Long-lived Charged Massive Particles Research Articles

Search for charged massive long-lived particles ats=1.96 TeV

We present a search for charged massive long-lived particles (CMLLPs) that are pair produced in p-pbar collisions at sqrt(s)= 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider. Our result is a combination of two searches where either one or both CMLLPs are reconstructed in the detector. We select events with muon-like particles that have both speed and ionization energy loss dE/dx different from muons produced in p-pbar collisions. In the absence of evidence for CMLLPs corresponding to 6.3 fb-1 of integrated luminosity, we set limits on the CMLLP masses in several supersymmetric models, excluding masses below 278 GeV for long-lived gaugino-like charginos, and masses below 244 GeV for long-lived higgsino-like charginos at the 95% C.L. We also set limits on the cross section for pair production of long-lived scalar tau leptons that range from 0.04 pb to 0.008 pb for scalar tau lepton masses of 100 to 300 GeV.

Structure of dark matter halos in warm dark matter models and in models with long-lived charged massive particles

We study the formation of non-linear structures in warm dark matter (WDM) modelsand in a long-lived charged massive particle (CHAMP) model.CHAMPs with a decay lifetime of about 1 yr induce characteristic suppression in the matter power spectrum at subgalactic scales through acoustic oscillations in the thermal background. We explore structure formation in such a model.We also study three WDM models, where the dark matter particles are producedthrough the following mechanisms:i) WDM particles are produced in the thermal background and then kinematically decoupled; ii) WDM particles are fermions produced by the decay of thermal heavy bosons; and iii) WDM particles are produced by the decay of non-relativistic heavy particles.We show that the linear matter power spectra for the three models are all characterised by the comoving Jeans scale at the matter-radiation equality.Furthermore, we can also describe the linear matter power spectrum for the long-lived CHAMP model in terms of a suitably defined characteristic cut-off scale kCh,similarly to the WDM models.We perform large cosmological N-body simulations to study the non-lineargrowth of structures in these four models.We compare the halo mass functions, the subhalo mass functions, and the radial distributions of subhalos in simulated Milky Way-size halos.For the characteristic cut-off scale kcut = 51 h Mpc−1, the subhalo abundance ( ∼ 109Msun) is suppressed by a factor of ∼ 10 compared with the standard ΛCDM model. We then study the models with kcut ≃ 51, 410, 820 h Mpc−1,and confirm that the halo and the subhalo abundances and the radial distributionsof subhalos are indeed similar between the different WDM models and the long-lived CHAMP model.The result suggests that the cut-off scale kcut not only characterises the linearpower spectra but also can be used to predict the non-linear clustering properties.The radial distribution of subhalos in Milky Way-size halos isconsistent with the observed distribution for kcut ∼ 50−800 h Mpc−1; such models resolve the so-called ``missing satellite problem".

A search for charged massive long-lived particles at D0

Results are presented on a search for charged massive long-lived particles (CMLLPs), based on 5.2 fb − 1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron $p\!\bar{p}$ collider. This search selects events in which one or more particles are reconstructed as muons but their speed and ionization energy loss (dE/dx) are different from muons produced in beam–beam collisions. CMLLPs have been predicted by several theories of physics beyond the Standard Model. In this search we exclude pair-produced long-lived gaugino-like charginos with masses below 251 GeV and higgsino-like charginos with masses below 230 GeV at 95% CL, as well as long-lived stop quarks with masses below 265 GeV. We place cross-section limits on long-lived staus as 0.04 to 0.006 pb for stau masses in the range 100 to 300 GeV.

Search for Charged Massive Long-Lived Particles

We report on a search for charged massive long-lived particles (CMLLPs), based on 5.2 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron pp collider. We search for events in which one or more particles are reconstructed as muons but have speed and ionization energy loss (dE/dx) inconsistent with muons produced in beam collisions. CMLLPs are predicted in several theories of physics beyond the standard model. We exclude pair-produced long-lived gauginolike charginos below 267 GeV and Higgsino-like charginos below 217 GeV at 95% C.L., as well as long-lived scalar top quarks with mass below 285 GeV.

Big-bang nucleosynthesis with a long-lived charged massive particle includingHe4spallation processes

We propose helium-4 spallation processes induced by long-lived stau in supersymmetric standard models, and investigate an impact of the processes on light elements abundances. We show that, as long as the phase space of helium-4 spallation processes is open, they are more important than stau-catalyzed fusion and hence constrain the stau property.

Searching for high speed long-lived charged massive particles at the LHC

The conventional way to search for long-lived CHArged Massive Particles (CHAMPs) is to identify slow (small $\beta$) tracks using delayed time of flight and high ionization energy loss. But at the 7-14 TeV center of mass energy of the LHC, a CHAMP may be highly boosted (high $\beta$) and therefore look more like a minimum ionizing particle, while for high momentum muons (more than $\sim$500 GeV/c) the radiative effect dominates energy deposition. This suggests a new strategy to search for CHAMPs at the LHC. Using energy deposition from different detector components, we construct a boosted decision tree discriminant to separate high momentum CHAMPs from high momentum muons. This method increases substantially the CHAMP search potential and it can be used to distinguish possible di-CHAMP or CHAMP-muon resonance models from di-muon resonance models. We illustrate the new method using a mGMSB model and a recently proposed di-CHAMP model and we give updated CHAMP mass limits for these two models using the recent CDF CHAMP results.

Cosmology with long-lived charged massive particles

We investigate the evolution of the bound state of negatively charged massive particles (CHAMPs) with light elements and discuss its cosmological consequences and the constraint. By numerically solving the Boltzmann equation, we study the time evolutions of such bound states. Since most of negative CHAMPs are captured by 4He, its bound state is positively charged and couples with the electromagnetic plasma. When charged particles constitute a dominant non-relativistic component, density fluctuations of matter cannot grow due to the acoustic damping. This results in the suppression of matter power spectrum from which a severe constraint can be obtained. By arguing constraints from other aspects of cosmology, we show that the constraint from large scale structure gives most stringent one in some representative cases.

Measuring Lifetimes of Long-Lived Charged Massive Particles Stopped in LHC Detectors

Long-lived charged massive particles (CHAMPs) appear in various particle physics models beyond the standard model. In this Letter, we discuss the prospects for studying the stopping and decaying events of such long-lived CHAMPs at the LHC detectors, and show that the lifetime measurement (and the study of decay products) is possible with the LHC detectors for a wide range of the lifetime O(0.1)-O(10(10)) sec, by using periods of no pp collision. Even a short lifetime of order 1 sec can be measured by (i) identifying the stopping event with the on-line event filter, (ii) immediately making a beam-dump signal which stops the pp collision of the LHC, and at the same time (iii) changing the trigger menu to optimize it for the detection of a CHAMP decay in the calorimeter. Other possibilities are also discussed.

Search for Long-Lived Massive Charged Particles in 1.96 TeVpp¯Collisions

We performed a signature-based search for long-lived charged massive particles produced in 1.0 fb-1 of pp[over ] collisions at sqrt[s]=1.96 TeV, collected with the CDF II detector using a high transverse-momentum (pT) muon trigger. The search used time of flight to isolate slowly moving, high-pT particles. One event passed our selection cuts with an expected background of 1.9+/-0.2 events. We set an upper bound on the production cross section and, interpreting this result within the context of a stable scalar top-quark model, set a lower limit on the particle mass of 249 GeV/c2 at 95% C.L.

Search for Long-Lived Charged Massive Particles with the D0 Detector

We search for long-lived charged massive particles using 1.1 fb;{-1} of data collected by the D0 detector at the Fermilab Tevatron pp[over ] Collider. Time-of-flight information is used to search for pair produced long-lived tau sleptons, gauginolike charginos, and Higgsino-like charginos. We find no evidence of a signal and set 95% C.L. cross section upper limits for staus, which vary from 0.31 to 0.04 pb for stau masses between 60 and 300 GeV. We also set lower mass limits of 206 GeV (171 GeV) for pair produced charged gauginos (Higgsinos).

Extremely long-lived charged massive particles as a probe for reheating of the Universe

We discuss the impact of charged massive particle big bang nucleosynthesis to explore the nature of the reheating of the Universe in the case that a new extremely long-lived charged massive particle (CHAMP) exists. If the mass of the CHAMP is within collider reach and its lifetime is longer than ${10}^{4}\text{ }\text{ }\mathrm{s}$, the comparison between the charged big bang nucleosynthesis prediction and observed $^{6}\mathrm{Li}$ abundances may indicate nonstandard reheating in the early Universe without relying on details of the decay properties. Even if the CHAMP mass is outside the reach of colliders, the cosmological considerations may provide a nontrivial hint for the existence of such very heavy long-lived CHAMPs from the late Universe if the daughter particles are the dominant component of the present dark matter. We consider a low reheating temperature model as an example of the nonstandard reheating scenarios.

Bounds on long-lived charged massive particles from Big Bang nucleosynthesis

The Big Bang nucleosynthesis (BBN) process in the presence of charged massive particles(CHAMPs) is studied in detail. All currently known effects due to the existence of boundstates between CHAMPs and nuclei, including possible late-time destruction of6Li and 7Li, are included. The study sets conservative bounds on CHAMP abundances in the decaytime range . It is stressed that the production of6Li at early timesT∼10 keV is overestimatedby a factor ∼10 when the approximation of the Saha equation for the4He boundstate fraction is utilized. To obtain conservative limits on the abundance of CHAMPs, a Monte Carlo analysiswith ∼3 × 106 independent BBN runs, varying the reaction rates of 19 different reactions, is performed.The analysis yields the surprising result that, except for small areas in the particleparameter space, conservative constraints on the abundance of decaying charged particlesare currently very close to those of neutral particles. It is shown that, in the case that therates of a number of heretofore unconsidered reactions may be determined reliably in thefuture, it is conceivable that the limit on CHAMPs in the early Universe could be tightenedby orders of magnitude.

Big bang nucleosynthesis with long-lived charged massive particles

We consider big bang nucleosynthesis (BBN) with long-lived charged massive particles. Before decaying, the long-lived charged particle recombines with a light element to form a bound state like a hydrogen atom. This effect modifies the nuclear-reaction rates during the BBN epoch through the modifications of the Coulomb field and the kinematics of the captured light elements, which can change the light element abundances. It is possible for heavier nuclei abundances such as $^{7}\mathrm{Li}$ and $^{7}\mathrm{Be}$ to decrease sizably, while the ratios ${Y}_{p}$, D/H, and $^{3}\mathrm{He}/\mathrm{H}$ remain unchanged. This may solve the current discrepancy between the BBN prediction and the observed abundance of $^{7}\mathrm{Li}$. If future collider experiments find signals of a long-lived charged particle inside the detector, the information of its lifetime and decay properties could provide insights into not only the particle physics models but also the phenomena in the early Universe, in turn.

Search for long-lived charged massive particles in pp collisions at square root s = 1.8 TeV.

We report a search for the production of long-lived charged massive particles in a data sample of 90 pb(-1) of square root[s]=1.8 TeV pp collisions recorded by the Collider Detector at Fermilab. The search uses the muonlike penetration and anomalously high ionization energy loss signature expected for such a particle to discriminate it from backgrounds. The data are found to agree with background expectations, and cross section limits of O(1) pb are derived using two reference models, a stable quark and a stable scalar lepton.