Searches for supersymmetry at high-energy colliders

This review summarizes the state of the art in searches for supersymmetry at colliders on the eve of the Large Hadron Collider era. Supersymmetry is unique among extensions of the standard model in being motivated by naturalness, dark matter, and force unification, both with and without gravity. At the same time, weak-scale supersymmetry encompasses a wide range of experimental signals that are also found in many other frameworks. Motivations for supersymmetry are recalled and the various models and their distinctive features are reviewed. Searches for neutral and charged Higgs bosons and standard-model superpartners at the high energy frontier are summarized comprehensively, considering both canonical and noncanonical supersymmetric models, and including results from the LEP collider at CERN, HERA at DESY, and the Fermilab Tevatron.

Figure 1

(Color online) Renormalization group evolution of scalar and gaugino mass parameters from the GUT scale $M_{\mathrm{GUT}}\simeq 2\times {10}^{16}\mathrm{GeV}$ to the weak scale in a representative mSUGRA model. From 178.

Figure 2

(Color online) Sparticle spectra for representative models with gravity-, gauge-, and anomaly-mediated SUSY breaking. The masses are normalized to $M_2$, the Wino mass parameter at the weak scale. In the gravity-mediated case, two example spectra are presented: one for “no-scale” models with $m_0=0$, and another for $m_0=5M_2$. In the anomaly-mediated case, the sleptons are tachyonic in the minimal case—additional effects are required to raise these to a viable range. From 186.

Figure 3

(Color online) The upper bound on the factor ${\xi }^2$ by which the square of the SM $HZZ$ coupling is multiplied, as provided by the LEP experiments (66). The full curve is the observed limit, the dashed curve is the median expected limit in the absence of signal, and the bands are the 68% and 95% probability regions around the expected limit.

Figure 4

(Color online) Domains excluded at 95% CL and 99.7% CL by the four LEP experiments (197) in the $(m_h,\tan \beta )$ plane in the $m_h$-max (top) and no-mixing (bottom) benchmark scenarios, with $m_t=174.3\mathrm{GeV}$. The light-shaded regions are not accessible theoretically. The dashed lines represent the boundaries of the domains expected to be excluded at 95% CL in the absence of signal. The upper boundaries of the physical regions are indicated for four top quark masses: 169.3, 174.3, 179.3, and $183\mathrm{GeV}$, from left to right.

Figure 5

(Color online) Visible mass distribution in the $(e∕\mu ){\tau }_{\mathrm{had}}$ channels from the CDF search for $\varphi \to \tau \tau$ (87). The signal contribution indicated corresponds to the cross section upper limit set with this data.

Figure 6

(Color online) Domains in the $(m_A,\tan \beta )$ plane excluded by the CDF search for $\varphi \to \tau \tau$ (87). The domains excluded at LEP are also indicated.

Figure 7

(Color online) Fit to the mass of the two jets with highest transverse momenta in the CDF sample of events with three $b$-tagged jets. The contributions of the various multijet backgrounds and of a signal with a mass of $150\mathrm{GeV}$ are indicated. From 89.

Figure 8

(Color online) Domain in the $(m_A,\tan \beta )$ plane excluded by the DØ search for $\varphi \to b\overline{b}$ in events with three $b$-tagged jets in the $m_h$-max scenario. From 101.

Figure 9

(Color online) Domain in the $(m_A,\tan \beta )$ plane excluded by the DØ search for $\varphi \to {\tau }^{+}{\tau }^{-}$ produced in association with a $b$ quark in the $m_h$-max scenario. The light shaded region is the extension of the LEP exclusion region to $\tan \beta >50$. From 99.

Figure 10

(Color online) Limit on the charged Higgs boson mass as a function of $B(H^{+}\to {\tau }^{+}{\nu }_{\tau })$, from the combined data of the four LEP experiments at center-of-mass energies from $189\text{to}209\mathrm{GeV}$. The expected exclusion limit is shown as a thin solid line and the observed limit as a thick solid line; the shaded region is excluded. From 165.

Figure 11

(Color online) For a charged Higgs boson mass of $100\mathrm{GeV}$, the branching ratios for the top quark decay into $H^{+}b$, under the assumption that $B(t\to W^{+}b)+B(t\to H^{+}b)=1$, and for the various $H^{+}$ decay channels, as a function of $\tan \beta$. From 98.

Figure 12

(Color online) Limit on the mass of the charged Higgs boson as a function of $\tan \beta$ from the DØ search in top quark decays. From 98.

Figure 13

(Color online) For a leptophobic charged Higgs boson, upper limit on the branching ratio $B(t\to H^{+}b)$ as a function of the Higgs boson mass from a CDF search in top quark decays. From 88.

Figure 14

(Color online) Region in the $(m_{{\tilde{\mu }}_R},m_{{\tilde{\chi }}_1^0})$ plane excluded by the searches for smuons at LEP. The dotted contour is drawn under the assumption that the smuon decay branching ratio into $\mu {\tilde{\chi }}_1^0$ is 100%. From 174.

Figure 15

(Color online) Regions in the $(\mu ,M_2)$ plane excluded by the LEP I constraints (1), and by the searches for charginos (2), neutralinos (3), and sleptons (4) at LEP II, for $\tan \beta =\sqrt{2}$ and $m_0=75\mathrm{GeV}$. Region (5) is excluded by the Higgs boson searches at LEP II. From 64.

Figure 16

(Color online) Lower mass limit for the lightest neutralino as a function of $\tan \beta$, inferred in the conventional scenario from searches at LEP for charginos, sleptons, and neutral Higgs bosons. The dashed contour is the limit obtained for large $m_0$. From 173.

Figure 17

(Color online) Region in the $(m_{\tilde{g}},m_{\tilde{q}})$ plane excluded by DØ and by earlier experiments. The upper right light-shaded band represents the uncertainty associated with scale and PDF choices. The solid curve in this band corresponds to the nominal scale and PDF choices. The curves marked “LEP2” represent the indirect limits inferred from the LEP chargino and slepton searches. From 19.

Figure 18

(Color online) Region in the $(m_{\tilde{t}},m_{{\tilde{\chi }}_1^0})$ plane excluded by DØ and by earlier experiments. The light-shaded band represents the uncertainty associated with scale and PDF choices. The solid curve in this band corresponds to the nominal scale and PDF choices. From 18.

Figure 19

(Color online) Regions in the $(m_{\tilde{t}},m_{{\tilde{\chi }}_1^0})$ plane excluded by CDF for $m_{{\tilde{\chi }}^{\pm }}=125.8\mathrm{GeV}$ and for various values of the branching fraction for the ${\tilde{\chi }}^{\pm }\to \mathcal{l}\nu {\tilde{\chi }}_1^0$ decay. From 90.

Figure 20

(Color online) Regions in the $(m_0,m_{1∕2})$ plane excluded by the DØ search for trileptons. From 22.

Figure 21

(Color online) Mass of the invisible system recoiling against pairs of photons at LEP. From 172.

Figure 22

(Color online) Domain excluded by CDF in the plane of neutralino NLSP mass and lifetime (40; 91).

Figure 23

(Color online) Domain excluded at LEP in the $({\log }_{10}\tau ,m_{\tilde{\tau }})$ plane, where $\tau$ is the lifetime in seconds and $m_{\tilde{\tau }}$ is the mass of a stau NLSP in GMSB. The shaded region is the excluded domain and the dashed curve is the expected boundary of the exclusion region. From 169.