searches for squarks with h1 at hera - tu dresdenvest/talks/dis04_talk.pdf · searches for squarks...

Searches for squarks with H1 at HERA

Anja Vest

I. Physikalisches Institut RWTH Aachen

On behalf of the H1 Collaboration

DIS workshop, April 15, 2004

B SUSY and R–Parity

B Phenomenology of 6Rp SUSY ine±p scattering

B Squark decays & 6Rp SUSY results(DESY-04-025)

– MSSM exclusion limits– mSUGRA exclusion limits

B Bosonic stop decay:Interpretation & exclusion limits(final results)

B Summary and outlook

Supersymmetry (SUSY)

SM particles spin SUSY partners spinqL, qR

12 qL, qR 0

lL, lR12 lL, lR 0

γ, Z0,W±

h0,H±,H0, A0

}10

{χ0

1, χ02, χ

03, χ

04

χ±1 , χ±2

1212

g 1 g 12

MSSM: 105 parameters, but

– The masses and couplings of χ0i , χ±j and g are determined by the parameteres

µ, tan β, M2

– Gaugino mass parameters M1, M2, M3 unify to m1/2 at the GUT scale

– Sfermion masses are free parameters

mSUGRA model:

– m0 (m1/2) common mass for scalar fields (gauginos) at the GUT scale

– REWSB → model completely determined by m0, m1/2, tan β, sign µ, A0

Anja Vest, I. Physikalisches Institut RWTH Aachen DIS workshop, April 15, 2004 1

R–Parity and R–Parity violation

Definition: RP = (−1)3B+L+2S → RP = 1 for all SM particles→ RP = −1 for all SUSY particles

• The MSSM is RP–conserving

→ all SUSY particles are produced in pairs→ the LSP is stable (candidate for cold dark matter)

The superpotential in the general MSSM has additional 6Rp terms:

W 6Rp= λijkLiLjek︸︷︷︸

L/

+λ′ijkLiQjdk︸︷︷︸L/

+λ′′ijkuidjdk︸︷︷︸B/

...

λ~l

l

l

~q~l

q (q)

l (q)( )

λ’ λ’’~q

q

q

HERA

→ Resonant production of single SUSY particles→ SUSY particles can decay into SM particles (⇒ LSP no more stable)


Phenomenology of 6Rp SUSY in e±p scattering at HERA

Production of squarks (q) in s–channel via λ′ijk with masses up to√

s

94–97 and 99/00: ∼ 106 pb−1 e+p ⇒ λ′1j1: e+d −→ uL, cL, tL98/99: ∼ 14 pb−1 e−p ⇒ λ′11k: e−u −→ dR, sR, bR

Cross sections in NWA: σ(e+p → ujL) ∼ λ′21jk · dk(x =

M2q

s )

σ(e−p → dkR) ∼ λ′21jk · uj(x =

M2q

s )

Direct 6Rp decays:

(Leptoquark–like)

Squark Decay Modes in Rp/ SUSY

1) direct Rp/ Decays (Leptoquark-like):

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PSfrag replacements

e+

p

λ′1jk

λ′1jk

e+

dka)

ujL

dk

PSfrag replacements

e+

pλ′

1jk

λ′1jk

e+

dk

a)

ujL

dk

e−

p

λ′1jk

λ′1jk

e−, νe

uj, djb)uj

dkR

Signature : High pT e(ν) + jet

⇒ Look for NC (CC)–like events at high pT

• dominant channel at high masses (high λ′1jk)

• only dkR (e−p collisions) can decay to νq

Squark Decay Modes in Rp/ SUSY

1) direct Rp/ Decays (Leptoquark-like):

PSfrag replacements

e+

p

λ′1jk

λ′1jk

e+

dka)

ujL

dk

��

��

��

��

��

��

��

��

��

PSfrag replacements

e+

pλ′

1jk

λ′1jk

e+

dk

a)

ujL

dk

e−

p

λ′1jk

λ′1jk

e−, νe

uj, djb)uj

dkR

Signature : High pT e(ν) + jet

⇒ Look for NC (CC)–like events at high pT

• dominant channel at high masses (high λ′1jk)

• only dkR (e−p collisions) can decay to νq

Signature: high PT e(ν) + jet ⇒ look for NC (CC) –like events at high PT

→ only dkR (e−p collisions) can decay to νq


Squark gauge decay into quark + gaugino

q → χ0i q q → χ±i q′ q → gq

Subsequent gaugino decay:

→ 6Rp gaugino decays into 2 quarks +(e± or νe)→ χ0

i with i > 1, g decays into lighter χ and 2 fermions

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��

��

��

��

��

��

PSfrag replacements

e−

u

dkR

d

χ0i , g

χ01

e+

e−u

dk

λ′11k

λ′11k

(a)

��

��

��

��

��

��

��

��

��

PSfrag replacements

e−

udk

R

dχ0

i , gχ0

1

e+

e−

udk

λ′11k

λ′11k

(a)

e+

d

ujL

u, d

χ0i , χ

+i , g

χ+1

eqq

(νeqq)

χ01

W+

q′, l+

q, νl

λ′1j1

λ′1j1(b)

Figure 2: Gauge decays of squarks. Example decays of the emerging neutralino, chargino orgluino are shown in the dashed boxes for (a) the χ0

1 and (b) the χ+1 .

coupling λ′ into SM fermions. According to equation (1), the dR-type squarks can decay eitherinto e− + uj or νe + dj, while the uL-type squarks decay into e+ + dk only. The 6Rp squarkdecays, proceeding directly via the couplings λ′

11k and λ′1j1, are illustrated in figure 1.

Squarks can also decay via their usual Rp conserving gauge couplings, as shown in figure 2.The uL-type squarks can undergo a gauge decay into states2 involving a neutralino χ0

i (i =1 . . . 4), a chargino χ+

i (i = 1, 2) or a gluino g. In contrast, dR-type squarks decay to χ0i or

g only and decays into charginos are suppressed, since the supersymmetric partners of right-handed quarks do not couple to winos.

The final state of these gauge decays depends on the subsequent gaugino decay, of whichexamples are shown in figure 2. Neutralinos χ0

i with i > 1 as well as charginos (gluinos) areexpected to undergo gauge decays into a lighter χ and two SM fermions (two quarks), througha real or virtual gauge boson or sfermion (squark). The decay chain ends with the 6Rp decay ofone sparticle, usually the lightest supersymmetric particle (LSP), assumed here to be a χ0, χ±

or g. 6Rp decays of gauginos are mainly relevant for the lightest states. Neutralinos may undergothe 6Rp decays χ0 → e±qq′ or χ0 → νqq, the former (latter) being more frequent if the χ0 isdominated by its photino (zino) component. Gluinos can undergo the same 6Rp decays. Whena χ0 or a g decays via an 6Rp coupling into a charged lepton, both the “right” and the “wrong”charge lepton (with respect to the incident beam) are equally probable, the latter case leading tostriking, largely background-free signatures for lepton number violation. In contrast, the onlypossible 6Rp decays for charginos are χ+ → νukdj and χ+ → e+dkdj.

The ujL (dk

R) decay chains analysed in this paper are classified by event topology, as de-scribed in table 2. This classification relies on the number of charged leptons and/or hadronicjets in the final state, and on the presence of missing momentum. The channels labelled eq andνq are the squark decay modes which proceed directly via 6Rp couplings, while the remainingchannels result from the gauge decays of the squark and are characterised by multijet (MJ) finalstates. The channels labelled e+MJ , e−MJ and νMJ involve one or two SUSY fermions (χor g) denoted by X and Y in table 2. The channels e`MJ and ν`MJ necessarily involve twoSUSY fermions.

2The mass eigenstates χ0

i (χ±i ) are mixed states of the photino, the zino and the neutral higgsinos (the winosand the charged higgsinos). The g is the SUSY partner of the gluon.

6

⇒ Large variety of decay modes with lepton(s) + multiple jets


Squark decay modes

Channel Decay process Event topology

eq qλ′→ eq high pT e + 1 jet

νq dkR

λ′→ νed missing pT + 1 jet

e±MJq → qX X

λ′→ e±qqX → qq Y

Yλ′→ e±qq

e (both charges)+ multiple jets

νMJ

q → qX Xλ′→ νqq

X → qq YX → νν Y

Yλ′→ νqq

missing pT+ multiple jets

elMJ

q → qX X → `ν` Y

X → `+`− Y

X → e+e− Y

Yλ′→ e±qq, νqq

e+ ` (e or µ)

+ multiple jets

νlMJ

q → qX X → `ν` YX → νν Y

X → µ+µ− Y

Yλ′→ νqq, eqq

` (e or µ)+ missing pT+ multiple jets

e+p collisions

10-2

10-1

1

100 150 200 25010

-2

10-1

1

100 150 200 250

10-2

10-1

1

100 150 200 250

Mslepton=Msquark u∼

L-type

sum

νMJelMJ

eqνlMJ

e+MJ, e−MJ

(c)

Msquark (GeV)

BR Mslepton=Msquark d

∼R-type

sume+MJ, e−MJ

eq, ν

q

νMJ

(d)

Msquark (GeV)

BR

Mslepton=90GeV u∼

L-type

sum

eq

e+ M

J

e−MJ

νMJ

elMJ

νlMJ

(e)

Msquark (GeV)

BR Mslepton=90GeV d

∼R-type

sume+MJ, e−MJ

eq, ν

q

νMJ

(f)

Msquark (GeV)

BR

10-2

10-1

1

100 150 200 250

almost full coverage of BR’s !


Gauge decay into quark + gaugino: H1 e+p analysis

Selection cuts: ∼> 2 jets with P jetT > 15 GeV

angular cuts

eMJ + X selection

P eT > 6 GeV, high ye

angular cuts

1

10

10 2

50 100 150 200 250 300Minv (GeV)

even

ts e+MJ channel

H1

l e+p data

(a)

MC DIS + γp150 GeV squark

(arb. norm.)

typical efficiencies: 30− 50%

νMJ+ X selection

6PT > 26 GeV

2

4

6

8

10

12

14

50 100 150 200 250 300Mrec (GeV)

even

ts νMJ channel

H1

l e+p data

(a)

MC DIS + γp150 GeV squark

(arb. norm.)

typical efficiencies: 30− 60%


Squark decay modes

Channel Event topology e+p data (SM) e−p data (SM)

eq high pT e + 1 jet 632 (628± 46) 204 (192± 14)

νq missing pT + 1 jet – 261 (269± 21)

e±MJe (both charges)

+ multiple jets

e+MJ :

72 (67.5± 9.5)

e−MJ :

0 (0.20± 0.14)

e+MJ :

20 (17.9± 2.4)

e−MJ :

0 (0.06± 0.02)

νMJmissing pT

+ multiple jets30 (24.3± 3.6) 12 (10.1± 1.4)

elMJ

e

+ ` (e or µ)

+ multiple jets

eeMJ :

0 (0.91± 0.51)

eµMJ :

0 (0.91± 0.38)

eeMJ :

0 (0.13± 0.03)

eµMJ :

0 (0.20± 0.04)

νlMJ

` (e or µ)

+ missing pT

+ multiple jets

νeMJ :

0 (0.74± 0.26)

νµMJ :

0 (0.61± 0.12)

νeMJ :

0 (0.21± 0.07)

νµMJ :

0 (0.16± 0.03)

all decay modes checked in detail ⇒ no deviation from SM expectation


Interpretation of the data in the MSSM

relevant SUSY parameters:

M2, µ, tanβ, λ′1jk, Mq

Squark masses and couplings arefree parameters

⇒ set limits on λ′1jk vs. Mq

⇒ SUSY parameter scan

tanβ = 6−300 < µ < 300 GeV−70 < M2 < 350 GeV

e+p data e−p data

10-2

10-1

1

100 125 150 175 200 225 250 275

10-2

10-1

1

100 125 150 175 200 225 250 275

Unconstrained MSSM, j=1,2

tan β = 6-300 < µ < 300 GeV70 < M2 < 350 GeV

MLSP > 30 GeV imposed

(a)

EXCLUDED

EXCLUDED IN PART O

F

PARAMETER SPACE

λ, 111 (

ββ0ν)

λ, 121

(APV)

Msquark (GeV)

λ, 1j1

H1

10-2

10-1

1

100 125 150 175 200 225 250 275

10-2

10-1

1

100 125 150 175 200 225 250 275

Unconstrained MSSM, k=1,2

tan β = 6-300 < µ < 300 GeV70 < M2 < 350 GeV


(a)

EXCLUDED

EXCLUDED IN PART OF PARAMETER SPACE

λ, 111 (

ββ0ν)

λ, 112

(CCU)

Msquark (GeV)

λ, 11k

H1

10-2

10-1

1

100 125 150 175 200 225 250 275

10-2

10-1

1

100 125 150 175 200 225 250 275

Unconstrained MSSM, j=3

tan β = 6-300 < µ < 300 GeV70 < M2 < 350 GeV


(b)

EXCLUDED

EXCLUDED IN PART O

F

PARAMETER SPACE

λ, 131

(APV)

H1

Msquark (GeV)

λ, 131

10-2

10-1

1

100 125 150 175 200 225 250 275

10-2

10-1

1

100 125 150 175 200 225 250 275

Unconstrained MSSM, k=3

tan β = 6-300 < µ < 300 GeV70 < M2 < 350 GeV


(b)

EXCLUDED

EXCLUDED IN PART OF PARAMETER SPACE

λ, 113

(CCU)

Msquark (GeV)

λ, 113

H1

uL, cL dR, sR

tL bR


Interpretation of the data in the mSUGRA model

Only five parameters: tanβ, m1/2, m0, A0, sign µ

set limits for λ′1j1, λ′11k = 0.3 (e.m. coupling):

e+p data e−p data

0

20

40

60

80

100

120

140

160

180

0 50 100 150 200 250 300 350

m(u∼)=260 GeV

m(u ∼)=275 GeV

D0 (j=1,2)

not allowed

m(t ∼1 )=240 GeV

m(t∼1 )=270 GeV

H1

(b)µ < 0, A 0 = 0

mSUGRA, λ, 1j1 = 0.3, tanβ=6

MLSP < Mb

excluded for j=3

excluded for j=1,2

m0 (GeV)

m1/

2 (G

eV)

0

20

40

60

80

100

120

140

160

180

0 50 100 150 200 250 300 3500

20

40

60

80

100

120

140

160

180

0 50 100 150 200 250 300 350

not allowed

m(d∼)=200 GeV

m(d∼)=260 GeV

m(d∼)=280 GeV

(b)

µ < 0, A 0 = 0

mSUGRA, λ, 11k = 0.3, tanβ=6

MLSP < Mb

excluded for k=3

excluded for k=1,2

H1

m0 (GeV)

m1/

2 (G

eV)

D0 limit

limits fortanβ = 2comparable

HERA sensitivity follows isomass curve:

u, c, t excluded up to 275 GeV; d, s, b excluded up to 285 GeV


mSUGRA limits

Large part of SUSY parameter space excluded for small tanβ by MSSM Higgs searchat LEP

exclusion limits assuming m0 = m1/2 = M vs. tan β:

80

100

120

140

160

180

5 10 15 20 25 30 35 40 45 50

b∼ (λ

, 113=0.3)

d∼, s

∼ (λ, 11k=0.3, k=1,2)

u∼, c

∼ (λ, 1j1=0.3, j=1,2)

t∼ (λ, 131=0.3)

m0= m1/2= M, µ < 0, A0= 0

not a

llowe

d

H1 95% CL

mSUGRA

tan β

M (G

eV)

80

100

120

140

160

180

5 10 15 20 25 30 35 40 45 50

u, c: constant → small mixing

d, s: constant → small mixing;larger cross section

b: mixing important fortanβ ∼> 10

t: mixing important for all tanβ;τ final states for tanβ ∼> 37


Bosonic stop decay t → bW

In the third generation: Mq not negligible ⇒ large mixing between qL and qR:(q1

q2

)=

(cos θq sin θq

− sin θq cos θq

) (qL

qR

)q = b, t: presumably the lightest squarks

Mb < Mt (different from ’usual’ MSSM)

q 6→ q′χ (kinematically not accessible)

→ bosonic stop decay t → bW

θt and θb

are freeparameters

t

b

W+

d

e+

d

νe

ν, q′

`+, q

λ′

131

λ′

131

Signature: 3 jets + 6PT or jet + ` + 6PT

−→ high PT lepton events observed at H1

Interpretation of these events as decay products from bosonic

stop decays (T. Kon et al., Mod. Phys. Lett. A12 (1997) 3143)

kinematic range: Mt > Mb + MW

virtual W decay strongly suppressed & the direct6Rp decay t → ed dominates for Mt ∼

< Mb + MW


Bosonic stop decay: H1 analysis

t → bW → νd eν t → bW → νd µν

[GeV]TM0 50 100 150 200 250 300

Eve

nts

10-2

10-1

1

10

[GeV]TM0 50 100 150 200 250 300

Eve

nts

10-2

10-1

1

10p data+e

SM260 GeV stop

channelmissTjeP

a)

(arb. norm.)

H1

[GeV]TM0 50 100 150 200 250 300

Eve

nts

10-2

10-1

1

10

[GeV]TM0 50 100 150 200 250 300

Eve

nts

10-2

10-1

1

10p data+e

SM260 GeV stop

channelmissTPµj

b)H1

(arb. norm.)

[GeV]recM0 50 100 150 200 250 300

Eve

nts

10-2

10-1

1

10

[GeV]recM0 50 100 150 200 250 300

Eve

nts

10-2

10-1

1

10p data+e

SM260 GeV stop

channelmissTjjjP

c)

(arb. norm.)

H1

[GeV]eM0 50 100 150 200 250 300

Eve

nts

10-1

1

10

102

103

[GeV]eM0 50 100 150 200 250 300

Eve

nts

10-1

1

10

102

103

p data+eSM260 GeV stop

ed channel

(arb. norm.)

H1d)

[GeV]t~ M180 200 220 240 260 280

BR

0

0.2

0.4

0.6

0.8

1

= 0.6 radb~

θ

= 1.2 radb~

θ

ed)→ t~BR(

’)f f→W , W b~ → t~BR(

sum

[GeV]t~ M180 200 220 240 260 280

BR

0

0.2

0.4

0.6

0.8

1

almost full coverage of BR’s

Selection cuts:

P `T > 10 GeV

P JetT > 10(20, 15) GeV6PT> 12(25)GeV

t → bW → νd qq t → ed

typical efficiencies: 30− 50% → slight excess in jµ6PT channel but

no significant deviation from SM expectation

Mb = 100GeV


Bosonic stop decay: Interpretation of high PT lepton events

For each channel: calculate cross section σt(Mt) = NData−NSMε·BR·L

[GeV]t~ M180 200 220 240 260 280

[pb

]t~σ

-202468

1012

channelmissTjeP

channelmissTPµj

channelmissTjjjP H1

[GeV]t~ M180 200 220 240 260 280

[pb

]t~σ

-202468

1012 • Slight discrepancy between data and

SM only observed in the jµ6PT

channel but not confirmed in thejjj 6PT or je6PT channels

• The probability that the event ratein the jjj 6PT channel fluctuatessuch that it is comparable with thecross section in the jµ6PT channelis ∼ 0.5%− 1%

⇒ The high PT lepton candidates cannot be interpreted as scalar tops.

⇒ Set limits on SUSY parameters!


Bosonic stop decay: exclusion limits in the MSSM

SUSY parameter scan

→ scan also: Mb and the mixing angles θt (relevant for production cross section)θb (relevant for bosonic stop decay)

tanβ = 100.6 < θt, θb < 1.2

400 < µ < 1000 GeVM2 = 1000 GeV

comparaple results fortanβ = 10M2 = 400GeV

[GeV]t~

M180 200 220 240 260 280

[GeV

]b~

M

100

120

140

160

180

200 Excluded in part of parameter spaceExcluded

< 1.2b~

θ , t~

θ0.6 < < 1000 GeVµ400 GeV <

= 1000 GeV2M = 10βtan

= 0.3131’λ

H1b)

[GeV]t~

M180 200 220 240 260 280

131

’λ

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

[GeV]t~ M180 200 220 240 260 280

131

’λ

10-2

10-1

1Excluded in part of parameter space

[GeV]t~ M180 200 220 240 260 280

131

’λ

10-2

10-1

1

< 1.2b~θ , t~θ0.6 < < 1000 GeVµ400 GeV <

= 1000 GeV2M = 10βtan

= 100 GeVb~ MH1

Excluded

λ′131 = 0.3 Mb = 100GeV

→ Stop masses up to ∼ 275GeV excluded for λ′131 = 0.3


Summary & outlook

• Squarks have been searched for in all e+p and e−p H1 data (Lint ≈ 120 pb−1)

⇒ no evidence for squark production found

• Limits were derived in the SUSY parameter space

⇒ Squark masses up to 275GeV (uj) and 285GeV (dk)excluded for λ′

1jk = 0.3

mSUGRA limits (on m0, m1/2) are competitive to LEP and TeVatron

• Complementary analysis: bosonic stop decay

A slight excess in the jµ6PT channel is observed, butno evidence for stop production found

⇒ The high PT lepton events observed at H1 cannot be interpreted as stops.

• Stop masses up to ∼ 275GeV excluded for λ′131 = 0.3


Summary & outlook

Outlook• HERA II:

– polarised e± beams:

e+R + dL → uj

L

e−L + uL → dkR

needed for 6Rp SUSY searches at HERA II

– higher luminosity: ∼ 1 fb−1 per experiment

• higher√

s would also be helpful for 6Rp SUSY searches

u∼

L-production

Mass (GeV)

Ee=27.5 Ep=920.

Ee=30. Ep=920.Ee=30. Ep=1000.

10-3

10-2

10-1

150 200 250 300

σ


searches for squarks with h1 at hera - tu dresdenvest/talks/dis04_talk.pdf · searches for squarks...

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