Overview of AMSB and a search at ATLAS

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Overview of AMSB and a search at ATLAS

• Rishiraj Pravahan
• UTA

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Content

• What is AMSB?
• Attractive features?
• Drawbacks?
• Expected signatures
• Questions

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What is ASMB

• Anomaly mediated SUSY breaking!
• Hypothesis weak scale supersymmetry i.e. some
  superpartners at 1 TeV
• We know that SUSY is broken
• Question is how, where
• I will have more notes on these topics over
  time on this wiki
• It is not possible to break SUSY at TeV scale
  within MSSM. So there are different solutions

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mSUGRA

• Susy is broken in a hidden sector
• The scale is M 1011 GeV
• Transmitted to the visible sector by Gravity
  messenger(s)

• Disadvantges
• Predicts unobserved Flavour Changing neutral
  currents
• needs fine tuning
• Problems with CP violating processes

• Advantages
• Minimal set of parameters
• Theoretically better understood
• Available tools, softwares etc.

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GMSB

• SUSY is broken in hidden sector
• Scale of M 10 TeV
• Transmitted to the messenger sector (gauge
  (s)particles) and then to the visible sector

• Advantages
• No FCNC
• Only five extra parameters from SM
• Very characteristic mass spectrum with light
  gravitino as LSP
• Long lived NLSPs

• Disadvantages
• Extensive searches have not resulted in any
  indication of GSMB in D0 Run II or LEP II
• Dipanjan should know more!

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AMSB

• Another SUSY breaking mechanism but not in a
  hidden sector.
• It has been noted that all SUSY breaking
  mechanism involve anomaly mediation from a
  sequestered sector
• AMSM predicts that the dominant SUSY breaking
  mechanism lies in the Anomaly Mediation from the
  sequestered sector. Such sectors might be in
  another Brane and transmission happens through
  gravity.

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Advantages

• Theoretically very elegant
• Does everything GMSB does
• Very simple parameter space with

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Distadvantages

• ALL SLEPTONS ARE TACHIONS!!
• THE LSP CANNOT BE DARK MATTER

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mASMB

• The simplest way to solve the tachionic slepton
  problemis to add an extra parameter m0
  Universal Scalar Mass to ASMB.
• Dark matter can be axions. Also solved by the
  bulk-brane scenarios/string theories.
• Certainly according to Frank this makes the model
  ugly!
• This model is called mASMB
• Numerous other solutions exist, notable among
  them are, Deflected AMSB, Gaugomaly mediation,
  and Gaugino Assisted ASMB
• Note I have been looking into all the different
  mechanisms and I personally favour the gaugino
  assisted mediated processes as promising. They
  contain the elegance of AMSB with the advantages
  of GSMB with the tachionic slepton problem solved
  by the presence of gauge mediation as well. Most
  theory work right now is going on in this sector
  as theorist do not think MSUGRA is a viable SUSY
  breaking mechanism. Not much is done in terms of
  phenomenology or experimental (MC) searches. May
  be in our group we can discuss some sort of a
  merger of the Gaugino assisted study with the
  ASMB study. This also has promising channels with
  Tau decays. May be Paul can comment.

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Some phenomenological details of mASMB

• With m0 0 Mi (ßgi/gi) m3/2 where
• gi gauge coupling constant
• ßgi corresponding RG beta functions
• For i 1,2,3, Mi are the Gaugino masses
• This says that,
• M1 M2 M3 2.8 1 7.1 so the
• WINO is the LSP and the Gluino is an order of
  magnitude heavier.
• Note Theoretical consideration that the scalar
  masses are proportional to the gauge and Yukawa
  couplings, guarantees universality between first
  and second generation scalar flavours thus
  eliminating SUSY flavour problems. They also
  solve the SUSY CP problem.

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Continuesgt

• the LSP is a wino
• the wino and chargino masses are nearly
  degenerate this is a very characteristic
  signature
• If ?m mchargino mwino then, for ?m lt 200 the
  chargino can live long to penetrate few
  centimeters into the detector.
• Squark masses are insensitive to m0 and mASMB
  based searches are mostly applicable to mSUGRA
  and other ASMB scenarios and vice-versa.
• Nearly mass degenerate and highly mixed same
  flavour sleptons
• The LSP candidate depends on the choice of m0 ,
  the other possibilities being, the sneutrino or
  stau for low values of other parameters

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Example of mASMB mass spectrum
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Example of mASMB mass spectrum
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Search Strategy Possibilities (As per
discussion with Frank)

• The only existing paper on discovery potential of
  AMSB at the LHC is by Barr et. al. Aug 2002. No
  search for ATLAS is underway
• Search for physics with heavy flavour b tagging
• Search for nearly degenerate sleptons using the
  egde endpoints in the effective mass distribution
  of the dileptons (this is suggested in a paper by
  F Paige, hep-ph/0001249, 2000 but has not been
  done by anyone, to his knowledge) (See reference
  slide 15)
• Look at the different channels for the gluino to
  squark decays and use combinatorics!
• Look at b1 and t1 decays into bs and neutralinos
  or charginos respectively and their consequent
  decay into pions and neutralino LSP. Use the
  method of MT2 . (See reference slide 16).
• Look for Charginos in the detector. This requires
  being friends with inner detector people.
• Note I will put details of each study on the
  wikipage as I learn enough and make notes.

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The dilepton mass distributions.
16
Athens workshop
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Questions

• I seem to be the only one working in this at
  ATLAS. Anyone else interested?
• Should we as a group look into gauge assisted
  ASMB scenarios?
• Can I use the same (AOD) files generated by the
  group?
• We need to (ask) make changes to the MC to
  generate data corresponding to the theories. Is
  it worth it? Can we get theorists on board?