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Looking For New Physics With


Looking For New Physics With Can K l (Johns Hopkins University) Work done with David E. Kaplan and Matthew McEvoy A Long Expected Party We have all been waiting ... – PowerPoint PPT presentation

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Title: Looking For New Physics With

Looking For New Physics With
  • Can Kiliç (Johns Hopkins University)
  • Work done with David E. Kaplan and Matthew McEvoy

A Long Expected Party
  • We have all been waiting eagerly for the LHC to
    turn on in order to see new physics.
  • The LHC will operate with a CM energy of 14 TeV
    and a design luminosity of 100 fb-1/year.
  • The two multi-purpose detectors at the LHC are
    ATLAS and CMS.

The LHC The Lord of the Rings? One ring to find
them all.
Threes Company
  • But let us not forget that there is more than
    ATLAS and CMS to the LHC story.
  • While I have little to say about ALICE, LHCB is
    designed to study b-physics, and is optimized for
    seeing displaced vertices.
  • Furthermore because of its reduced luminosity,
    LHCB is more sensitive to soft new physics
    signals with heavy flavor tags and can have an
    edge over the all-purpose detectors.

Looking Forward
  • Unlike ATLAS and CMS, the LHCB does not have full
    coverage, it is limited to a forward cone of
  • The beam is detuned to 2 fb-1/year in order to
    reduce pile-up. (LHCB has 1 event/crossing,
    ATLAS/CMS have 5 at low luminosity and 23 at high
  • The main components of the detector are the
    vertex locator, inner/outer trackers, Cherenkov
    detectors, pile-up detector, ECAL, HCAL and muon

Less Is More
  • The LHCB vertex detectors have 21 stations of
    300µ-strip detector module pairs which are
    retractable and can move as close as 8mm to the
    beam (4cm for CMS, 5cm for ATLAS).
  • The data processing is different in LHCB compared
    to ATLAS/CMS in that displaced vertices are not
    required to be part of a jet.
  • Sophisticated Cherenkov detectors give excellent
    particle-id capabilities and thus improved
    b-tagging efficiency.
  • 2 kHz bandwidth for b-physics (compared to 15 Hz
    for ATLAS/CMS)

SUSY in Distress
  • For all its successes (GCU, DM, Hierarchy
    Problem), SUSY has a hard time coping with the
    LEP bound of mhgt114 GeV.
  • Pushing the Higgs mass above this bound in
    minimal SUSY scenarios requires heavy stops and
    leads to severe fine tuning.
  • One way out of this conundrum is to extend the
    MSSM. We win if we can make the Higgs heavier or
    if we can make it decay in a channel that softens
    the LEP bounds.
  • In SUSY models with a singlet both these things
    are not only possible, but generic. F term
    contributions to the Higgs potential from the
    singlet can help make the Higgs boson heavier
    without severe fine tuning while the additional
    degrees of freedom modify its decay modes.

How I Learned to Stop Worrying and Love the
  • The µ problem in the MSSM has to do with
    explaining the smallness of the µHuHd term in the
    superpotential required for viable EWSB. This
    problem is avoided in extended SUSY models where
    µltSgt, S being a singlet superfield.
  • For a light Higgs boson the largest coupling to
    the SM relevant for decays is yb1/40 which means
    any allowed decay mode of the Higgs to BSM
    particles is generically dominant. In particular,
    the dominant Higgs decay mode in the NMSSM can be
  • a, being light and part of a singlet can only
    decay through mixing with the Higgs, so it adopts
    couplings to the SM proportional to the Yukawas.
    Consequently, a will generically decay to the
    heaviest kinematically allowed fermion pair. The
    coupling to down type quarks is further enhanced
    by tan ß.
  • For generic regions of parameter space, this
    makes the dominant Higgs decay mode 4 b-quarks.
    This is the channel we would like to discover at

A Needle in a Haystack
  • The production mechanism for the Higgs is still
    through glue-fusion and the cross section is
    25pb (LO) for mh115 GeV, this is expected to
    increase significantly at higher orders, but the
    background (mainly 4b production in QCD) is only
    done to LO and is gt100nb.
  • We generate the signal using PYHTIA and the
    background using ALPGEN (4b / 4bj) showered
    through PYTHIA. For our analysis sample we
    require 4 displaced vertices within the LHCB
    acceptance region. This leaves about 0.04 of the
    signal and 0.02 of the background.

Details of Analysis, Estimates of Significance
  • Then we construct 4 cones of ?R0.6 using the
    displaced vertices as seeds and the best pairing
    is found by minimizing ?Rp12 ?Rp22.
  • The four-momentum of each a-candidate (cone
    pairs) is reconstructed using calorimeter towers
    with gt1GeV.
  • The invariant masses ma and mh are calculated.
  • We define Q1 mh - 3ma and Q2 mh 1/3ma and
    plot the data in a Q1 Q2 double histogram (bin
    size 5GeV x 10GeV).
  • We look for the greatest excess in a 3 x 5 region
    to find the best fit.
  • Our current estimate for the significance in one
    years data is 2-3s, depending on the b-tagging

Other Interesting SUSY scenarios for LHCB (David
E. Kaplan, Keith Rehermann arXiv 0705.3426)
  • A different extension of SUSY is through
    violation of R-parity. Since there are very
    strong bounds from proton decay and from lepton
    number conservation, the easiest way to implement
    RPV is through the superpotential term UcDcDc.
  • The collider phenomenology in such models is
    quite different from the MSSM, the bounds on
    superpartner masses is reduced and the Higgs mass
    can be significantly below the LEP bound if mh gt
  • The LSP itself is unstable and decays to three
    jets through an of-shell squark. This means that
    SUSY events are devoid of both leptons and MET, a
    very bleak scenario for triggering
    considerations. The same can be true for Higgs
    physics as well.
  • One distinguishing feature of such scenarios is a
    macroscopic decay length for the LSP, which
    makes it possible for LHCB to trigger on such

Other Interesting SUSY scenarios for LHCB (David
E. Kaplan, Keith Rehermann arXiv 0705.3426)
  • The RPV coupling of the neutralino favors decays
    to heavier quarks. This makes the most likely
    decay product (cbs), except for a heavy LSP that
    can go to (tbs).
  • Considering squarks as the primary production
    process, the analysis requires one displaced
    vertex with 5 tracks in the acceptance and large
    invariant mass (gt2mb). The main background is
    multi b (c) production, in particular events
    where two displaced vertices cannot be
    distinguished. Depending on RPV parameters,
    squark masses up to 700 GeV can be within
    discovery reach.
  • Considering Higgs decay to neutralinos as the
    primary production process, the analysis requires
    both displaced vertices to be within acceptance.
    For generic regions of parameter space this leads
    to 103 events/year with negligible background.

More Exotic Possibilities Hidden Valley
Models Strassler, Zurek (hep-ph0604261,0605193,06
  • In the class of hidden valley models there is a
    new physics sector which is neutral under SM, and
    the two sectors only talk through heavy degrees
    of freedom.
  • Because of the energy barrier, it is plausible
    for the new physics to have completely evaded LEP
    and TeVatron searches.
  • In one such model, the new physics is a copy of
    QCD, and the primary production mechanism is that
    of v-quark pairs which v-hadronize.
  • Most v-hadrons will be unseen but there can be
    states which carry the right quantum numbers to
    decay to a SM current, for scalars the helicity
    flip required makes Gm, so a likely final state
    is b-quarks.

More Exotic Possibilities Hidden Valley
Models Strassler, Zurek (hep-ph0604261,0605193,06
  • The signatures of such models can be very
    unusual, there can be a large number of jets in
    the final state with possible heavy flavor tags,
    and the v-hadrons themselves may have macroscopic
    decay lengths.
  • If only few states decay to SM within the
    detector, the visible part of the event can be
    soft and our ability to see the new physics may
    be limited to identifying displaced vertices and
    heavy flavors. In fact the jets can be on top of
    each other which is bad for triggering on
    reconstructed objects.
  • A different class of models has the Higgs boson
    as the bridge between the SM and the new physics,
    providing a non-SUSY scenario with non-standard
    Higgs decays which has very similar collider
    signatures to the NMSSM, in such a case covering
    all bases detector-wise may again be crucial.
  • Finally, SUSY-HV models can fake RPV, if the LSvP
    is lighter than the LSsP, so in SUSY events most
    of the MET is transformed into v-hadrons with
    their characteristic phenomenology.
  • While HV models may appear theoretically
    unmotivated, many benchmark BSM frameworks with
    small Z2 breaking can produce similar signatures.

  • Most experimental search strategies are based on
    a few benchmark new physics frameworks whose
    specific collider signatures may be less generic
    than we have come to believe.
  • While for most people LHC is synonymous to
    ATLAS/CMS, there are BSM physics scenarios that
    give rise to softer final state particles without
    large MET, many such scenarios can involve heavy
    flavors which could give LHCB an edge for early
  • We have shown that LHCB is quite relevant for the
    search of a Higgs boson dominantly decaying to 4
    b-jets. There is potential for increasing the
    significance using better detector simulation.
  • RPV-SUSY and hidden valley scenarios also fall
    into the above class of models.
  • What is your favorite nightmare LHC scenario?
    Maybe LHCB can help..
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