Search for Supersymmetry at the LHC in Events with Jets and Missing Transverse Energy

Abstract

A search for events with jets and missing transverse energy is performed in a data sample of pp collisions collected at ffiffi ffi s p ¼ 7 TeV by the CMS experiment at the LHC. The analyzed data sample corresponds to an integrated luminosity of 1:14 fb À1 . In this search, a kinematic variable T is used as the main discriminator between events with genuine and misreconstructed missing transverse energy. The standard model (SM) of particle physics is generally considered to be valid only at low energy scales and is expected to be superseded by a more complete theory at higher scales. Supersymmetric (SUSY) extensions to the SM [1-8] introduce a large number of new particles with the same quantum numbers as their SM partners, but differing by half a unit of spin. If R-parity conservation [9] is assumed, supersymmetric particles, such as squarks and gluinos, are produced in pairs and decay to the lightest, stable supersymmetric particle (LSP . This Letter presents a search for SUSY based on a data sample corresponding to an integrated luminosity of 1:14 AE 0:05 fb À1 . The search strategy follows Ref.[23] and is designed to be sensitive to 6 E T signatures in events with two or more energetic jets. The search is not optimized for any particular model of SUSY and is applicable to other new physics scenarios with a 6 E T signature. In this Letter, nevertheless, the results are interpreted in the constrained minimal supersymmetric extension of the standard model (CMSSM) [28][29][30]. The CMSSM is described by the following five parameters: the universal scalar and gaugino mass parameters, m 0 and m 1=2 ; the universal trilinear soft SUSY-breaking parameter, A 0 ; the ratio of the vacuum expectation values of the two Higgs doublets, tan; and the sign of the Higgs mixing parameter, . We consider only parameter sets for which the LSP is the lightest neutralino. The following example parameter set, referred to as LM6, is used to illustrate possible CMSSM yields: m 0 ¼ 85 GeV, m 1=2 ¼ 400 GeV, A 0 ¼ 0, tan ¼ 10, and > 0.A detailed description of the CMS apparatus can be found in Ref. [31]. Its central feature is a superconducting solenoid providing an axial magnetic field of 3.8 T. The bore of the solenoid is instrumented with several particle detection systems. Charged particle trajectories are measured by a silicon pixel and strip tracker system, with full azimuth () coverage and a pseudorapidity () acceptance from À2:5 to þ2:5. Here, À ln½tanð=2Þ and is the polar angle with respect to the counterclockwise beam direction. A lead tungstate crystal electromagnetic calorimeter (ECAL) and a brass or scintillator hadron calorimeter surround the tracking volume and provide coverage in from À3 to þ3. The forward hadron calorimeter extends symmetrically the coverage by a further two units in . Muons are identified in gas ionization detectors embedded in the steel return yoke of the magnet. The CMS detector is nearly hermetic, which allows for momentum-balance measurements in the plane transverse to the beam axis.

Interpreting LHC SUSY searches in the phenomenological MSSM

“…SS 2ℓ, and OS 2ℓ denote same-sign and opposite-sign dileptons, respectively. The α T [14], SS [15], and OS [16] results were published by the CMS Collaboration.…”

Supersymmetric dark matter in the harsh light of the Large Hadron Collider

“…Another important target is the search for direct pair production of neutralinos. A reaction q + q →ÑÑ; [7] even one in which the final state is completely invisible, can be detected if the initial quarks emit gluons or photons. This always happens to some degree, with the characteristic transverse momenta of the initial state radiation being distributed logarithmically up to the mass of the produced particlers.…”

Stop the top background of the stop search

“…Supersymmetry has been extensively searched for at colliders, and so far we have not found any evidence for it. The latest LHC search results constrain the masses of the gluino and (light generation) squarks in the minimal supergravity [1][2][3] or constrained minimal supersymmetric standard model (MSSM) [4] to be greater than about 1 TeV [5,6]. At face value, it may imply a serious fine-tuning of the electroweak scale if SUSY exists.…”