6,222 research outputs found
Hunting for neutral, long-lived exotica at the LHC using a missing transverse energy signature
Searches at the Large Hadron Collider (LHC) for neutral, long-lived particles
have historically relied on the detection of displaced particles produced by
their decay the detector volume. In this paper we study the
potential of the complementary signature comprising of the missing transverse
energy () signal, traditionally used to look for dark matter, e.g.,
the lightest supersymmetric particle (LSP), to extend the LHC coverage to
models with long-lived (LL) particles when they decay the
detector. Using CMS and ATLAS analyses at the 8 TeV LHC, we set an upper limit
at the 95% confidence level (CL) on the production cross sections for two
specific scenarios: (i) a model with a heavy non-standard model Higgs boson
decaying to a LL scalar and (ii) an R-parity violating RPV SUSY model with a LL
neutralino.
We show that this method can significantly extend the LHC sensitivity to
neutral, LL particles with arbitrary large lifetimes and that the limits
obtained from a signal are comparable to those from displaced
particle searches for decay distances above a few meters. Results obtained in
this study do not not depend on the specific decay channel of the LL particle
and therefore are model-independent in this sense. We provide limits for the
whole two-dimensional plane in terms of the mass of the LL particle and the
mass of the mediator up to masses of 2 TeV including particular benchmarks
studied in the original experimental papers. We have made these limits
available in the form of a grid which can be used for the interpretation of
various other new physics models.Comment: 28 page
The CMS Tracker Readout Front End Driver
The Front End Driver, FED, is a 9U 400mm VME64x card designed for reading out
the Compact Muon Solenoid, CMS, silicon tracker signals transmitted by the
APV25 analogue pipeline Application Specific Integrated Circuits. The FED
receives the signals via 96 optical fibers at a total input rate of 3.4 GB/sec.
The signals are digitized and processed by applying algorithms for pedestal and
common mode noise subtraction. Algorithms that search for clusters of hits are
used to further reduce the input rate. Only the cluster data along with trigger
information of the event are transmitted to the CMS data acquisition system
using the S-LINK64 protocol at a maximum rate of 400 MB/sec. All data
processing algorithms on the FED are executed in large on-board Field
Programmable Gate Arrays. Results on the design, performance, testing and
quality control of the FED are presented and discussed
Hard Corrections as a Probe of the Symmetry Breaking Sector
Non-decoupling effects related to a large affecting non-oblique
radiative corrections in vertices () and boxes (- mixing
and ) are very sensitive to the particular mechanism of spontaneous
symmetry breaking. We analyze these corrections in the framework of a chiral
electroweak standard model and find that there is only one operator in the
effective lagrangian which modifies the longitudinal part of the boson
without touching the oblique corrections. The inclusion of this operator
affects the vertex, the - mixing and the CP-violating
parameter , generating interesting correlations among the hard
corrections to these observables, for example, the maximum
vertex correction allowed by low energy physics is about one
percent.Comment: LaTex, 8 pages, 1 postscript figure include
New Physics at the LHC. A Les Houches Report: Physics at TeV Colliders 2009 - New Physics Working Group
We present a collection of signatures for physics beyond the standard model
that need to be explored at the LHC. First, are presented various tools
developed to measure new particle masses in scenarios where all decays include
an unobservable particle. Second, various aspects of supersymmetric models are
discussed. Third, some signatures of models of strong electroweak symmetry are
discussed. In the fourth part, a special attention is devoted to high mass
resonances, as the ones appearing in models with warped extra dimensions.
Finally, prospects for models with a hidden sector/valley are presented. Our
report, which includes brief experimental and theoretical reviews as well as
original results, summarizes the activities of the "New Physics" working group
for the "Physics at TeV Colliders" workshop (Les Houches, France, 8-26 June,
2009).Comment: 189 page
Les Houches 2011: Physics at TeV Colliders New Physics Working Group Report
We present the activities of the "New Physics" working group for the "Physics
at TeV Colliders" workshop (Les Houches, France, 30 May-17 June, 2011). Our
report includes new agreements on formats for interfaces between computational
tools, new tool developments, important signatures for searches at the LHC,
recommendations for presentation of LHC search results, as well as additional
phenomenological studies.Comment: 243 pages, report of the Les Houches 2011 New Physics Group; fix
three figure
L1 track finding for a time multiplexed trigger
At the HL-LHC, proton bunches will cross each other every 25. ns, producing an average of 140 pp-collisions per bunch crossing. To operate in such an environment, the CMS experiment will need a L1 hardware trigger able to identify interesting events within a latency of 12.5. μs. The future L1 trigger will make use also of data coming from the silicon tracker to control the trigger rate. The architecture that will be used in future to process tracker data is still under discussion. One interesting proposal makes use of the Time Multiplexed Trigger concept, already implemented in the CMS calorimeter trigger for the Phase I trigger upgrade. The proposed track finding algorithm is based on the Hough Transform method. The algorithm has been tested using simulated pp-collision data. Results show a very good tracking efficiency. The algorithm will be demonstrated in hardware in the coming months using the MP7, which is a μTCA board with a powerful FPGA capable of handling data rates approaching 1. Tb/s.This project has received funding from the European Union׳s Seventh Framework Programme for research, technological development and demonstration under grant agreement no. 317446
Recent Results on the Performance of the CMS Tracker Readout System
The CMS Silicon Tracker comprises a complicated set of hardware and software components that have been thoroughly tested at CERN before final integration of the Tracker. A vertical slice of the full readout chain has been operated under near-final conditions. In the absence of the tracker front-end modules, simulated events have been created within the FED (Front End Driver) and used to test the readout reliability and efficiency of the final DAQ (Data Acquisition). The data are sent over the S-Link 64 bit links to the FRL(Fast Readout Link) modules at rates in excess of 200 MBytes/s per FED depending on setup and conditions. The current tracker DAQ is fully based on the CMS communication and acquisition tool XDAQ. This paper discusses setup and results of a vertical slice of the full Tracker final readout system comprising 2 full crates of FEDs, 30 in total, read out through 1 full crate of final FRL modules. This test is to complement previous tests done at Imperial College[3] taking them to the next level in order to prove that a complete crate of FRLs using the final DAQ system, including all subcomponents of the final system both software and hardware with the exception of the detector modules themselves, is capable of sustained readout at the desired rates and occupancy of the CMS Tracker. Simulated data are created with varying hit occupancy (1-10%) and Poisson distributed trigger rates (<200KHz) and the resulting behaviour of the system is recorded. Data illustrating the performance of the system and data readout are presented
Search for CP Violation in the Decay Z -> b (b bar) g
About three million hadronic decays of the Z collected by ALEPH in the years
1991-1994 are used to search for anomalous CP violation beyond the Standard
Model in the decay Z -> b \bar{b} g. The study is performed by analyzing
angular correlations between the two quarks and the gluon in three-jet events
and by measuring the differential two-jet rate. No signal of CP violation is
found. For the combinations of anomalous CP violating couplings, and , limits of \hat{h}_b < 0.59h^{\ast}_{b} < 3.02$ are given at 95\% CL.Comment: 8 pages, 1 postscript figure, uses here.sty, epsfig.st
Search for the glueball candidates f0(1500) and fJ(1710) in gamma gamma collisions
Data taken with the ALEPH detector at LEP1 have been used to search for gamma
gamma production of the glueball candidates f0(1500) and fJ(1710) via their
decay to pi+pi-. No signal is observed and upper limits to the product of gamma
gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have
been measured to be Gamma_(gamma gamma -> f0(1500)). BR(f0(1500)->pi+pi-) <
0.31 keV and Gamma_(gamma gamma -> fJ(1710)). BR(fJ(1710)->pi+pi-) < 0.55 keV
at 95% confidence level.Comment: 10 pages, 3 figure
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