-
The GlueX Collaboration,
A. AlekSejevs,
S. Barkanova,
M. Dugger,
B. Ritchie,
I. Senderovich,
E. Anassontzis,
P. Ioannou,
C. Kourkoumeli,
G. Voulgaris, [......],
M. McCaughan,
M. Pennington,
L. Pentchev,
Y. Qiang,
E. S. Smith,
A. Somov,
S. Taylor,
T. Whitlatch,
E. Wolin,
B. Zihlmann
[show abstract]
[hide abstract]
ABSTRACT: The primary motivation of the GlueX experiment is to search for and
ultimately study the pattern of gluonic excitations in the meson spectrum
produced in $\gamma p$ collisions. Recent lattice QCD calculations predict a
rich spectrum of hybrid mesons that have both exotic and non-exotic $J^{PC}$,
corresponding to $q\bar{q}$ states ($q=u,$ $d,$ or $s$) coupled with a gluonic
field. A thorough study of the hybrid spectrum, including the identification of
the isovector triplet, with charges 0 and $\pm1$, and both isoscalar members,
$|s\bar{s}\ >$ and $|u\bar{u}\ > + |d\bar{d}\ >$, for each predicted hybrid
combination of $J^{PC}$, may only be achieved by conducting a systematic
amplitude analysis of many different hadronic final states. Detailed studies of
the performance of the \gx detector have indicated that identification of
particular final states with kaons is possible using the baseline detector
configuration. The efficiency of kaon detection coupled with the relatively
lower production cross section for particles containing hidden strangeness will
require a high intensity run in order for analyses of such states to be
feasible. We propose to collect a total of 200 days of physics analysis data at
an average intensity of $5\times 10^7$ tagged photons on target per second.
This data sample will provide an order of magnitude statistical improvement
over the initial GlueX running, which will allow us to begin a program of
studying mesons and baryons containing strange quarks. In addition, the
increased intensity will permit us to study reactions that may have been
statistically limited in the initial phases of GlueX. Overall, this will lead
to a significant increase in the potential for \gx to make key experimental
advances in our knowledge of hybrid mesons and excited $\Xi$ baryons.
05/2013;
-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badelek,
F. Balestra, [......],
G. K. Mallot,
A. Mann,
C. Marchand,
A. Martin,
J. Marzec,
T. Matsuda,
G. Meshcheryakov,
W. Meyer,
T. Michigami,
Yu. V. Mikhailov
-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badelek,
F. Balestra, [......],
M. Wilfert,
R. Windmolders,
W. Wislicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: The gluon polarisation in the nucleon was measured using open charm
production by scattering 160 GeV/c polarised muons off longitudinally polarised
protons or deuterons. The data were taken by the COMPASS collaboration between
2002 and 2007. A detailed account is given of the analysis method that includes
the application of neural networks. Several decay channels of D^0 mesons are
investigated. Longitudinal spin asymmetries of the D meson production
cross-sections are extracted in bins of D^0 transverse momentum and energy. At
leading order QCD accuracy the average gluon polarisation is determined as
(Delta g/G)^LO=-0.06 +/- 0.21 (stat.) +/- 0.08 (syst.) at the scale <mu^2> ~13
(GeV/c)^2 and an average gluon momentum fraction ~ 0.11. For the first time,
the average gluon polarisation is also obtained at next-to-leading order QCD
accuracy as (Delta g/G)^NLO = -0.13 +/- 0.15 (stat.) +/- 0.15 (syst.) at the
scale <mu^2> ~ 13 (\GeV/c)^2 and ~ 0.20.
11/2012;
-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badelek,
F. Balestra, [......],
M. Wilfert,
R. Windmolders,
W. Wislicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: The production of D* and D mesons in inelastic scattering of 160 GeV/c muons
off a ^6LiD target has been investigated with the COMPASS spectrometer at CERN
for 0.003 (GeV/c)^2 < Q^2 < 10 (GeV/c)^2 and 3x10^-5< x_Bj < 0.1. The study is
based on 8100 events where a D^0 or anti D^0 is detected subsequently to a D*+
or D*- decay, and on 34000 events, where only a D^0 or anti D^0 is detected.
Kinematic distributions of D*, D and K*_2 are given as a function of their
energy E, transverse momentum p_T, energy fraction z, and of the virtual photon
variables nu, Q^2 and x_Bj. Semi-inclusive differential D* production
cross-sections are compared with theoretical predictions for D* production via
photon-gluon fusion into open charm. The total observed production
cross-section for D*+/- mesons with laboratory energies between 22 and 86 GeV
is 1.9 nb. Significant cross-section asymmetries are observed between D*+ and
D*- production for nu<40 GeV and z>0.6.
European Physical Journal C 11/2012; 72(12). · 3.63 Impact Factor
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The GlueX Collaboration,
M. Dugger,
B. Ritchie,
E. Anassontzis,
P. Ioannou,
C. Kourkoumeli,
G. Voulgaris,
N. Jarvis,
W. Levine,
P. Mattione, [......],
M. Ito,
D. Lawrence,
L. Pentchev,
Y. Qiang,
E. S. Smith,
A. Somov,
S. Taylor,
T. Whitlatch,
E. Wolin,
B. Zihlmann
[show abstract]
[hide abstract]
ABSTRACT: The primary motivation of the GlueX experiment is to search for and
ultimately study the pattern of gluonic excitations in the meson spectrum
produced in gamma p collisions. Recent lattice QCD calculations predict a rich
spectrum of hybrid mesons that have both exotic and non-exotic JPC,
corresponding to q q-bar (q=u, d, or s) states coupled with a gluonic field. A
thorough study of the hybrid spectrum, including the identification of the
isovector triplet, with charges 0 and +-1, and both isoscalar members, |s
s-bar> and |u u-bar> + |d d-bar>, for each predicted hybrid combination of JPC,
may only be achieved by conducting a systematic amplitude analysis of many
different hadronic final states. We propose the development of a kaon
identification system, supplementing the existing GlueX forward time-of-flight
detector, in order to cleanly select meson and baryon decay channels that
include kaons. Once this detector has been installed and commissioned, we plan
to collect a total of 200 days of physics analysis data at an average intensity
of 5 x 10^7 tagged photons on target per second. This data sample will provide
an order of magnitude statistical improvement over the initial GlueX data set
and, with the developed kaon identification system, a significant increase in
the potential for GlueX to make key experimental advances in our knowledge of
hybrid mesons and Cascade baryons.
10/2012;
-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badełek,
F. Balestra, [......],
M. Wilfert,
R. Windmolders,
W. Wiślicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: The transverse target spin azimuthal asymmetry A_UT in hard exclusive
production of rho^0 mesons was measured at COMPASS by scattering 160 GeV/c
muons off transversely polarised protons and deuterons. The measured asymmetry
is sensitive to the nucleon helicity-flip generalised parton distributions E^q,
which are related to the orbital angular momentum of quarks in the nucleon. The
Q^2, x_B and p_t^2 dependence of A_UT is presented in a wide kinematic range.
Results for deuterons are obtained for the first time. The measured asymmetry
is small in the whole kinematic range for both protons and deuterons, which is
consistent with the theoretical interpretation that contributions from GPDs E^u
and E^d approximately cancel.
07/2012;
-
A. Thiel,
A. V. Anisovich,
D. Bayadilov,
B. Bantes,
R. Beck,
Yu. Beloglazov,
M. Bichow,
S. Böse,
K. -Th. Brinkmann,
Th. Challand, [......],
V. Sokhoyan,
V. Sumachev,
U. Thoma,
H. van Pee,
D. Walther,
Ch. Wendel,
U. Wiedner,
A. Wilson,
A. Winnebeck,
Y. Wunderlich
[show abstract]
[hide abstract]
ABSTRACT: The first measurement is reported of the double-polarization observable G in
photoproduction of neutral pions off protons, covering the photon energy range
from 620 to 1120 MeV and the full solid angle. G describes the correlation
between the photon polarization plane and the scattering plane for protons
polarized along the direction of the incoming photon. The observable is highly
sensitive to contributions from baryon resonances. The new results are compared
to the predictions from SAID, MAID, and BnGa partial wave analyses. In spite of
the long-lasting efforts to understand {\gamma}p -> p{\pi} 0 as the simplest
photoproduction reaction, surprisingly large differences between the new data
and the latest predictions are observed which are traced to different
contributions of the N (1535) with spin-parity J^P = 1/2^- and N (1520) with
J^P = 3/2^- . In the third resonance region, where N (1680) with J^P = 5/2^+
production dominates, the new data are reasonably close to the predictions.
07/2012;
-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badełek,
F. Balestra, [......],
L. Wang,
R. Windmolders,
W. Wislicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: The cross section for production of charged hadrons with high transverse
momenta in scattering of 160 GeV/c muons off nucleons at low photon
virtualities has been measured at the COMPASS experiment at CERN. The results,
which cover transverse momenta from 1.1 to 3.6 GeV/c, are compared to a
next-to-leading order perturbative Quantum Chromodynamics (NLO pQCD)
calculation in order to evaluate the applicability of pQCD to this process in
the kinematic domain of the experiment. The shape of the calculated
differential cross section as a function of transverse momentum is found to be
in good agreement with the experimental data, but the normalization is
underestimated by NLO pQCD. This discrepancy may point towards the relevance of
terms beyond NLO in the pQCD framework. The dependence of the cross section on
the pseudo-rapidity and on the charge of the hadrons is also discussed.
07/2012;
-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badelek,
F. Balestra, [......],
M. Wilfert,
R. Windmolders,
W. Wislicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: The COMPASS Collaboration at CERN has measured the transverse spin azimuthal
asymmetry of charged hadrons produced in semi-inclusive deep inelastic
scattering using a 160 GeV positive muon beam and a transversely polarised NH_3
target. The Collins asymmetry of the proton was extracted in the Bjorken x
range 0.003<x<0.7. These new measurements confirm with higher accuracy previous
measurements from the COMPASS and HERMES collaborations, which exhibit a
definite effect in the valence quark region. The asymmetries for negative and
positive hadrons are similar in magnitude and opposite in sign. They are
compatible with model calculations in which the u-quark transversity is
opposite in sign and somewhat larger than the d-quark transversity distribution
function. The asymmetry is extracted as a function of Bjorken $x$, the relative
hadron energy $z$ and the hadron transverse momentum p_T^h. The high statistics
and quality of the data also allow for more detailed investigations of the
dependence on the kinematic variables. These studies confirm the leading-twist
nature of the Collins asymmetry.
05/2012;
-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badelek,
F. Balestra, [......],
M. Wilfert,
R. Windmolders,
W. Wislicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: The COMPASS Collaboration at CERN has measured the transverse spin azimuthal
asymmetry of charged hadrons produced in semi-inclusive deep inelastic
scattering using a 160 GeV positive muon beam and a transversely polarised NH_3
target. The Sivers asymmetry of the proton has been extracted in the Bjorken x
range 0.003<x<0.7. The new measurements have small statistical and systematic
uncertainties of a few percent and confirm with considerably better accuracy
the previous COMPASS measurement. The Sivers asymmetry is found to be
compatible with zero for negative hadrons and positive for positive hadrons, a
clear indication of a spin-orbit coupling of quarks in a transversely polarised
proton. As compared to measurements at lower energy, a smaller Sivers asymmetry
for positive hadrons is found in the region x > 0.03. The asymmetry is
different from zero and positive also in the low x region, where sea-quarks
dominate. The kinematic dependence of the asymmetry has also been investigated
and results are given for various intervals of hadron and virtual photon
fractional energy. In contrast to the case of the Collins asymmetry, the
results on the Sivers asymmetry suggest a strong dependence on the
four-momentum transfer to the nucleon, in agreement with the most recent
calculations.
05/2012;
-
M. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. Austregesilo,
B. Badełek,
F. Balestra,
J. Ball,
J. Barth, [......],
Q. Weitzel,
R. Windmolders,
W. Wiślicki,
H. Wollny,
K. Zaremba,
E. Zemlyanichkina,
M. Ziembicki,
J. Zhao,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: The longitudinal polarisation transfer from muons to Λand
[`\varLambda]\bar{\varLambda}
hyperons,
DLL\varLambda([`\varLambda])D_{LL}^{\varLambda(\bar{\varLambda})}
, has been studied in deep-inelastic scattering off an unpolarised isoscalar target at the COMPASS experiment at CERN. The
spin transfers to Λand
[`\varLambda]\bar{\varLambda}
produced in the current fragmentation region exhibit different behaviours as a function of x and x
F
. The measured x and x
F
dependences of D
LL
Λ
are compatible with zero, while
DLL[`\varLambda]D_{LL}^{\bar{\varLambda}}
tends to increase with x
F
, reaching values of 0.4–0.5. The resulting average values are D
LL
Λ
= −0.012±0.047±0.024 and
DLL[`\varLambda]D_{LL}^{\bar{\varLambda}}
= 0.249±0.056±0.049. These results are discussed in the frame of recent model calculations.
European Physical Journal C 04/2012; 64(2):171-179. · 3.63 Impact Factor
-
F. W. Wieland,
J. Barth,
K. -H. Glander,
J. Hannappel,
N. Jöpen, F. Klein,
E. Klempt,
R. Lawall,
D. Menze,
M. Ostrick,
E. Paul,
I. Schulday,
W. J. Schwille
[show abstract]
[hide abstract]
ABSTRACT: The reaction γp → K
+
Λ(1520) was measured in the energy range from threshold to 2.65 GeV with the SAPHIR detector at the electron stretcher facility
ELSA in Bonn. The Λ(1520) production cross-section was analyzed in the decay modes pK
−, $
n\bar K^0
$
n\bar K^0
, Σ
±
π
∓, and Λπ
+
π
− as a function of the photon energy and the squared four-momentum transfer t . While the cross-sections for the inclusive reactions rise steadily with energy, the cross-section of the process γp → K
+
Λ(1520) peaks at a photon energy of about 2.0 GeV, falls off exponentially with t , and shows a slope flattening with increasing photon energy. The angular distributions in the t-channel helicity system indicate neither a K nor a K
* exchange dominance. Rather, the rapid change of the angular distribution with energy suggests that, in addition to t -channel K and K* exchange, amplitudes for formation of nucleon resonances in the s-channel play an important role.
European Physical Journal A 04/2012; 47(4):1-11. · 2.19 Impact Factor
-
GDH and Collaborations,
J. Ahrens,
S. Altieri,
J. R. M. Annand,
H. -J. Arends,
R. Beck,
M. A. Blackston,
C. Bradtke,
A. Braghieri,
N. d’Hose, [......],
T. Pinelli,
D. Protopopescu,
G. Reicherz,
Ch. Rohlof,
G. Rosner,
T. Rostomyan,
D. Ryckbosch,
G. Tamas,
A. Thomas,
H. R. Weller
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the total cross-section for the g \gamma
n
® \rightarrow
p
p- \pi^{-}_{}
p0 \pi^{0}_{} reaction has been measured for the first time at incident photon energies from 450 to 800MeV. The measurement was performed
with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. Both the measured
unpolarized and the helicity-dependent observables are not well described by the existing theoretical models.
European Physical Journal A 04/2012; 47(3):1-8. · 2.19 Impact Factor
-
GDH and Collaborations,
J. Ahrens,
S. Altieri,
J. R. M. Annand,
H. -J. Arends,
R. Beck,
M. A. Blackston,
C. Bradtke,
A. Braghieri,
N. d'Hose, [......],
M. Rost,
T. Rostomyan,
D. Ryckbosch,
M. Schumacher,
B. Seitz,
G. Tamas,
A. Thomas,
R. Van de Vyver,
H. R. Weller,
F. Zapadtka
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the total cross-section and the invariant-mass distributions in the (pπ±) and (π+π-) final states for the γp → pπ+π- reaction have been measured for the first time at incident photon energies from 400 to 800MeV. The measurement was performed
with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. Although this
channel is found to be predominantly excited by the intermediate production of a Δπ state, both the measured unpolarized and
the helicity-dependent observables are generally not well described by the existing theoretical models.
European Physical Journal A 04/2012; 34(1):11-21. · 2.19 Impact Factor
-
The GDH and Collaborations,
J. Ahrens,
S. Altieri,
J. R. M. Annand,
H. -J. Arends,
R. Beck,
M. A. Blackston,
C. Bradtke,
A. Braghieri,
N. d’Hose, [......],
D. Protopopescu,
G. Reicherz,
Ch. Rohlof,
G. Rosner,
T. Rostomyan,
D. Ryckbosch,
M. Schwamb,
G. Tamas,
A. Thomas,
H. R. Weller
[show abstract]
[hide abstract]
ABSTRACT: The helicity dependence of the differential cross-section for the g \gamma
d
® \rightarrow
p \pi
NN reactions has been measured for the first time in the D \Delta -resonance region. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility
of the MAMI accelerator in Mainz. The data show that the main reaction mechanisms for the p± \pi^{{\pm}}_{}
NN channels are the quasi-free N
p \pi processes on one bound nucleon with nuclear dynamics playing a minor role. On the contrary, for the p0 \pi^{0}_{}
np channel nuclear mechanisms involving the reabsorption of the photoproduced p0 \pi^{0}_{} by the np pair have to be taken into account to reproduce the experimental data.
European Physical Journal A 04/2012; 44(2):189-201. · 2.19 Impact Factor
-
The COMPASS Collaboration,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. Austregesilo,
B. Badełek,
F. Balestra,
J. Barth, [......],
R. Windmolders,
W. Wiślicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
J. Zhao,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: Azimuthal asymmetries in semi-inclusive production of positive (h
+) and negative hadrons (h
−) have been measured by scattering 160 GeV muons off longitudinally polarised deuterons at CERN. The asymmetries were decomposed
in several terms according to their expected modulation in the azimuthal angle φ of the outgoing hadron. Each term receives contributions from one or several spin and transverse-momentum-dependent parton
distribution and fragmentation functions. The amplitudes of all φ-modulation terms of the hadron asymmetries integrated over the kinematic variables are found to be consistent with zero within
statistical errors, while the constant terms are nonzero and equal for h
+ and h
− within the statistical errors. The dependencies of the φ-modulated terms versus the Bjorken momentum fraction x, the hadron fractional momentum z, and the hadron transverse momentum phTp_{h}^{T} were studied. The x dependence of the constant terms for both positive and negative hadrons is in agreement with the longitudinal double-spin
hadron asymmetries, measured in semi-inclusive deep-inelastic scattering. The x dependence of the sin φ-modulation term is less pronounced than that in the corresponding HERMES data. All other dependencies of the φ-modulation amplitudes are consistent with zero within the statistical errors.
European Physical Journal C 04/2012; 70(1):39-49. · 3.63 Impact Factor
-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badellek,
F. Balestra, [......],
L. Wang,
R. Windmolders,
W. Wislicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlevd,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: First measurements of azimuthal asymmetries in hadron-pair production in
deep-inelastic scattering of muons on transversely polarised ^6LiD (deuteron)
and NH_3 (proton) targets are presented. The data were taken in the years
2002-2004 and 2007 with the COMPASS spectrometer using a muon beam of 160 GeV/c
at the CERN SPS. The asymmetries provide access to the transversity
distribution functions, without involving the Collins effect as in single
hadron production. The sizeable asymmetries measured on the NH_ target indicate
non-vanishing u-quark transversity and two-hadron interference fragmentation
functions. The small asymmetries measured on the ^6LiD target can be
interpreted as indication for a cancellation of u- and d-quark transversities.
02/2012;
-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badelek,
F. Balestra, [......],
L. Wang,
R. Windmolders,
W. Wislicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: We present a determination of the gluon polarisation Delta g/g in the
nucleon, based on the longitudinal double-spin asymmetry of DIS events 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/c polarised muon
beam scattering off a polarised ^6LiD target. The gluon polarisation is
evaluated by a Neural Network approach for three intervals of the gluon
momentum fraction x_g covering the range 0.04 < x_g < 0.27. The values obtained
at leading order in QCD do not show any significant dependence on x_g. Their
average is Delta g/g = 0.125 +/- 0.060 (stat.) +/- 0.063 (syst.) at x_g=0.09
and a scale of mu^2 = 3 (GeV/c)^2.
02/2012;
-
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. Austregesilo,
B. Badelek,
F. Balestra,
J. Barth,
G. Baum, [......],
N. V. Vlassov,
R. Windmolders,
W. Wiślicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: The COMPASS collaboration at CERN has investigated the \pi^- \gamma -> \pi^-
\pi^- \pi^+ reaction at center-of-momentum energy below five pion masses,
sqrt(s) < 5 m(\pi), embedded in the Primakoff reaction of 190 GeV pions
impinging on a lead target. Exchange of quasi-real photons is selected by
isolating the sharp Coulomb peak observed at smallest momentum transfers, t' <
0.001 (GeV/c)^2. Using partial-wave analysis techniques, the scattering
intensity of Coulomb production described in terms of chiral dynamics and its
dependence on the 3\pi-invariant mass m(3\pi) = sqrt(s) were extracted. The
absolute cross section was determined in seven bins of $\sqrt{s}$ with an
overall precision of 20%. At leading order, the result is found to be in good
agreement with the prediction of chiral perturbation theory over the whole
energy range investigated.
11/2011;
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ABSTRACT: This article describes the implementation of a mean-timer and coincidence
logic on a Virtex-5 FPGA for trigger purposes in a particle physics experiment.
The novel feature is that the mean-timing and the coincidence logic are not
synchronized with a clock which allows for a higher resolution of approximately
400 ps, not limited by a clock frequency.
09/2011;
