Searches and EW physics at HERA

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Searches and EW physics at HERA
5th Rencontres du VietNam 2004 New Views in
Particle Physics
Sascha Caron (NIKHEF)
(former Aachen)
HERA
P(920 GeV)
e(27.5 GeV)
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HERA
HERMES
HERA collides 27.5 GeV e with 920 GeV protons at
vs320 (300) GeV
HERA-B
HERA2 luminosity, polarized e beam and detector
upgrades
Lumi produced by HERA (pb-1)

• Recorded data samples
• HERA 1
• 40pb-1 ep (300 GeV)
• 15pb-1 e-p (320 GeV)
• 65pb-1 ep (320)
• HERA 2
• 50pb-1 ep (320)

day of running
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HERA physics on 1 transparency
NC deep inelastic scattering
CC deep inelastic scattering
Q2 - squared momentum transfer between e and p
W production
Multilepton production
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Searches and EW physics at HERA

• Electroweak tests in deep inelastic scattering
• Systematic tests of the SM at high PT
• Measurements of W production and multi-lepton
  processes

• Various dedicated searches for new physics
• SUSY, Contact Interactions, Quark Radius,
  anomalous
• top couplings, LQ, H, magnetic monopoles,
  large ED, excited fermions and more

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(Deep) inelastic scattering at HERA
HERA probes eq interactions at photon
virtualities Q2 from 0 (photoproduction, ?q) up
to 4104 GeV2
NC
unique facility
CC
Test of EW sector with W (CC) and gamma/Z
(NC) propagators
Unification of weak and e.m. forces at high Q2
(more in HERA QCD talks)
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Contact Interactions
Results on Leptoquarks, general Contact
Interactions, Large Extra Dimensions, Quarks
Radius
New interactions between e and q can be modeled
by 4-fermion contact interactions Parametrized
by additional terms in the lagrangian
Limits on quark radius (classical form
factor) Rqlt 10-18 m (ZEUS and H1) or vector
contact interaction couplings of up to 5 TeV
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A general Search for new phenomena

• Systematic search for
• deviations from the SM
• All final states are
• considered in one analysis
• Objects (e, µ, jet, ?, ?)
• with PTgt20 GeV are analyzed
• Data is classified to
• exclusive channels
• Good agreement for
• (almost) all channels

Event yields are also available for HERA2 data!
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A general search for new phenomena
Mall and SPT distributions are systematically
investigated using a search algorithm Find in
each channel the region with the greatest
deviation
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A general search for new phenomena
Derive for each event class the probability P to
observe a deviation anywhere in the spectrum as
large as found in the data


Smallest P found in µ-jet-?, e-jet and e-e
channels

Repeat the whole analysis with many MC (pseudo
data) experiments each with the H1 luminosity
About 3 (S PT) and 25 (Mall) of MC experiments
have a deviation larger than that of µ-j-? final
state
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Isolated lepton events
ep ? jet (PT,X) PT,miss lepton
main SM contribution is W production
Results from dedicated analysis
e
p
HERA 1
(observed/expected)
PTxgt25GeV e channel µ ?
H1 ep (118 pb-1) 4/1.480.25 6/1.440.25 0/0.53
ZEUS (130 pb-1) 2/2.90.5 5/2.750.2 2/0.12
Agreement in hadronic channel (with large
background)
HERA 2
excess of events at H1 no excess in HERA1 ZEUS
data clarification needs more lumi
PTxgt25 GeV e channel µ
H1 ep (45 pb-1) 3/0.740.15 0/0.760.1
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Anomalous top production
Compare the l-jet-? events with models, e.g.
single top production with anomalous couplings
between tuZ and tu?
Selection cuts optimized for top
H1 excess in leptonic channels (3e, 2µ
with SM exp. 1.3 0.2) no excess in
hadronic channel ZEUS no excess in hadron or
lepton channels
Limits on top cross sections and couplings
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Multilepton events
Measurement of multilepton events Process ep ?
ll (e) mainly via 2-photon collisions
Some interesting events at high mass
Mllgt100 GeV ee channel eee channel
H1 HERA12 (165 pb-1) 3/0.440.1 3/0.310.08
ZEUS (130 pb-1) 2/0.770.1 0/0.370.04
No excess in muon channels
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SUSY_at_HERA
Example sbottom production
HERA RP violating SUSY ? single production of
squarks via couplings ?ijk
Large variety of squark decay modes ? many final
states are considered
For ?0.3 Msquarkgt275 GeV for all squarks
types in nearly full parameter space small
couplings improvement of indirect low-energy
limits
Also interpretations in terms of MSUGRA model
parameters
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Summary
High energy ep collisions at HERA are a unique
testing ground for the SM Various searches for
new physics are performed (model independent and
dedicated) Some interesting events are found
and HERA 2 has just started !