Search for Gravitinos in R-Parity violating Supersymmetry at HERA. SLAC experimental seminar Claus Horn (DESY / Univ. Hamburg). Introduction HERA & ZEUS SUSY processes at HERA Analysis Summary & Outlook. SUSY Motivation. Coleman-Mandula theorem / Haag-Lopuszanski-Sohnius theorem
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Search for Gravitinos in R-Parity violating Supersymmetry at HERA
SLAC experimental seminar
Claus Horn (DESY / Univ. Hamburg)
HERA & ZEUS
SUSY processes at HERA
Summary & Outlook
SUSY is our last chance to discover a
fundamental space-time symmetry!
27.5 GeV e±
e± p collider, in Hamburg
Protons: 920 GeV
Leptons: 27.5 GeV
CMS-Energy: 320 GeV
HERA I (1992-2000)
L=1.6 1031 cm-2s-1
HERA II (2002-2007)
L=7.0 1031 cm-2s-1
p 920 GeV
HERA II: polarised lepton beam also at H1 & ZEUS.
Calorimeter: Uranium Scintillator
Central Tracking Detector:Drift Chamber
Weight: 3500T, Size: 12m ×10m ×19m
In MSSM SUSY breaking is introduced “by hand“
via soft terms. over 100 free parameters!
Postulate superpartner for each SM particle with
same QNs but spin different by ½.
Q|boson> = |fermion> Q+|fermion> = |boson> [H,Q]=0
No superpartners with same masses are observed.
SUSY is a broken symmetry.
MSSM: Minimal number of sparticles and couplings.
LSP is always gravitino.
Typically very light:
Candidate for dark matter (even in RPV models).
Possible NLSPs: neutralino, stau, (right-handed slepton)
Distinct event signature: photon/tau + missing energy.
Super trace theorem: SUSY breaking not possible in visible sector. ->Hidden Sector Models
Example for generation
of sfermion masses:
GMSB parameters: sqrt(F), Mmess, N, L, tan(b), sign(m)
+1 for SM particles
-1 for sparticles
Multiplicative discrete symmetry: RP=(-1)3B+L+2S
RPC: sparticles pair-produced, LSP stable
Most general Lagrangian contains additional trilinear terms
in superpotential which violate RP:
Unique initial state HERA ideal place to look for l‘ couplings.
Former analyses looked for resonant squark production.
squarks are heavy.
Motivation: Check all possible SUSY channels at HERA
before start of LHC.
Particles are producedon-shell (same for all SUSY models).
Decay depends on sparticle spectra of SUSY model.
Sparticle creation at HERA:
Choose RPV vertices
Mark sparticle lines with a „~“.
In the case of RPC: C-like loops result.
Number of SUSY propagators
Number of SUSY particles
Physics description on an abstract level to reduce complexity.
All vertices of the MSSM !
(neglecting pure bosonic SM vertices and Higgs)
Single slepton production.
Only SM propagators.
All l‘ couplings can be investigated.
Signature e.g. in GMSB: l+G
s=0.2pb for m(l)=100 GeV.
After all cuts: 55 abstract diagrams of sparticle production.
Additionally consider dominant sparticle decays:
Complete list of SUSY signatures at HERA.
Characteristic signatures for different
SUSY models / scenarios.
Example of new found diagram:
(now investigated by new PhD student)
Investigated data set (1996-2005) e- p : L=155 pb-1
e+ p : L=145 pb-1
Total: L=300 pb-1 (HERA I and HERA II)
First ZEUS thesis with complete data set!
via slepton exchange:
R-parity violating decay channels
e±+ multiple jets
n + multiple jets
jet + g + missing energy
Simulated events (SUSYGEN+Geant detector simulation)
Loos selection to maximize signal efficiency!
Data/MC : 4751/4787 e70%-77% -> good agreement.
Data/MC : 1254/1275 e61%-68% -> good agreement.
One dimensional cuts do not maximize S/B (for a given
signal efficiency) if correlations between variables exist.
Only select events in signal
Disadvantage: A lot of MC needed.
Advantages compared to:
Box size needs to be fixed before
counting starts, however counting
several too small boxes is faster
than counting one too big box.
1-dim factor for which N Nmin.
# events /box ~ (box_size)dim
Advantages of variable bin size method:
Less parameters have to be set by hand.
More events get classified.
More accurate results.
Selection of best set of
Purity and efficiency after
different discriminant cuts.
ZEUS data 1996-2005
No excess observed in signal region!
No excess observed in signal region!
Effects of model parameters sometimes interchangeable,
or have only small effect.
Set limits on process parameters.
Slepton mass treated as free parameter.
Limit set in mass plane of process particles m(e)-m(c).
For l‘111=1 sparticle
masses of up to
m(e) < 360 GeV and
m(c) < 190 GeV can
be excluded at 95%CL.
Best existing limits
in RPV GMSB!
Limits calculated for different strengths of l‘ coupling.
Dominating decay channels:
RPV decays get important:
Contribution from different gauginos:
Low sqrt(F): Lightest neutralino dominates.
High sqrt(F): Partly contribution from lightest chargino.
Neutralino is NLSP for low N and high tanb.
c = (W, H)
c0 = ( H0, Z0, g )
Gauginos are superposition:
High cross section requires:
1. Small higgsino component (for large eec coupling)
2. Large photino component (for GMSB decay into photon)
Variation of M and sign(m):
Different RPV couplings:
Variation of N:
Dependence on sqrt(F):
Similar limits are valid in large part of GMSB parameter space!
SUSY gauge couplings are the same as in SM.
Cross sections only surpressed by mass terms.
At high energies SUSY production rates are similar to SM!
Measure SUSY spectrum:
Corrections to the Higgs mass:
Cancelation requires fine tuning
to 17 orders of magnitude!
Contributions of SM particles
and their superpartners
compensate each other.
Renormalisation Group Equations describe running of
the coupling constants due to screening / antiscreening.
Slope depends on number and masses of particles
in the model.
Examples of best current limits:
LEP: m(c0) > 45GeV (RPV)
m(c±) > 103GeV
selectronR > 100 GeV
smuonR > 95 GeV
stauR > 86 GeV
D0: sneutrinoR > 460 GeV
(l132=0.05 & l‘311=0.16)
D0: squark > 320 GeV
gluino > 232 GeV
HERA: squark > 275 GeV (l‘1j1=0.3)
Explain origin of SUSY breaking!
Spontaneous SUSY breaking in SM sector not possible
supertrace theorem-> sum rules between particle and
sparticle masses, e.g.: excluded!
Hidden sector models
AMSB, gMSB, ...
where the al are positively correlated with tanb.
Possible abstract diagrams:
C3: disfavoured due to high limits on squark masses
C7: - “ –
C6: lepto-quark search / contact interaction
C5: -> gaugino production analysis !
RPC MSSMRPV MSSMGMSB
RPC MSSM: missing E, e / m / t
RPV MSSM: 2 jets / 2 l / 2jets+2l
GMSB: l + g + G~
Squarks decay in the same way.
55 abstract diagrams.
Diagrams with squarks are neglected.
Characteristic signatures for different models!
With two outgoing lines: C5
With three outgoing lines and one sparticle: F4-2
With three outgoing lines and two sparticles: D1
Gamma not too forward (small dependence on m(c)),
PT Jacobian peak ~ m(c) smeared out by LT.
Gravitino reconstruction: (E-pz)G + (E-Pz)DET =55 GeV
Neutralino mass: m(c)² = (pg+pG)²
Selectron: Qe² = (pe-pc)²
For low sqrt(F):
Different RPV couplings
pick different quarks from p,
dependent on e-/e+.
Example for x-section ratios:
(HERA I &
Ordering depends on L(e-)/L(e+).
ZEUS data 96-00:
Electron selection works fine.
at low sqrt(F):
Contribution from lightest neutralino dominates.
at high sqrt(F):
Partly contribution from lightest chargino.
For high values of N stau NLSP is favoured.
Stau is NLSP for small M and high tanb:
In region where lightest neutralino is NLSP:
Importance of GMSB-decay/RPV-decay depend on sqrt(F)
and strength of l‘ coupling.
(At least twice the data lumi.)
Energy scale of CAL cells: 2.5% 0.6%
(fhac & bhac: ±2%, rhac: ±3%, emc: ±1.5%)
Luminosity measurement: 2.25% 2.25%
Ariadne => MEPS: 1.7% (less) --
PDF uncertainty: 7% 7%
Scale uncertainty: -- 10%
Signal efficiency: -- 2.5%
|zVtx| < 40 cm ±10 cm 1.9% 2%
Q²jb > 700 GeV² ±100 GeV² 1.9% 0.4%
Pt > 20 GeV ± 4 GeV 5.6% 2.5%
Yjb > 0.1 ± 0.02 2.3% 0.1%
Df(jet,g) > 3.0 rad ± 0.033 rad (2°) 0.5% 1.4%
Modified frequentist method by Thomas Junk.
Likelihood Ratio for multi-channel analysis.Estimator function needed:
CL = 1 – P(s+b) / P(b)
Sytematic Uncertainties: Average over systematic variations on s and b in all channels, assuming Gaussian distribution with lower cutoff at zero.
(fermion,sfermion) = (spin ½, spin 0)
(gauge boson, gauginos) = (spin 1, spin ½)
Use discriminant bins for S, B and data for limit calculation.
Generate events for each parameter point.
Better: Seperate event generation and parameter scan!
Use slim or Nlim as interface.
For m produced particles decaying into n different decay channels.
Difficult to handle!
1. Straightforward method
2. Seperate event generation
and parameter scan.
If different prod. Particles and different decay channels contribute:
Difficult to handle!
LHC 5s discovery curves
Complicated decay channels: g~ -> q~q -> cqq -> l~lqq -> cllqq
Problem is to seperate different SUSY channels.
Higher luminosity at similar energy
Precision measurements of SUSY parameters!