Search for heavy charged long-lived particles in proton-proton collisions at $\sqrt{s} = 13$ TeV using an ionisation measurement with the \mbox{ATLAS} detector

The ATLAS collaboration
No Journal Information, 2018

Abstract (data abstract)
This Letter presents a search for heavy charged long-lived particles produced in proton--proton collisions at $\sqrt{s}=13$ TeV at the LHC using a data sample corresponding to an integrated luminosity of $36.1$ fb$^{-1}$ collected by the ATLAS experiment in 2015 and 2016. These particles are expected to travel with a velocity significantly below the speed of light, and therefore have a specific ionisation higher than any high-momentum Standard Model particle of unit charge. The pixel subsystem of the ATLAS detector is used in this search to measure the ionisation energy loss of all reconstructed charged particles which traverse the pixel detector. Results are interpreted assuming the pair production of $R$-hadrons as composite colourless states of a long-lived gluino and Standard Model partons. No significant deviation from Standard Model background expectations is observed, and lifetime-dependent upper limits on $R$-hadron production cross-sections and gluino masses are set, assuming the gluino always decays in two quarks and a stable neutralino. $R$-hadrons with lifetimes above 1.0 ns are excluded at the $95\%$ confidence level, with lower limits on the gluino mass ranging between 1290 GeV and 2060 GeV. In the case of stable $R$-hadrons, the lower limit on the gluino mass at the $95\%$ confidence level is 1890 GeV.

  • Event Yields 1

    10.17182/hepdata.83962.v1/t1

    The number of events in each CR, VR, and SR for the predicted background, for the expected contribution from the...

  • Event Yields 2

    10.17182/hepdata.83962.v1/t2

    The number of events in each CR, VR, and SR for the predicted background, for the expected contribution from the...

  • Cutflow 1

    10.17182/hepdata.83962.v1/t3

    Expected number of $R$-hadron signal events at different stages of the selection, normalised to $36.1$ fb$^{-1}$. Shown for three different...

  • Cross section UL 1

    10.17182/hepdata.83962.v1/t4

    The observed and expected 95% CL upper limits on model-independent visible cross-sections, along with the observed $p0$ values, for the...

  • Cross section UL 2

    10.17182/hepdata.83962.v1/t5

    The observed and expected 95% CL upper limits on model-independent visible cross-sections, along with the observed $p0$ values, for the...

  • Mass windows definition

    10.17182/hepdata.83962.v1/t6

    For each gluino lifetime and mass in the signal samples, the lower boundary of the mass window in which at...

  • Acceptance / Efficiency 1

    10.17182/hepdata.83962.v1/t7

    Acceptance and efficiency for a representative set of pair-produced gluino signal samples. The mass of the gluino ($m(\tilde{g})$), its lifetime...

  • SR plot 1

    10.17182/hepdata.83962.v1/t8

    The reconstructed candidate track mass distributions for observed data, predicted background, and the expected contribution from two signal models in...

  • SR plot 2

    10.17182/hepdata.83962.v1/t9

    The reconstructed candidate track mass distributions for observed data, predicted background, and the expected contribution from two signal models in...

  • UL Cross section 1

    10.17182/hepdata.83962.v1/t10

    The 95% CL upper limit on the cross-section as a function of mass for gluinos with lifetime $\tau = 10$...

  • UL Cross section 2

    10.17182/hepdata.83962.v1/t11

    The 95% CL upper limit on the cross-section as a function of mass for stable gluino $R$-hadrons, with the observed...

  • Exclusion contour 1 (obs.)

    10.17182/hepdata.83962.v1/t12

    Observed 95% lower limits on the gluino mass in the gluino lifetime--mass plane. The excluded area is to the left...

  • Exclusion contour 1 (exp.)

    10.17182/hepdata.83962.v1/t13

    Expected 95% lower limits on the gluino mass in the gluino lifetime--mass plane. The excluded area is to the left...

  • UL Cross section 3

    10.17182/hepdata.83962.v1/t14

    The 95% CL upper limit on the cross-section as a function of mass for gluinos with lifetime $\tau = 1$...

  • UL Cross section 4

    10.17182/hepdata.83962.v1/t15

    The 95% CL upper limit on the cross-section as a function of mass for gluinos with lifetime $\tau = 3$...

  • UL Cross section 5

    10.17182/hepdata.83962.v1/t16

    The 95% CL upper limit on the cross-section as a function of mass for gluinos with lifetime $\tau = 30$...

  • UL Cross section 6

    10.17182/hepdata.83962.v1/t17

    The 95% CL upper limit on the cross-section as a function of mass for gluinos with lifetime $\tau = 50$...

  • Reconstructed Mass 1

    10.17182/hepdata.83962.v1/t18

    The relationship between generated and reconstructed mass for gluino $R$-hadrons. Above 1500 GeV, the reconstructed mass falls below the generated...

  • Acceptance / Efficiency MET 1

    10.17182/hepdata.83962.v1/t19

    The parameterised efficiency for events to pass metastable event selections (including trigger, E$_{T}^{miss}$, and event cleaning requirements) as a function...

  • Acceptance / Efficiency MET 2

    10.17182/hepdata.83962.v1/t20

    The parameterised efficiency for events to pass metastable event selections (including trigger, E$_{T}^{miss}$, and event cleaning requirements) as a function...

  • Acceptance / Efficiency Particle 1

    10.17182/hepdata.83962.v1/t21

    The parameterised efficiency for particles to pass full track selections in the metastable signal region, as function of the particle’s...

  • Acceptance / Efficiency Particle 2

    10.17182/hepdata.83962.v1/t22

    The parameterised efficiency for particles to pass full track selections in the metastable signal region, as function of the particle’s...

  • Acceptance / Efficiency Particle 3

    10.17182/hepdata.83962.v1/t23

    The parameterised efficiency for particles to pass full track selections in the metastable signal region, as function of the particle’s...

  • Acceptance / Efficiency Particle 4

    10.17182/hepdata.83962.v1/t24

    The parameterised efficiency for particles to pass full track selections in the metastable signal region, as function of the particle’s...

  • Acceptance / Efficiency Particle 5

    10.17182/hepdata.83962.v1/t25

    The parameterised efficiency for particles to pass full track selections in the metastable signal region, as function of the particle’s...

  • Acceptance / Efficiency Particle 6

    10.17182/hepdata.83962.v1/t26

    The parameterised efficiency for particles to pass full track selections in the metastable signal region, as function of the particle’s...

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