Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC

131

Measurement of the underlying event activity at the LHC with √ s = 7 TeV and comparison with √ s = 0.9 TeVThe CMS collaboration E-mail: cms-publication-committee-chair@cern.chAbstract: A measurement of the underlying activity in events with a jet of transverse momentum in the several GeV region is performed in proton-proton collisions at √ s = 0.9 and 7 TeV, using data collected by the CMS experiment at the LHC. The production of charged particles with pseudorapidity |η| < 2 and transverse momentum p T > 0.5 GeV/c is studied in the azimuthal region transverse to that of the leading set of charged particles forming a track-jet. A significant growth of the average multiplicity and scalar-p T sum of the particles in the transverse region is observed with increasing p T of the leading trackjet, followed by a much slower rise above a few GeV/c. For track-jet p T larger than a few GeV/c, the activity in the transverse region is approximately doubled with a centreof-mass energy increase from 0.9 to 7 TeV. Predictions of several QCD-inspired models as implemented in pythia are compared to the data.

Section: Jhep09(2011)109mentioning

confidence: 99%

Measurement of the underlying event activity at the LHC with $ \sqrt {s} = 7 $ TeV and comparison with $ \sqrt {s} = 0.9 $ TeV

Chatrchyan¹,

Khachatryan²,

Sirunyan³

et al. 2011

131

“…For illustration, figure 7 presents the number density in the plateau of the Transverse region for p T > 0.5 GeV/c (our measurement as well as the value measured by CDF at 1.8 TeV) compared with dN ch /dη| η=0 of charged particles with p T > 0.5 GeV/c in minimum-bias events [32] (scaled by 1/2π). 2 The UE activity in the plateau region is more 2 These data are for events that have at least one charged particle in |η| < 2.5.…”

Section: Jhep07(2012)116mentioning

confidence: 99%

Underlying Event measurements in pp collisions at $ \sqrt {s} = 0.9 $ and 7 TeV with the ALICE experiment at the LHC

Abelev¹,

Quintana²,

Adamová³

et al. 2012

We present measurements of Underlying Event observables in pp collisions at √ s = 0.9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum p T,LT in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different p T thresholds: 0.15, 0.5 and 1.0 GeV/c. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track p T threshold considered. Data are compared to Pythia 6.4, Pythia 8.1 and Phojet. On average, all models considered underestimate the multiplicity and summed p T in the Transverse region by about 10-30%.

“…The discovery channel is defined as the set of cuts which satisfies S > max[5, 5σ, 0.2B] and maximizes S/ √ S + B, where S (B) is the number of signal (background) events. The ATLAS collaboration estimates [29,30] that the systematic uncertainty on the data-driven background determination can range from 20% to 50% for 1 fb −1 . In order to incorporate these uncertainties in our discovery analysis, we take the conservative value of 50% for the total background systematical uncertainty and add it in quadrature to the statistical error ( √ B).…”

Section: Jhep05(2011)120mentioning

confidence: 99%

“…In order to incorporate these uncertainties in our discovery analysis, we take the conservative value of 50% for the total background systematical uncertainty and add it in quadrature to the statistical error ( √ B). The total uncertainty on the BG is then given by (0.5B) 2 + B and it is used to compute the signal significance σ [29,30].…”

Section: Jhep05(2011)120mentioning

confidence: 99%

Fine-tuning implications for complementary dark matter and LHC SUSY searches

Cassel

Ghilencea

Kraml

et al. 2011

The requirement that SUSY should solve the hierarchy problem without undue fine-tuning imposes severe constraints on the new supersymmetric states. With the MSSM spectrum and soft SUSY breaking originating from universal scalar and gaugino masses at the Grand Unification scale, we show that the low-fine-tuned regions fall into two classes that will require complementary collider and dark matter searches to explore in the near future. The first class has relatively light gluinos or squarks which should be found by the LHC in its first run. We identify the multijet plus E miss T signal as the optimal channel and determine the discovery potential in the first run. The second class has heavier gluinos and squarks but the LSP has a significant Higgsino component and should be seen by the next generation of direct dark matter detection experiments. The combined information from the 7 TeV LHC run and the next generation of direct detection experiments can test almost all of the CMSSM parameter space consistent with dark matter and EW constraints, corresponding to a fine-tuning not worse than 1:100. To cover the complete low-fine-tuned region by SUSY searches at the LHC will require running at the full 14 TeV CM energy; Open Access doi:10.1007/JHEP05(2011)120 JHEP05(2011)120in addition it may be tested indirectly by Higgs searches covering the mass range below 120 GeV.