[PPT] - Tau Leptons at HERA Linus Lindfeld University of Zurich, PowerPoint Presentation

SLIDE 1

1

Linus Lindfeld University of Zurich, Switzerland

Int. Workshop on Tau Lepton Physics, Nara, Japan

September 14-17, 2004

Introduction
Isolated taus + Pt

miss at ZEUS

Tau pairs at H1
Isolated taus at H1
Search for H++

✁

τ+τ+

Search for LFV LQ decays into taus
Tau Leptons at HERA

T U R I C E N S I S U N I V E R S I T A S

MDCCC XXXIII

SLIDE 2

2

The ep-collider HERA

Two storage rings each with 6,3 km circumference in opposite direction for

protons (E=920 GeV, Ip=100 mA) and electrons/positrons (E=27.6 GeV, Ie=50 mA), supported by DESY in Hamburg, Germany.

Two interaction points where electrons and

protons collide

Detectors around interaction point to

reconstruct event (H1, ZEUS)

Interaction rate 10.4 MHz, every 96 ns
Center-of-mass energy:

GeV s 320 ≈

Hadron Electron Ring Accelerator (HERA): Integrated ep-luminosity up to now ~ 200 pb-1

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

SLIDE 3

3

The experiments ZEUS and H1

p e p

Main components:

Muon chambers
Instr. iron (streamer tubes)
Calorimeter
Drift chambers
Silicon strip detectors

e

27.6 GeV 920 GeV

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

SLIDE 4

4

ep-collisions

p P=(Ep,p

→ p)

Xp x•P Xq q=-Q e+ k=(Ee,p

→ e)

e+ / νe k’ p Xp q q’ W+ e+ ν

– e

Neutral Current (NC) Charged Current (CC)

SM Photoproduction (Q2 ~ 0) and Deep-Inelastic Scattering (DIS) (Q2 > 4 GeV2):

Q2 = -(k-k') = -q2 four momentum transfer squared x = -q2 / (2Pq) Bjorken scaling variable y = (qP) / (kP) inelasticity, i.e. energy loss of electron in proton rest frame s = 2kP = Q2 / (xy) electron-proton center of mass energy squared

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

SLIDE 5

5

ep-collisions with tau leptons

p Xp q W+ l+ νl q’ q’ e+ e+

p u,c t b W+ νl

–, q –

l+,q’ e+ e+ κγ

p Xp l- l+ e+ e+

Tau Processes at HERA:

W-Production with W

τ ν

σ < 0.1 pb, i.e. less than 20 events! Lepton-Pair-Production via Photon-Photon-Fusion σ ~ 10 pb (Pt

τ > 8 GeV)

hidden in large background Anomalous top-Production via FCNC

Standard Model New Physics

and more ...

LQ qj µ+, τ + qi e+ λei λlj

Resonant Leptoquark production with LFV decay to tau

✁

Tau lepton important in seaches for new physics

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

SLIDE 6

6

Signature of a tau lepton

Strategy:

high-pT electron in direction of pT

miss

high-pT muon in direction of pT

miss (calo.)

narrow high-pT jet in direction of pT

miss

tau almost decays at vertex (c

✁ ✂

88

✄

m) decay modes: Characteristic for hadronic decay:

tau jet has low mass
"pencil-like" jet with low charged multiplicity
narrow cluster
1-3 tracks to narrow cluster

τ + − → e+νe¯ ντ 17.9% τ + − → µ+νµ¯ ντ 17.6% τ + − → h+¯ ντ + neutrals 50.3% τ + − → 2h+h−¯ ντ + neutrals 14.0% τ + − → ≥ 5h±¯ ντ + neutrals 0.1%

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

SLIDE 7

7

log(1- )

1 2 3 Events 10

4

10

3

10

2

10

1

1 10 10

2

ZEUS 94-00 data Single Top MC SM W only

log(1- )

1 2 3 Events 10

4

10

3

10

2

10

1

1 10 10

2

> 0.95

verflow

Isolated tau leptons + PT

miss at ZEUS

)

mean

log(1-L

1 2 3 4 Events 10

3

10

2

10

1

1 10 10

2

10

3

)

mean

log(1-L

1 2 3 4 Events 10

3

10

2

10

1

1 10 10

2

10

3

)

mean

log(R

0.5 1 1.5 2 Events 10

3

10

2

10

1

1 10 10

2

10

3

p

+

ZEUS 99-00 e CC DIS

ν

τ → W

)

mean

log(R

0.5 1 1.5 2 Events 10

3

10

2

10

1

1 10 10

2

10

3

)

rms

log(L

1 2 3 4 Events 10

3

10

2

10

1

1 10 10

2

10

3

)

rms

log(L

1 2 3 4 Events 10

3

10

2

10

1

1 10 10

2

10

3

)

rms

log(R

0.5 1 1.5 2 Events 10

3

10

2

10

1

1 10 10

2

10

3

)

rms

log(R

0.5 1 1.5 2 Events 10

3

10

2

10

1

1 10 10

2

10

3

(GeV)

jet

M 10 20 30 Events 10

3

10

2

10

1

1 10 10

2

10

3

(GeV)

jet

M 10 20 30 Events 10

3

10

2

10

1

1 10 10

2

10

3

subj

N 5 10 Events 10

3

10

2

10

1

1 10 10

2

10

3

subj

N 5 10 Events 10

3

10

2

10

1

1 10 10

2

10

3

0.5 1 d dn N 1 10

3

10

2

10

1

p

+

ZEUS 99-00 e CC DIS

ν

τ → W

0.5 1 d dn N 1 10

3

10

2

10

1

(GeV)

had T

P 20 40 60 80 100 Events 10

3

10

2

10

1

1 (GeV)

had T

P 20 40 60 80 100 Events 10

3

10

2

10

1

1

Jet-Shape observables combined with a probability-density-estimation method to a discriminant variable:

D D D

D(x)= ρsig(x) ρsig(x)+ρbg(x)

D>0.95

Preselection: 7 / 2.2 events (obs. / exp.) D > 0.95: 3 / 0.4 Pt

had > 25 GeV:

2 / 0.2 Pt

had > 40 GeV:

1 / 0.07

+0.12

0.13

+0.05

0.05

+0.02

0.02

D

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

+0.39

0.58

Lint= 130 pb-1

SLIDE 8

8

T

P

T

tau candidate, p =39 GeV

Isolated tau leptons + Pt

miss at ZEUS

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

SLIDE 9

9

Tau pairs at H1

/ GeV

T

P

5 10 15 20 25 30 35 40 45 50

Events

10

2

10

1

1 10 10

2

10

3

= 15

data

N 3.9 ± = 17.6

SM

N

H1 Data (prelim.) All SM Processes SM error TauPair

H1 Preliminary

/ GeV

T

P

5 10 15 20 25 30 35 40 45 50

Events

10

2

10

1

1 10 10

2

10

3

/ GeV

T

P

5 10 15 20 25 30 35 40 45 50

Events

10

2

10

1

1 10 10

2

10

3

= 1

data

N 1.2 ± = 1.9

SM

N

H1 Data (prelim.) All SM Processes SM error TauPair

H1 Preliminary

/ GeV

T

P

5 10 15 20 25 30 35 40 45 50

Events

10

2

10

1

1 10 10

2

10

3

p Xp l- l+ e+ e+

Search for hadronic „one-prong“ and „three-prong“ tau decays with a neural network algorithm based on hadronic jet-shape variables yields: 15 / 17.6 ± 3.9 unlike-sign events (obs. / exp.) 1 / 1.9 ± 1.2 like-sign event (obs. / exp.)

unlike-sign like-sign

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

Lint= 108 pb-1

SLIDE 10

10

Tau pairs at H1

Run 248568 Event 27325 Class: 4 11 12 13 15 16 19 20 24 28 29 .

Z

e

+ p

e

+ + (

X ) µ+

µ h h+ h

TA U-PA IR CANDID AT E

h h+ h e+ µ+ µ+ h h+ h e+

H1

Tau-Pair Candidate e+p

e+τ+τ− (X)

µ+ νµντ h+h-h- ντ

e p

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

SLIDE 11

11

Isolated tau leptons + Pt

miss at H1

0.1 0.2 0.3 0.4 0.5 0.6

2

10

1

10 1 10

2

10

3

10 0.1 0.2 0.3 0.4 0.5 0.6

2

10

1

10 1 10

2

10

3

10 = 26

data

N 4.4 ± = 24.2

SM

N

H1 Preliminary

H1 Data (prelim.) All SM Processes SM Error SM W

Jet

R Events

10 20 30 40 50 60 70 80

2

10

1

10 1 10

2

10

3

10 10 20 30 40 50 60 70 80

2

10

1

10 1 10

2

10

3

10 = 26

data

N 4.4 ± = 24.2

SM

N

H1 Preliminary

H1 Data (prelim.) All SM Processes SM Error SM W

/ GeV

X T

P Events

10 20 30 40 50 60 70 80

2

10

1

10 1 10

2

10 10 20 30 40 50 60 70 80

2

10

1

10 1 10

2

10

= 5

data

N 1.3 ± = 5.8

SM

N

H1 Preliminary

H1 Data (prelim.)

All SM Processes

SM Error SM W single top

(arb. norm)

/ GeV

X T

P Events

Preselection: 26 events (obs. / exp.) RJet < 0.12: 5 / 5.81±1.36 Pt

X > 25 GeV:

0 / 0.53±0.10 Pt

X > 40 GeV:

0 / 0.22±0.05 Cut-based analysis is restricted to hadronic „one-prong“ tau decays: A jet with one isolated track pointing to a typical narrow hadronic energy depositon

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

Lint= 108 pb-1

SLIDE 12

12

Search for H++

τ+τ+

e+(-) H++(--) e-(+) p,X p

γ(Z)

e+(-) H++(--) e-(+) p,X p

γ(Z)

e+(-) H++(--) e-(+) p,X p

γ(Z)

0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.2 0.3 0.4 80 90 100 110 120 130 140 150

MH (GeV) σ*BR (pb) H1 Higgs search: H±± limits H1 Preliminary H±±→ µ±µ± H±±→ e±e± H±±→ e±µ± H±±→ τ±τ±

Search for like-sign tau pairs is based on two isolated high PT tracks and includes leptonic and hadronic decays of the tau shows: 1 / 2.12 ± 0.32 unlike-sign events (obs. / exp.) 0 / 1.03 ± 0.19 like-sign events (obs. / exp.)

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

Lint= 65 pb-1

SLIDE 13

13

Search for LFV LQ decays into taus

LQ qj µ+, τ + qi e+ λei λlj

Leptoquarks couple to both quarks and leptons: SM DIS s-channel u-channel Leptoquarks color triplet bosons fractional charge Both lepton and baryon number

Parameters

mass coupling quantum numbers

narrow resonance in x at:

γZ(W +) qi e+(νe) qi e+ LQ ¯ qj µ+, τ + ¯ qi e+ λej λil

x0 = M 2

LQ

s

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

SLIDE 14

14

Search for LFV LQ decays into taus at H1

10 20 30

1

10 1 10

2

10

3

10 / GeV

jet2

M events

H1 Prelim. SM 250 GeV

L

V

(arb. norm.) q’ τ → eq

20 40 60 80

1

10 1 10

2

10

3

10 / GeV

T miss

P events

H1 Prelim. SM 250 GeV

L

V

(arb. norm.) q’ τ → eq

0.2 0.4 0.6 0.8 1

1

10 1 10

2

10

3

10

jet2

R events

H1 Prelim. SM 250 GeV

L

V

(arb. norm.) q’ τ → eq

0.5 1 1.5 2 1 10

2

10

track

D events

H1 Prelim. SM 250 GeV

L

V

(arb. norm.) q’ τ → eq

100 200 300

2

10

1

10 1 10 / GeV

LQ

M events

H1 Prelim. SM 250 GeV

L

V

(arb. norm.)

q’ τ → eq

Cut-based analysis is restricted to hadronic tau decays: A jet with one to three isolated tracks pointing to a typical narrow hadronic energy depositon. The missing energy (neutrinos from tau decay) is aligned with the tau-jet. Final selection yields: 1 / 0.56 ± 0.16 events (obs. / exp.)

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

Lint= 66 pb-1

SLIDE 15

15

Search for LFV LQ decays into taus at H1

100 150 200 250 300 350

3

10

2

10

1

10 1 / GeV

LQ

M

eq

λ =

q τ

λ

u,d)

+

(e

R 1/2

S u)

+

(e

L 1/2

S d)

+

(e

L 1/2

S

~

Excluded at 95% C.L.

= 0.5

q τ → LQ

BR H1 Preliminary

100 150 200 250 300 350

3

10

2

10

1

10 1 / GeV

LQ

M

eq

λ =

q τ

λ

u,d)

+

(e

L 1

V u)

+

(e

R

V

~

d)

+

(e

R

V d)

+

(e

L

V

Excluded at 95% C.L.

= 0.5

q τ → LQ

BR H1 Preliminary

No significant deviation from SM found
Limits are set on couplings to Leptoquarks mediating

lepton flavor violation

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

SLIDE 16

16

Search for LFV LQ decays into taus at ZEUS

log(rmean)

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Events

1 10 10

2

10

3

p 94-00

±

ZEUS (prel.) e Background MC m=240 (GeV) τ LFV

log(rrms)

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Events

1 10 10

2

log(1-lmean)

0.5 1 1.5 2 2.5 3 3.5 4

Events

1 10 10

2

log(lrms)

0.5 1 1.5 2 2.5 3 3.5 4

Events

1 10 10

2

n. subjets

1 2 3 4 5 6 7 8 9 10

Events

1 10 10

2

(GeV)

jet

M

5 10 15 20 25

Events

1 10 10

2

ZEUS

τ D

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Events 1 10 10

2

p 94-00

±

ZEUS (prel.) e Background MC m=240 (GeV) τ LFV m=600 (GeV) τ LFV

φ ∆

20 40 60 80 100 120 140 160 180 Events 1 10 10

2

ZEUS

φ ∆

20 40 60 80 100 120 140 160 180

Events

10

2

10

1

1 10 10

2

p 94-00

±

ZEUS (prel.) e Background MC m=240 (GeV) τ LFV

ZEUS

Search for hadronic tau decays with a discriminant variable D based on hadronic jet-shape variables yields: Preselection: 119 / 131.2 ± 4 events (obs. / exp.) D > 0.9: 8 / 11.2 ± 1.5 ∆φ < 20o: 0 / 1.7 ± 0.4 A cut-based selection for leptonic decays reveals no candidate and is combined for exclusion limits

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

Lint= 130 pb-1

SLIDE 17

17

Search for LFV LQ decays into taus at ZEUS

ZEUS

(GeV)

LQ

M

150 200 250 300

q τ

β ×

1

eq

λ

10

3

10

2

10

1

1

L 1/2

S

~

R 1/2

S

L 1/2

S

p 94-00

+

a) ZEUS (prel.) e e x c l u d e d a t 9 5 % C . L .

(GeV)

LQ

M

150 200 250 300

q τ

β ×

1

eq

λ

10

3

10

2

10

1

1

R

,V

L

V

R

V

~

L 1

V

p 94-00

+

b) ZEUS (prel.) e e x c l u d e d a t 9 5 % C . L .

(GeV)

LQ

M

150 200 250 300

1

eq

λ

10

3

10

2

10

1

1

e X τ → B e π → τ ν ν π → K

L 1/2

S

~

p 94-00

+

c) ZEUS (prel.) e

j

q τ

λ =

1

eq

λ

(GeV)

LQ

M

150 200 250 300

1

eq

λ

10

3

10

2

10

1

1

e τ → B e π → τ K e → τ

R

V p 94-00

+

d) ZEUS (prel.) e

j

q τ

λ =

1

eq

λ

ZEUS

(GeV)

LQ

M

150 200 250 300

q τ

β ×

1

eq

λ

10

3

10

2

10

1

1

R

S

~

R

,S

L

S

L 1

S

p 98-99

a) ZEUS (prel.) e

excluded at 95% C.L.

(GeV)

LQ

M

150 200 250 300

q τ

β ×

1

eq

λ

10

3

10

2

10

1

1

L 1/2

V

L 1/2

V

~

R 1/2

V

p 98-99

b) ZEUS (prel.) e

excluded at 95% C.L.

(GeV)

LQ

M

150 200 250 300

1

eq

λ

10

3

10

2

10

1

1

e τ → B e π → τ K e → τ R

S

~

p 98-99

c) ZEUS (prel.) e

j

q τ

λ =

1

eq

λ

(GeV)

LQ

M

150 200 250 300

1

eq

λ

10

3

10

2

10

1

1

e X τ → B e π → τ ν ν π → K L 1/2

V

p 98-99

d) ZEUS (prel.) e

j

q τ

λ =

1

eq

λ

No candidate event was found and limits on LQ are set e+p-collisions e-p-collisions

Linus Lindfeld, University of Zurich TAU'04, Nara, Japan September 17, 2004

SLIDE 18

18

Summary

The tau lepton appears rarely in SM ep-collisions at HERA Detecting taus at HERA is a difficult business It's worth looking for taus, because a significant excess would immediately indicate new physics Recent analyses searching for new physics in ep-collisions succeeded in developing tools to detect taus efficiently 3 outstanding tau events seen with the ZEUS detector might already reveal new physics The searches for tau leptons help to set exclusion limits on new phenomena like FCNC, doubly charged Higgs or Leptoquarks