frame of the pair have been measured for the first time. Their dependence on the pi(+) pi(-) invariant mass can be understood as being due to the interference between relative P-wave (isovector) and S-, D-wave (isoscalar) states of the two pions. The increase in magnitude of (P-1) as Bjorken x increases is interpreted in the framework of generalized parton distributions as an enhancement of flavour non-singlet qq exchange for larger values of x, which leads to a sizable admixture of isoscalar and isovector pion pairs. In addition, the interference between P-wave and D-wave states separately for transverse and longitudinal pion pairs has been studied. The data indicate that in the f(2)(1270) region at [Q(2)] = 3 GeV2 higher-twist effects can be as large as the leading-twist longitudinal component.
Phys.Lett.B599:212-222,2004. 02/2013;
-
HERMES Collaboration,
A. Airapetian,
N. Akopov,
Z. Akopov,
E. C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian,
E. Avetisyan,
S. Belostotski, [......],
C. Vogel,
S. Wang,
S. Yaschenko,
Z. Ye,
S. Yen,
W. Yu,
V. Zagrebelnyy,
D. Zeiler,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: Multiplicities in semi-inclusive deep-inelastic scattering are presented for
each charge state of \pi^\pm and K^\pm mesons. The data were collected by the
HERMES experiment at the HERA storage ring using 27.6 GeV electron and positron
beams incident on a hydrogen or deuterium gas target. The results are presented
as a function of the kinematic quantities x_B, Q^2, z, and P_h\perp. They
represent a unique data set for identified hadrons that will significantly
enhance our understanding of the fragmentation of quarks into final-state
hadrons in deep-inelastic scattering.
12/2012;
-
A. Accardi,
J. L. Albacete,
M. Anselmino,
N. Armesto,
E. C. Aschenauer,
A. Bacchetta,
D. Boer,
W. Brooks,
T. Burton,
N. -B. Chang, [......],
D. Trbojevic,
T. Ullrich,
R. Venugopalan,
S. Vigdor,
W. Vogelsang,
C. Weiss,
B. -W. Xiao,
F. Yuan,
Y. -H. Zhang,
L. Zheng
[show abstract]
[hide abstract]
ABSTRACT: This White Paper presents the science case of an Electron-Ion Collider (EIC),
focused on the structure and interactions of gluon-dominated matter, with the
intent to articulate it to the broader nuclear science community. It was
commissioned by the managements of Brookhaven National Laboratory (BNL) and
Thomas Jefferson National Accelerator Facility (JLab) with the objective of
presenting a summary of scientific opportunities and goals of the EIC as a
follow-up to the 2007 NSAC Long Range plan. This document is a culmination of a
community-wide effort in nuclear science following a series of workshops on EIC
physics and, in particular, the focused ten-week program on "Gluons and quark
sea at high energies" at the Institute for Nuclear Theory in Fall 2010. It
contains a brief description of a few golden physics measurements along with
accelerator and detector concepts required to achieve them, and it benefited
from inputs from the users' communities of BNL and JLab. This White Paper
offers the promise to propel the QCD science program in the U.S., established
with the CEBAF accelerator at JLab and the RHIC collider at BNL, to the next
QCD frontier.
12/2012;
-
A. Airapetian,
N. Akopov,
Z. Akopov,
E. C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian,
E. Avetisyan,
H. P. Blok,
A. Borissov, [......],
I. Vilardi,
S. Wang,
S. Yaschenko,
Z. Ye,
S. Yen,
W. Yu,
V. Zagrebelnyy,
D. Zeiler,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: Beam-helicity and beam-charge asymmetries in the hard exclusive
leptoproduction of real photons from an unpolarised hydrogen target by a 27.6
GeV lepton beam are extracted from the HERMES data set of 2006-2007 using a
missing-mass event selection technique. The asymmetry amplitudes extracted from
this data set are more precise than those extracted from the earlier data set
of 1996-2005 previously analysed in the same manner by HERMES. The results from
the two data sets are compatible with each other. Results from these combined
data sets are extracted and constitute the most precise asymmetry amplitude
measurements made in the HERMES kinematic region using a missing-mass event
selection technique.
Journal of High Energy Physics 07/2012; 1207((2012)):032/24. · 5.83 Impact Factor
-
The HERMES Collaboration,
A. Airapetian,
N. Akopov,
Z. Akopov,
E. C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian,
E. Avetisyan,
S. Belostotski, [......],
V. Vikhrov,
I. Vilardi,
S. Wang,
S. Yaschenko,
Z. Ye,
S. Yen,
V. Zagrebelnyy,
D. Zeiler,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: The beam-helicity asymmetry in exclusive electroproduction of real photons by
the longitudinally polarized HERA positron beam scattering off an unpolarized
hydrogen target is measured at HERMES. The asymmetry arises from deeply virtual
Compton scattering and its interference with the Bethe--Heitler process.
Azimuthal amplitudes of the beam-helicity asymmetry are extracted from a data
sample consisting of $ep\rightarrow ep\gamma$ events with detection of all
particles in the final state including the recoiling proton. The installation
of a recoil detector, while reducing the acceptance of the experiment, allows
the elimination of background from $ep\rightarrow eN\pi\gamma$ events, which
was estimated to contribute an average of about 12% to the signal in previous
HERMES publications. The removal of this background from the present data
sample is shown to increase the magnitude of the leading asymmetry amplitude by
0.054 +/- 0.016 to -0.328 +/- 0.027 (stat.) +/- 0.045 (syst.).
Journal of High Energy Physics 06/2012; 2012(10). · 5.83 Impact Factor
-
The Hermes collaboration,
A. Airapetian,
N. Akopov,
Z. Akopov,
E. C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian,
E. Avetisyan,
S. Belostotski, [......],
I. Vilardi,
C. Vogel,
S. Wang,
S. Yaschenko,
H. Ye,
Z. Ye,
W. Yu,
D. Zeiler,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: Longitudinal double-spin asymmetries of charged hadrons with high transverse momentum p
T
have been measured in electroproduction using the Hermes detector at Hera. Processes involving gluons in the nucleon have been enhanced relative to others by selecting hadrons with p
T
typically above 1 GeV. In this kinematic domain the gluon polarization has been extracted in leading order making use of
the model embedded in the Monte Carlo Generator Pythia 6.2. The gluon polarization obtained from single inclusive hadrons in the p
T
range 1 GeV < p
T
< 2.5 GeV using a deuterium target is
\fracDgg(
x
,
m2
) = 0.049±0.034( stat )±0.010( sys\text-exp ) - 0.099 + 0.126( sys\text-models ) \frac{{\Delta g}}{g}\left( {\left\langle x \right\rangle, \left\langle {{\mu^2}} \right\rangle } \right) = 0.049\pm 0.034\left( {stat} \right)\pm 0.010\left( {sys\text{-}exp} \right)_{ - 0.099}^{ + 0.126}\left( {sys\text{-}models} \right) at a scale
m2
= 1.35\textGe\textV2 \left\langle {{\mu^2}} \right\rangle = 1.35\;{\text{Ge}}{{\text{V}}^2} and
x
= 0.22 \left\langle x \right\rangle = 0.22 . For different final states and kinematic domains, consistent values of
\fracDgg \frac{{\Delta g}}{g} have been found within statistical uncertainties using hydrogen and deuterium targets.
KeywordsLepton-Nucleon Scattering
Journal of High Energy Physics 04/2012; 2010(8):1-47. · 5.83 Impact Factor
-
HERMES Collaboration,
A. Airapetian,
N. Akopov,
Z. Akopov,
E. C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian,
E. Avetisyan,
S. Belostotski, [......],
I. Vilardi,
S. Wang,
S. Yaschenko,
Z. Ye,
S. Yen,
W. Yu,
V. Zagrebelnyy,
D. Zeiler,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: The azimuthal cos{\phi} and cos2{\phi} modulations of the distribution of
hadrons produced in unpolarized semi-inclusive deep-inelastic scattering of
electrons and positrons off hydrogen and deuterium targets have been measured
in the HERMES experiment. For the first time these modulations were determined
in a four-dimensional kinematic space for positively and negatively charged
pions and kaons separately, as well as for unidentified hadrons. These
azimuthal dependences are sensitive to the transverse motion and polarization
of the quarks within the nucleon via, e.g., the Cahn, Boer-Mulders and Collins
effects.
04/2012;
-
The ALICE Collaboration,
K. Aamodt,
N. Abel,
U. Abeysekara,
A. Abrahantes Quintana,
A. Acero,
D. Adamová,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs, [......],
X. Zhang,
D. Zhou,
S. Zhou,
J. Zhu,
A. Zichichi,
A. Zinchenko,
G. Zinovjev,
M. Zinovjev,
Y. Zoccarato,
V. Zycháček
[show abstract]
[hide abstract]
ABSTRACT: On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton
bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450GeV per beam. Although
the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the
collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region
was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with
the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used
these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |η|<0.5, we obtain dN
ch/dη=3.10±0.13(stat.)±0.22(syst.) for all inelastic interactions, and dN
ch/dη=3.51±0.15(stat.)±0.25(syst.) for non-single diffractive interactions. These results are consistent with previous measurements
in proton–antiproton interactions at the same centre-of-mass energy at the CERN Sp
[`(p)]\overline{\mathrm{p}}
S collider. They also illustrate the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware
and software of the ALICE experiment, in this early start-up phase.
European Physical Journal C 04/2012; 65(1):111-125. · 3.63 Impact Factor
-
The ALICE Collaboration,
K. Aamodt,
N. Abel,
U. Abeysekara,
A. Abrahantes Quintana,
A. Abramyan,
D. Adamová,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs, [......],
X. Zhang,
D. Zhou,
S. Zhou,
J. Zhu,
A. Zichichi,
A. Zinchenko,
G. Zinovjev,
Y. Zoccarato,
V. Zycháček,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The production of π
+, π
−, K+, K−, p, and [`(p)]\overline{\mathrm{p}} at mid-rapidity has been measured in proton-proton collisions at Ös = 900GeV\sqrt{s} = 900~\mathrm{GeV} with the ALICE detector. Particle identification is performed using the specific energy loss in the inner tracking silicon
detector and the time projection chamber. In addition, time-of-flight information is used to identify hadrons at higher momenta.
Finally, the distinctive kink topology of the weak decay of charged kaons is used for an alternative measurement of the kaon
transverse momentum (p
t) spectra. Since these various particle identification tools give the best separation capabilities over different momentum
ranges, the results are combined to extract spectra from p
t=100MeV/c to 2.5 GeV/c. The measured spectra are further compared with QCD-inspired models which yield a poor description. The total yields and
the mean p
t are compared with previous measurements, and the trends as a function of collision energy are discussed.
European Physical Journal C 04/2012; 71(6):1-22. · 3.63 Impact Factor
-
K. Aamodt,
A. Abrahantes Quintana,
D. Adamová,
A. M. Adare,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs,
S. Aguilar Salazar,
Z. Ahammed,
N. Ahmad, [......],
P. Zelnicek,
A. Zenin,
I. Zgura,
M. Zhalov,
X. Zhang,
D. Zhou,
A. Zichichi,
G. Zinovjev,
Y. Zoccarato,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: The production of mesons containing strange quarks ($\mbox {$\mbox {, φ) and both singly and doubly strange baryons ($\mbox {$\mbox {, $\mbox {$\mbox {, and $\mbox {$\mbox {) are measured at mid-rapidity in pp collisions at
_boxclose_boxclose_boxclose\sqrt{s}=0.9TeV{\rm TeV} with the ALICE experiment at the LHC. The results are obtained from the analysis of about 250k minimum bias events recorded
in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at mid-rapidity for inelastic pp collisions are presented. For mesons, we report yields
(〈dN/dy〉) of 0.184±0.002(stat.)±0.006(syst.) for $\mbox {$\mbox { and 0.021±0.004(stat.)±0.003(syst.) forφ. For baryons, we find 〈dN/dy〉=0.048±0.001(stat.)±0.004(syst.) for $\mbox {$\mbox {, 0.047±0.002(stat.)±0.005(syst.) for $\mbox {$\mbox { and 0.0101±0.0020(stat.)±0.0009(syst.) for $\mbox {$\mbox {. The results are also compared with predictions for identified particle spectra from QCD-inspired models and provide a baseline
for comparisons with both future pp measurements at higher energies and heavy-ion collisions.
European Physical Journal C 04/2012; 71(3):1-24. · 3.63 Impact Factor
-
The HERMES Collaboration,
A. Airapetian,
N. Akopov,
Z. Akopov,
A. Andrus,
E. C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian,
E. Avetissian, [......],
S. Wang,
S. Yaschenko,
H. Ye,
Y. Ye,
Z. Ye,
S. Yen,
W. Yu,
D. Zeiler,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive ρ
0 electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized hydrogen and
deuterium targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal polarization of the beam are extracted
in the kinematic region 1<Q
2<7GeV2, 3.0<W<6.3GeV, and −t<0.4 GeV2. Within the given experimental uncertainties, a hierarchy of relative sizes of helicity amplitudes is observed. Kinematic
dependences of all SDMEs on Q
2 and t are presented, as well as the longitudinal-to-transverse ρ
0 electroproduction cross-section ratio as a function ofQ
2. A small but statistically significant deviation from the hypothesis of s-channel helicity conservation is observed. An indication is seen of a contribution of unnatural-parity-exchange amplitudes;
these amplitudes are naturally generated with a quark-exchange mechanism.
European Physical Journal C 04/2012; 62(4):659-695. · 3.63 Impact Factor
-
The ALICE Collaboration,
K. Aamodt,
N. Abel,
U. Abeysekara,
A. Abrahantes Quintana,
A. Abramyan,
D. Adamová,
M. M. Aggarwal,
G. Aglieri Rinella,
A. G. Agocs, [......],
X. Zhang,
D. Zhou,
S. Zhou,
J. Zhu,
A. Zichichi,
A. Zinchenko,
G. Zinovjev,
Y. Zoccarato,
V. Zycháček,
M. Zynovyev
[show abstract]
[hide abstract]
ABSTRACT: Charged-particle production was studied in proton–proton collisions collected at the LHC with the ALICE detector at centre-of-mass
energies 0.9TeV and 2.36TeV in the pseudorapidity range |η|<1.4. In the central region (|η|<0.5), at 0.9TeV, we measure charged-particle pseudorapidity density dNch/dh = 3.02±0.01(stat.)+0.08-0.05(syst.)\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta=3.02\pm 0.01(\mathit{stat.})^{+0.08}_{-0.05}(\mathit{syst.}) for inelastic interactions, and dNch/dh = 3.58±0.01(stat.)+0.12-0.12(syst.)\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta=3.58\pm0.01(\mathit{stat.})^{+0.12}_{-0.12}(\mathit{syst.}) for non-single-diffractive interactions. At 2.36TeV, we find dNch/dh = 3.77±0.01(stat.)+0.25-0.12(syst.)\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta=3.77\pm0.01(\mathit{stat.})^{+0.25}_{-0.12}(\mathit{syst.}) for inelastic, and dNch/dh = 4.43±0.01(stat.)+0.17-0.12(syst.)\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta=4.43\pm0.01(\mathit{stat.})^{+0.17}_{-0.12}(\mathit{syst.}) for non-single-diffractive collisions. The relative increase in charged-particle multiplicity from the lower to higher energy
is 24.7%±0.5%(stat.)+5.7-2.8%(syst.)24.7\%\pm0.5\%(\mathit{stat.})^{+5.7}_{-2.8}\%(\mathit{syst.}) for inelastic and 23.7%±0.5%(stat.)+4.6-1.1%(syst.)23.7\%\pm0.5\%(\mathit{stat.})^{+4.6}_{-1.1}\%(\mathit{syst.}) for non-single-diffractive interactions. This increase is consistent with that reported by the CMS collaboration for non-single-diffractive
events and larger than that found by a number of commonly used models. The multiplicity distribution was measured in different
pseudorapidity intervals and studied in terms of KNO variables at both energies. The results are compared to proton–antiproton
data and to model predictions.
European Physical Journal C 04/2012; 68(1):89-108. · 3.63 Impact Factor
-
The HERMES Collaboration,
A. Airapetian,
N. Akopov,
Z. Akopov,
E. C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian,
E. Avetisyan,
H. P. Blok, [......],
I. Vilardi,
S. Wang,
S. Yaschenko,
Z. Ye,
S. Yen,
W. Yu,
V. Zagrebelnyy,
D. Zeiler,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: Beam-helicity and beam-charge asymmetries in the hard exclusive
leptoproduction of real photons from an unpolarised hydrogen target by a 27.6
GeV lepton beam are extracted from the HERMES data set of 2006-2007 using a
missing-mass event selection technique. The asymmetry amplitudes extracted from
this data set are more precise than those extracted from the earlier data set
of 1996-2005 previously analysed in the same manner by HERMES. The results from
the two data sets are compatible with each other. Results from these combined
data sets are extracted and constitute the most precise asymmetry amplitude
measurements made in the HERMES kinematic region using a missing-mass event
selection technique.
03/2012;
-
H. Avakian,
M. Battaglieri,
E. Cisbani,
M. Contalbrigo,
U. D'Alesio,
R. De Leo,
R. Devita,
P. Di Nezza, D. Hasch,
V. Kubarovsky,
M. Mirazita,
M. Osipenko,
L. Pappalardo,
P. Rossi
[show abstract]
[hide abstract]
ABSTRACT: Since the discovery of strangeness almost five decades ago, interest in this
degree of freedom has grown up and now its investigation spans the scales from
quarks to nuclei. Measurements with identified strange hadrons can provide
important information on several hot topics in hadronic physics: the strange
distribution and fragmentation functions, the nucleon tomography and quark
orbital momentum, accessible through the study of the {\it generalized} parton
distribution and the {\it transverse momentum dependent} parton distribution
functions, the quark hadronization in the nuclear medium, the hadron
spectroscopy and the search for exotic mesons.
The CLAS12 large acceptance spectrometer in Hall B at the Jefferson
Laboratory upgraded with a RICH detector together with the 12 GeV CEBAF high
intensity, high polarized electron beam can open new possibilities to study
strangeness in hard processes allowing breakthroughs in all those areas.
This paper summarizes the physics case for a RICH detector for CLAS12. Many
topics have been intensively discussed at the International Workshop "Probing
Strangeness in Hard Processes" (PSHP2010) \cite{PSHP-workshop} held in
Frascati, Italy in October 2010. The authors of this papers like to thank all
speakers and participants of the workshop for their contribution and very
fruitful discussion.
02/2012;
-
A Airapetian,
N Akopov,
Z Akopov,
EC Aschenauer,
W Augustyniak,
R Avakian,
A Avetissian,
E Avetisyan,
S Belostotski,
N Bianchi, [......],
V Vikhrov,
I Vilardi,
S Wang,
S Yaschenko,
Z Ye,
S Yen,
V Zagrebelnyy,
D Zeiler,
B Zihlmann,
P Zupranski
[show abstract]
[hide abstract]
ABSTRACT: A measurement of the virtual-photon asymmetry A(2)(x, Q(2)) and of the spin-structure function g(2)(x, Q(2)) of the proton are presented for the kinematic range 0.004 < x < 0.9 and 0.18 GeV2 < Q(2) < 20 GeV2. The data were collected by the HERMES experiment at the HERA storage ring at DESY while studying inclusive deep-inelastic scattering of 27.6 GeV longitudinally polarized leptons off a transversely polarized hydrogen gas target. The results are consistent with previous experimental data from CERN and SLAC. For the x-range covered, the measured integral of g(2)(x) converges to the null result of the Burkhardt-Cottingham sum rule. The x(2) moment of the twist-3 contribution to g(2)(x) is found to be compatible with zero.
European Physical Journal C 01/2012; 72(3):7. · 3.63 Impact Factor
-
A. Airapetian,
N. Akopov,
Z. Akopov,
E. C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian,
E. Avetisyan,
S. Belostotski,
N. Bianchi, [......],
V. Vikhrov,
I. Vilardi,
S. Wang,
S. Yaschenko,
Z. Ye,
S. Yen,
V. Zagrebelnyy,
D. Zeiler,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: A measurement of the virtual-photon asymmetry A_2(x,Q^2) and of the
spin-structure function g_2(x,Q^2) of the proton are presented for the
kinematic range 0.004 < x < 0.9 and 0.18 GeV^2 < Q^2 < 20 GeV^2. The data were
collected by the HERMES experiment at the HERA storage ring at DESY while
studying inclusive deep-inelastic scattering of 27.6 GeV longitudinally
polarized leptons off a transversely polarized hydrogen gas target. The results
are consistent with previous experimental data from CERN and SLAC. For the
x-range covered, the measured integral of g_2(x) converges to the null result
of the Burkhardt-Cottingham sum rule. The x^2 moment of the twist-3
contribution to g_2(x) is found to be compatible with zero.
12/2011;
