A
bstract
Results of searches for heavy stable charged particles produced in pp collisions at
= 7 and 8 TeV are presented corresponding to an integrated luminosity of 5.0 fb
−1
and 18.8 fb
−1
, ...respectively. Data collected with the CMS detector are used to study the momentum, energy deposition, and time-of-flight of signal candidates. Leptons with an electric charge between
e
/3 and 8
e
, as well as bound states that can undergo charge exchange with the detector material, are studied. Analysis results are presented for various combinations of signatures in the inner tracker only, inner tracker and muon detector, and muon detector only. Detector signatures utilized are long time-of-flight to the outer muon system and anomalously high (or low) energy deposition in the inner tracker. The data are consistent with the expected background, and upper limits are set on the production cross section of long-lived gluinos, scalar top quarks, and scalar
τ
leptons, as well as pair produced long-lived leptons. Corresponding lower mass limits, ranging up to 1322 GeV/
c
2
for gluinos, are the most stringent to date.
This paper presents distributions of topological observables in inclusive three- and four-jet events produced in pp collisions at a centre-of-mass energy of 7Formula: see text with a data sample ...collected by the CMS experiment corresponding to a luminosity of 5.1Formula: see text. The distributions are corrected for detector effects, and compared with several event generators based on two- and multi-parton matrix elements at leading order. Among the considered calculations, MadGraph interfaced with pythia6 displays the overall best agreement with data.
The inclusive jet cross section for proton-proton collisions at a centre-of-mass energy of 7Formula: see text was measured by the CMS Collaboration at the LHC with data corresponding to an integrated ...luminosity of 5.0Formula: see text. The measurement covers a phase space up to 2Formula: see text in jet transverse momentum and 2.5 in absolute jet rapidity. The statistical precision of these data leads to stringent constraints on the parton distribution functions of the proton. The data provide important input for the gluon density at high fractions of the proton momentum and for the strong coupling constant at large energy scales. Using predictions from perturbative quantum chromodynamics at next-to-leading order, complemented with electroweak corrections, the constraining power of these data is investigated and the strong coupling constant at the Z boson mass Formula: see text is determined to be Formula: see text, which is in agreement with the world average.
Transverse momentum spectra of charged particles are measured by the CMS experiment at the CERN LHC in pPb collisions at Formula: see textFormula: see text, in the range Formula: see textFormula: see ...text and pseudorapidity Formula: see text in the proton-nucleon center-of-mass frame. For Formula: see textFormula: see text, the charged-particle production is asymmetric about Formula: see text, with smaller yield observed in the direction of the proton beam, qualitatively consistent with expectations from shadowing in nuclear parton distribution functions (nPDF). A pp reference spectrum at Formula: see textFormula: see text is obtained by interpolation from previous measurements at higher and lower center-of-mass energies. The Formula: see text distribution measured in pPb collisions shows an enhancement of charged particles with Formula: see textFormula: see text compared to expectations from the pp reference. The enhancement is larger than predicted by perturbative quantum chromodynamics calculations that include antishadowing modifications of nPDFs.
The purely electroweak (EW) cross section for the production of two jets in association with a Z boson, in proton-proton collisions at Formula: see text, is measured using data recorded by the CMS ...experiment at the CERN LHC, corresponding to an integrated luminosity of 19.7Formula: see text. The electroweak cross section for the Formula: see text final state (with Formula: see text or Formula: see text and j representing the quarks produced in the hard interaction) in the kinematic region defined by Formula: see textFormula: see text, Formula: see textFormula: see text, transverse momentum Formula: see textFormula: see text, and pseudorapidity Formula: see text, is found to be Formula: see text, in agreement with the standard model prediction. The associated jet activity of the selected events is studied, in particular in a signal-enriched region of phase space, and the measurements are found to be in agreement with QCD predictions.
A measurement of the cross section for the production of top quark–antiquark pairs (
t
t
¯
) in association with a vector boson V (W or Z) in proton-proton collisions at
s
=
8
TeV
is presented. The ...results are based on a dataset corresponding to an integrated luminosity of 19.5 fb
-
1
recorded with the CMS detector at the LHC. The measurement is performed in three leptonic (e and
μ
) channels: a same-sign dilepton analysis targeting
t
t
¯
W
events, and trilepton and four-lepton analyses designed for
t
t
¯
Z
events. In the same-sign dilepton channel, the
t
t
¯
W
cross section is measured as
σ
t
t
¯
W
=
170
-
80
+
90
(stat)
±
70
(syst)
fb
, corresponding to a significance of 1.6 standard deviations over the background-only hypothesis. Combining the trilepton and four-lepton channels, a direct measurement of the
t
t
¯
Z
cross section,
σ
t
t
¯
Z
=
200
-
70
+
80
(stat)
-
30
+
40
(syst)
fb
-
1
, is obtained with a significance of 3.1 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive
t
t
¯
V
process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.
Dijet production has been measured in
p
Pb
collisions at a nucleon–nucleon centre-of-mass energy of 5.02
TeV
. A data sample corresponding to an integrated luminosity of 35
nb
-
1
was collected using ...the Compact Muon Solenoid detector at the Large Hadron Collider. The dijet transverse momentum balance, azimuthal angle correlations, and pseudorapidity distributions are studied as a function of the transverse energy in the forward calorimeters (
E
T
4
<
|
η
|
<
5.2
). For
p
Pb
collisions, the dijet transverse momentum ratio and the width of the distribution of dijet azimuthal angle difference are comparable to the same quantities obtained from a simulated
p
p
reference and insensitive to
E
T
4
<
|
η
|
<
5.2
. In contrast, the mean value of the dijet pseudorapidity is found to change monotonically with increasing
E
T
4
<
|
η
|
<
5.2
, indicating a correlation between the energy emitted at large pseudorapidity and the longitudinal motion of the dijet frame. The pseudorapidity distribution of the dijet system in minimum bias
p
Pb
collisions is compared with next-to-leading-order perturbative QCD predictions obtained from both nucleon and nuclear parton distribution functions, and the data more closely match the latter.
Spectra of identified charged hadrons are measured in pPb collisions with the CMS detector at the LHC at
s
N
N
=
5.02
TeV
. Charged pions, kaons, and protons in the transverse-momentum range
p
T
≈
...0.1
–1.7
GeV/
c
and laboratory rapidity
|
y
|
<
1
are identified via their energy loss in the silicon tracker. The average
p
T
increases with particle mass and the charged multiplicity of the event. The increase of the average
p
T
with charged multiplicity is greater for heavier hadrons. Comparisons to Monte Carlo event generators reveal that
Epos Lhc
, which incorporates additional hydrodynamic evolution of the created system, is able to reproduce most of the data features, unlike
Hijing
and
Ampt
. The
p
T
spectra and integrated yields are also compared to those measured in pp and PbPb collisions at various energies. The average transverse momentum and particle ratio measurements indicate that particle production at LHC energies is strongly correlated with event particle multiplicity.
A study of color coherence effects in pp collisions at a center-of-mass energy of 7
TeV
is presented. The data used in the analysis were collected in 2010 with the CMS detector at the LHC and ...correspond to an integrated luminosity of 36 pb
-
1
. Events are selected that contain at least three jets and where the two jets with the largest transverse momentum exhibit a back-to-back topology. The measured angular correlation between the second- and third-leading jet is shown to be sensitive to color coherence effects, and is compared to the predictions of Monte Carlo models with various implementations of color coherence. None of the models describe the data satisfactorily.
PDF
