Masahiro Kuze, for H1, ZEUS Collaborations
Recent results on searches for signals of physics beyond Standard Model at the ep collider HERA are reviewed. Limits obtained for contact interaction models, large extra dimensions and finite quark radius are presented. Searches for excited-fermion resonances yield unique limits on excited electrons and neutrinos. Finally, measurement of W production cross section in ep collision is presented.
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Recent results of searches for events containing isolated leptons and missing transverse momentum at HERA are presented. Searches in this final state have yielded notable excesses over Standard Model expectations in the past. Searches for isolated leptons in channels corresponding to all three generations of leptons over the full HERA running period are now available. The combined H1+ZEUS results for searches for electrons and muons are compatible with the Standard Model.
The latest results from the ep HERA collider both within the Standard (electroweak) Model and beyond are reviewed. Most of the results are based on the full HERA data sample, which corresponds to an integrated luminosity of about 0.5 fb-1 per experiment (H1 or ZEUS).
The H1 and ZEUS collaborations have used the HERA I data to search for physics beyond the SM and to test electroweak physics in electron-proton collisions. The new period of data taking (HERA II) has started and first HERA II analyses become available. An overview is given of recent highlights, including isolated lepton and multi-lepton events, tests of models of new physics and the first systematic search for deviations in all final states with high transverse momentum.
An overview of experimental results on searches for new phenomena at HERA is presented. The complementarity with searches performed at other experiments is discussed and the prospects for a discovery, using the full HERA data to be delivered until mid-2007, are presented.
Recent results from the H1 and ZEUS experiments are reported on electroweak physics and on searches for new physics. All results are in good agreement with the Standard Model.
The exclusive diffractive production of vector mesons and real photons in ep collisions has been studied at HERA in a wide kinematic range. Here the most recent experimental results are presented together with a Regge-type model and projects for new diffractive studies at LHC.
Searches for contact interactions, leptoquark bosons and excited fermions carried out at the HERA ep collider are presented here. The searches are based on ~ 40 pb^-1 of e+ p data per experiment collected at a centre of mass energy ~ 300 GeV. First results on e- p data collected in 1998-1999 are also presented.
Recent results from searches for physics beyond the Standard Model (SM) in $e^\pm$-proton collisions at a center of mass energy of 300 -- 318 GeV at HERA are presented. Searches for excitations of fermions and for the production of squarks in R-parity-violating Supersymmetry (SUSY) are reviewed.
Recent results on searches for physics beyond the Standard Model obtained by the H1 and ZEUS experiments are reported here. After a brief introduction to the HERA collider, indirect searches for contact interactions and extra-dimensions are presented as well as direct searches for new physics including leptoquarks, lepton-flavour violation, squarks produced by R-parity violation and excited fermions. New results from isolated lepton events and single top searches are also presented. Finally the future prospects of HERA-2 are shown.
At HERA, new physics processes beyond the SM are probed in e^+/- proton collisions at a center of mass energy of 300-318 GeV. Recent results on searches obtained by the H1 and ZEUS experiments are presented with an emphasis on data taken in e^-p collisions in the years 1998/99 and in e^+p collisions in the years 1999 and 2000.
Recent results on searches for new physics at Run II of the Tevatron and highlights from HERA are reported. The searches cover many different final states and a wide range of models. All analyses have at this point led to negative results, but some interesting anomalies have been found.
The HERA collaborations, H1 and ZEUS, have searched for physics beyond the Standard Model in ep collisions at centre-of-mass energies of up to 319 GeV. In this article the experimental results coming from the HERA I phase are summarised and the constraints on theories of new physics including Contact Interactions, Large Extra Dimensions, Leptoquarks, FCNC and various scenarios in R-parity violating supersymmetry are discussed. In addition the first results on searches for new physics coming from the upgraded HERA II collider are presented.
Searches for physics beyond the Standard Model are reported from electron-proton collisions at a center of mass energy of 318 GeV. Results on a completely model independent search for deviations from Standard Model predictions at large transverse momenta are reported as well as generic searches for contact interactions, leptoquarks and excited fermions from the H1 and ZEUS experiments.
Signals of physics beyond the Standard Model at HERA have been searched for by the H1 and ZEUS collaborations. Results are reported about searches of contact interaction effects, leptoquarks, R-parity violating squarks, excited fermions and single top production. The analyses used the data set collected during the HERA phase I, consisting in about 110 (15) pb^{-1} of e^+p (e^-p) collisions per experiment. No evidence for new physics has been found and limits have been set on the parameters of the models considered.
HERA, the only ep collider, operated in the years 1992-2007 at centre-of-mass energies of 300-320 GeV in Hamburg, Germany. Deep inelastic neutral and charged current scattering at HERA provides the possibility to study the structure of the proton, the dynamics of strong interactions and test quantum chromodynamics (QCD) over a huge kinematic range. Both, neutral and charged current interactions provide complementary information on the QCD and electroweak parts of the Standard Model. In addition, HERA data allow for indirect searches for new phenomena originating at large scales, however, no ev…
The high energy programme of the HERA collider ended in March 2007. During the whole HERA programme, a combined total integrated luminosity of 1 fb$^{-1}$ was collected by the H1 and ZEUS experiments. In this context, an overview of the most recent results of both experiments concerning searches for new physics is presented. The topics covered are searches for contact interactions, leptoquarks and excited leptons, as well as studies of the isolated lepton and multi-lepton topologies, and a general signature based search.
The latest status of searches at HERA for physics beyond the Standard Model is summarized on behalf of the H1 and ZEUS collaborations. Emphasis is put on production of resonant particles accessible within the HERA center-of-mass energy, such as leptoquarks, squarks in R-parity-violating supersymmetry or excited fermions. Most of the results presented here are based on the full available statistics of positron-proton collisions, and also preliminary results from very recent electron-proton running are presented. Results which have been updated since this Ringberg '99 Workshop are also included.
Results of a general search for new phenomena at high transverse momentum and of a dedicated search for events with isolated leptons and missing transverse momentum are reported. These searches were performed on a data sample collected at HERA in e+-p collisions with the H1 detector in the period 1994-2004. The results obtained in the isolated lepton search are compared with those obtained by the ZEUS collaboration in the period 1994-2000 and limits on the anomalous FCNC production of single top events are presented.
Searches for R-parity violating supersymmetry performed at the H1 experiment are presented. Emphasis is put on searches for squarks, which may be resonantly produced at the HERA $ep$ collider in supersymmetry where R-parity is violated. The preliminary results presented here were obtained using data collected at a centre-of-mass energy of 320 GeV and corresponding to an integrated luminosity of 63 pb$^{-1}$.
Signals of QCD instanton induced processes are searched for in deep-inelastic ep scattering at HERA in a kinematic region defined by the Bjorken scaling variables x>0.001, 0.1<y<0.6 and polar angle of the scattered positron >156 degrees. Upper limits are derived from the expected instanton-induced final state properties based on the QCDINS Monte Carlo model.
Searches for physics beyond the Standard Model have been performed in high-energy $e^{\pm}p$ collisions at HERA. No significant deviation from the Standard Model has been observed while searching for contact interactions, extra dimensions, leptoquarks, R-parity violating squarks and excited fermions. Exclusion limits have been inferred which extend or complement bounds from other colliders. The H1 collaboration has observed a puzzling excess of events with an high $P_t$ isolated lepton and missing transverse momentum, and interpretation as flavour changing neutral currents has been explored.
Various searches for leptoquarks, scalar quarks in $R_p$-violating supersymmetric models, and excited fermions performed by the HERA experiments H1 and ZEUS are reviewed. No evidence for new particle production was observed from data collected by both experiments since 1994 in either electron-proton and positron-proton collisions. Stringent limits derived on the masses and couplings of these new particles are compared whenever appropriate with those from LEP, the Tevatron and low energy experiments.
The high energy program of the HERA $ep$ collider ended in March 2007, where data equivalent to an integrated luminosity of $\sim$ 0.5 fb$^{-1}$ has been collected by the H1 experiment. In this context, some of the most recent results from H1 about searches for new phenomena are presented.
Heavy excited electrons and neutrinos have been sought by the H1 and ZEUS experiments at HERA. For the e* (nu*) searches, 120 pb^-1 (16 pb^-1) of ep collision data have been analysed. No evidence for any excited lepton has been found, and limits on the characteristic couplings have been derived.
In this talk a search for the single production of top quarks performed at the H1 experiment is presented. No evidence for anomalous top production via FCNC processes is found and limits on the anomalous magnetic coupling constant κ_{tuγ} are given.
Recent results on the searches for new physics in ep collisions at HERA using the ZEUS and H1 detectors are presented. No evidence for excited fermions or supersymmetric particles within the context of the Minimal Supersymmetric Standard Model nor R-parity violation has been found using an integrated luminosity of up to 20 inv pb. New limits have therefore been established.
A search for events with one or more isolated leptons in the final state is performed on a data sample collected in e+-p collisions with the H1 and ZEUS detectors at the HERA collider. The data sample corresponds to an integrated luminosity of ~1 fb-1, representing the full HERA high-energy data set. The yields of single, di- and tri-lepton events are measured and compared to the Standard Model predictions, looking for possible deviations. No significant discrepancy with respect to the Standard Model expectations is observed.
Searches for excited electrons and neutrinos have been performed using the complete HERA I and II data samples collected by the H1 detector at $\sqrt{s}=320$ GeV corresponding to an integrated luminosity of up to 435 pb$^{-1}$. In absence of a signal, the limits on the ratio of the coupling to the compositeness scale derived extend the excluded region to higher masses than has been possible in previous searches.
Recent results of searches for new physics at HERA using the complete data sample corresponding to about 0.5/fb per experiment are reviewed. Searches for leptoquarks, isolated leptons (electrons, muons and taus) and a generic search for new physics in many topologies are reported. No evidence for new physics is found. The ep collisions at HERA are ideally suited to search for resonantly produced squarks in SUSY with R-parity violation. It is highlighted how the present results can be interpreted in this way.
A search for excited neutrinos, the analysis of multi-lepton final states, a search for doubly charged Higgs production and a general search for high-Pt phenomena at HERA are reported. The searches use data samples of ep collisions with a centre-of-mass energy sqrt(s)=320 GeV collected by the H1 and ZEUS experiments at HERA in the years 1994-2005 with integrated luminosities up to 296 pb^-1. Overall no significant deviations of the experimental observations from the Standard Model (SM) expectation are found.
A search for excited neutrinos produced in electron--proton collisions is performed using a data sample corresponding to an integrated luminosity of 114 pb$^{-1}$ recently collected by the H1 detector at HERA. In absence of a signal, the measurement is interpreted within a minimal model parameterised in terms of couplings and compositness scale. New parameter regions, beyond other colliders sensitivities, are explored by the present preliminary analysis.
We present a search for excited neutrinos using e^-p data taken by the H1 experiment at HERA at a center-of-mass energy of 318 GeV with an integrated luminosity of 15 pb-1. No evidence for excited neutrino production is found. Mass dependent exclusion limits are determined for the ratio of the coupling to the compositeness scale, f/Lambda, independently of the relative couplings to the SU(2) and U(1) gauge bosons. These limits extend the excluded region to higher masses than has been possible in previous searches at other colliders.
The H1 and ZEUS collaborations at HERA have searched for signatures of physics beyond the Standard Model using high Q^2 neutral current deep inelastic electron-proton and positron-proton scattering events. No significant deviations from Standard Model predictions were observed. Various eeqq contact interaction models have been considered. Limits on the compositeness scale in general eeqq contact interaction models, mass to the Yukawa coupling ratio for heavy leptoquarks, the effective Planck mass scale in models with large extra dimensions and the effective quark charge radius are presented.
Preliminary H1 results on dedicated searches for QCD instanton induced processes in DIS are presented. The investigations are based on the expected characteristics of their hadronic final state. Searches were performed in the kinematical region x > 0.001, 0.1 < y < 0.6 and the polar angle of scattered positron greater than 156 degrees.
A search for first-generation leptoquarks was performed in electron-proton and positron-proton collisions recorded with the ZEUS detector at HERA in 2003-2007 using an integrated luminosity of 366 pb^-1. Final states with an electron and jets or with missing transverse momentum and jets were analysed, searching for resonances or other deviations from the Standard Model predictions. No evidence for any leptoquark signal was found. The data were combined with data previously taken at HERA, resulting in a total integrated luminosity of 498 pb^-1. Limits on the Yukawa coupling, lambda, of leptoqua…
A search for events with an isolated high-energy lepton and large missing transverse momentum has been performed with the ZEUS detector at HERA using a total integrated luminosity of 504 $\mathrm{pb}^{-1}$. The results agree well with Standard Model predictions. The cross section for production of single $W$ bosons in electron-proton collisions with unpolarised electrons is measured to be $0.89^{+0.25}_{-0.22}$ (stat.) $\pm{0.10}$ (syst.) pb.
A direct search has been made for magnetic monopoles produced in e^+ p collisions at a centre of mass energy of 300 GeV at HERA. The beam pipe surrounding the interaction region in 1995-1997 was investigated using a SQUID magnetometer to look for stopped magnetic monopoles. During this time an integrated luminosity of 62 pb^{-1} was delivered. No magnetic monopoles were observed and charge and mass dependent upper limits on the e^+ p production cross section are set.
A search for single top production in ep collisions using the complete high energy data from HERA is presented. This search is based on the analysis of events containing isolated leptons (electrons or muons) and missing transverse momentum PTmiss. In the absence of a signal, an upper limit on the top production cross section sigma_ep -> etX < 0.16 pb is established at the 95% confidence level, corresponding to an upper bound on the anomalous magnetic coupling kappa_tug < 0.14. The search is complemented by a search for events containing an isolated tau lepton and PTmiss and the measurement of …
Recent results on searches for new particles at the electron-proton collider HERA are reported. Based on roughly 100pb-1 of e^+p data and 16pb-1 of e^-p data per experiment, taken in the years 1994-2000, the H1 and ZEUS collaborations have derived new exclusion limits for the direct production of excited fermion states and leptoquarks. The latter are searched for in different decay channels, including lepton-flavor violating decays. The production of R_P-violating squarks followed by leptoquark-like decays to lepton and quark is studied, as are cascade decays yielding multi-jet plus lepton sig…
Recent results from searches for physics beyond the Standard Model (SM) in electron/positron-proton collisions at HERA at center-of-mass energies of 300 and 320 GeV are presented. They were performed on a data sample collected in the period 1994-2004 by the H1 and ZEUS collaborations. The data have been analysed searching for leptoquarks, light gravitinos in R-parity violating supersymmetric models and magnetic monopoles. Results of a general search for new phenomena at high transverse momentum and of a dedicated search for events with isolated leptons and missing transverse momentum are also …
A search for anomalous single-top production, ep -> etX, t -> Wb, has been made with the ZEUS detector at HERA using an integrated luminosity of 130 pb^-1. No evidence for top-quark production was found in either the leptonic or the hadronic decay channel of the W boson. The resulting constraints on single-top production via quark-flavour changing neutral current (FCNC) transitions exclude a substantial region in the FCNC t-u-gamma coupling not ruled out by other experiments.
The latest results from the H1 and ZEUS collaborations are presented on rare Standard Model processes and searches for physics Beyond the Standard Model. Intriguing events containing high transverse momentum leptons are observed by H1 and many competitive limits are set by both collaborations on the production of new particles in a variety of supersymmetry scenarios.
A search for scalar and vector leptoquarks coupling to first generation fermions is performed in the H1 experiment at the ep collider HERA. The analysis uses e^- p data collected in 1998 and 1999 at a centre-of-mass energy of 320 GeV, corresponding to an integrated luminosity of 15 pb^-1. No evidence for the direct production of such particles is found in a data sample with a large transverse momentum final state electron or with large missing transverse momentum, and constraints on leptoquark models are established. For a Yukawa coupling of electromagnetic strength leptoquarks are excluded fo…
The H1 and ZEUS collaborations have searched for signals of physics beyond the Standard Model in ep collisions at a center-of-mass energy of 301-319 GeV. During the HERA I phase each experiment accumulated an integrated luminosity of about 110 pb^{-1} for e^+p and about 15 pb^{-1} for e^-p collisions. The data have been analysed searching for contact interaction effects, leptoquarks, lepton flavor violation, squarks in R-parity violating supersymmetric models, excited fermions and FCNC single top production. In this article a summary of the results is given.
The H1 and ZEUS collaborations at HERA have searched for signatures of physics beyond the Standard Model with high Q^2 neutral current deep inelastic electron-proton and positron-proton scattering events. No significant deviations from Standard Model predictions were observed. Various eeqq contact nteraction models have been considered. Limits on the compositeness scale in general eeqq contact interaction models, mass to the Yukawa coupling ratio for heavy leptoquarks, the effective Planck mass scale in models with large extra dimensions and the effective quark charge radius are presented.
We report on a search for the flavor-changing neutral current decay $D^0 \to μ^+μ^-$ using $50 \times 10^6$ events recorded with a dimuon trigger in interactions of 920 GeV protons with nuclei by the HERA-B experiment. We find no evidence for such decays and set a 90% confidence level upper limit on the branching fraction $Br(D^0 \to μ^+μ^-) <2.0 \times 10^{-6}$.
A search for first generation scalar and vector leptoquarks produced in ep collisions is performed by the H1 experiment at HERA. The full H1 data sample is used in the analysis, corresponding to an integrated luminosity of 446 pb^-1. No evidence for the production of leptoquarks is observed in final states with a large transverse momentum electron or with large missing transverse momentum, and constraints on leptoquark models are derived. For leptoquark couplings of electromagnetic strength lambda=0.3, first generation leptoquarks with masses up to 800 GeV are excluded at 95% confidence level.
A search for excited electron e* production is described in which the electroweak decays e*->e gamma, e*->e Z and e*->nu W are considered. The data used correspond to an integrated luminosity of 120 pb^(-1) taken in e^(+-)p collisions from 1994 to 2000 with the H1 detector at HERA at centre-of-mass energies of 300 and 318 GeV. No evidence for a signal is found. Mass dependent exclusion limits are derived for the ratio of the couplings to the compositeness scale, f/Lambda. These limits extend the excluded region to higher masses than has been possible in previous direct searches for excited ele…
HERA is the only high energy electron-proton collider in the world today and hence has unique opportunities both to probe the structure of the proton and to search for physics beyond the Standard Model. Results are presented for measurements of both neutral and charged current cross sections, and for searches for exotic processes involving direct electron-quark interactions (leptoquarks and R-parity violating SUSY), generic coupling models (contact interactions) and exclusive final states (isolated leptons and missing PT, single top production and pentaquarks). Exclusion limits on proposed mod…
A search for excited fermions f^* of the first generation in e^+p scattering at the collider HERA is presented using H1 data with an integrated luminosity of 37 pb^(-1). All electroweak decays of excited fermions, f^* -> f gamma, f W, f Z are considered and all possible final states resulting from the Z or W hadronic decays or decays into leptons of the first two generations are taken into account. No evidence for f^* production is found. Mass dependent exclusion limits on cross-sections and on the ratio of coupling constants to the compositeness scale are derived.
A search for excited quarks is performed using the full ep data sample collected by the H1 experiment at HERA, corresponding to a total integrated luminosity of 475 pb^-1. The electroweak decays of excited quarks q* -> q gamma, q* -> q Z and q* -> q W with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for first generation excited quark production is found. Mass dependent exclusion limits on q* production cross sections and on the ratio f/Lambda of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the…
Recent results from H1, ZEUS, HERMES and HERA-B on searches for exotic baryons in ep collisions, eD scattering and pA scattering at HERA are reviewed. Evidence for the production of the strange pentaquark Theta^+ and of a narrow anti-charmed baryon decaying to D^{*-}p together with negative results of pentaquark searches at HERA are presented.
Inclusive production of K0S K0S in ep collisions was studied with the ZEUS detector. Significant production of JPC=2++ tensor mesons and of the 0++ glueball candidate f0(1710) was seen. Masses and widths were compared with previous experiments. The H1 Collaboration saw a charm pentaquark candidate in the D*p spectrum at 3.1 GeV, which was not confirmed by a ZEUS higher statistics search. With the full HERA data, H1 did not see a signal in this region. Masses, widths and helicity parameters of excited charm and charm-strange mesons were measured by ZEUS. Rates of c-quarks hadronising into these…
A search has been made for lepton-flavor-violating interactions, e+ p -> mu/tau X, at a center-of-mass energy of 300 GeV with an integrated luminosity of 47.7 pb^-1 using the ZEUS detector at HERA. No evidence was found for lepton-flavor violation and constraints were derived on leptoquarks that could mediate such interactions. Some of the constraints are also applicable to lepton-flavor-violating processes mediated by squarks in R-parity-violating supersymmetric models. In some cases involving heavy quarks and especially for the tau channel, the ZEUS constraints are the most stringent publish…
Recent results from H1 and ZEUS on searches for exotic baryons in $ep$ collisions at HERA are reviewed. Evidence for the production of the strange pentaquark $Θ^+$ and of a narrow anti-charmed baryon decaying to $D^{*-} p$ together with negative results of pentaquark searches at HERA are presented.
A search for single top quark production is performed in the full ep data sample collected by the H1 experiment at HERA, corresponding to an integrated luminosity of 474 pb^-1. Decays of top quarks into a b quark and a W boson with subsequent leptonic or hadronic decay of the W are investigated. A multivariate analysis is performed to discriminate top quark production from Standard Model background processes. An upper limit on the top quark production cross section via flavour changing neutral current processes sigma (ep -> etX) < 0.25 pb is established at 95% CL. Limits on the anomalous coupl…
A search for stop production in R-parity-violating supersymmetry has been performed in $e^{+}p$ interactions with the ZEUS detector at HERA, using an integrated luminosity of 65 pb$^{-1}$. At HERA, the R-parity-violating coupling $λ'$ allows resonant squark production, $e^+d\to\tilde{q}$. Since the lowest-mass squark state in most supersymmetry models is the light stop, $\tilde{t}$, this search concentrated on production of $\tilde{t}$, followed either by a direct R-parity-violating decay, or by the gauge decay to $b\tildeχ^+_{1}$. No evidence for stop production was found and limits were set …
A search for QCD-instanton-induced events in deep inelastic ep scattering has been performed with the ZEUS detector at the HERA collider, using data corresponding to an integrated luminosity of 38 pb^{-1}. A kinematic range defined by cuts on the photon virtuality, Q^2 > 120 GeV^2, and on the Bjorken scaling variable, x > 10^{-3}, has been investigated. The QCD-instanton induced events were modelled by the Monte Carlo generator QCDINS. A background-independent, conservative 95% confidence level upper limit for the instanton cross section of 26 pb is obtained, to be compared with the theoretica…
Searches for narrow baryonic states in the K0s-p, K+p, Xi-pi and bar{X}+pi decay channels are reported. The data were collected with the ZEUS detector at HERA using an integrated luminosity of 121 pb-1. The searches were performed in the central rapidity region of inclusive deep inelastic scattering at an $ep$ centre-of-mass energy of 300--318 GeV for exchanged photon virtuality, Q2, above 1 GeV2. The results support the existence of a narrow baryonic state with strangeness in K0s-p and K0s-\bar{p} decay channels, consistent with the pentaquark prediction. No pentaquark signals were found in t…
A search for excited electrons is performed using the full $e^{\pm}p$ data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb$^{-1}$. The electroweak decays of excited electrons ${e}^{*}\to{e}γ$, ${e}^{*}\to{e}Z$ and ${e}^{*}{\to}νW$ with subsequent hadronic or leptonic decays of the $W$ and $Z$ bosons are considered. No evidence for excited electron production is found. Mass dependent exclusion limits on $e^*$ production cross sections and on the ratio $f/Λ$ of the coupling to the compositeness scale are derived within gauge mediated models. These lim…
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