SLIDE 1
MODEL DEPENDENT SEARCHES FOR NEW PHYSICS AT HERA
Giuseppe Barbagli-INFN Firenze
representing the collaborations
Outline:
- Introduction. HERA
- INTRODUCTION. HERA
MODEL DEPENDENT SEARCHES FOR NEW PHYSICS AT HERA Giuseppe - - PowerPoint PPT Presentation
MODEL DEPENDENT SEARCHES FOR NEW PHYSICS AT HERA Giuseppe - - PowerPoint PPT Presentation
MODEL DEPENDENT SEARCHES FOR NEW PHYSICS AT HERA Giuseppe Barbagli-INFN Firenze representing the collaborations Outline: Introduction. HERA Leptoquarks and LFV Excited fermions Anomalous top coupling Contact Interactions. Conclusions
SLIDE 2
SLIDE 3
LEPTOQUARKS
Many extensions of the Standard Model predict Bosons with both Lepton and Baryon numbers. Phenomenological model of Buchm¨ uller-R¨ uckl-Wyler (BRW):
- invariance under SU(3)C × SU(2)L × U(1)Y
- L and B conservation
- 7 Scalar and 7 Vector (4 decaying into both eq and νq)
- fermion number F = 3B + L = 0, 2
- coupling to either LH or RH leptons, not both
- fixed branching ratio into eν 1, 1/2, νq 0, 1/2
F = 0 e−¯ q or e+q ⇒ best sought in e+p F = 2 e−q or e+¯ q ⇒ best sought in e−p Different regimes: MLQ << √s : resonant production, dominated by s-channel
e± qi λeqi LQ λℓqj ℓ qj e± ¯ qj ℓ ¯ qi λeqi λℓqj
MLQ >> √s : both s- and u-channel contribute, analysis in terms of contact interactions.
SLIDE 4
FIRST GENERATION LEPTOQUARKS-1
No excess seen in mass spectra (e-jet, ν-jet). The use of polarization of both signs within the HERA II sample enhances the sensitivity to individual LQ species.
/ GeV
LQ
M 100 150 200 250 300 Events / 20 GeV 1 10
2
10
3
10
4
10 / GeV
LQ
M 100 150 200 250 300 Events / 20 GeV 1 10
2
10
3
10
4
10
NC H1 Data (prelim.) SM SM Uncertainty
Leptoquark Search, HERA I+II
H1
)
- 1
p (449 pb
±
e
/ GeV
LQ
M 100 150 200 250 300 Events / 20 GeV 1 10
2
10
3
10 / GeV
LQ
M 100 150 200 250 300 Events / 20 GeV 1 10
2
10
3
10
CC H1 Data (prelim.) SM SM Uncertainty
Leptoquark Search, HERA I+II
H1
)
- 1
p (428 pb
±
e
SLIDE 5
FIRST GENERATION LEPTOQUARKS-2
200 250 300 350 400
- 2
10
- 1
10 1
/ GeV
LQ
M λ
d) ν u,
- (e
0,L
S H1 prelim. single LQ H1 (94-00) single LQ D0 pair prod. L3 indir. limit
200 250 300 350 400
- 2
10
- 1
10 1
Excluded )
- 1
Leptoquark Search, HERA I+II (449 pb
SLIDE 6
LEPTON FLAVOUR VIOLATION
Mediated by LQs in family non-diagonal models. e± replaced by a µ or a τ in the final state. H1 looked for ep → µX mediated by F = 2 LQ in e−p data. Signature: isolated muon and jet, back to back in events with high missing Pt. SM background: lepton pair production, real W, photoproduction, DIS.
GeV
X µ da
M
50 100 150 200 250 300 350 400
Events / 50 GeV
- 2
10
- 1
10 1 10
GeV
X µ da
M
50 100 150 200 250 300 350 400
Events / 50 GeV
- 2
10
- 1
10 1 10
p
- H1 data HERA II e
SM SM uncertainty
GeV
X µ da
M
50 100 150 200 250 300 350 400
Events / 50 GeV
- 2
10
- 1
10 1 10 Search for Lepton Flavour Violation H1 preliminary
/ GeV
LQ
M
100 200 300 400 500 600
eq
λ =
q µ
λ
- 3
10
- 2
10
- 1
10 1
/ GeV
LQ
M
100 200 300 400 500 600
eq
λ =
q µ
λ
- 3
10
- 2
10
- 1
10 1
H1 HERA I +II (prelim.) single LQ H1 HERA I single LQ ) ν e → D0 pair prod. (qq
e x c l u d e d H1 preliminary
L
S Search for Lepton Flavour Violation
SLIDE 7
EXCITED FERMIONS
Gauge mediated model for compositeness of fermions (Hagiwara et al.): excited fermions with spin and isospin 1/2 with both left-handed, F ∗
L, and
right-handed components, F ∗
R,in weak isodoublets.
Transitions between known fermions, FL, and excited states F ∗, magnetic de-excitation. Λ compositeness scale. Parameters f, f ′ and fs weight factors of the three gauge groups (U(1), SU(2), SU(3)). At least one of f, f ′ and fs must be non-zero. Relations between f, f ′ and fs, fix branching ratios of excited-fermion decays; cross section then depends only on f/Λ.
SLIDE 8
EXCITED ELECTRONS
e* e p γ / Z e, ν γ / Z p, X γ, Z, W
Looked for e∗ → eγ e∗ → eZ with Z → q¯ q and e∗ → νW with W → qq′. No evidence. Improved limits using HERA II.
e* Mass [GeV]
50 100 150 200 250 300 350
Events
5 10 15 20 25 30 35 40 45
e* Mass [GeV]
50 100 150 200 250 300 350
Events
5 10 15 20 25 30 35 40 45
H1 Data (prelim.) All SM
H1
γ e → Search for e* )
- 1
s = 320 GeV, 435 pb √ Search for e*, HERA I+II (
e* Mass [ GeV ]
100 120 140 160 180 200 220 240 260 280 300
]
- 1
[GeV Λ f /
- 4
10
- 3
10
- 2
10
- 1
10
e* Mass [ GeV ]
100 120 140 160 180 200 220 240 260 280 300
]
- 1
[GeV Λ f /
- 4
10
- 3
10
- 2
10
- 1
10
e* Mass [ GeV ]
100 120 140 160 180 200 220 240 260 280 300
]
- 1
[GeV Λ f /
- 4
10
- 3
10
- 2
10
- 1
10 )
- 1
s = 320 GeV, 435 pb √ Search for e*, HERA I+II (
f = + f’
H1
LEP (direct) LEP (indirect) )
- 1
H1 HERA I (120 pb )
- 1
H1 HERA I+II (435 pb (preliminary) )
- 1
CDF Run II (202 pb = 1/(Me*) Λ f /
SLIDE 9
EXCITED NEUTRINOS
ν* e p W ν, e X γ, Z, W
Looked for ν∗ → νγ ν∗ → νZ with Z → q¯ q and ν∗ → eW with W → qq′. No evidence. Improved limits using HERA II. e−p data have the advantage of enhancing the CC cross section.
* Mass [GeV] ν
100 120 140 160 180 200 220 240 260 280 300 320
]
- 1
[GeV Λ f /
- 3
10
- 2
10
- 1
10 1
* Mass [GeV] ν
100 120 140 160 180 200 220 240 260 280 300 320
]
- 1
[GeV Λ f /
- 3
10
- 2
10
- 1
10 1
)
- 1
p, 184 pb
- * at HERA (e
ν Search for
f = - f’
L3
H1
= 1 / M Λ f / * ν
H1
* Mass [GeV] ν
100 120 140 160 180 200 220 240 260 280 300 320
]
- 1
[GeV Λ f /
- 3
10
- 2
10
- 1
10 1
* Mass [GeV] ν
100 120 140 160 180 200 220 240 260 280 300 320
]
- 1
[GeV Λ f /
- 3
10
- 2
10
- 1
10 1
)
- 1
p, 184 pb
- * at HERA (e
ν Search for
f = + f’
DELPHI
H1
= 1 / M Λ f / * ν
H1
H1 paper arxiv:0802.1858
SLIDE 10
ANOMALOUS TOP COUPLING
At HERA top quarks can only be singly produced. SM, single-top production proceeds due to (CC) reaction ep → νt¯ bX. SM cross section at HERA is less than 1 fb ⇒ any observed single-top event must come from physics beyond the SM. FCNC reaction: incoming lepton exchanges a γ or Z with an up-type quark in the proton, yielding a top quark in the final state most sensitive to a coupling of the type tqγ. u-quark dominant at large x ⇒ production of single top quarks is most sensitive to a coupling of the type tuγ. Deviations in terms of couplings of the type tuV (with V = γ, Z0). Effective Lagrangian contains magnetic coupling kg and vector coupling vz assumed to be real and positive. kg and vz zero at tree level and extremely small at the one-loop level in SM.
SLIDE 11
RESULTS
e e γ/Z0 u t κtuγ/vtuZ ¯ q/¯ l q′/ν W+ b
H1 searched for single top: t → bW → ePtmiss jet
- r → µPtmiss jet in a multivariate analysis
Background from SM : mainly real W production. σep→etX < 0.16 pb Most stringent limit to date: ktuγ <0.14
|
γ tu
κ |
- 1
10 1
|
tuZ
v |
- 1
10 1
|
γ tu
κ |
- 1
10 1
|
tuZ
v |
- 1
10 1
= 0
tcZ
= v
γ tc
κ = 175 GeV
t
m
H1 Preliminary (HERA I+II) Excluded
- Excl. by ZEUS
- Excl. by CDF
- Excl. by L3
SLIDE 12
VARIABLES
ELECTRON CHANNEL MUON CHANNEL
/ GeV
b T
P
20 40 60 80
Events
2 4 6 8 10
H1 Data (prelim.) All SM W MC Top MC
/ GeV
b T
P
20 40 60 80
Events
2 4 6 8 10
/ GeV
b T
P
20 40 60 80
Events
2 4 6 8 10
/ GeV
b T
P
20 40 60 80
Events
1 2 3 4 5
/ GeV
b T
P
20 40 60 80
Events
1 2 3 4 5
/ GeV
b T
P
20 40 60 80
Events
1 2 3 4 5
/ GeV
b ν e
M
100 150 200 250
Events
1 2 3 4 5 6 7 8
/ GeV
b ν e
M
100 150 200 250
Events
1 2 3 4 5 6 7 8
/ GeV
b ν e
M
100 150 200 250
Events
1 2 3 4 5 6 7 8
/ GeV
b ν µ
M
100 150 200 250
Events
0.5 1 1.5 2 2.5
/ GeV
b ν µ
M
100 150 200 250
Events
0.5 1 1.5 2 2.5
/ GeV
b ν µ
M
100 150 200 250
Events
0.5 1 1.5 2 2.5 e W
θ cos
- 1
- 0.5
0.5
Events
1 2 3 4 5 6 e W
θ cos
- 1
- 0.5
0.5
Events
1 2 3 4 5 6 e W
θ cos
- 1
- 0.5
0.5
Events
1 2 3 4 5 6 µ W
θ cos
- 1
- 0.5
0.5
Events
0.5 1 1.5 2 2.5 3 3.5 4 µ W
θ cos
- 1
- 0.5
0.5
Events
0.5 1 1.5 2 2.5 3 3.5 4 µ W
θ cos
- 1
- 0.5
0.5
Events
0.5 1 1.5 2 2.5 3 3.5 4
SLIDE 13
DISCRIMINANT
ELECTRON CHANNEL MUON CHANNEL
D
0.2 0.4 0.6 0.8 1
Events
- 1
10 1 10
H1 Data (prelim.) All SM W MC Top MC
D
0.2 0.4 0.6 0.8 1
Events
- 1
10 1 10
D
0.2 0.4 0.6 0.8 1
Events
- 1
10 1 10
D
0.2 0.4 0.6 0.8 1
Events
- 1
10 1
D
0.2 0.4 0.6 0.8 1
Events
- 1
10 1
D
0.2 0.4 0.6 0.8 1
Events
- 1
10 1
SLIDE 14
CONTACT INTERACTIONS
e
γ
- Z
q q e q q e e e e q q
η
4-fermion contact interactions (CI) describe effects from processes at much higher scales, which could alter the SM distributions at high Q2 and interfere with the predictions at intermediate Q2. Vector terms (scalar and tensor are already costrained): LCI =
q=u,d
X
α,β=L,R
ηq
αβ(¯
eαγµeα)(¯ qβγµqβ) ηαβ = ǫ
g2
CI
Λ2 define the structure of the model. gCI = 4π ǫ = ±1
Contact interaction effects could come from the exchange of extra gauge bosons (Z’), production or exchange of leptoquarks or squarks, compositeness, gravitational effects or finite quark radius.
SLIDE 15
Contact Interaction scale
ηαβ = ± 1
Λ2
Q2 (GeV2) N/NCTEQ5D Contact Interactions Limits (prel.)
ZEUS
ZEUS 94-04 e+p VV Λ− = 8.0 TeV VV Λ+ = 6.3 TeV Q2 (GeV2) N/NCTEQ5D Contact Interactions Limits (prel.) ZEUS 98-06 (prel.) e-p AA Λ− = 6.7 TeV AA Λ+ = 6.1 TeV
1 10 10
3
10
4
0.8 1 1.2 10
3
10
4
1 10 10
3
10
4
0.8 1 1.2 10
3
10
4
SLIDE 16
RR RL LR LL U6 U5 U4 U3 U2 U1 X6 X5 X4 X3 X2 X1 VA AA VV
- 0.4
- 0.2
0.2 0.4
±1/Λ2 (TeV-2)
ZEUS
94-00 e±p
- 1/Λ2 best fit value
+1/Λ2 best fit value allowed ±1/Λ2 range
Λ− (TeV) Λ+ (TeV)
8.0 6.3 6.7 6.1 3.2 3.5 4.9 4.7 5.5 4.7 6.6 5.3 5.4 4.9 5.5 4.5 3.8 4.6 5.8 5.4 6.5 5.3 7.9 6.2 6.0 5.1 6.6 5.0 4.1 5.1 4.7 4.2 2.0 3.7 2.2 3.6 4.5 3.7
94-06 (prel.) e±p
Limits for effective mass scale : Λeeqq 2.2-8.0 TeV
SLIDE 17
Heavy Leptoquarks
Limits on MLQ/λ: 0.45-2.08 TeV
Q2 (GeV2) N/NCTEQ5D Limits on Heavy Leptoquarks (prel.)
ZEUS
ZEUS 94-04 e+p SL
1/2
M/λ=0.87 TeV VL
1/2
M/λ=0.45 TeV Q2 (GeV2) N/NCTEQ5D Limits on Heavy Leptoquarks (prel.) ZEUS 98-06 (prel.) e-p V1
L M/λ=2.08 TeV
S1
L M/λ=0.73 TeV
1 10 10
3
10
4
0.8 1 1.2 10
3
10
4
1 10 10
3
10
4
0.8 1 1.2 10
3
10
4
SLIDE 18
Large Extra Dimensions
In some 4 + n dimensional string theories (Arkani-Hamed-Dimopoulos-Dvali model) compactified extra dimensions have size R ≃ 1 mm. Effective Planck scale MS related to MP ≃ 1019 GeV : M 2
P = M 2+n S
Rn Graviton can propagate into the extra dimension, visible in the ordinary 4 dimensions as a Kaluza-Klein tower of excited states with spacing ∆m =
1
- R. Such
states can be summed up to MS, give sizeable effects, equivalent to a contact interaction term ηG =
λ M4
S where λ ≃ 1 (Giudice, Rattazzi, Wells).
Interfence with Standard Model can be constructive or destructive.
SLIDE 19
Limits on Mass Scale of Extra Dimensions
e q
1 2 3
G G G ...
Q2 (GeV2) N/NCTEQ5D Large Extra Dimensions Limits (prel.)
ZEUS
ZEUS 94-04 e+p MS
− = 0.9 TeV
MS
+ = 0.88 TeV
Q2 (GeV2) N/NCTEQ5D Large Extra Dimensions Limits (prel.) ZEUS 98-06 (prel.) e-p
1 10 10
3
10
4
0.8 1 1.2 10
3
10
4
1 10 10
3
10
4
0.8 1 1.2 10
3
10
4
Limits on MS λ =-1 MS > 0.9 TeV λ =+1 MS > 0.88 TeV LEP, Tevatron limits ≃ 1 TeV
SLIDE 20
Quark Radius-1
e q Z γ R q
Classical approach to the search for quark substructure. Charge distribution of radius Rq in the quark can be described using a form factor: dσ dQ2 = dσSM dQ2 · (1 − R2
q
6 · Q2)2) (assuming the electron to be pointlike) This leads to a decrease of cross sections at high Q2. ZEUS Rq < 0.62 · 10−16 cm
Q2 (GeV2) N/NCTEQ5D Quark Radius Limits (prel.)
ZEUS
ZEUS 94-06 (prel.) e±p Rq
2 = (0.62 ⋅10-16cm)2
Rq
2 = -(0.8 ⋅10-16cm)2
1 10 10
3
10
4
0.8 0.9 1 1.1 1.2 10
3
10
4
SLIDE 21
Quark Radius-2
H1 Rq < 0.74 · 10−16 cm
CTEQ6D 2
/dQ σ / d
2
/dQ σ d
0.6 0.8 1 1.2 1.4
)
- 1
H1 Quark Radius Limit HERA I+II (435 pb
p + e
Normalisation Uncertainty PDF Uncertainty m (95% CL)
- 18
10 ⋅ = 0.74
q
R
)
2
(GeV
2
Q
3
10
4
10
0.6 0.8 1 1.2 1.4
H1 Preliminary p
- e
SLIDE 22
CONCLUSIONS
- Complete statistics of 15 years of HERA data taking can be exploited to
improve the sensitivity of the searches for new physics in a unique environment.
- H1 and ZEUS at HERA have performed a number of model dependent
searches finding no evidence for Leptoquarks or Lepton Flavor Violation, for excited electrons or excited neutrinos. New limits on the anomalous top coupling were set studying the production of single top. And limits on the contact interaction scales and quark radius were updated fitting the DIS differential cross sections at high Q2.
- Further improvements expected from using the whole HERA II luminosity
- Combination of H1 and ZEUS data for some of these searches is underway.
SLIDE 23
BACKUP SLIDES
SLIDE 24
LEPTON FLAVOUR VIOLATION-2
/ GeV
LQ
M
100 150 200 250 300 350 400 450 500 550 600
eq
λ =
q µ
λ
- 3
10
- 2
10
- 1
10 1
u)
- (e
L
S u)
- (e
R
S d)
- (e
R
S ~ d)
- u,e
- (e
L 1
S
E x c l u d e d a t 9 5 % C . L . Search for Lepton Flavour Violation H1 preliminary HERA I + II / GeV
LQ
M
100 150 200 250 300 350 400 450 500 550 600
eq
λ =
q µ
λ
- 3
10
- 2
10
- 1
10 1 d)
- (e
L 1/2
V d)
- u,e
- (e
R 1/2
V u)
- (e
L 1/2
V ~
E x c l u d e d a t 9 5 % C . L . Search for Lepton Flavour Violation H1 preliminary HERA I + II
Limits on coupling vs mass for scalar and vector LQs mediating LFV.
SLIDE 25
Contact Interaction sources
Exchange of extra gauge bosons Exchange of LQ Gravitational effects Production of LQ, squark Compositeness Quark radius
Z’
e e q q e q q
LQ, q
~
e
LQ’
e e q q e e q q
e q e q
1 2 3
G G G ... Z γ R q