Transcript Searches for New Phenomena

5th Rencontres du VietNam – New Views in Particle Physics
Hanoi, 5-11 August 2004
Searches for New Phenomena :
Where do we stand …
and what we might learn within the coming years …
Emmanuelle PEREZ
CEA-Saclay, DSM / DAPNIA / Spp
Rencontres du VietNam, Hanoi
1
10 August 2004
Searches for New Physics : why, where, how…
Mechanism of the EW symmetry breaking ?
 Higgs (i.e. fundamental scalar) ? Find it…
#doublets, triplets ? CP ?
 structure of the Higgs sector ?
 solution of the hierarchy problem ? SUSY  MPl ? “Little Higgs”   10 TeV ?
extra dimensions  no hierarchy ?
 no Higgs ? Dynamical breaking ? ( H ~ condensate )
extra-dim physics ? ( H ~ Gauge Field|4d )
In most scenarios, new physics is expected at the TeV scale.
Also hoped for, that NP might answer some of the questions unexplained by the SM.
Various strategies to track new physics, e.g. :
- high precision measurements ( need good theoretical control )
- rare decays (K & B) , LFV processes
- searches for Dark Matter
- searches at high energy colliders  Tevatron, HERA
- model driven searches
- exploit at best the experimental knowledge of our detectors
Some complementarities between these different approaches.
E. Perez
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Good performances of our facilities !
_
Tevatron pp, s = 1.96 TeV CDF & D0
Run I (92-96) :  110 pb-1 / exp
Restart in may 2001   0.6 fb-1 delivered
Tevatron Run II
1032 cm2s-1
6.1031
HERA
ep, s = 320 GeV
until summer 2000 :  120 pb-1 / exp
Serious background problems at the
restart (fall 01)
Required
time,
now solved
1032 cm2 s-1
threshold broken
on July 16th !
HERA is
now operating
with twice
the 2000
peak lumi
Peak lumi
Peak lumi average
2.1031
H1 &
ZEUS
2004
HERA-II
(e+ p)
2003
2002
HERA-II analyses : up to  50 pb-1
Analyses presented here  200 pb-1
of Run II data (2002 & 2003)
NB: expect several new results in the coming weeks ! some with up to  350 pb-1 !
+ LEP data ! Very relevant constraints on NP !
E. Perez
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some final combinations are still to come
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Hunting the SM Higgs Boson
• Status :
Direct searches at LEP  MH > 114.4 GeV @ 95% C.L.
EW fits ( latest Mtop = 178.0  4.3 GeV) : MH < 237 GeV
(LEP EW WG, April 2004)
LEP final combination for MSSM Higgs coming soon…
(new Mtop required new databases with , BR etc…)
LEP is finalizing investigations of non-standard
scenarios (invisible h, bosophilic Higgs, CP-violation…)
• Until the start-up of (physics at) LHC, Higgs searches
are in the hands of the Tevatron experiments :
a few
10-1
pb
gg  H
HW
“Light” Higgs, M < 130 GeV :
H  bb
• Best S/B in leptonic W/Z decays
• Large bckgd from W/Z + jets  b tagging !
• Importance of a good mass resolution !
H bb
“Heavy” Higgs, M > 130 GeV :
H  WW
E. Perez
MH (GeV)
H  WW(*)
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Clean dilepton + ET,miss signature
Tevatron Searches for a light SM Higgs
WH  bbl with l = e,
First analyses exist !
Exploit kinematics and
topology, require
1 (2) b-tag in D0 (CDF)
Still a factor ~ 50 larger
than SM predictions !
CDF Run II Prelim., 162 pb-1
Exp. limit
Obs. limit
(WH) x BR < 5 pb
for MH = 115 GeV
(also T  WT lbb)
- Full GEANT simulation, 396 ns, RunIIb Si.
- experience from current data (bckgd, (Mbb) )
Integrated Lumi (fb-1)
(impact of cancellation of Si. upgrades still to be assessed)
End 2008 :
10 between
4 & 8 fb-1
E. Perez
Challenging anyway !
No “golden” channel …
8.5
5
06
07
08
09
Fermilab-Pub-03/320-E
8.5
4.4
05
Updated sensitivity study
4.4 fb-1
5
Combining
WH & ZH,
D0 & CDF
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Tevatron Searches for a Heavy SM Higgs
Final states investigated : ee + ET,miss, e + ET,miss,  + ET,miss
( H  WW* )
(combined ll + ET,miss in the CDF analysis)
L  160 – 200 pb-1
Backgrounds from W + jet(s), Z/DY, WW
e
Exploit spin correlations : leptons small
No excess w.r.t. SM predictions…
x-section enhanced
w.r.t. SM via heavy
4th generation quarks
in the ggH loop
Will soon be sensitive …
Higgs = condensate RtL
(H) x BR(H  WW) < 5.6 pb
for MH = 160 GeV
i.e. a factor ~ 20 larger than SM predictions
SM Higgs : need ~ 4 fb-1 for sensitivity @ 95% CL
Perez
E.E.Perez
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SUSY & Non standard Higgses
• Higgs in SUSY models : extended Higgs sector h, H, A, H 
Two free parameters, e.g. MA and tan = vu/vd
- Often : one Higgs  looks like HSM
 95% CL sensitivity over the allowed M range_
- Else : low (W+Higgs) but (Higgs+bb)
_
enhanced at large tan  4b !
- Difficult cases : SM = H heavy, or bb
look for A  , use partially reco’ed mass
• Doubly charged Higgses :
CDF Run II
240 pb-1
D0, hep-ex/0404015
CDF, hep-ex/0406073
MSSM constraints
Mh < 135 GeV
  e/ + had.
For tan = 30,
sensitivity
still a factor
~ 10 away
from MSSM
H++ appear in e.g. L- R symmetric models :
SU(2)L x SU(2)R broken by Higgs triplet
(or extended Higgs sector by a triplet with Y=2).
136 GeV
Might explain small (Majorana)  masses.
Evidence of 0 at the Heidelberg-Moscow experiment ?
H++ couples to fermions via unknown Yukawa couplings, not related
to masses. SUSY L–R models predict low H++ masses, below  1 TeV
113 GeV
 Search for (high mass) same-sign dileptons
(CDF also searched for quasi-stable H++ , M > 134 GeV)
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H++ and the HERA multilepton events
Events with  2 leptons in final state. Mainly produced via 
H1 data 94-00 : excess of 2e+3e events at
high M12 = mass of two highest PT e
No such
obs. / exp.
H1 94-00 data
excess
expt
seen in
H1 ( 115 pb-1)
The H1 evts
selection
ZEUS
are not
2e, M12 > 100 GeV 3 / 0.30  0.04
data
consistent
3e, M12 > 100 GeV 3 / 0.23  0.04
(different angular
with
ranges in both
H1, EPJ C31 (2003) 17
++
e  H (e)  ee(e)
analyses)
H1 analysis extended to include 45 pb-1 of 03-04 data
163 pb-1 H1 Prelim.,
Extended to other 2l & 3l topologies :
HERA I+II
ee, , e, eee, e, ee
• no new 2e / 3e evt at M12 > 100 GeV
(but one high mass 3e event …)
• one e event at M > 100 GeV
2l + 3l
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E. Perez
Altogether, at PT > 100 GeV :
Nobs = 4, Nexp = 0.61  0.11
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

e
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Hunting Supersymmetry…
For the last  20 years, SUSY has been “the standard non-standard theory”…
-
Provides a technical solution for the “hierarchy” problem
The only symmetry which prevents to add a mass term m2 H+H
Unification of couplings : works well with SM + SUSY
Possibly provides an additional source of CP
Different models and phenomenology depending on :
- the SUSY breaking mechanism (gravity mediated, or gauge interactions, anomalies ?)
- whether or not the LSP (Lightest Supersymmetric Particle) is stable
 Typical signatures with ET,miss , or , or large multiplicities or etc…
LEP
All sparticles (but the gluino)
democratically produced.
Strong bounds on constrained
models.
Mass bounds  100 GeV
NB: no model independent
bound on the LSP mass
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Tevatron
Production of squarks & gluinos
dominates – but large bckgd
Cleaner signatures from 
production (e.g. multileptons)
but smaller cross-sections
HERA
Most relevant process is the
RpV resonant production of a
squark
SUSY might also manifest itself in precision measurements,
rare decays, Dark Matter searches etc…
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SUSY : GMSB at the Tevatron
Gauge Mediated SUSY Breaking :
(10-6 expected !)
- naturally avoids large unwanted FCNC
- revival of interest in GMSB following “the” CDF Run I event
NB : LEP analyses made the GMSB interpretation unlikely
~
- LSP = gravitino G ( < keV), pheno. depends on NSLP
~
0
When NLSP = Neutralino :  1  G
Inclusive search for  + ET,miss – might come from 02 1 production
(no spectacular eeET,miss event observed so far in Run II data)
Large instrumental background (jets faking a ), determined from the data.
NB : Tevatron will provide very relevant data for
the jet 0 fragmentation… cf H   @ LHC !!
Interpretation within
a “minimal” GMSB
model : (D0 Prelim, 185 pb-1)
M(01) > 105 GeV
M(1) > 192 GeV
185 pb-1
01 mass (GeV)
Similar results from CDF
Perez
E.E.Perez
World best10 limit !
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SUGRA-like SUSY at the Tevatron
LSP usually the 01. RPC  ET,miss
• Pair production of q~ / g~
large , Signature jets + ET,miss
D0 Run II, Prelim., 85 pb-1
Z () + jets
Large bckgd
from multijet prod. !
search domain
~
D0 : pair production of squarks, q  q 01
Interpretation
q~ > 292 GeV, (for some values
within mSUGRA: ~
g > 333 GeV of parameters)
Better than in Run I… but still stronger LEP
bounds in this very constrained model !
~ sleptons +   squarks )
(roughly,   g,
CDF : light sbottom squarks (156 pb-1)
~
~
~
g pair production, g  bb1
D0 Prelim., 147 – 250 pb-1
• Chargino + Neutralino production ( 02 1 )
 trilepton final states
Low  x BR but clean signatures
eel + el + l +
same-sign 
Need high L and combined analyses
Getting close to the unexplored mSUGRA region !
E. Perez
11 tan 
NB : importance of  id. at large
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New Physics Searches in rare decays
• bs
(examples)
 stops + charginos
BR (SM) = (3.70  0.30) x 10 –4
Good agreement with CLEO & Belle :
BR (exp) = (3.34  0.68) x 10-4 i.e. not much room for SUSY here …
Note: SUSY constraints are model-dependent
(mixing in the down squark sector)
• Bd,s  +-
SM  (3.4  0.5) x 10
J/

-9

SUSY :  (tan )6 could reach 10-6 !
’
tan 
SM signal
X 106
 (1S,2S,3S)
M (GeV)
_
Tevatron :  (bb)  100 b  sensitivity !
For Bd0 :
Slightly
New CDF upper bounds on BR( Bs,d   ) :
better
-7
hep-ex/0403032
Br(Bd  ) < 1.5 x 10
than
Submitted
to
PRL
Belle 2003 !
Br(Bs  ) < 5.8 x 10-7
Similar sensitivity from D0
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The muon anomalous magnetic moment
aHAD ?
(g-2) sensitive probe to New Physics …
But uncertainties on the SM prediction :
from    had
from e+e-  had
Recent developments :
Disagree…
• Summer 03: revised analysis of CMD-2 data  better agree with , but still…
• exp. measurement of E821 using - : average value goes up a bit
(+ & - combined)
aexp = 11 659 208 (6) x 10-10
0.5 ppm !
• underestimation of isospin breaking corrections to the  data due to -0 mass
splitting? … controversial … (Davier, hep-ex/0312065; Ghozzi & Jegerlehner, DESY 03-155)
• reevaluation of part of aLBL(Melnikov & Vainshtein,
1.4
hep-ph/0312226)
would shift the expected value by ~ + 50 10-11
• e+e-  4 at BaBar using ISR photons :
somehow in-between e+e- & , closer to  data …
• (e+e-  ) by KLOE at DANE (s  1 GeV) :
confirms the other e+e- measurements …hep-ex/
2.7
Winter 04
0407048
Still puzzling… but new data from BaBar and KLOE might help understand…
E. Perez
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SUSY Searches and a
In any case, aSUSY cannot be too large ! e.g. aSUSY < 80 x 10-10 (very conservative)
Martin & Wells,
aSUSY > 0
| aSUSY |  tan  / m2SUSY
PRD67, 015002 (2003)
500
>0
tan  = 50
tan  = 20
0
M ( chargino )
1000
Encroaches on the “trileptons” domain of the Tevatron
If aSUSY “signal” is confirmed :
- upper bounds on M(chargino) & M(sleptons)
 encouraging for collider searches
 (p) (pb)
0
At large tan  :
difficult to have chargino & sleptons both light
Baltz & Gondolo, PRD67, 06503 (2003)
10-6
-10
~
although ’s and l might be too heavy for Tevatron… 10
- encouraging for direct 0 CDM searches
(squarks & Higgs not too heavy i.e. (p) not too small)
NB : however can have large (p) while aSUSY  0 …
E. Perez
e.g. if aSUSY > 11 x 10-10
14
CDMS II,
Edelweiss II
100
M ( LSP )
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1000
Constraints & Sensitivities on mSUGRA
If DM = 01 : 2 bounds from WMAP 0.095 < LSP < 0.13
White domains allowed if 01 is only a part of the CDM
(Antares, Icecube)
“focus point”,   WW
Very precise !!
“funnel”,
  A
 from Sun
tan  = 10
LSP
too
large
100
sfermion
exchange
& ~
-l
coannihil.
10
1000
m0 (Gev)
m0 (Gev)
1000
tan  = 55
CDMS II,
Edelweiss II
1 x 10-8
Bs   < 2 x 10-8
Run II
3-leptons
100
100
Tri
100
m1/2 (GeV) 1000
leptons
- ~
 co-annihilation
Run II
aSUSY not too large Requires m  O(10 GeV)
CDMS II,
Edelweiss II
m1/2 (GeV)
1000
Plots from L. Roszkowski hep-ph/0404052; bounds from V. Bertin
et al. hep-ph/0204135, Run II Workshop hep-ph/0003154
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Beyond Minimal SUGRA…
mSUGRA is becoming very tightly constrained… But (examples of way-outs) :
• Relaxing universality : constraints on LSP much more easily fulfilled
Belanger et al.,
hep-ph/0407218
e.g. increase M1 or decrease M3  m( ) decreases  co-annihilation  
Lower M3  ~q & ~g searches at the Tevatron not so severely constrained by LEP…
• SO(10) SUSY Grand Unified Theories
Large interest, e.g. in view of neutrino masses !
Minimal models not so severely constrained by LSP (lighter A)
1st & 2nd gene. sfermions are heavy ! i.e. no effect on (g-2)
Large tan  sensitivity of Bs  at the Tevatron !
Direct DM searches :   10-9 – 10-7 pb, i.e. encouraging
May see   e in the difficult “funnel” region !
Yt = Yb = Y = Y
m2atm  m2t / MGUT
e.g. Masiero & Vempati, hep-ph/0407325
• DM mainly consists of something else …
(axions, gravitinos, axinos, Kaluza-Klein states,…)
Stable stop
above  100 GeV
~
 In some cases, might expect stable ~ or t
Search for charged slowly moving particles (TOF)
 0  DM if Rparity = (-1)3B+L+2S is not conserved …
Might affect rare decays e.g. K 
For neutrinos : mechanism to generate (Majorana) mass terms
At colliders : single production of SUSY particles, less Emiss
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Rp and the HERA events with lepton + PT,miss
_
HERA I & II, e & 
No such excess in ZEUS
(but candidates in  channel)
H1 in HERA-II data
(45 pb-1) :
8 new events,
3 at PTX > 25 GeV
H1 Prelim.,
163 pb-1
(includes e-p HERA-I data)
E. Perez
M(sbottom) (GeV)
e
Rp
Example : resonant stop production at HERA via ’131
Assume heavy gauginos & light sbottom.
~ ~
Dominant decay : t  b W  jet + P T,miss + W
H1 Collab.,PLB 561,
Main bckd when W  l :
-1
HERA-I, 105 pb : 241 (2003)
• Data not consistent
PTX
H1 e+ p data
Combined e & 
~
with
t
production (3 chan)
PTX > 25 GeV 10 / 2.92  0.49
• Other interpretations
(W prod)
X > 40 GeV
P
6
/
1.08

0.22
T
 1 pb
considered e.g. FCNC top
At PTX > 25 GeV :
Nobs = 14
Nexp = 5.1  1.0
17Stay tuned !!!
(HERA-I)
’131 = 0.3
H1 Collab.,
hep-ex/0405070
M(stop) (GeV)
Lepton + Quark Resonances : Leptoquarks
Apparent symmetry between the lepton & quark sectors ?
Exact cancellation of QED triangular anomaly ?
cf Rp
squarks
ee
• LQs appear in many extensions of SM
(enlarged gauge structure, compositeness, technicolor…)
• Connect lepton & quark sectors
• Scalar or Vector color triplet bosons
• Carry both L and B, frac. em. charge
ZEUS, PRD68 052004 (2003)
 (unknown) Yukawa coupling lepton-quark-LQ
ej channel at HERA
ZEUS e+p
94-00
jj channel at Tevatron
CDF Run II Prelim.,
191 pb-1
Not an easy channel !
Look for a resonant peak in M spectra
E. Perez
 reduced background
18
Large bckgd, but well controled
(LP’03)
e = BR( LQ  eq )
e
1
1
0.5
0.5
0
Run II bounds
D0
238
CDF (LP’03)
232
D0 (eejj)
145
197
D0 (ejj)
CDF
117
D0 Run II + Run I :
M > 253 GeV for =1
• Tevatron probes
large masses for large
e independently of 
 = BR (LQ  eq)
Constraints on 1st & 2nd generation Leptoquarks
• HERA better probes LQs with small  provided
that  not too small
 Complementarity of both facilities
CDF II Prelim,
198 pb-1
MLQ (GeV)
NB : at HERA, e+ / e- +
polarisation could help in disentangling
the LQ quantum nbs
2nd gene,  = 1
2nd (and 3rd ) generation LQs also
looked for at the Tevatron.
For LQ  j, similar sensitivity as
for LQ  ej.
M(LQ2) > 241 GeV
E. Perez
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Searches for new resonances : dilepton
• New heavy gauge boson Z ’, e.g. L-R models, or E6 GUT inspired, Little Higgs Z’…
• Kaluza-Klein gravitons in some extra-dim. models
• (Color-singlet) technirho in Technicolor models …
D0 & CDF searched for ee &  resonances :
Main bckgds @ high M :
q
cotan 
“Little
_
Higgs”
q
ZH
•
CDF II Prelim, 200 pb-1
Z’H  ee
ee
DY,
QCD “fake”

DY
Z’ Run II direct
bounds between
570 & 780 GeV
For E6 inspired models,
already competitive
with indirect LEP
bounds (430-670 GeV)
First constraints
(direct) on “Little (although “minimal”
models predict
Higgs” models !
heavier ZH, 2-6 TeV)
E. Perez
E. Perez
20

Z’ Bounds
ee
95% CL
200 pb-1
200 pb-1
D0 Run II Prelim.
SM couplings
E6, 
E6, 
E6, 
780 GeV
Kaluza-Klein Gravitons
Why is the gravity so weak, i.e. MPl >>> MEW ?
All attempts  higher dim. space, with n compactified extra dimensions
• “Localized gravity” on a “brane” at d  0 from our brane; propagation of gravity
in the extra dim is exponentially damped due to the (tuned) space-time metric
PRL 83 (1999) 3370;
Randall & Sundrum models; “usual” version : n=1, Rc  Planck length
PRL 83 (1999) 4690
• “Strong gravity” ; fundamental scale ~ TeV; gravity appears weaker in 4d because flux lines
are “diluted” in large extra dim. Large Rc  0.1 mm. Not excluded by gravity measurements
Arkani-Hamed, Dimopoulos, Dvali, PLB 429 (1998) 263 revived ideas from Antoniadis, PLB 246 (1990) 377.
In localized gravity :
Spin 2
resonance
G(k) heavy, G(1)  TeV
Coupling of G(k) to SM fields  TeV
(determined by some model param, k/MPl  0.1)
For k / MPl = 0.1 : masses below
690 GeV ruled out at 95% C.L.
Coupling k/MPl
Graviton propagate in extradim  Kaluza-Klein modes
Most stringent
collider bounds
(also D0 Prelim, ee final states)
so
E. Perez
21 far.


345 pb-1
ee
G(1) mass (GeV)
Kaluza-Klein Gravitons in Large Extra Dim
Very different phenomenology if “large” extra dimensions.
4+n dim
4 dim
Massless graviton G(k)
Massive graviton
G(k)
G(k) with quantized momentum qT = k/R in extra dim :
m2 = 0 = ( E2-p4d2 )-qT2  m4d2 = qT2
R  0.1 mm i.e. 1/R  1 meV  Mass “continuum”,
“first” states very light !!
ADL Prelim., Summer 04
Coupling of G(k) to SM fields  1 / MPl  G(k) stable !
e+e-   G (k)
with momentum qT = k/R
with m2 = k2/R2
• Direct production at colliders
compensated by huge multiplicity of states
1 / MPl
ee & 
• Indirect effect on SM aplitudes due to virtual exchange :
D0 Run II Prelim.
200 pb-1
SM + MS = 1.1 TeV
Effective coupling : A   / MS4
QCD
“fake”
Perez
E.E.Perez
n=2 : MD > 1.6 TeV
n=4 : MD > 0.9 TeV
D0 Run II + Run I, ee &  : MS > 1.43 TeV
Most stringent collider bound
22
Tevatron 2 fb-1 
MS upduto
 2 TeV
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08/04
Conclusions
The search for new physics is a very active field.
Tevatron & HERA are working very well, the experiments might “see” something
in the near future !
Constraints set on many models, often the most stringent up to date.
The example of SUSY searches shows the nice complementarity between
different experimental approaches :
direct searches, rare decays, precision measurements, Dark Matter searches …
“Searches” is a very rich field of physics.
It is likely to remain the case – even more ? – after direct evidence for
New Physics at (e.g.) the LHC
( if SUSY : consistent value for LSP, additional CP phases, mixing in the
squark sector, possible relations with the  mixing etc …)
No doubt that using most of the experimental data to reach the understanding
we aim at will be fun !
E. Perez
23
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Backup & Divers…
E. Perez
24
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“Signature Based” Searches for NP
Pionnered by DZero with
(Quasi) “model-independent” search for new physics :
the full Run I sample
• definition of objects (e, , , , jet, W, Z, …)
D0, PRD64, 012004 (2001)
• look at data vs SM in all “channels” with > 1 object
• in each channel, find the part of  space with largest deviation (e.g. in M,  pT )
• quantify the agreement using “Gedanken” (Mock, MC) expts
# Events
Applied recently to the full sample of H1 data
2B
H1, contrib paper #195
• overall very good agreement H1 data / SM
• retrieves the “lepton-jet-ET,miss” and
“multi-electron” anomalies
3B
-j-
H1 Prelim
45 pb-1
HERA-II
Requires a very good understanding of
detector
& backgrounds !
E. Perez
4B
(dedicated analyses might be more sensitive)
25
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Excited quarks & other j-j resonances
q
• Dijet resonances predicted in various models
q*
g
- New fermions, e.g. excited quarks
q
g
 expect signal in q /Z, q W depending on fs vs f & f’
fs / 
- new gauge bosons, Z’, W’ (but signal mainly in the dilepton channels)
- new massive colored bosons, e.g. SU(3)1 x SU(3)2  SU(3)QCD
Narrow
resonances
compared to
(Mjj)  10% Mjj
( chiral color, colorons, topgluons…)
• Axigluon & (flavor univ.) colorons :
assuming
(qqg) = (qqG)
M > 1130 GeV
First direct bound > 1 TeV !!
• Excited quarks :
 X BR (pb)
• Look for a narrow resonance in the di-jet spectrum : use a simple background
parametrization for d/dM and search for bumps  resolution
CDF Run II, 75 pb-1, Prelim.
10
1
M > 760 GeV
(f=f’=fs=1,  = M)
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26
200
1100
Resonance
mass
(GeV) 08/04
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du VietNam,
HERA events with isolated lepton + PT,miss
HERA I data
HERA I
E. Perez
27
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