-
STAR Collaboration,
L. Adamczyk,
J. K. Adkins,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
A. V. Alakhverdyants,
I. Alekseev,
J. Alford,
C. D. Anson, [......],
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva,
M. Zyzak
[show abstract]
[hide abstract]
ABSTRACT: A study is reported of the same- and opposite-sign charge-dependent azimuthal
correlations with respect to the event plane in Au+Au collisions at 200 GeV.
The charge multiplicity asymmetries between the up/down and left/right
hemispheres relative to the event plane are utilized. The contributions from
statistical fluctuations and detector effects were subtracted from the
(co-)variance of the observed charge multiplicity asymmetries. In the mid- to
most-central collisions, the same- (opposite-) sign pairs are preferentially
emitted in back-to-back (aligned on the same-side) directions. The charge
separation across the event plane, measured by the difference, $\Delta$,
between the like- and unlike-sign up/down $-$ left/right correlations, is
largest near the event plane. The difference is found to be proportional to the
event-by-event final-state particle ellipticity (via the observed second-order
harmonic $v_2^{\rm obs}$, where $\Delta=(1.3\pm1.4({\rm
stat})^{+4.0}_{-1.0}({\rm syst}))\times10^{-5}+(3.2\pm0.2({\rm
stat})^{+0.4}_{-0.3}({\rm syst}))\times10^{-3}v_2^{\rm obs}$ for 20-40% Au+Au
collisions. The implications for the proposed chiral magnetic effect (\cme) are
discussed.
03/2013;
-
STAR Collaboration,
L. Adamczyk,
J. K. Adkins,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
I. Alekseev,
J. Alford,
C. D. Anson,
A. Aparin, [......],
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva,
M. Zyzak
[show abstract]
[hide abstract]
ABSTRACT: Azimuthal angular correlations of charged hadrons with respect to the axis of
a reconstructed (trigger) jet in Au+Au and p+p collisions at $\sqrt{s_{NN}} =
200$ GeV in STAR are presented. The trigger jet population in Au+Au collisions
is biased towards jets that have not interacted with the medium, allowing
easier matching of jet energies between Au+Au and p+p collisions while
enhancing medium effects on the recoil jet. The associated hadron yield of the
recoil jet is significantly suppressed at high transverse momentum
($p_{T}^{assoc}$) and enhanced at low $p_{T}^{assoc}$ in Au+Au collisions,
which is indicative of medium-induced parton energy loss in ultrarelativistic
heavy-ion collisions.
02/2013;
-
STAR Collaboration,
L. Adamczyk,
J. K. Adkins,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
I. Alekseev,
J. Alford,
C. D. Anson,
A. Aparin, [......],
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva,
M. Zyzak
[show abstract]
[hide abstract]
ABSTRACT: Recent experimental results from the STAR collaboration suggest
event-by-event charge separation fluctuations perpendicular to the event plane
in non-central heavy-ion collisions. Here we present the correlator previously
used split into its two component parts to reveal correlations parallel and
perpendicular to the event plane. The results are from a high statistics 200
GeV Au+Au collisions data set collected by the STAR experiment at RHIC. We
explicitly count units of charge separation from which we find clear evidence
for more charge separation fluctuations perpendicular than parallel to the
event plane. We also employ a modified correlator to study the possible P-even
background in same and opposite charge correlations.
02/2013;
-
STAR Collaboration,
L. Adamczyk,
J. K. Adkins,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
I. Alekseev,
J. Alford,
C. D. Anson,
A. Aparin, [......],
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva,
M. Zyzak
[show abstract]
[hide abstract]
ABSTRACT: We present measurements of three-dimensional correlation functions of
like-sign low transverse momentum kaon pairs from sqrt(sNN)=200 GeV Au+Au
collisions. A Cartesian surface-spherical harmonic decomposition technique was
used to extract the kaon source function. The latter was found to have a
three-dimensional Gaussian shape and can be adequately reproduced by
Therminator event generator simulations with resonance contributions taken into
account. Compared to the pion one, the kaon source function is generally
narrower and does not have the long tail along the pair transverse momentum
direction. The kaon Gaussian radii display a monotonic decrease with increasing
transverse mass m_T over the interval of 0.55<=m_T<=1.15 GeV/c^2. While the
kaon radii are adequately described by the m_T-scaling in the outward and
sideward directions, in the longitudinal direction the lowest m_T value exceeds
the expectations from a pure hydrodynamical model prediction.
02/2013;
-
STAR Collaboration,
L. Adamczyk,
J. K. Adkins,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
I. Alekseev,
J. Alford,
C. D. Anson,
A. Aparin, [......],
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva,
M. Zyzak
[show abstract]
[hide abstract]
ABSTRACT: We present a study of the average transverse momentum ($p_t$) fluctuations
and $p_t$ correlations for charged particles produced in Cu+Cu collisions at
midrapidity for $\sqrt{s_{NN}} =$ 62.4 and 200 GeV. These results are compared
with those published for Au+Au collisions at same energies, to explore the
system size dependence. In addition to the collision energy and system size
dependence, the $p_t$ correlations results have been studied as functions of
the collision centralities, the ranges in $p_t$, the pseudo-rapidity $\eta$,
and the azimuthal angle $\phi$, for which the correlations are measured. The
square root of the measured $p_t$ correlations when scaled by mean-$p_t$ are
found to be independent of both colliding beam energy and system size studied.
The transport based model calculations are found to have a better quantitative
agreement with the measurements compared to models which incorporate only
jet-like correlations.
01/2013;
-
STAR Collaboration,
L. Adamczyk,
J. K. Adkins,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
I. Alekseev,
J. Alford,
C. D. Anson,
A. Aparin, [......],
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva,
M. Zyzak
[show abstract]
[hide abstract]
ABSTRACT: We report measurements of the third harmonic coefficient of the azimuthal
anisotropy, v_3, known as triangular flow. The analysis is for charged
particles in Au+Au collisions at $\sqrtsNN = 200$ GeV, based on data from the
STAR experiment at the Relativistic Heavy Ion Collider. Two-particle
correlations as a function of their pseudorapidity separation are fit with
narrow and wide Gaussians. Measurements of triangular flow are extracted from
the wide Gaussian, from two-particle cumulants with a pseudorapidity gap, and
also from event plane analysis methods with a large pseudorapidity gap between
the particles and the event plane. These results are reported as a function of
transverse momentum and centrality. A large dependence on the pseudorapidity
gap is found. Results are compared with other experiments and model
calculations.
01/2013;
-
L. Adamczyk,
J. K. Adkins,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
I. Alekseev,
J. Alford,
C. D. Anson,
A. Aparin,
D. Arkhipkin, [......],
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva,
M. Zyzak
[show abstract]
[hide abstract]
ABSTRACT: Elliptic flow ($v_{2}$) values for identified particles at mid-rapidity in
Au+Au collisions, measured by the STAR experiment in the Beam Energy Scan at
RHIC at $\sqrt{s_{NN}}=$ 7.7--62.4 GeV, are presented. A beam-energy dependent
difference of the values of $v_{2}$ between particles and corresponding
anti-particles was observed. The difference increases with decreasing beam
energy and is larger for baryons compared to mesons. This implies that, at
lower energies, particles and anti-particles are not consistent with the
universal number-of-constituent-quark (NCQ) scaling of $v_{2}$ that was
observed at $\sqrt{s_{NN}}=$ 200 GeV.
01/2013;
-
L. Adamczyk,
J. K. Adkins,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
I. Alekseev,
J. Alford,
C. D. Anson,
A. Aparin,
D. Arkhipkin, [......],
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva,
M. Zyzak
[show abstract]
[hide abstract]
ABSTRACT: Measurements of the elliptic flow, $v_{2}$, of identified hadrons
($\pi^{\pm}$, $K^{\pm}$, $K_{s}^{0}$, $p$, $\bar{p}$, $\phi$, $\Lambda$,
$\bar{\Lambda}$, $\Xi^{-}$, $\bar{\Xi}^{+}$, $\Omega^{-}$, $\bar{\Omega}^{+}$)
in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5, 19.6, 27, 39 and 62.4 GeV
are presented. The measurements were done at mid-rapidity using the Time
Projection Chamber and the Time-of-Flight detectors of the STAR experiment
during the Beam Energy Scan program at RHIC. A significant difference in the
$v_{2}$ values for particles and the corresponding anti-particles was observed
at all transverse momenta for the first time. The difference increases with
decreasing center-of-mass energy, $\sqrt{s_{NN}}$ (or increasing baryon
chemical potential, $\mu_{B}$) and is larger for the baryons as compared to the
mesons. This implies that particles and anti-particles are no longer consistent
with the universal number-of-constituent quark (NCQ) scaling of $v_{2}$ that
was observed at $\sqrt{s_{NN}}=$ 200 GeV. However, for the group of particles
NCQ scaling at $(m_{T}-m_{0})/n_{q}>$ 0.4 GeV/$c^{2}$ is not violated within
$\pm$10%. The $v_{2}$ values for $\phi$ mesons at 7.7 and 11.5 GeV are
approximately two standard deviations from the trend defined by the other
hadrons at the highest measured $p_{T}$ values.
01/2013;
-
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
C. Alexa,
V. Andreev,
S. Antonelli,
P. Antonioli,
A. Antonov, [......],
W. Zeuner,
Z. Zhang,
B. O. Zhautykov,
N. Zhmak,
A. Zichichi,
R. Žlebčík,
H. Zohrabyan,
Z. Zolkapli,
F. Zomer,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: Measurements of open charm production cross sections in deep-inelastic ep
scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced
cross sections sigma_red^{c\bar{c}} for charm production are obtained in the
kinematic range of photon virtuality 2.5<Q2<2000 GeV2 and Bjorken scaling
variable 0.00003<x<0.05. The combination method accounts for the correlations
of the systematic uncertainties among the different data sets. The combined
charm data together with the combined inclusive deep-inelastic scattering cross
sections from HERA are used as input for a detailed NLO QCD analysis to study
the influence of different heavy flavour schemes on the parton distribution
functions. The optimal values of the charm mass as a parameter in these
different schemes are obtained. The implications on the NLO predictions for
W^{\pm} and Z production cross sections at the LHC are investigated. Using the
fixed flavour number scheme, the running mass of the charm quark is determined.
11/2012;
-
ZEUS collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
O. Zabiegalov,
A. F. Żarnecki,
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
A. Zichichi,
Z. Zolkapli,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: The production of Z0 bosons in the reaction ep -> eZ0p*, where p* stands for
a proton or a low-mass nucleon resonance, has been studied in ep collisions at
HERA using the ZEUS detector. The analysis is based on a data sample collected
between 1996 and 2007, amounting to 496 pb-1 of integrated luminosity. The Z0
was measured in the hadronic decay mode. The elasticity of the events was
ensured by a cut on eta_max < 3.0, where eta_max is the maximum pseudorapidity
of energy deposits in the calorimeter defined with respect to the proton beam
direction. A signal was observed at the Z0 mass. The cross section of the
reaction ep -> eZ0p* was measured to be sigma(ep -> eZ0p*) = 0.13 +/- 0.06
(stat.) +/- 0.01 (syst.) pb, in agreement with the Standard Model prediction of
0.16 pb. This is the first measurement of Z0 production in ep collisions.
10/2012;
-
ZEUS Collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
M. Zolko,
D. S. Zotkin
-
L. Adamczyk,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
A. V. Alakhverdyants,
I. Alekseev,
J. Alford,
B. D. Anderson,
C. D. Anson,
D. Arkhipkin, [......],
W. M. Zhang,
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva
[show abstract]
[hide abstract]
ABSTRACT: We report STAR measurements of the longitudinal double-spin asymmetry ALL, the transverse single-spin asymmetry AN, and the transverse double-spin asymmetries AΣ and ATT for inclusive jet production at mid-rapidity in polarized p+p collisions at a center-of-mass energy of √s=200 GeV. The data represent integrated luminosities of 7.6 pb-1 with longitudinal polarization and 1.8 pb-1 with transverse polarization, with 50%–55% beam polarization, and were recorded in 2005 and 2006. No evidence is found for the existence of statistically significant jet AN, AΣ, or ATT at mid-rapidity. Recent model calculations indicate the AN results may provide new limits on the gluon Sivers distribution in the proton. The asymmetry ALL significantly improves the knowledge of gluon polarization in the nucleon.
Phys. Rev. D. 08/2012; 86(3).
-
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo,
O. Arslan, [......],
A. F. Żarnecki,
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: A search for first-generation leptoquarks was performed in electron-proton and positron-proton collisions recorded with the ZEUS detector at HERA in 2003–2007 using an integrated luminosity of 366 pb-1. Final states with an electron and jets or with missing transverse momentum and jets were analyzed, searching for resonances or other deviations from the standard model predictions. No evidence for any leptoquark signal was found. The data were combined with data previously taken at HERA, resulting in a total integrated luminosity of 498 pb-1. Limits on the Yukawa coupling, λ, of leptoquarks were set as a function of the leptoquark mass for different leptoquark types within the Buchmüller-Rückl-Wyler model. Leptoquarks with a coupling λ=0.3 are excluded for masses up to 699 GeV.
Phys. Rev. D. 07/2012; 86(1).
-
STAR Collaboration,
L. Adamczyk,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
A. V. Alakhverdyants,
I. Alekseev,
J. Alford,
C. D. Anson,
D. Arkhipkin, [......],
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva,
M. Zyzak
[show abstract]
[hide abstract]
ABSTRACT: We report a high precision measurement of the transverse single spin
asymmetry $A_N$ at the center of mass energy $\sqrt{s}=200$ GeV in elastic
proton-proton scattering by the STAR experiment at RHIC. The $A_N$ was measured
in the four-momentum transfer squared $t$ range $0.003 \leqslant |t| \leqslant
0.035$ $\GeVcSq$, the region of a significant interference between the
electromagnetic and hadronic scattering amplitudes. The measured values of
$A_N$ and its $t$-dependence are consistent with a vanishing hadronic spin-flip
amplitude, thus providing strong constraints on the ratio of the single
spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated
by the Pomeron amplitude at this $\sqrt{s}$, we conclude that this measurement
addresses the question about the presence of a hadronic spin flip due to the
Pomeron exchange in polarized proton-proton elastic scattering.
06/2012;
-
The STAR Collaboration,
L. Adamczyk,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
A. V. Alakhverdyants,
I. Alekseev,
J. Alford,
B. D. Anderson,
C. D. Anson, [......],
W. M. Zhang,
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva
[show abstract]
[hide abstract]
ABSTRACT: Measurements of the differential cross-section and the transverse single-spin
asymmetry, A_N, vs. x_F for pi0 and eta mesons are reported for 0.4 < x_F <
0.75 at an average pseudorapidity of 3.68. A data sample of approximately 6.3
pb^{-1} was analyzed, which was recorded during p+p collisions at sqrt{s} = 200
GeV by the STAR experiment at RHIC. The average transverse beam polarization
was 56%. The cross-section for pi0 is consistent with a perturbative QCD
prediction, and the eta/pi0 cross-section ratio agrees with previous
mid-rapidity measurements. For 0.55 < x_F < 0.75, A_N for eta (0.210 +- 0.056)
is 2.2 standard deviations larger than A_N for pi0 (0.081 +- 0.016).
05/2012;
-
ZEUS Collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
A. F. Zarnecki,
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: Inclusive-jet cross sections have been measured in the reaction ep->e+jet+X
for photon virtuality Q2 < 1 GeV2 and gamma-p centre-of-mass energies in the
region 142 < W(gamma-p) < 293 GeV with the ZEUS detector at HERA using an
integrated luminosity of 300 pb-1. Jets were identified using the kT, anti-kT
or SIScone jet algorithms in the laboratory frame. Single-differential cross
sections are presented as functions of the jet transverse energy, ETjet, and
pseudorapidity, etajet, for jets with ETjet > 17 GeV and -1 < etajet < 2.5. In
addition, measurements of double-differential inclusive-jet cross sections are
presented as functions of ETjet in different regions of etajet.
Next-to-leading-order QCD calculations give a good description of the
measurements, except for jets with low ETjet and high etajet. The influence of
non-perturbative effects not related to hadronisation was studied. Measurements
of the ratios of cross sections using different jet algorithms are also
presented; the measured ratios are well described by calculations including up
to O(alphas2) terms. Values of alphas(Mz) were extracted from the measurements
and the energy-scale dependence of the coupling was determined. The value of
alphas(Mz) extracted from the measurements based on the kT jet algorithm is
alphas(Mz) = 0.1206 +0.0023 -0.0022 (exp.) +0.0042 -0.0035 (th.); the results
from the anti-kT and SIScone algorithms are compatible with this value and have
a similar precision.
05/2012;
-
L. Adamczyk,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
A. V. Alakhverdyants,
I. Alekseev,
J. Alford,
B. D. Anderson,
C. D. Anson,
D. Arkhipkin, [......],
W. M. Zhang,
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva
[show abstract]
[hide abstract]
ABSTRACT: We report measurements of the charge-separated W+(-)→e+(-)+νe(ν̅ e) and Z/γ*→e+e- production cross sections at mid-rapidity in proton-proton collisions at √s=500 GeV. These results are based on 13.2 pb-1 of data recorded in 2009 by the STAR detector at RHIC. Production cross sections for W bosons that decay via the eν channel were measured to be σ(pp→W+X)·BR(W+→e+νe)=117.3±5.9(stat)±6.2(syst)±15.2(lumi) pb, and σ(pp→W-X)·BR(W-→e-ν̅ e)=43.3±4.6(stat)± 3.4(syst)±5.6(lumi) pb. For Z/γ* production, σ(pp→Z/γ*X)·BR(Z/γ*→e+e-)=7.7±2.1(stat)-0.9+0.5(syst)±1.0(lumi) pb was measured for di-lepton invariant masses me+e- between 70 and 110 GeV/c2. First measurements of the W cross section ratio, σ(pp→W+X)/σ(pp→W-X), at √s=500 GeV are also reported. Theoretical predictions, calculated using recent parton distribution functions, are found to agree with the measured cross sections.
Phys. Rev. D. 05/2012; 85(9).
-
The STAR Collaboration,
L. Adamczyk,
G. Agakishiev,
M. M. Aggarwal,
Z. Ahammed,
A. V. Alakhverdyants,
I. Alekseev,
J. Alford,
B. D. Anderson,
C. D. Anson, [......],
W. M. Zhang,
X. P. Zhang,
Y. Zhang,
Z. P. Zhang,
F. Zhao,
J. Zhao,
C. Zhong,
X. Zhu,
Y. H. Zhu,
Y. Zoulkarneeva
[show abstract]
[hide abstract]
ABSTRACT: We report STAR measurements of the longitudinal double-spin asymmetry A_LL,
the transverse single-spin asymmetry A_N, and the transverse double-spin
asymmetries A_Sigma and A_TT for inclusive jet production at mid-rapidity in
polarized p+p collisions at a center-of-mass energy of sqrt{s} = 200 GeV. The
data represent integrated luminosities of 7.6 /pb with longitudinal
polarization and 1.8 /pb with transverse polarization, with 50-55% beam
polarization, and were recorded in 2005 and 2006. No evidence is found for the
existence of statistically significant jet A_N, A_Sigma, or A_TT at
mid-rapidity. Recent model calculations indicate the A_N results may provide
new limits on the gluon Sivers distribution in the proton. The asymmetry A_LL
significantly improves the knowledge of gluon polarization in the nucleon.
05/2012;
-
S. Chekanov,
M. Derrick,
S. Magill,
S. Miglioranzi,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
N. Pavel, [......],
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
M. Soares,
J. Standage,
J. Whyte,
The ZEUS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: A search for stop production in R-parity-violating supersymmetry has been performed in e+p interactions with the ZEUS detector at HERA, using an integrated luminosity of 65pb-1. At HERA, the R-parity-violating coupling λ’ allows resonant squark production, e+d®[(q)\tilde]e^+d\to\tilde{q}. Since the lowest-mass squark state in most supersymmetry models is the light stop, [(t)\tilde]\tilde{t}, this search concentrated on production of [(t)\tilde]\tilde{t}, followed either by a direct R-parity-violating decay, or by the gauge decay to b[(c)\tilde]+1b\tilde{\chi}^+_{1}. No evidence for stop production was found and limits were set on λ’131 as a function of the stop mass in the framework of the minimal supersymmetric standard model. The results have also been
interpreted in terms of constraints on the parameters of the minimal supergravity model.
European Physical Journal C 04/2012; 50(2):269-281. · 3.63 Impact Factor
-
The ZEUS collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
M. Zolko,
D. S. Zotkin,
Z. Zulkapli
[show abstract]
[hide abstract]
ABSTRACT: Measurements of the cross sections for charged current deep inelastic scattering in e
+
p collisions with a longitudinally polarised positron beam are presented. The measurements are based on a data sample with
an integrated luminosity of 132pb−1 collected with the ZEUS detector at HERA at a centre-of-mass energy of 318GeV. The total cross section is presented at positive
and negative values of the longitudinal polarisation of the positron beams. The single-differential cross-sections dσ/dQ
2, dσ/dx and dσ/dy are presented for Q
2>200GeV2. The reduced cross-section [(s)\tilde]\tilde{\sigma} is presented in the kinematic range 200<Q
2<60 000GeV2 and 0.006<x<0.562. The measurements agree well with the predictions of the Standard Model. The results are used to determine a lower
limit on the mass of a hypothetical right-handed W boson.
European Physical Journal C 04/2012; 70(4):945-963. · 3.63 Impact Factor
