1. 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)

2. Sascha Caron (NIKHEF) at Recontres du Vietnam 2004
HERA
HERMES
HERA collides 27.5 GeV e±
with 920 GeV protons at
√s=320 (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 e+p (300 GeV)
≈15pb-1 e-p (320 GeV)
≈65pb-1 e+p (320)
HERA 2:
≈50pb-1 e+p (320)
day of running
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

3. 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
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

4. 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
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

5. (Deep) inelastic scattering at HERA
HERA probes eq interactions
at photon virtualities Q2
from ≈ 0 (photoproduction, γq)
up to 4*104 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)
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

6. Sascha Caron (NIKHEF) at Recontres du Vietnam 2004
Results on: Leptoquarks,
general Contact Interactions,
Large Extra Dimensions,
Quarks Radius
Contact Interactions
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):
Rq< m (ZEUS and H1)
or vector contact interaction
couplings of up to 5 TeV
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

7. Sascha Caron (NIKHEF) at Recontres du Vietnam 2004
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, γ, ν)
with PT>20 GeV are analyzed
Data is classified to
exclusive channels
Good agreement for
(almost) all channels
Event yields are also available
for HERA2 data!
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

8. Sascha Caron (NIKHEF) at Recontres du Vietnam 2004
A general search
for new phenomena
Mall and ΣPT
distributions
are systematically
investigated using
a search algorithm:
Find in each channel
the region with the
greatest deviation
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

9. Sascha Caron (NIKHEF) at Recontres du Vietnam 2004
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-ν, e-jet and e-e
channels
Repeat the whole analysis
with many MC (pseudo data) experiments each with the H1 luminosity
About 3% (Σ PT) and 25% (Mall) of
MC experiments have a deviation
larger than that of μ-j-ν final state
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

10. Isolated lepton events
ep → jet (PT,X)+ PT,miss+ lepton
main SM contribution is W production
Results from dedicated analysis:
HERA 1:
(observed/expected) e p
PTx>25GeV
e channel μ Τ
H1 e+p
(118 pb-1)
4/1.48±0.25
6/1.44±0.25
0/0.53
ZEUS
(130 pb-1)
2/2.9±0.5
5/2.75±0.2
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
PTx>25 GeV
e channel μ
H1 e+p
(45 pb-1)
3/0.74±0.15
0/0.76±0.1
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

11. Anomalous top production
Compare the l-jet-ν events
with models, e.g. single top
production with anomalous
couplings between tuZ and
tuγ
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
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

12. Sascha Caron (NIKHEF) at Recontres du Vietnam 2004
Multilepton events
Measurement of multilepton events
Process: ep → ll (e)
mainly via 2-photon collisions
Some interesting events at high mass:
Mll>100 GeV
ee channel
eee channel
H1 HERA1+2
(165 pb-1)
3/0.44±0.1
3/0.31±0.08
ZEUS
(130 pb-1)
2/0.77±0.1
0/0.37±0.04
No excess in muon channels
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

13. Sascha Caron (NIKHEF) at Recontres du Vietnam 2004
Example: sbottom production
HERA: RP violating SUSY
→ single production of squarks
via couplings Λ’ijk
Large variety of squark decay modes
→ many final states are considered
For λ’=0.3 : Msquark>275 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
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004

14. Sascha Caron (NIKHEF) at Recontres du Vietnam 2004
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 !
Sascha Caron (NIKHEF) at Recontres du Vietnam 2004