Searches andSearches and EW EW physics at HERAphysics at HERA

55thth Rencontres du VietNam 2004 Rencontres du VietNam 2004New Views in Particle PhysicsNew Views in Particle Physics Sascha Caron (NIKHEF) (former Aachen)

P(920 GeV) e(27.5 GeV)

HERA

Sascha Caron (NIKHEF) at Recontres du Vietnam 20042

HERAHERA

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)

HERA collides 27.5 GeV e±

with 920 GeV protons at √s=320 (300) GeV

Lum

i pro

duce

d by

HE

RA

(pb

-

1)

day of running

HERMES

HERA-BHERA2 – luminosity, polarizede beam and detector upgrades

Sascha Caron (NIKHEF) at Recontres du Vietnam 20043

HERA physics on 1 transparencyHERA physics on 1 transparency

Q2 = - squared momentum transfer between e and p

NC deep inelastic scattering CC deep inelastic scattering

W production Multilepton production

Sascha Caron (NIKHEF) at Recontres du Vietnam 20044

Searches and EW physics at Searches and EW physics at HERAHERA

o Electroweak tests in deep inelastic scattering

o Systematic tests of the SM at high PT

o Measurements of W production and multi-lepton processes

o 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 20045

(Deep) inelastic scattering at HERA(Deep) inelastic scattering at HERA

NC

CC

HERA probes eq interactionsat photon virtualities Q2

from ≈ 0 (photoproduction, γq)up to 4*104 GeV2

unique facility

Test of EW sector withW (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 20046

Contact Interactions Contact Interactions

Limits on quark radius(classical form factor):Rq< 10-18 m (ZEUS and H1)or vector contact interaction couplings of up to 5 TeV

Results on: Leptoquarks,general Contact Interactions,Large Extra Dimensions,Quarks RadiusNew interactions between

e and q can be modeled by 4-fermion contact interactionsParametrized by additional terms in the lagrangian

Sascha Caron (NIKHEF) at Recontres du Vietnam 20047

A general Search for A general Search for new phenomenanew 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 20048

A general searchA general searchfor new phenomenafor new phenomena

Mall and ΣPT

distributions are systematically investigated using a search algorithm:

Find in each channelthe region with thegreatest deviation

Sascha Caron (NIKHEF) at Recontres du Vietnam 20049

A general search for A general search for new phenomenanew phenomena

Derive for each event class the probability P to observea deviation anywhere in the spectrum as large as found inthe data

Repeat the whole analysis with many MC (pseudo data) experiments each with the H1 luminosity

Smallest P found inμ-jet-ν, e-jet and e-e channels

About 3% (Σ PT) and 25% (Mall) ofMC experiments have a deviationlarger than that of μ-j-ν final state

^

^

Sascha Caron (NIKHEF) at Recontres du Vietnam 200410

Isolated lepton eventsIsolated lepton events

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

e p

ep → jet (PT,X)+ PT,miss+ lepton

Results from dedicated analysis:HERA 1:

PTx>25 GeV e channel μ

H1 e+p

(45 pb-1)

3/0.74±0.15 0/0.76±0.1

HERA 2:

main SM contribution is W production

Agreement in hadronic channel(with large background)

excess of events at H1 no excess in HERA1 ZEUS data clarification needs more lumi

(observed/expected)

Sascha Caron (NIKHEF) at Recontres du Vietnam 200411

Anomalous top productionAnomalous top production

Compare the l-jet-ν events with models, e.g. single topproduction with anomalous couplings between tuZ andtuγ

Selection cuts optimized fortop

H1: excess in leptonic channels (3e, 2μ with SM exp. 1.3 ± 0.2) no excess in hadronic channelZEUS: no excess in hadron or lepton channels

Limits on top cross sections and couplings

Sascha Caron (NIKHEF) at Recontres du Vietnam 200412

Multilepton eventsMultilepton events

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

Measurement of multilepton eventsProcess: ep → ll (e) mainly via 2-photon collisions

Some interesting events at high mass:

No excess in muon channels

Sascha Caron (NIKHEF) at Recontres du Vietnam 200413

SUSY@HERASUSY@HERAHERA: RP violating SUSY→ single production of squarksvia couplings Λ’ijk

Also interpretations in terms of MSUGRA model parameters

For λ’=0.3 : Msquark>275 GeV forall squarks types in nearly full parameter space

small couplings: improvement of indirect low-energy limits

Large variety of squark decay modes→ many final states are considered

Example: sbottom production

Sascha Caron (NIKHEF) at Recontres du Vietnam 200414

SummarySummary

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 !