First measurements of azimuthal asymmetries in hadron-pair production in deep-inelastic scattering of muons on transversely polarised LiD6 (deuteron) and NH3 (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 NH3 target indicate non-vanishing u-quark transversity and two-hadron interference fragmentation functions. The small asymmetries measured on the LiD6 target can be interpreted as indication for a cancellation of u- and d-quark transversities.
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.
The K− over K+ multiplicity ratio is measured in deep-inelastic scattering, for the first time for kaons carrying a large fraction z of the virtual-photon energy. The data were obtained by the ...COMPASS collaboration using a 160 GeV muon beam and an isoscalar 6LiD target. The regime of deep-inelastic scattering is ensured by requiring Q2>1(GeV/c)2 for the photon virtuality and W>5GeV/c2 for the invariant mass of the produced hadronic system. Kaons are identified in the momentum range from 12 GeV/c to 40 GeV/c, thereby restricting the range in Bjorken-x to 0.01<x<0.40. The z-dependence of the multiplicity ratio is studied for z>0.75. For very large values of z, i.e.z>0.8, we observe the kaon multiplicity ratio to fall below the lower limits expected from calculations based on leading and next-to-leading order perturbative quantum chromodynamics. Also, the kaon multiplicity ratio shows a strong dependence on the missing mass of the single-kaon production process. This suggests that within the perturbative quantum chromodynamics formalism an additional correction may be required, which takes into account the phase space available for hadronisation.
Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic Scattering (SIDIS) on unpolarised nucleons allows one to get information on the intrinsic transverse momentum of quarks in a ...nucleon and on the Boer-Mulders function through the measurement of azimuthal modulations in the cross section. These modulations were recently measured by the HERMES experiment at DESY on proton and deuteron targets, and by the COMPASS experiment using the CERN SPS muon beam and a 6LiD target. In both cases, the amplitudes of the cosϕh and cos2ϕh modulations show strong kinematic dependences for both positive and negative hadrons. It has been known since some time that the measured final-state hadrons in those SIDIS experiments receive a contribution from exclusive diffractive production of vector mesons, particularly important at large values of z, the fraction of the virtual photon energy carried by the hadron. In previous measurements of azimuthal asymmetries this contribution was not taken into account, because it was not known that it could distort the azimuthal modulations. Presently, a method to evaluate the contribution of the exclusive reactions to the azimuthal asymmetries measured by COMPASS has been developed. The subtraction of this contribution results in a better understanding of the kinematic effects, and the remaining non-zero cos2ϕh modulation gives indication for a non-zero Boer-Mulders effect.
Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron ...muoproduction with photon virtuality
Q
2
>
1
(
GeV
/
c
)
2
. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/
c
polarised muon beam impinging on a polarised
6
LiD target. By analysing the full range in hadron transverse momentum
p
T
, the different
p
T
-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation
Δ
g
/
g
is evaluated at leading order in pQCD at a hard scale of
μ
2
=
⟨
Q
2
⟩
=
3
(
GeV
/
c
)
2
. It is determined in three intervals of the nucleon momentum fraction carried by gluons,
x
g
, covering the range
0.04
<
x
g
<
0.28
and does not exhibit a significant dependence on
x
g
. The average over the three intervals,
⟨
Δ
g
/
g
⟩
=
0.113
±
0
.
038
(
stat
.
)
±
0
.
036
(
syst
.
)
at
⟨
x
g
⟩
≈
0.10
, suggests that the gluon polarisation is positive in the measured
x
g
range.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report on a measurement of hard exclusive π0 muoproduction on the proton by COMPASS using 160GeV/c polarised μ+ and μ− beams of the CERN SPS impinging on a liquid hydrogen target. From the average ...of the measured μ+ and μ− cross sections, the virtual-photon proton cross section is determined as a function of the squared four-momentum transfer between initial and final proton in the range 0.08(GeV/c)2<|t|<0.64(GeV/c)2. The average kinematics of the measurement are 〈Q2〉=2.0(GeV/c)2, 〈ν〉=12.8GeV, 〈xBj〉=0.093 and 〈−t〉=0.256(GeV/c)2. Fitting the azimuthal dependence reveals a combined contribution by transversely and longitudinally polarised photons of (8.2±0.9stat−1.2+1.2|sys)nb/(GeV/c)2, as well as transverse-transverse and longitudinal-transverse interference contributions of (−6.1±1.3stat−0.7+0.7|sys)nb/(GeV/c)2 and (1.5±0.5stat−0.2+0.3|sys)nb/(GeV/c)2, respectively. Our results provide important input for modelling Generalised Parton Distributions. In the context of the phenomenological Goloskokov-Kroll model, the statistically significant transverse-transverse interference contribution constitutes clear experimental evidence for the chiral-odd GPD E‾T.
Background: Tobacco use is the leading cause of Preventable death, Tobacco use during adolescence increases the risk of persistent addiction, leading to regular and sustained tobacco use in ...adulthood. Objective: To assess the prevalence and practice of tobacco use among the school going adolescents in a block of Vadodara district, Gujarat. Material & Methods: Multiphase sampling was done to select the sample students (13 to 17 years) from private and government schools in a selected block of Vadodara. A cross-sectional study including 1045 students was carried out using a pre-designed and pre-tested proforma. Results: Out of 1045 students, 3% (n=32) tried cigarette smoking ever, one or two puffs and 1.8% (19 students) of students were current cigarette or beedi smokers. Around 27.9% students and 23% students admitted that at least one of their parents and friends smoked cigarettes, respectively. About 24% and 44% of the students were exposed to passive smoking at home and outside home, respectively. Conclusions: Present study provides the baseline information of prevalence of smoking and attitude of school going adolescents towards smoking in Gujarat. The result gives an alarm to work upon tobacco control among adolescents and make them aware about the hazards.
Exclusive production of ω mesons was studied at the COMPASS experiment by scattering 160 GeV/c muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries ...were measured in the range of photon virtuality 1 (GeV/c)2<Q2<10 (GeV/c)2, Bjorken scaling variable 0.003<xBj<0.3 and transverse momentum squared of the ω meson 0.05 (GeV/c)2<pT2<0.5 (GeV/c)2. The measured asymmetries are sensitive to the nucleon helicity-flip Generalised Parton Distributions (GPD) E that are related to the orbital angular momentum of quarks, the chiral-odd GPDs HT that are related to the transversity Parton Distribution Functions, and the sign of the πω transition form factor. The results are compared to recent calculations of a GPD-based model.
Single hadron azimuthal asymmetries of positive and negative hadrons produced in muon semi-inclusive deep inelastic scattering off longitudinally polarised deuterons are determined using the 2006 ...COMPASS data and also combined all deuteron COMPASS data. For each hadron charge, the dependence of the azimuthal asymmetry on the hadron azimuthal angle
ϕ
is obtained by means of a five-parameter fitting function that besides a
ϕ
-independent term includes four modulations predicted by theory:
sin
ϕ
,
sin
2
ϕ
,
sin
3
ϕ
and
cos
ϕ
. The amplitudes of the five terms have been extracted, first, for the hadrons in the whole available kinematic region. In further fits, performed for hadrons from a restricted kinematic region, the
ϕ
-dependence is determined as a function of one of three variables (Bjorken-
x
, fractional energy of virtual photon taken by the outgoing hadron and hadron transverse momentum), while disregarding the others. Except the
ϕ
-independent term, all the modulation amplitudes are very small, and no clear kinematic dependence could be observed within experimental uncertainties.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In the fragmentation of a transversely polarized quark several left–right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal ...modulation known as the Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair production we have investigated for the first time the dependence of these three asymmetries on the difference of the azimuthal angles of the two hadrons. The similarity of transversity induced single and di-hadron asymmetries is discussed. A new analysis of the data allows quantitative relationships to be established among them, providing for the first time strong experimental indication that the underlying fragmentation mechanisms are all driven by a common physical process.
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