BSM searches at HERA

John MartinUniversity of Toronto / ZEUS

for H1 and ZEUS

LISHEP 2006 J. Martin 2

Running conditions

HERA-II running very well Lumi high and still increasing

for both e+p and e-p (1.5 pb-

1/day achieved) Polarization at ~ 40% Expect >600 pb-1/expt. from

HERA-II by June 2007 (HERA-I was ~120 pb-1/expt.,

almost all e+p)

e-p 215 pb-1

2005

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Outline

General BSM searches Intriguing excess in isolated lepton events? Multi-lepton events

Search for eq type resonances HERA good for single particle production with

Yukawa coupling to eq LQ, Rp violating SUSY, LFV Gaugino and gravitino searches

Contact interactions Magnetic monopoles

NB: HERA generally has little SM background for BSM searches

Q2

e e,

p

xP

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General search

H1: model independent search for new phenomena by topology (as D0)

isolated, high PT particles: e, , , jet,

PTpart > 20 GeV, 10 < part < 140, D(- )part >

1.0

use probability estimator sensitive to narrow resonances, unusual events, broad signals similar sensitivity to dedicated searches

basic agreement with SM, except …

-j- : 4 data / 0.8 ± 0.2

Data from HERA-I

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Intriguing excess at H1…

Isolated leptons and missing PT

X

e, SM W production ~ 1 pb-1

Background from mis-measured DIS and di-lepton events

H1

e+p

e-p

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The latest H1 numbers

Choose cut at PTX >25 GeV, ~ best discrimination

between background and decay of a heavy particle, like top.

% of SM expectation from W production

3.4 excess

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But ZEUS…

H1 continues to see an excess in e+p (recall HERA I was almost all e+p), but not in e-p

ZEUS doesn’t confirm H1 and ZEUS expectations from SM agree for electron

analysis ZEUS muon analysis not yet finished

Still a puzzle, more data needed

Isolated e candidates 12 < PTX < 25 GeV PT

X > 25 GeV

ZEUS (prel.) HERA I 99-00 (66 pb-1) 1 / 1.04 ± 0.11 (57%) 1 / 0.92 ± 0.09 (79%)

ZEUS (prel.) HERA II 03-04 (40 pb-1) 0 / 0.46 ± 0.10 (64%) 0 / 0.58 ± 0.09 (76%)

ZEUS e+p data with similar cuts, purity:

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Isolated events with PT,miss

hadrons use 6 jet-shape variables

to suppress QCD background

For PTX> 25 GeV

ZEUS observes 2 events expect 0.12 0.02 Anomalous top, stop, another

heavy particle?? But, H1 sees no events

Both Hera-I data, await HERA-II results…

What about the channel?

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Anomalous FCNC couplings Search for single top production via

W decay to e, , or jets

high PTX ( > 40 GeV, ZEUS)

H1 cuts Mt > 140 GeV

SM background negligible:

No evidence found, set limits H1 excess needs tu ~ 0.2, still just about compatible with FCNC top production

Iso-lepton events: single top?

Wbtu *

fb1 Xbtep

LISHEP 2006 J. Martin 10

Or bosonic stop decay?

Consider model with :

For bosonic decay, slight excess only in jPT

miss channel

No excess in ej channel

Iso-lepton events therefore unlikely to arise from bosonic decay of stop

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Search for 2 leptons (PT1 , PT

2 > 10, 5 GeV) in sample of 209 pb-1 (45 pb-1 e-p, 164 pb-1 e+p) - interactions ~ 1pb-1

Overall agreement with SM:

But, for PT > 100 GeV : Nobs = 4 (3 ee, 1 e Nexp = 0.81 0.14

3 ee, 3 eee, 2 eevents withM12 > 100 GeV

Multi-lepton events (H1)

e+p

H1 excess,not in ZEUS

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H1 analysis extended to include 05 data no new 2e/3e event at high M12 one new eμμ event at Mμμ > 100 GeV one new eμμ event at Meμ > 100 GeV

for ΣPT > 100 GeV:

Nobs = 4 Nexp = 1.1 0.2

highest ΣPT events appear in e+p collisions

Multi-lepton events (update)

(275 pb-1)

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Doubly charged Higgs?

H++(--) occurs in BSM models extending the Higgs sector, such as L-R symmetric models

Search for high mass di-leptons with same charge as beam

Only 1 ee event found, no ee events anomalous multi-lepton events unlikely to be

doubly charged Higgs, so set limits LEP, Tevatron better except for off-diagonal

couplings

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Generic Leptoquarks Search for resonance in e-jets, e-

Likelihood analysis in Mej, cos*

e+

e

LQ

LQ

q

q

LQ

LQ

depend on Yukawa coupling,

LQe

q

e,

q

LQ

e+

e

q

q

LQ

e

q

q

e

Coupling limits for BRW LQs

7 scalars, 7 vectors

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Comparison to Tevatron

HERA complementary to Tevatron: Tevatron good for high BR

to eq. Background is severe for q decay of LQ

HERA can reach to low BR to eq for reasonable coupling

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LQ mediated LFV

Search for high PT After optimizing cuts:

ZEUS: 0 candidates (SM: 0.43±0.08 , 2.3±0.5 ) H1: 1 candidate (SM: 0.56±0.16)

Low mass: set limits with ,eg, eq = q , q

High mass: set bounds on eq lq / M2LQ(TeV-2)

e: low energy limits generally better e: ZEUS results generally better

eb b

eb s

Similar results from H1best non-ZEUS limit

ZEUS limit

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R-parity violating SUSY

At HERA probe:

Search in both l-jet and gauge decays (multi-jets and leptons)

No evidence found at ZEUS or H1

e+ d u Lj via ’1j1

e- u d Rk via ’11k

~

~

'

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Limits largely independent of MSSM parameters Improved limits from HERA up to 255 GeV for

Coupling limits in MSSM H1: unconstrained model with

sfermion masses free parameters, gluino mass ~ M3 at EW scale (common gaugino mass m1/2 at GUT scale)

ZEUS: stop search with 1st and 2nd generation squark masses set to 1 TeV

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in mSUGRA assume also a common scalar mass m0 at GUT scale (gives a 5 parameter SUSY model)

H1 HERA-I data: LEP limits better except for stop Tevatron limits weaker

due to large branching ratio to jets + missing ET

HERA-II will improve sensitivity to RPV stop

Limits in mSUGRA model

L3 (tan = 2)

D0 Run Ij=1,2

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Gaugino production

Production by RPV t-channel slepton exchange

Search in ejj channel with multi-variate discriminant against NC DIS background

No deviation from SM

ZEUS Prelim., LP05

HERA extends LEP limits in part of parameter space

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For small m: neutralino masses up ~ 120 GeV are excluded for ’ = 1.0 Complementary to Tevatron,

where production is by pairs or

If gravitino is the LSP

Gauge mediated symmetry breaking (GMSB) has N extra “messenger” fields of mass M to transmit the SB NLSP is neutralino or slepton

Search for high PT + missing ET (bkgrd: radiative CC)

1

~ 02

~1

~

D0 bound

D0 bound

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Excited fermions

Fermion substructure excited fermions

For f/=1/MF* , 95% upper limits: e* 250 GeV (H1) q* 205 GeV (ZEUS) * 135 (f=f’), 158 (f=-f’) GeV (ZEUS)

for *, e-p 100x more sensitive than e+p

await HERA-II e-p analysis

..22

1 ** chFB

YfgWgfFL LRFF

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Contact interaction

HERA-I form factor fit gives Rq < 0.85 . 10-18 m Can also set limits on eqeq contact interactions

e-

e+

sRLji

jiL

,,,

4

Pari

ty c

onse

rvin

gu q

uark

only

APV

lim

its

Similar limits from LEP, Tevatron

n extra dimensions? Graviton exchange effective coupling

nD

nP MRM 22 ~

1,4

DSS

G MMM

Limits close to 1 TeV

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Magnetic monopoles?

Dirac monopoles: large magnetic charge, highly ionizing Some BSM models predict light monopoles Could stop in beampipe and stay trapped

Cut 1994-7 beampipe into strips passed through superconducting coil system sensitive to 0.1gD

4/2Dg gecgD 2/

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Summary

Many BSM scenarios have been studied at HERA Most results still from HERA-I (~120 pb-1/expt, almost all e+p) Competitive and/or complementary to LEP, Tevatron

Only possible sign of BSM physics are the anomalous W-like events from H1: need more data

HERA-II will provide a data set of > 600 pb-1/expt with lepton polarization, both e+p and e-p new sensitivity to BSM physics with higher cross section in e-p Still some chance of a discovery before the LHC