Search for Nearly Mass-Degenerate Charginos and Neutralinos at LEP

Abbiendi, G.; OPAL Collaboration

doi:10.1140/epjc/s2003-01237-x

Published 2003 | Version v1

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Search for Nearly Mass-Degenerate Charginos and Neutralinos at LEP

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A search was performed for charginos with masses close to the mass of the lightest neutralino in e+e- collisions at centre-of-mass energies of 189-209 GeV recorded by the OPAL detector at LEP. Events were selected if they had an observed high-energy photon from initial state radiation, reducing the dominant background from two-photon scattering to a negligible level. No significant excess over Standard Model expectations has been observed in the analysed data set corresponding to an integrated luminosity of 570pb-1. Upper limits were derived on the chargino pair-productin cross-section and lower limits on the chargino mass were derived in the context of the Minimal Supersymmetric Extension of the Standard Model for the gravity and anomaly mediated Supersymmetry breaking scenarios.

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CERN annual report 2004-3.1401

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A search was performed for charginos with masses close to the mass of the lightest neutralino in e+e- collisions at centre-of-mass energies of 189-209 GeV recorded by the OPAL detector at LEP. Events were selected if they had an observed high-energy photon from initial state radiation, reducing the dominant background from two-photon scattering to a negligible level. No significant excess over Standard Model expectations has been observed in the analysed data set corresponding to an integrated luminosity of 570pb-1. Upper limits were derived on the chargino pair-productin cross-section, and lower limits on the chargino mass were derived in the context of the Minimal Supersymmetric Extension of the Standard Model for the gravity and anomaly mediated Supersymmetry breaking scenarios.

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arXiv:hep-ex_0210043.pdf

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00000 noimg: The luminosity weighted mean centre-of-mass energy and integrated luminosity of each energy bin.: Number of expected background events and number of candidates after each cut. The first three rows list the contributions to the expected background from fermion-pair, four-fermion and two-photon events. The hadronic two-photon events passing the two-photon veto are those produced with generators without QED radiative corrections. The errors are statistical. All numbers correspond to the full analysed data set (569.9 pb$^{-1}$). For the final cuts F1 and F2 a chargino mass of $\M{\CHI{\pm}{1}}=80\,\GeV$ and a mass difference of $\DM{}{}=1\,\GeV$ were assumed.: Number of expected background events and number of candidates after the final cut F2 for a selection of (\M{\CHI{\pm}{1}}, \DM{}{}) points. The errors are statistical. All numbers correspond to the full analysed data set (569.9 pb$^{-1}$).: The left column lists the signal efficiency and relative statistical and systematic uncertainties at $\sqrt{s}=208\,\GeV$ for $\M{\CHI{\pm}{1}}=80\,\GeV$ and $\DM{}{}=1\,\GeV$ after the final cut F2. The right column shows the total number of expected background events and the absolute statistical and systematic uncertainties for $\M{\CHI{\pm}{1}}=80\,\GeV$ and $\DM{}{}=1\,\GeV$ after the final cut F2.: Lower chargino mass limits at the 95\% C.L. within the mSUGRA framework. The limits are valid for $0.5\,\GeV\leqslant\DM{}{}\leqslant5.0\,\GeV$ and zero chargino lifetime. md5:71c026e17d9c48fdd3072eed1f6853bd	9.6 kB	Preview Download
00001 Variables used as cleaning cuts. The OPAL data are indicated by points with error bars (statistical error) and the background distributions by the histograms. Signal distributions are plotted as dashed lines and correspond to a chargino with $\M{\CHI{\pm}{1}}= 80\,\GeV$ and $\DM{}{}=1\,\GeV$. The accumulated events for $\sqrt{s}=$189 -- 209 \GeV are shown. Each plot shows the distribution after the cuts on the preceeding variables. The arrows indicate the accepted regions. md5:c72ec75dfe6f3816cf7f9b5af7c0359f	38.0 kB	Preview Download
00002 Variables used in the final event selection. The OPAL data are indicated by points with error bars (statistical error) and the background distributions by the histograms. Signal distributions are plotted as dashed lines and correspond to a chargino with $\M{\CHI{\pm}{1}}= 80\,\GeV$ and $\DM{}{}=1\,\GeV$. The accumulated events for $\sqrt{s}=$189 -- 209 \GeV are shown. Each plot shows the distribution after the cuts on the preceeding variables. The arrows indicate the accepted regions. md5:0982b18a7c43b88424e96ca32198facd	34.2 kB	Preview Download
00003 Number of expected background events (a) and number of candidates (b) passing the final selection cuts. The accumulated events for $\sqrt{s}=$189 -- 209 \GeV are shown. md5:29cd6a545faacfd7cc89b7f7ff950f4f	54.2 kB	Preview Download
00004 Absolute signal efficiency (number of selected signal events normalised to the number of generated events), $\varepsilon$, and relative efficiency (number of selected signal events normalised to a subset of generated events with $\ETg>0.025\sqrt{s}$ and $\|\cos\theta^\gamma\|&lt;0.985$), $\varepsilon^\prime$, at $\sqrt{s}=208\,\GeV$ for a constant mass difference $\DM{}{}=1\,\GeV$ ((a)+(c)) and for a constant chargino mass $\M{\CHI{\pm}{1}} = 80\,\GeV$ ((b)+(d)). The efficiencies for the gaugino-like scenario are indicated by the points. The circles correspond to the efficiencies in the case of a higgsino-like chargino. md5:58f69e4f37ad64386efc69615ff2c8b7	37.0 kB	Preview Download
00005 Upper signal cross-section limit rescaled to $\sqrt{s}=208\,\GeV$ at the 95\% confidence level as a function of the mass difference and the chargino mass (a) and for a constant mass difference of $\DM{}{}=1\,\GeV$ (b). The band in (b) indicates the $\pm2\sigma$ interval around the median expected value. md5:8ca7d355695d1b911926239cc3aa33f2	49.1 kB	Preview Download
00006 Signal cross-sections as a function of the chargino mass at $\sqrt{s}=208\,\GeV$. The shaded band shows the cross-sections in case of a gaugino-like chargino for sneutrino masses ranging from 100 to 1000 \GeV. The dashed line corresponds to the higgsino-like scenario. md5:8d2b7de5ec51e777b49c309c65ed2fe1	22.8 kB	Preview Download
00007 Lower mass limits at the 95\% confidence level for various scenarios. These limits are valid for the case of a 100\% branching ratio $\CHI{\pm}{1}\to\CHI{0}{1}\mathrm{W}^{\pm(\star)}$. The limits shown for $\DM{}{}&lt;0.5\,\GeV$ are only valid with the assumption of a zero chargino lifetime. For the gaugino-like scenario with a light sneutrino (b) the same signal efficiencies as in the case of a heavy sneutrino (a) were assumed. md5:cbd9e0d4117d028dadb521be9a9a5b3c	28.7 kB	Preview Download
00008 Exclusion regions at 95\% C.L. in the $\mu$-$M_2$ plane within the mSUGRA framework for two values of $M_1/M_2$ and two different values of $\tan\beta$. The kinematic boundaries $(45\,\GeV&lt;\M{\CHI{\pm}{1}}&lt;104\,\GeV)$ are shown by the thick line. The thin line indicates the \DM{}{} region considered. The shaded areas are the regions excluded by this analysis for $\M{\CHI{\pm}{1}}&lt;92\,\GeV$. md5:f3f17c3372b102de2f89a01a16408f5c	50.0 kB	Preview Download
00009 Exclusion regions at 95\% C.L. in the $\tan\beta$-$m_{3/2}$ plane for various values of $m_0$ within the AMSB framework. The kinematic boundaries $(45\,\GeV&lt;\M{\CHI{\pm}{1}}&lt;104\,\GeV)$ are shown by the thick line. The region below $\tan\beta=1.5$ is theoretically inaccessible. The thin line indicates the \DM{}{} region considered. The shaded areas are the regions excluded by this analysis. md5:ac807e69c66bdbb9a0f9e6a61df24bf0	41.4 kB	Preview Download

Additional details

Approval Report Number: CERN-EP-2002-063
CDS: 582984
Aleph number: 002341568CER

Is part of: Report: cern-annual-report:2004-3.1401 (Other)
Is variant form of: Other: 600094 (Inspire); Other: arXiv:hep-ex/0210043 (arXiv); Other: CERN-EP-2002-063 (CDS Report Number)
References: Other: http://weblib.cern.ch/abstract?CERN-EP-2002-063 (URL)

Submitted: 2002-07-25

preprint

Department: EP - Experimental Physics Department
Accelerator: CERN LEP
Experiment: OPAL

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Search for Nearly Mass-Degenerate Charginos and Neutralinos at LEP

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