Z yields jets+. gamma. as a signal for R-parity violation Page: 2 of 8
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Z —» jets -f 7 as a Signal for R-Parity Violation
JoAnne L. Hewett
High Energy Physics Division, Argonne National Laboratory,
Argonne, IL 60439 USA
Supersymmetric models with explicit R-parity violation can induce new rare decay
modes of the Z boson into single supersymmetric particles. Here, the rate and signature
for one such decay, Z £7 r: examined, where it is found that the rate is at least
an order of magnitude smaller than that for Z —► H7, even with larger values of the
R-parity violating couplings.
General supersymmetric extensions of the Standard Model contain dimension 4 and 5 operators
which violate baryon (B) and lepton (L) number and lead to unacceptably rapid proton decay,
Additional symmetries are then applied to suppress these operators. In the minimal supersym-
metric standard model (MSSM) the discrete symmetry matter parity (or R-p^rity) is applied to
prohibit all the dimension 4 B and L violating operators (with the assumption that the dimension
5 operators are suppressed by a large unified mass scale). Each field and its super-partner then
possess a conserved multiplicative quantum number which is given by R = (-1)2S+3B+L, where S
denotes the spin of the particle. In this notation all standard fields have the assignment R — -hi,
while their super-partners have R = — 1. Conservation of R-parity has two direct consequences;
(i) sparticles can only be produced in pairs, and (ii) the lightest supersymmetric particle (LSP)
must be stable and experience neither electromagnetic or strong interactions. All supersymmetric
collider searches rely on the first condition, and most search techniques also depend heavily on a
signature of an excess of missing energy.
However, given the absence of any experimental verification of the MSSM, perhaps we should
feel compelled to re-examine the above assumptions and investigate alternative supersymmetric
models. (This could appear more attractive than dismissing supersymmetry altogether, or to keep
pushing the supersymmetric mass scale to larger values!) One such alternative, supersymmetric
models with broken R-parity, has enjoyed a revival[l, 2] in the literature. These models contain
the minimal superfield content and break R-parity either spontaneously, by the sneutrino acquiring
a vacuum expectation value, or explicitly through terms contained in the superpotential. The
most general gauge and supersymmetry invariant superpotential is given by
w = hijL^hE^ + Kfi+ h-jQiHiUj,
U^AE'h + K.^QiDi (1)
where ijk are generation indices, the h‘s and A’s are a priori unknown Yukawa coupling constants,
Ql, Li, Ur, Dr, represent the chiral superfields containing the left-handed quark and
lepton doublets, the right-handed u-quark, d-quark, and charged lepton singlets, and the two
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Hewett, J.L. Z yields jets+. gamma. as a signal for R-parity violation, article, February 1, 1992; United States. (https://digital.library.unt.edu/ark:/67531/metadc1066975/m1/2/: accessed March 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.