A
bstract
We describe a proposal to add a set of very forward detectors to the CMS experiment for the high-luminosity era of the Large Hadron Collider to search for beyond the standard model ...long-lived particles, such as dark photons, heavy neutral leptons, axion-like particles, and dark Higgs bosons. The proposed subsystem is called
FACET
for
F
orward-
A
perture
C
MS
E
x
T
ension, and will be sensitive to any particles that can penetrate at least 50 m of magnetized iron and decay in an 18 m long, 1 m diameter vacuum pipe. The decay products will be measured in detectors using identical technology to the planned CMS Phase-2 upgrade.
The direct CP violation parameter Re(ϵ′/ϵ) has been measured from the decay rates of neutral kaons into two pions using the NA48 detector at the CERN SPS. The 2001 running period was devoted to ...collecting additional data under varied conditions compared to earlier years (1997–1999). The new data yield the result: Re(ϵ′/ϵ)=(13.7±3.1)×10−4. Combining this result with that published from the 1997, 98 and 99 data, an overall value of Re(ϵ′/ϵ)=(14.7±2.2)×10−4 is obtained from the NA48 experiment.
A search is presented for baryon number violating interactions in top quark production and decay. The analysis uses data from proton-proton collisions at a center-of-mass energy of 13 TeV, collected ...with the CMS detector at the LHC with an integrated luminosity of 138 fb^{-1}. Candidate events are selected by requiring two oppositely charged leptons (electrons or muons) and exactly one jet identified as originating from a bottom quark. Multivariate discriminants are used to separate the signal from the background. No significant deviation from the standard model prediction is observed. Upper limits are placed on the strength of baryon number violating couplings. For the first time the production of single top quarks via baryon number violating interactions is studied. This allows the search to set the most stringent constraints to date on the branching fraction of the top quark decay to a lepton, an up-type quark (u or c), and a down-type quark (d, s, or b). The results improve the previous bounds by 3 to 6 orders of magnitude based on the fermion flavor combination of the baryon number violating interactions.A search is presented for baryon number violating interactions in top quark production and decay. The analysis uses data from proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC with an integrated luminosity of 138 fb^{-1}. Candidate events are selected by requiring two oppositely charged leptons (electrons or muons) and exactly one jet identified as originating from a bottom quark. Multivariate discriminants are used to separate the signal from the background. No significant deviation from the standard model prediction is observed. Upper limits are placed on the strength of baryon number violating couplings. For the first time the production of single top quarks via baryon number violating interactions is studied. This allows the search to set the most stringent constraints to date on the branching fraction of the top quark decay to a lepton, an up-type quark (u or c), and a down-type quark (d, s, or b). The results improve the previous bounds by 3 to 6 orders of magnitude based on the fermion flavor combination of the baryon number violating interactions.
This report summarizes the radiation damage and the light transmission efficiency studies done on air core light guides with three different types of reflective material: two types of aluminized ...Mylar and a highly reflective plastic film from 3M called Radiant Mirror Film. The variations in light transmission efficiencies of these reflective materials have been studied with respect to the wavelengths of the incident light. The light transmission with one type of aluminized Mylar, which shows better reflectivity in UV range, deteriorated 14% after 10 Mrad of /spl gamma/-ray irradiation from a 9.5 kCurie /sup 137/Cs source. Light guides with the other type of aluminized Mylar and Radiant Mirror Film do not seem to be affected from radiation, and they show superior light transmission efficiency in the visible region.
A search for exotic decays of the Higgs boson (
) with a mass of 125
to a pair of light pseudoscalars
is performed in final states where one pseudoscalar decays to two
quarks and the other to a pair ...of muons or
leptons. A data sample of proton-proton collisions at
corresponding to an integrated luminosity of 138
recorded with the CMS detector is analyzed. No statistically significant excess is observed over the standard model backgrounds. Upper limits are set at 95% confidence level (
) on the Higgs boson branching fraction to
and to
via a pair of
s. The limits depend on the pseudoscalar mass
and are observed to be in the range (0.17-3.3)
and (1.7-7.7)
in the
and
final states, respectively. In the framework of models with two Higgs doublets and a complex scalar singlet (2HDM+S), the results of the two final states are combined to determine upper limits on the branching fraction
at 95%
, with
being a muon or a
lepton. For different types of 2HDM+S, upper bounds on the branching fraction
are extracted from the combination of the two channels. In most of the Type II 2HDM+S parameter space,
values above 0.23 are excluded at 95%
for
values between 15 and 60
.
Proton-proton interactions resulting in final states with two photons are studied in a search for the signature of flavor-changing neutral current interactions of top quarks ( t ) and Higgs bosons ( ...H ). The analysis is based on data collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb-1 . No significant excess above the background prediction is observed. Upper limits on the branching fractions ( B ) of the top quark decaying to a Higgs boson and an up ( u ) or charm ( c ) quark are derived through a binned fit to the diphoton invariant mass spectrum. The observed (expected) 95% confidence level upper limits are found to be 0.019% (0.031%) for B ( t → Hu ) and 0.073% (0.051%) for B ( t → Hc ) . These are the strictest upper limits yet determined.
The double differential cross sections of the Drell-Yan lepton pair (
, dielectron or dimuon) production are measured as functions of the invariant mass
, transverse momentum
, and
. The
observable, ...derived from angular measurements of the leptons and highly correlated with
, is used to probe the low-
region in a complementary way. Dilepton masses up to 1
are investigated. Additionally, a measurement is performed requiring at least one jet in the final state. To benefit from partial cancellation of the systematic uncertainty, the ratios of the differential cross sections for various
ranges to those in the Z mass peak interval are presented. The collected data correspond to an integrated luminosity of 36.3
of proton-proton collisions recorded with the CMS detector at the LHC at a centre-of-mass energy of 13
. Measurements are compared with predictions based on perturbative quantum chromodynamics, including soft-gluon resummation.
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