University of Freiburg

Maxim Titov(on behalf of D0 Collaboration)

European Physics Conference (EPS 2005), Lissabon, 21. 07. 2005 European Physics Conference (EPS 2005), Lissabon, 21. 07. 2005

Acceptance:Acceptance:Electrons: |Electrons: |3.03.0

Muons: |Muons: |22Jets: |Jets: || < 4.2| < 4.2

Results presented in this talk are basedResults presented in this talk are based on integrated luminosity of 200 – 400 pbon integrated luminosity of 200 – 400 pb-1-1

More than double of this datasetMore than double of this datasetis already on the tapeis already on the tape

1 fb1 fb-1-1

Run II started March 2001:Run II started March 2001:• Higher energyHigher energy (1.8 TeV -> 1.96 TeV)(1.8 TeV -> 1.96 TeV)

• Higher antiproton intensityHigher antiproton intensity(6*6 bunches -> 36*36 bunches)(6*6 bunches -> 36*36 bunches)

Leptoquarks (LQ) predicted to exist in various SM extensions (e.g. GUT, technicolor,Leptoquarks (LQ) predicted to exist in various SM extensions (e.g. GUT, technicolor,SUSY with R-parity violation, composite models, superstring-inspired E6-models):SUSY with R-parity violation, composite models, superstring-inspired E6-models):

• Connection of lepton and quark sectorConnection of lepton and quark sector(color-triplet field, fractional electric charge, both lepton and quark numbers);(color-triplet field, fractional electric charge, both lepton and quark numbers);

HERA: Buchmuller–Ruckl–Wyler (BRW) Minimal LQ ModelHERA: Buchmuller–Ruckl–Wyler (BRW) Minimal LQ Model (Phys. Lett.B191(1987) 442)(Phys. Lett.B191(1987) 442)(7 scalar and 7 vector leptoquarks with fermion numbers F = - (3B + L) = 0 or 2)(7 scalar and 7 vector leptoquarks with fermion numbers F = - (3B + L) = 0 or 2)

TEVATRON: LQ pair production does not depend on its electroweak properties TEVATRON: LQ pair production does not depend on its electroweak properties No need to use specific model, but number of constraints on LQ are coming from:No need to use specific model, but number of constraints on LQ are coming from:

• Atomic parity violation (APV) experimentsAtomic parity violation (APV) experiments

• Baryon and Lepton number conservation (to avoid rapid proton decays)Baryon and Lepton number conservation (to avoid rapid proton decays)

• Family diagonal – LQ couples to a single leptonic and quark generation (to avoid FCNC)Family diagonal – LQ couples to a single leptonic and quark generation (to avoid FCNC)

• Chiral coupling (to avoid deviations from universality in leptonic Chiral coupling (to avoid deviations from universality in leptonic decays) decays)

D0 Limits for scalar leptoquarks are only presented in this talk:D0 Limits for scalar leptoquarks are only presented in this talk:

Scalar leptoquarks are less model dependent & typicallyScalar leptoquarks are less model dependent & typicallyhave lower production cross sectionhave lower production cross section limits could be valid for vector LQ limits could be valid for vector LQ

Scalar LQ pair production:Scalar LQ pair production:

• Quark-antiquark annihilation and gluon fusionQuark-antiquark annihilation and gluon fusion(qq annihilation is dominant for M(qq annihilation is dominant for MLQLQ > 100 GeV) > 100 GeV)

Phys.Rev Lett.79(1997)341; Phys.Rev.D59,015001(1998)Phys.Rev Lett.79(1997)341; Phys.Rev.D59,015001(1998)

• The gluon-leptoquark coupling is simplyThe gluon-leptoquark coupling is simplygiven by the strong couplinggiven by the strong coupling

• Cross section is independent of YukawaCross section is independent of Yukawa leptoquark-lepton-quark coupling (leptoquark-lepton-quark coupling (LQLQ):): ( ( LQLQ contributes only ~ 1% of total cross contributes only ~ 1% of total cross section in t-channel of qq annihilation)section in t-channel of qq annihilation)

Scalar LQ Production Scalar LQ Production NLONLO ~ 0.3 pb at M ~ 0.3 pb at MLQLQ ~ 200 GeV): ~ 200 GeV):

LQ Decay:LQ Decay:

= LQ branching fraction = LQ branching fraction to charged lepton and quarkto charged lepton and quark

LQ experimental signatures: LQ experimental signatures:

11stst generation: 2e+2j, e+2j+MET, 2j + MET generation: 2e+2j, e+2j+MET, 2j + MET22ndnd generation: 2 generation: 2+2j, +2j, +2j+MET, 2j + MET+2j+MET, 2j + MET

Combined D0-CDF Run I 1Combined D0-CDF Run I 1stst generation LQ limit:generation LQ limit:

MMLQ1LQ1 > 242 GeV for > 242 GeV for = 1.0 = 1.0(hep-ex/9810015)(hep-ex/9810015)

Selection:Selection: 2 2 (E (ETT> 15 GeV) + 2 jets (E> 15 GeV) + 2 jets (ETT> 25GeV) + Z veto; > 25GeV) + Z veto; Main SM backgrounds: Z/Drell Yan + jets, ttbarMain SM backgrounds: Z/Drell Yan + jets, ttbar

SSTT = E = ETT(j1) + E(j1) + ETT(j2) + E(j2) + ETT((1) + E1) + ETT((2):2):

Run II D0 analysis have been performed in Run II D0 analysis have been performed in qq channel (294 pbqq channel (294 pb-1-1): ):

Only the combination with the smallerOnly the combination with the smaller mass difference min(M1(mass difference min(M1(j)-M2(j)-M2(j)) of thej)) of the two LQ candidates in the event is chosentwo LQ candidates in the event is chosen

NEW ! ! !

NEW ! ! !

Sensitivity to LQ decays is studied using a two-dimensional distribution:Sensitivity to LQ decays is studied using a two-dimensional distribution: Scalar sum of transverse energies (SScalar sum of transverse energies (STT) ) vs. Dimuon invariant mass Mvs. Dimuon invariant mass M

The observed limit is calculated using CLThe observed limit is calculated using CLSS = CL = CLS+BS+B / CL / CLB B (T. Junk, NIMA434(1999) 435)(T. Junk, NIMA434(1999) 435)

NEW ! ! !

NEW ! ! !

Modified frequentistModified frequentist approachapproach

All events are arranged in 4 bins events are arranged in 4 bins choice of binning follows the ratio of choice of binning follows the ratio of the expected signal over background (S/B) for a leptoquark mass of 240 GeVthe expected signal over background (S/B) for a leptoquark mass of 240 GeV

D0 Run II Limits (294 pbD0 Run II Limits (294 pb-1-1):):

MMLQLQ > 247 GeV > 247 GeV ((jj channel, jj channel, LQLQ > 182 GeV > 182 GeV ((jj channel, jj channel, = 0.5) = 0.5)

The mass limit is extracted from the The mass limit is extracted from the intersection of the lower edge of theintersection of the lower edge of the

(NLO) with the observed upper (NLO) with the observed upper bound to the cross sectionbound to the cross section

CDF Run II CDF Run II (~200 pb(~200 pb-1-1):):(CDF Note 7216)(CDF Note 7216)

MMLQLQ > 241 GeV > 241 GeV ( ( = 1.0) = 1.0)MMLQLQ > 175 GeV > 175 GeV ( ( = 0.5) = 0.5)

D0 Combined (Run I + Run II):D0 Combined (Run I + Run II):(D0 Note 4829)(D0 Note 4829)

MMLQ LQ > 251 GeV> 251 GeV ((= 1.0)= 1.0) MMLQLQ > 204 GeV > 204 GeV (( = 0.5) = 0.5)

D0 Run II Limits (252 pbD0 Run II Limits (252 pb-1-1):):

MMLQLQ > 241 GeV > 241 GeV (eejj channel, (eejj channel, LQLQ > 218 GeV > 218 GeV (combined eejj & e(combined eejj & ejjjj

channels for channels for = 0.5) = 0.5)

Also CDF in Run II using eeqq, Also CDF in Run II using eeqq, eeqq & qq & qq channels (~200 pbqq channels (~200 pb-1-1):):

(hep-ex/0506074)(hep-ex/0506074)

MMLQLQ > 236 GeV > 236 GeV ( ( = 1.0) = 1.0)MMLQLQ > 205 GeV > 205 GeV ( ( = 0.5) = 0.5)

Combined result as a function of Combined result as a function of

eejjeejj

D0 Combined (Run I + Run II):D0 Combined (Run I + Run II):(Phys. Rev.D71,071104(2005))(Phys. Rev.D71,071104(2005))

MMLQ LQ > 256 GeV> 256 GeV (eejj, (eejj, = 1.0)= 1.0)MMLQLQ > 234 GeV > 234 GeV (combined(combined eejj & eeejj & ejj. jj. = 0.5) = 0.5)

Four-fermion contact interaction can beFour-fermion contact interaction can be applied to:applied to: Compositeness, Leptoquarks, New gauge bosonsCompositeness, Leptoquarks, New gauge bosons

by an appropriate choice of coefficients by an appropriate choice of coefficients ABAB

SMSMNewNew

physicsphysics

Quark and leptons might be composite objects and bound states of moreQuark and leptons might be composite objects and bound states of morefundamental constituents (“preons”);fundamental constituents (“preons”);

Quark-Lepton compositeness can be expressed through effective coupling coefficients, Quark-Lepton compositeness can be expressed through effective coupling coefficients, which depends on the ratio of coupling constant gwhich depends on the ratio of coupling constant g00 over scale of compositeness over scale of compositeness ::

ABAB * g * g002 2 / /

ABAB ((ABAB – chiral structure of the interation; A,B – chiral structure of the interation; A,B L(eft) - R(ight) quark/lepton helicities) L(eft) - R(ight) quark/lepton helicities)

At At << s, multiple fermion production processes will dominate over SM two-body<< s, multiple fermion production processes will dominate over SM two-bodyfermion scattering processesfermion scattering processes

At At 22 >> s, flavor diagonal contact interaction will modify SM cross-section for >> s, flavor diagonal contact interaction will modify SM cross-section for elastic fermion-fermion scatteringelastic fermion-fermion scattering

New Physics appear from the interference of any new particle field (M ~ New Physics appear from the interference of any new particle field (M ~ ) associated ) associated to a characteristic energy scale (to a characteristic energy scale ( >> s) with the >> s) with the SMSM field field

Limits are obtained independentlyLimits are obtained independentlyfor each separate channel for each separate channel (LL, RR, RL, LR, VV, AA) (LL, RR, RL, LR, VV, AA)

of contact interaction Lagrangian andof contact interaction Lagrangian andABAB = -1 = -1 constructive interference constructive interference -: -: ABAB = +1 = +1 destructive interference destructive interference

Quark CompositenessQuark Compositeness is most sensitive to the deviation in production of high-transverseis most sensitive to the deviation in production of high-transverse momentum jets relative to SM predictions;momentum jets relative to SM predictions;

Quark-Lepton CompositenessQuark-Lepton Compositeness would modify Standard Model Drell-Yan (DY) would modify Standard Model Drell-Yan (DY)cross-section for lepton pair production at large invariant massescross-section for lepton pair production at large invariant masses

Quark-Lepton Composite Models:Quark-Lepton Composite Models:The modified dilepton cross-section isThe modified dilepton cross-section is controlled by compositeness scale controlled by compositeness scale

and interference sign (I) with SM:and interference sign (I) with SM:

(I ~ (I ~ ABAB is the interference of DY and is the interference of DY and contact term, C is the pure contact term) contact term, C is the pure contact term)

Run II D0 Analysis have been performed in: Run II D0 Analysis have been performed in: pp pp qq qq /Z /Z LL406 pb406 pb-1-1) and ) and pp pp qq qq /Z /Z ee (L ~ 271 pb-1) ee (L ~ 271 pb-1)

Di-muon Channel:Di-muon Channel: 2 isolated 2 isolated (p (pTT > 15 GeV), cosmic veto and M > 15 GeV), cosmic veto and M > 50 GeV; > 50 GeV;Di-electron Channel:Di-electron Channel: 2 electrons (p2 electrons (pT T > 25 GeV), M> 25 GeV), Meeee >120 GeV >120 GeV

/Z/Z :: A 95% CL upper limit on A 95% CL upper limit on is computed from is computed from 2-dimen. distributions (M2-dimen. distributions (Mvs. scattering angle cosvs. scattering angle cos

using DATA, background and signal MC;using DATA, background and signal MC;

/Z /Z ee: ee: Limit is calculated using a Bayesian analysisLimit is calculated using a Bayesian analysisof the shape of the mass distribution of eventsof the shape of the mass distribution of events

ZZ

ZZ eeee SM MonteSM Monte Carlo:Carlo:

SM +CI SM +CI ((++ = 2 TeV) = 2 TeV)

MMeeee MM cos

cos

Limits of Compositeness Scale Limits of Compositeness Scale ::

HERA:HERA: Phys. Lett. 568(203)35, hep-ex/9905039; Phys. Lett. 568(203)35, hep-ex/9905039; LEP:LEP: Phys. Lett.B489(2000) 81, Eur. Phys. J.C12(2000) 183, Phys. Lett.B489(2000) 81, Eur. Phys. J.C12(2000) 183, Eur. Phys. J.C.13(2000) 553, Eur. Phys. J.C.11(1999) 383; http://lepewwg.web.cern.ch/LEPEWWG/lep2 Eur. Phys. J.C.13(2000) 553, Eur. Phys. J.C.11(1999) 383; http://lepewwg.web.cern.ch/LEPEWWG/lep2

CDF: CDF: Phys. Rev. Lett.79(12)(1997)2198; Phys. Rev. Lett. 78,(1997)4307,Phys. Rev. Lett.79(12)(1997)2198; Phys. Rev. Lett. 78,(1997)4307, D0: D0: D0 Note 4552, Phys. Rev. Lett. 82(1999)2457,D0 Note 4552, Phys. Rev. Lett. 82(1999)2457, APV: APV: Phys. Lett.B480(2000)149Phys. Lett.B480(2000)149

D0 Run II Results in di-electron (L= 271 pbD0 Run II Results in di-electron (L= 271 pb-1-1) ) and di-muon channels (L = 406 pband di-muon channels (L = 406 pb-1-1): ):

Parity violating terms (LL, RR, LR, RL) are constrained by APV experiments with Parity violating terms (LL, RR, LR, RL) are constrained by APV experiments with > 11 TeV > 11 TeV

Lower Lower Limit: Limit: Upper Upper Limit: Limit:

• The performance of Tevatron improves steadily allowing to test experimentally The performance of Tevatron improves steadily allowing to test experimentally wider range of new phenomena searches for an ultimate theorywider range of new phenomena searches for an ultimate theory

• No evidence for leptoquarks and compositeness has been observedNo evidence for leptoquarks and compositeness has been observed

• Combined D0 Run I + Run II Limits for scalar leptoquarks allow to exclude:Combined D0 Run I + Run II Limits for scalar leptoquarks allow to exclude: 11stst LQ generation up to 256 GeV (for LQ generation up to 256 GeV (for = 1) = 1)22ndnd LQ generation up to 251 GeV (for LQ generation up to 251 GeV (for = 1) = 1)

• D0 Run II Limits from 4.2 Tev to 9.8 TeV (for different chirality models) are theD0 Run II Limits from 4.2 Tev to 9.8 TeV (for different chirality models) are the most stringent limits in the dimuon channel for the compositeness scale most stringent limits in the dimuon channel for the compositeness scale

• Start counting on > 1 fbStart counting on > 1 fb-1-1 data sample data sample

a new era for searches at hadron collidersa new era for searches at hadron colliders

Run II D0 analysis have been performed in eeqq and eRun II D0 analysis have been performed in eeqq and eqq channels (252 pbqq channels (252 pb-1-1): ):

Selection:Selection: 2 Electrons and 2 Jets2 Electrons and 2 Jets2j (E2j (ETT>20 GeV) + 2e (E>20 GeV) + 2e (ETT>25 GeV) + Z-veto;>25 GeV) + Z-veto;

Main Backrounds: ZDY+jets, multi-jetsMain Backrounds: ZDY+jets, multi-jets

SST T = = EETT(j1) + E(j1) + ETT(j2) + E(j2) + ETT(e1) + E(e1) + ETT(e2)>450 GeV(e2)>450 GeV

Selection:Selection: 1 Electron, 2 Jets and Missing ET:1 Electron, 2 Jets and Missing ET:2j (E2j (ETT>25 GeV) + e (E>25 GeV) + e (ETT>25 GeV) + >25 GeV) +

MET > 30 GeV + W-vetoMET > 30 GeV + W-vetoMain backrounds:W+2jets,multi-jets, ttbarMain backrounds:W+2jets,multi-jets, ttbar

SSTT = E = ETT(j1) + E(j1) + ETT(j2) + E(j2) + ETT(e1) + MET>330 GeV(e1) + MET>330 GeV

1 event (DATA) vs1 event (DATA) vs 0.5 +- 0.1 events expected0.5 +- 0.1 events expected

30% signal efficiency (M30% signal efficiency (MLQLQ ~ 240 GeV) ~ 240 GeV)

1 event (DATA) vs1 event (DATA) vs 3.6 +- 1.2 events expected3.6 +- 1.2 events expected

18% signal efficiency (M18% signal efficiency (MLQ LQ ~ 200 GeV)~ 200 GeV)

Run II D0 analysis have been performed in Run II D0 analysis have been performed in qq channels (85 pbqq channels (85 pb-1-1): ):

SM bkg 38.4 +-3.7QCD 3.1 +- 2.0

Total bkg 41.5 +- 4.2DATA events 44

LQ mass range 85 -109 GeV is excludedLQ mass range 85 -109 GeV is excludedBy the Run II Analysis By the Run II Analysis

D0 Run I LimitD0 Run I Limit:(Phys. Rev. D64(2001)092004:(Phys. Rev. D64(2001)092004))

H1 Collaboration, hep-ex/0506044H1 Collaboration, hep-ex/0506044

= 1 (LQ branching fraction = 1 (LQ branching fraction to charged lepton and quark)to charged lepton and quark)

LEP Limits: http://lepewwg.web.cern.ch/LEPEWWG/lep2LEP Limits: http://lepewwg.web.cern.ch/LEPEWWG/lep2

Run II D0 Analysis have been performed in: pp Run II D0 Analysis have been performed in: pp qq qq /Z /Z LL406 pb406 pb-1-1))Selection:Selection: 2 isolated 2 isolated (p (pTT > 15 GeV), > 15 GeV),

cosmic veto and Mcosmic veto and M > 50 GeV; > 50 GeV;Backgrounds: Backgrounds: and bb productionand bb production

A 95 % CL upper limit on composite scale A 95 % CL upper limit on composite scale is computed is computed from the fit, using DATA, background and signal MCfrom the fit, using DATA, background and signal MC

2-dimensional distributions (M2-dimensional distributions (Mvs cosvs cos

better confidence limits on better confidence limits on than using only 1-dim M than using only 1-dim M

cos(cos(**scattering angle,scattering angle,relative to the direction of the relative to the direction of the boost of the dimuon systemboost of the dimuon system

Run II D0 Analysis have been performed in: pp Run II D0 Analysis have been performed in: pp qq qq /Z /Z ee (L ~ 271 pb ee (L ~ 271 pb-1-1))

Selection:Selection: 2 electrons (p2 electrons (pTT > 25 GeV), M > 25 GeV), Meeee >120 GeV >120 GeVBackgrounds: multijet and Backgrounds: multijet and /jet events /jet events estimated from the same data sample estimated from the same data sample

MMeeee

Bayesian Method to setBayesian Method to set limit on limit on

(separately for each (separately for each chirality channel):chirality channel):

To get a 95 % CL limit on To get a 95 % CL limit on ::