Ponente
Sr.
Xabier Cid Vidal
(USC - IGFAE)
Descripción
- Introduction
Located in Geneva (Switzerland), LHCb is one of the 4 big detectors of the Large Hadron Collider (LHC), the largest particle accelerator in the world, in which proton-proton collisions have been taking place since 2009 at different unprecedented energies. LHCb is a forward spectrometer whose acceptance and specific features makes it very complementary to the rest of the LHC experiments.
LHCb has been able to produce many interesting measurements so far that have turned out to be very important to understand the composition and nature of matter at the most elemental scales. Examples of very well known results concerning flavor physics and spectroscopy are the first observation of the Bs→μμ decay [1], the measurement of the CP-violating phase ϕs [2] or the observation of J/ψp resonances consistent with pentaquark states [3].
However, in the last years, LHCb has been able to make relevant contributions in many other areas beyond those for which it was originally designed, a summary of which will be presented in this talk. More specifically, focus will be set on newest results and in those areas in which the author has worked more actively. These and many other results make LHCb currently a general purpose detector in the forward region.
- Direct searches for light particles
Several New Physics (NP) models predict the existence of particles beyond those of the Standard Model (SM) for whose detection LHCb is particularly well suited. The main reason for this is a flexible trigger, significantly softer than those of ATLAS and CMS, and the presence of unique detectors, such as RICH, which is able to provide a measurement of the mass of long lived charged particles. Among others, LHCb has searched for displaced particles decaying to jets [4] or semi-leptonically [5] as well as long-lived heavy charged particles [6]. Although no evidence for new particles has been found, these results are useful to constraint the parameter space of several NP models.
- Standard Model physics
The SM is currently our best approach to explain the dynamics and behavior of particles at the subatomic level. The LHCb detector allows performing several measurements to test the precision of the SM, in some cases to an unprecedented level at a hadron collider. In this regard, the LHCb measurements are very useful to constrain the internal structure of the proton measuring the Z production in the forward region [7] or to probe hard QCD in a unique environment, providing the first evidence for certain processes, such as W+cc [8]. Furthermore, LHCb is expected to make relevant contributions to Higgs physics in the mid-term. On this subject, a first search for the decays H→bb or cc, with the Higgs produced in association with a W or Z boson has already been performed [9].
- Physics with heavy ions
LHCb was not initially conceived for heavy ion physics. However, following the excellent performance of the detector and the increasing interest in this area at LHCb, data has been recorded in different configurations, including Pb-Pb, p-Pb and Pb-p collisions. Furthermore, LHCb can be turned into a fixed target experiment by injecting noble gases in the collision region. These special configurations can be very useful from a physics point of view. A remarkable example is that of the measurement of the anti-production in p-He collisions [10]. The production ratio between protons and anti-protons has been measured by several astroparticle experiments since it is a sensitive probe to dark matter in the Universe. Given that the dominant uncertainty to better understand this ratio comes from the anti-proton production, the measurement of the anti-proton production cross section in p-He collisions is crucial and becomes an excellent example of the contributions that LHCb can make in this regard.
- References
[1] LHCb Collaboration, Observation of the rare Bs→μμ decay from the combined analysis of CMS and LHCb data; Nature 522, 68-72 (2015).
[2] LHCb Collaboration, Measurement of the CP-violating phase ϕs in the decay Bs→J/ψϕ; PRL 108, 101803 (2012).
[3] LHCb Collaboration, Observation of J/ψp resonances consistent with pentaquark states in Λb→J/ψKp decays; PRL 115, 072001 (2015).
[4] LHCb Collaboration, Search for long-lived particles decaying to jet pairs with the LHCb Run 1 data (to appear as LHCb-PAPER-2016-065).
[5] LHCb Collaboration, Search for massive long-lived particles decaying semileptonically in the LHCb detector; EPJC (2017) 77: 224
[6] LHCb Collaboration, Search for long-lived heavy charged particles using a ring imaging Cherenkov technique at LHCb; EPJC 75 (2015) 595.
[7] LHCb Collaboration, Measurement of the forward Z boson production cross-section in pp collisions at √s = 13 TeV; JHEP 09 (2016) 136.
[8] LHCb Collaboration, Measurement of forward tt, W+bb and W+cc production in pp collisions at √s = 8 TeV; PLB767 (2017) 110.
[9] LHCb Collaboration, Search for H→bb or cc in association with a W or Z boson in the forward region of pp collisions; LHCb-CONF-2016-006
[10] LHCb Collaboration, Measurement of antiproton production in pHe collisions at √sNN = 110 GeV (to appear as LHCb-CONF-2017-002).
Autor primario
Sr.
Xabier Cid Vidal
(USC - IGFAE)
