Measuring masses of semi-invisibly decaying particles pair produced at hadron colliders

Abstract

We introduce a variable useful for measuring masses of particles pair produced at hadron colliders, where each particle decays to one particle that is directly observable and another particle whose existence can only be inferred from missing transverse momenta. This variable is closely related to the transverse mass variable commonly used for measuring the $W$ mass at hadron colliders, and like the transverse mass our variable extracts masses in a reasonably model independent way. Without considering either backgrounds or measurement errors we consider how our variable would perform measuring the mass of selectrons in a mSUGRA SUSY model at the LHC.

Figures (3)

• Figure 1: Diagram of the generic process that we consider. A hadronic collision that leads to a pair of particles being produced, which each decay into one particle that is observed with momenta $p_1$ and $p_2$ respectively; and one particle (shown as a wavy lines) that is not directly detected, and whose presence can only be inferred from the missing transverse momentum, $\hbox{${\bf p}$} / _T$.
• Figure 2: $M_{T2}$ distribution for the process $pp \to X + \tilde{l}^+_R \tilde{l}^-_R \to X + l^+ l^- \tilde{\chi}^0_1 \tilde{\chi}^0_1$ at the LHC. With $m_{\tilde{l}}=157.1\hbox{GeV}$ and $m_{\tilde{\chi}}=121.5\hbox{GeV}$, assuming the actual value for $m_{\tilde{\chi}}$ when calculating $M_{T2}$. The data with error bars are 1105 events, that the LHC would collect in approximately 1 year of running at low luminosity, i.e.${\cal L}\simeq 30\hbox{fb}^{-1}$. The histogram represents ${\cal L}\simeq 500\hbox{fb}^{-1}$ to show the shape of the distribution that would be obtained with huge statistics, with the normalization modified to be the same as ${\cal L}\simeq 30\hbox{fb}^{-1}$.
• Figure 3: Values of $m_{\tilde{l}}$ that would be obtained from that largest $M_{T2}$ value observed, where differing values of $m_{\tilde{\chi}}$ are used in the calculation of $M_{T2}$, for the 1105 events shown in figure \ref{['fig:mt2']}. All events have been generated with $m_{\tilde{l}}=157.1\hbox{GeV}$ and $m_{\tilde{\chi}}=121.5\hbox{GeV}$.