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P R L . 98, 041801 (2007)
FE R M IL A B -P U B -06/278-E
Experim ental discrimination between charge 2e/3 top quark and charge 4e/3 exotic
quark production scenarios
arXiv:hep-ex/0608044v2
26 Jan 2007
V.M . A bazov ,36 B. A b b o tt ,76 M. A bolins ,66 B.S. A charya ,29 M. A dam s ,52 T. A dam s ,50 M. A gelou ,18 S.H. A h n ,31
M. A h san ,60 G .D . A lexeev ,36 G. A lkhazov ,40 A. A lto n ,65 G. A lverson ,64 G.A. Alves ,2 M. A n astasoaie ,35
T. A ndeen ,54 S. A nderson ,46 B. A n d rieu ,17 M.S. A nzelc ,54 Y. A rnoud ,14 M. A rov ,53 A. Askew ,50 B. Â sm an ,41
A.C.S. Assis Je su s ,3 O. A tram en to v ,58 C. A u te rm a n n ,21 C. A vila ,8 C. Ay ,24 F. B a d a u d ,13 A. B ad e n ,62 L. B agby ,53
B. B a ld in ,51 D.V. B a n d u rin ,60 P. B an erjee ,29 S. B anerjee ,29 E. B arb eris ,64 P. B arg assa ,81 P. B a rin g e r ,59
C. B arn es ,44 J. B a rre to ,2 J.F . B a r tle tt ,51 U. B assler ,17 D. B a u e r ,44 A. B ean ,59 M. B egalli ,3 M. B egel ,72
C. B elang er-C h am p ag n e ,5 L. B ellan to n i ,51 A. Bellavance ,68 J.A . B enitez ,66 S.B. B eri ,27 G. B e rn a rd i ,17
R. B e rn h a rd ,42 L. B ern tzo n ,15 I. B e rtra m ,43 M. B esançon ,18 R. B euselinck ,44 V.A. B ezzubov ,39 P.C. B h a t ,51
V. B h a tn a g a r ,27 M. B in d er ,25 C. B isc a ra t ,43 K.M . B lack ,63 I. B lackler ,44 G. Blazey ,53 F . B lekm an ,44 S. B lessing ,50
D. B loch ,19 K. B loom ,68 U. B lum enschein ,23 A. B oehnlein ,51 O. B o eriu ,56 T.A . B o lto n ,60 G. B orissov ,43
K. B os ,34 T. B ose ,78 A. B ra n d t ,79 R. B rock ,66 G. B rooijm ans ,71 A. B ross ,51 D. B row n ,79 N .J. B u ch a n an ,50
D. B uchholz ,54 M. B u eh ler ,82 V. B uescher ,23 S. B u rd in ,51 S. B urke ,46 T.H . B u rn e tt ,83 E. B u sa to ,17 C.P. Buszello ,44
J.M . B u tle r ,63 P. C alfayan ,25 S. C alv et ,15 J. C am m in ,72 S. C aro n ,34 W . C arvalho ,3 B .C .K . Casey ,78 N.M. C ason ,56
H. C astilla-V aldez ,33 D. C h a k ra b o rty ,53 K .M . C h a n ,72 A. C h a n d ra ,49 F . C h arles ,19 E. C heu ,46 F. C hevallier ,14
D .K . C h o ,63 S. C hoi ,32 B. C h o u d h ary ,28 L. C hristofek ,59 D. C laes ,68 B. C lem ent ,19 C. C lem ent ,41 Y. C oadou ,5
M. C ooke ,81 W .E . C o o p er ,51 D. C oppage ,59 M. C o rcoran ,81 M .-C. C ousinou ,15 B. C ox ,45 S. C repe-R enaudin ,14
D. C u tts ,78 M. C w iok ,30 H. d a M o tta ,2 A. D as ,63 M. D as ,61 B. D avies ,43 G. D avies ,44 G.A. D avis ,54 K. D e ,79
P. de Jo n g ,34 S.J. de Jo n g ,35 E. De L a C ruz-B urelo ,65 C. De O liveira M a rtin s ,3 J.D . D eg en h ard t ,65 F. D eliot ,18
M. D e m a rte a u ,51 R. D em ina ,72 P. D em ine ,18 D. D enisov ,51 S.P. D enisov ,39 S. D esai ,73 H .T . D iehl ,51 M. D iesburg ,51
M. D oidge ,43 A. D om inguez ,68 H. D ong ,73 L.V. D udko ,38 L. D uflot ,16 S.R. D ugad ,29 D. D uggan ,50 A. D u p errin ,15
J. D yer ,66 A. D y sh k an t ,53 M. E a d s ,68 D. E d m u n d s ,66 T. E d w ard s ,45 J. E llison ,49 J. E lm sheuser ,25 V.D. E lv ira ,51
S. E n o ,62 P. E rm olov ,38 H. E v an s ,55 A. E vdokim ov ,37 V.N. E vdokim ov ,39 S.N. F a ta k ia ,63 L. Feligioni ,63
A.V. F erap o n to v ,60 T. F erb el ,72 F. F ied ler ,25 F. F ilth a u t ,35 W . F ish er ,51 H .E. F isk ,51 I. F leck ,23 M. F o rd ,45
M. F o rtn e r ,53 H. Fox ,23 S. F u ,51 S. Fuess ,51 T. G a d fo rt ,83 C .F. G alea ,35 E. G allas ,51 E. G alyaev ,56 C. G arcia ,72
A. G arcia-B ellido ,83 J. G a rd n e r ,59 V. G avrilov ,37 A. G ay ,19 P. G ay ,13 D. G ele ,19 R. G elhaus ,49 C .E. G erb e r ,52
Y. G ersh tein ,50 D. G illberg ,5 G. G in th e r ,72 N. G ollub ,41 B. G óm ez ,8 A. G oussiou ,56 P.D. G ran n is ,73 H. G reenlee ,51
Z.D. G reenw ood ,61 E.M . G regores ,4 G. G ren ier ,20 P h. G ris ,13 J.-F . G rivaz ,16 S. G rü n en d ah l ,51 M .W . G rünew ald ,30
F. G u o ,73 J. G uo ,73 G. G u tie rre z ,51 P. G u tierre z ,76 A. H aas ,71 N .J. H adley ,62 P. H aefner ,25 S. H agopian ,50
J. H aley ,69 I. H all ,76 R .E. H all ,48 L. H a n ,7 K. H an ag ak i ,51 P. H ansson ,41 K. H ard er ,60 A. H arel ,72
R. H arrin g to n ,64 J.M . H a u p tm a n ,58 R. H auser ,66 J. H ays ,54 T. H ebbeker ,21 D. H edin ,53 J.G . H egem an ,34
J.M . H einm iller ,52 A.P. H einson ,49 U. H eintz ,63 C. H ensel ,59 K. H ern er ,73 G. H esketh ,64 M.D. H ild re th ,56
R. H irosky ,82 J.D . H o b b s ,73 B. H oeneisen ,12 H. H o eth ,26 M. H ohlfeld ,16 S.J. H ong ,31 R. H ooper ,78 P. H ouben ,34
Y. H u ,73 Z. H u bacek ,10 V. H ynek ,9 I. Iashvili ,70 R. Illingw orth ,51 A.S. Ito ,51 S. J a b e e n ,63 M. Ja flre ,16 S. J a in ,76
K. Ja k o b s ,23 C. J a rv is ,62 A. Jen k in s ,44 R. Jesik ,44 K. Jo h n s ,46 C. Jo h n so n ,71 M. Jo h n so n ,51 A. Jonckheere ,51
P. Jo n sso n ,44 A. J u s te ,51 D. K afer ,21 S. K a h n ,74 E. K ajfasz ,15 A.M. K alin in ,36 J.M . K alk ,61 J.R . K a lk ,66
S. K a p p le r ,21 D. K arm an o v ,38 J. K a sp e r ,63 P. K a sp e r ,51 I. K a tsa n o s ,71 D. K a u ,50 R. K a u r ,27 R. K ehoe ,80
S.
K erm iche ,15 N. K h a la ty a n ,63 A. K h an ov ,77 A. K harchilava ,70 Y.M. K harzh eev ,36 D. K h atid z e ,71 H. K im ,79
T .J. K im ,31 M .H. K irby ,35 B. K lim a ,51 J.M . K ohli ,27 J.-P . K o n ra th ,23 M. K o p al ,76 V.M. K o rablev ,39 J. K o tch er ,74
B.
K o th a ri ,71 A. K oubarovsky ,38 A.V. K ozelov ,39 J. K ozm inski ,66 D. K ro p ,55 A. K ryem adhi ,82 T. K u h l ,24
A. K u m a r ,70 S. K u n o ri ,62 A. K u p co ,11 T. K u rca ,20’* J. K v ita ,9 S. L am m ers ,71 G. L an d sb erg ,78 J. Lazoflores ,50
A.-C. Le B ih a n ,19 P. L e b ru n ,20 W .M . L ee ,53 A. L eflat ,38 F. L ehner ,42 V. Lesne ,13 J. Leveque ,46 P. Lew is ,44 J. L i ,79
Q.Z. L i ,51 J.G .R . L im a ,53 D. L incoln ,51 J. L in n em an n ,66 V.V. L ipaev ,39 R. L ip to n ,51 Z. L iu ,5 L. L obo ,44
A. L obodenko ,40 M. L okajicek ,11 A. L ounis ,19 P. Love ,43 H .J. L u b a tti ,83 M. L ynker ,56 A.L. Lyon ,51 A.K .A. M aciel ,2
R .J. M a d a ra s ,47 P. M a ttig ,26 C. M agass ,21 A. M a g erk u rth ,65 A.-M. M agnan ,14 N. M akovec ,16 P.K. M al ,56
H.B. M albouisson ,3 S. M alik ,68 V.L. M alyshev ,36 H.S. M ao ,6 Y. M aravin ,60 M. M arten s ,51 R. M cC arthy ,73
D. M eder ,24 A. M elnitchouk ,67 A. M endes ,15 L. M endoza ,8 M. M erkin ,38 K .W . M e rritt ,51 A. M eyer ,21 J. M eyer ,22
M. M ich au t ,18 H. M iettin en ,81 T. M illet ,20 J. M itrevski ,71 J. M olina ,3 N.K. M ondal ,29 J. M onk ,45 R.W . M oore ,5
2
T. M oulik ,59 G.S. M u an za ,16 M. M ulders ,51 M. M ulhearn ,71 L. M undim ,3 Y.D. M u taf ,73 E. Nagy ,15
M. N aim u d d in ,28 M. N a ra in ,63 N.A. N au m an n ,35 H.A. N eal ,65 J.P . N egret ,8 P. N eustroev ,40 C. N oeding ,23
A. N om erotski ,51 S.F. N ovaes ,4 T. N u n n em an n ,25 V. O ’D ell ,51 D.C. O ’Neil ,5 G. O b ra n t ,40 V. O guri ,3 N. O liveira ,3
N. O sh im a ,51 R. O tec ,10 G .J. O tero y G arzo n ,52 M. O w en ,45 P. Padley ,81 N. P a ra s h a r ,57 S.-J. P a rk ,72 S.K. P a rk ,31
J. P a rso n s ,71 R. P a rtrid g e ,78 N. P a ru a ,73 A. P a tw a ,74 G. Paw loski ,81 P.M . P e re a ,49 E. P erez ,18 K. P e te rs ,45
P. P etro ff ,16 M. P e tte n i ,44 R. P ieg aia ,1 J. P ip e r ,66 M.-A. P leier ,22 P.L.M . P o d esta-L erm a ,33 V.M . P od stav k o v ,51
Y. Pogorelov ,56 M .-E. P o l ,2 A. P o m p o s ,76 B .G . P o p e ,66 A.V. P o p o v ,39 C. P o tte r ,5 W .L. P ra d o d a Silva ,3
H.B. P ro sp e r ,50 S. P ro to p o p e sc u ,74 J. Q ia n ,65 A. Q u a d t ,22 B. Q u in n ,67 M.S. R angel ,2 K .J. R a n i ,29 K. R a n ja n ,28
P.N. R atoff ,43 P. R enkel ,80 S. R eu cro ft ,64 M. R ijssenbeek ,73 I. R ip p -B au d o t ,19 F. R izatdinova ,77 S. R obinson ,44
R .F. R odrigues ,3 C. R oyon ,18 P. R ubinov ,51 R. R u ch ti ,56 V.I. R u d ,38 G. S a jo t ,14 A. S anchez-H ernández ,33
M.P. S an d ers ,62 A. S an to ro ,3 G. Savage ,51 L. Saw yer ,61 T. Scanlon ,44 D. Schaile ,25 R.D. Scham berger ,73
Y. Scheglov ,40 H. Schellm an ,54 P. Schieferdecker ,25 C. S c h m itt ,26 C. Schw anenberger ,45 A. S chw artzm an ,69
R. S chw ienhorst ,66 J. Sekaric ,50 S. S en g u p ta ,50 H. Severini ,76 E. S h ab alin a ,52 M. Sham im ,60 V. Shary ,18
A.A. S hchukin ,39 W .D . S h ep h ard ,56 R .K . S hivpuri ,28 D. Shpakov ,51 V. Siccardi ,19 R.A. Sidwell ,60 V. Sim ak ,10
V. S irotenko ,51 P. Skubic ,76 P. S lattery ,72 R.P. S m ith ,51 G .R . Snow ,68 J. Snow ,75 S. Snyder ,74 S. Soldner-R em bold ,45
X. Song ,53 L. Sonnenschein ,17 A. S opczak ,43 M. Sosebee ,79 K. S oustruznik ,9 M. Souza ,2 B. S purlock ,79 J. S ta rk ,14
J. Steele ,61 V. S tolin ,37 A. S to n e ,52 D.A. Stoyanova ,39 J. S tra n d b e rg ,41 S. S tra n d b e rg ,41 M.A. S tra n g ,70
M. S tra u ss ,76 R. S trü h m er ,25 D. S tro m ,54 M. S trovink ,47 L. S tu tte ,51 S. Sum ow idagdo ,50 A. S zn ajd e r ,3 M. Talby ,15
P. T am burello ,46 W . T aylor ,5 P. T elford ,45 J. Tem ple ,46 B. T iller ,25 M. T ito v ,23 V.V. T okm enin ,36 M. T om oto ,51
T. Toole ,62 I. T orchiani ,23 S. Towers ,43 T. Trefzger ,24 S. Trincaz-D uvoid ,17 D. T sybychev ,73 B. Tuchm ing ,18
C. Tully ,69 A.S. T u rc o t ,45 P.M . T u ts ,71 R. U n ala n ,66 L. U varov ,40 S. U varov ,40 S. U zunyan ,53 B. V achon ,5
P .J. van den B erg ,34 R. V an K o o te n ,55 W .M . van Leeuw en ,34 N. V arelas ,52 E.W . V arnes ,46 A. V a rta p e tia n ,79
I.A. Vasilyev ,39 M. V aupel ,26 P. V erdier ,20 L.S. V ertogradov ,36 M. Verzocchi ,51 F. V illeneuve-Seguier ,44 P. V in t ,44
J.-R . V lim a n t ,17 E. Von T oerne ,60 M. V outilainen,68’^ M. Vreeswijk ,34 H.D. W ahl ,50 L. W ang ,62 M .H.L.S W ang ,51
J. W archol ,56 G. W a tts ,83 M. W ayne ,56 M. W eber ,51 H. W eerts ,66 N. W erm es ,22 M. W etstein ,62 A. W h ite ,79
D. W icke ,26 G .W . W ilson ,59 S.J. W im penny ,49 M. W obisch ,51 J. W om ersley ,51 D .R. W ood ,64 T .R . W y a tt ,45
Y. X ie ,78 N. X u a n ,56 S. Y acoob ,54 R. Y am ada ,51 M. Y an ,62 T. Y asuda ,51 Y.A. Y atsunenko ,36 K. Y ip ,74
H.D. Yoo ,78 S.W . Y oun ,54 C. Y u ,14 J. Y u ,79 A. Yurkewicz ,73 A. Z atserklyaniy ,53 C. Z eitn itz ,26 D. Z hang ,51
T. Z hao ,83 B. Z hou ,65 J. Z hu ,73 M. Zielinski ,72 D. Ziem inska ,55 A. Ziem inski ,55 V. Z u tsh i ,53 and E .G . Zverev 38
(D 0 C ollaboration)
1 U niversidad de B u e n o s A ires, B u e n o s A ires, Argentina,
2L A F E X , C entro B rasileiro de P esquisas F ísicas, R io de Janeiro, B razil
3 U niversidade do E sta d o do R io de Janeiro, R io de Janeiro, B razil
4 In s titu to de F ísica Teórica,, U niversidade E sta d u a l P aulista, S a o P aulo, B razil
5 U niversity o f Alberta, E d m o n to n , A lberta, C anada, S im o n F raser U niversity, B urn a b y, B ritis h C olum bia, Canada,
York U niversity, Toronto, O ntario, C anada, and M cG ill U niversity, M ontreal, Quebec, C anada
6In s titu te o f H igh E n erg y P hysics, B eijin g , P e o p le ’s R epublic o f C hina
7 U n iversity o f S cien ce and Technology o f C hina, H efei, People ’s R epublic o f C hina
8 U niversidad de los A n d es, Bogotá, Colombia,
9 C en ter fo r P a rticle P hysics, Charles U niversity, Prague, Czech R epublic
10 Czech Technical U niversity, Prague, Czech R epublic
11 C en ter fo r P a rticle P hysics, In s titu te o f P hysics, A ca d e m y o f Scien ces o f the Czech R epublic, Prague, Czech R epublic
12 U niversidad S a n F rancisco de Q uito, Q uito, E cu a d o r
13Laboratoire de P h ysiq u e C orpusculaire, IN 2 P 3 -C N R S , U n iversité B la ise Pascal, C lerm ont-F errand, France
14Laboratoire de P hysique S u batom ique et de C osm ologie, IN 2 P 3 -C N R S , U niversite de Grenoble 1, Grenoble, France
15 C P P M , IN 2 P 3 -C N R S , U n iversité de la M éditerranée, M arseille, France
16IN 2 P 3 -C N R S , Laboratoire de l ’A ccéléra teu r L in éa ire, O rsay, France
17L P N H E , IN 2 P 3 -C N R S , U niversites P a ris V I and V II, P aris, France
18D A P N IA /S e r v ic e de P hysique des P articules, C E A , Saclay, France
19IP H C , IN 2 P 3 -C N R S , U n iversité L o u is P asteur, Strasbourg, France, and U n iversité de H a u te Alsace, M ulhouse, France
20I n s titu t de P hysiq u e N ucléaire de L yo n , IN 2 P 3 -C N R S , U n iversité C laude B ernard, V illeurbanne, France
21III. P h ysika lisch es In s titu t A , R W T H A achen, A achen, G erm a n y
22 P h ysika lisch es In s titu t, U n iversita t B o n n , B o n n , G erm a n y
23 P h ysika lisch es In s titu t, U niversita t Freiburg, Freiburg, G erm a n y
24 I n s titu t f ü r P hysik, U n iversita t M ainz, M ainz, G erm a n y
25L u d w ig -M a x im ilia n s-U n iv e rsita t M ün ch en , M ü n ch en , G erm a n y
26 Fachbereich P hysik, U n iversity o f W uppertal, W uppertal, G erm a n y
3
27P an ja b U niversity, C handigarh, In d ia
28 D elhi U niversity, D elhi, In d ia
29 Tata In s titu te o f F u n d a m en ta l Research, M um bai, In d ia
30 U n iversity College D ublin, D ublin, Ireland
31 K orea D etecto r Laboratory, K orea U niversity, Seoul, Korea,
32 S u n g K y u n K w a n U niversity, Suw on, K orea
33 C IN V E S T A V , M exico City, M exico
34F O M -In stitu te N IK H E F and U n iversity o f A m s te r d a m /N IK H E F , A m sterd a m , T he N eth erla n d s
35 R adboud U n iversity N ijm e g e n /N IK H E F , N ijm eg en , T he N eth erla n d s
36 J o in t In s titu te fo r N u clea r Research, D ubna, Russia,
37 In s titu te fo r Theoretical and E xp e rim e n ta l P hysics, M oscow, R u ssia
38 M oscow S ta te U niversity, M oscow, R u ssia
39 In s titu te fo r H igh E n erg y P hysics, P rotvino, R u ssia
40 P etersburg N u clea r P h ysics In s titu te , St. Petersburg, R u ssia
41L u n d U niversity, L u n d , Sw eden, R o ya l In s titu te o f Technology and S to ckh o lm U niversity, Stockholm , Sw eden, and
Uppsala U niversity, Uppsala, Sw eden
42 P h y sik I n s titu t der U niversitä t Z urich, Z urich, S w itzerla n d
43L a n ca ster U niversity, Lancaster, U nited K in g d o m
44Im p eria l College, L ondon, U nited K in g d o m
45 U niversity o f M a nchester, M anchester, U nited K in g d o m
46 U n iversity o f A rizo n a , Tucson, A riz o n a 85721, USA
47Law rence B erkeley N a tio n a l L aboratory a n d U niversity o f C alifornia, B erkeley, C alifo rn ia 94720, USA
48 C alifo rn ia S ta te U niversity, Fresno, C alifo rn ia 93740, USA
49 U n iversity o f C alifornia, R iversid e, C alifornia 92521, USA
50F lo rid a S ta te U niversity, Tallahassee, F lo rid a 32306, USA
51 F erm i N a tio n a l A ccelerator Laboratory, B ata via , Illin o is 60510, USA
52 U n iversity o f Illin o is at Chicago, Chicago, Illin o is 60607, USA
53N o rth e rn Illin o is U niversity, D eKalb, Illin o is 60115, USA
54N o rth w este rn U niversity, E v a n sto n , Illin o is 60208, USA
55In d ia n a U niversity, B loo m in g to n , In d ia n a 47405, USA
56 U n iversity o f N o tre D am e, N o tre D am e, In d ia n a 46556, USA
67P urdue U n iversity C alum et, H a m m o n d , In d ia n a 46323, USA
58Io w a S ta te U niversity, A m e s, Io w a 50011, USA
59 U n iversity o f K a n sa s, Lawrence, K a n sa s 66045, USA
60 K a n sa s S ta te U niversity, M a n h a tta n , K a n sa s 66506, USA
61 L o u isia n a Tech U niversity, R u sto n , L o u isia n a 71272, USA
62 U n iversity o f M aryland, College P ark, M a ryla n d 20742, USA
63B o sto n U niversity, B o sto n , M a ssa ch u setts 02215, USA
64 N o rth ea stern U niversity, B o sto n , M a ssa ch u setts 02115, USA
65 U n iversity o f M ichigan, A n n A rbor, M ich ig a n 48109, USA
66M ich ig a n S ta te U niversity, E a st L ansing, M ich ig a n 48824, USA
67 U n iversity o f M ississippi, U niversity, M ississip p i 38677, USA
68 U n iversity o f Nebraska, L incoln, N ebraska 68588, USA
69 P rin ce to n U niversity, P rin ceto n , N ew Jersey 08544, USA
70S ta te U n iversity o f N ew York, B uffalo, N ew York 14260, USA
71 C olum bia U niversity, N ew York, N ew York 10027, USA
72 U n iversity o f R ochester, R ochester, N ew York 14627, USA
73S ta te U n iversity o f N ew York, S to n y Brook, N ew York 11794, USA
74 B rookhaven N a tio n a l Laboratory, Upton, N ew York 11973, USA
75 L a n g sto n U niversity, L angston, O klahom a 73050, USA
76 U n iversity o f O klahom a, N o rm a n , O klahom a 73019, USA
77 O klahom a S ta te U niversity, S tillw a ter, O klahom a 74078, USA
78 B ro w n U niversity, P rovidence, R hode Isla n d 02912, USA
79 U n iversity o f Texas, A rlin g to n , Texas 76019, USA
80 S o u th e rn M eth o d ist U niversity, D allas, Texas 75275, USA
81 R ice U niversity, H ou sto n , Texas 77005, USA
82 U n iversity o f Virginia, C harlottesville, V irginia 22901, USA
83 U n iversity o f W ashington, Seattle, W a sh in g to n 98195, USA
(D ated : A u g u st 16, 2006)
W e p re se n t th e first e x p e rim e n ta l d isc rim in a tio n b e tw een th e 2 e /3 a n d 4 e /3 to p q u a rk electric
charg e scenarios, u sin g to p q u a rk p a irs (ii) p ro d u c e d in p p collisions a t \ / s = 1.96 T eV by th e F erm ilab
T e v a tro n collider. W e u se 370 p b _1 o f d a ta co llected b y th e D 0 e x p e rim en t a n d select e v en ts w ith
4
a t least one h ig h tra n sv e rse m o m e n tu m elec tro n or m u o n , h ig h tra n sv e rse en erg y im b alan ce, an d
fo u r or m o re je ts. W e d isc rim in a te b e tw een b- a n d b -q u ark je ts by u sin g th e ch arg e a n d m o m e n ta
of tra c k s w ith in th e je t cones. T h e d a ta is c o n siste n t w ith th e e x p e c te d electric charge, \q\ = 2 e /3 .
W e exclude, a t th e 92% C .L., t h a t th e sam p le is solely d u e to th e p ro d u c tio n o f exotic q u a rk p airs
Q Q w ith \q\ = 4 e /3 . W e place a n u p p e r lim it o n th e fra c tio n of Q Q p a irs p < 0.80 a t th e 90% C.L.
PA CS num bers: 13.85.Rm , 14.65.Ha
T h e heavy p article discovered by th e C D F and D0 col­
lab o ratio n s a t th e Ferm ilab T evatron p ro to n -an tip ro to n
collider in 1995 [1] is w idely recognized to be th e to p
q uark. C u rren tly m easured p ro p erties of th e p article are
consistent w ith sta n d a rd m odel (SM) ex p ectations for
th e to p q uark. However, m any of th e p ro p erties of the
p article are still p oorly known. In p articu lar, its electric
charge, a fu ndam ental q u a n tity ch aracterizing a particle,
has n o t yet been determ ined.
To d ate, it is possible to in te rp re t th e discovered p ar­
ticle as eith er a charge 2 e /3 or —4 e /3 q uark. In the
published to p q u ark analyses of th e C D F and D0 col­
lab o ratio n s [2 ], th ere is a two-fold am biguity in p air­
ing th e b-quarks an d th e W bosons in th e reaction
pp ^ t t ^ W + W - bb, an d equivalently, in th e electric
charge assignm ent of th e m easured particle. In addition
to th e SM assignm ent, t ^ W +b, “t ” ^ W - b is also con­
ceivable, in which case “t ” w ould actu ally be an exotic
q uark, Q, w ith charge q = —4 e /3 (charge-conjugate pro­
cesses are im plied). It is possible to fit Z ^ l + l - and
Z ^ bb d a ta assum ing a to p q u a rk m ass of m t = 270 GeV
an d a rig h t-h an d ed b-quark th a t m ixes w ith th e isospin
+ 1 /2 com ponent of an exotic doublet of charge —1e/3
an d —4 e /3 q uarks, (Q1 , Q 4 )R [3]. In th is scenario, the
—4 e /3 charge q u ark is th e p article discovered a t th e Tevatro n , an d th e to p quark, w ith m ass of 270 GeV, would
have so far escaped detection.
In th is L etter, we re p o rt th e first ex perim ental discrim ­
inatio n betw een th e 2 e/3 an d 4 e /3 charge scenarios. We
also consider th e case w here th e analyzed sam ple con­
tain s an ad m ix tu re of SM to p q uarks an d exotic quarks
an d place an u p p er lim it on th e exotic q u ark fraction.
O u r search s tra te g y assum es each q u ark decays 100% of
th e tim e to a W boson an d a b-quark. We use th e leptonplus-jets channel which arises w hen one W boson decays
leptonically an d one decays hadronically. T he charged
leptons (e /u ) originate from a direct W decay or from
W ^ t ^ e /u . We require th a t th e final sta te have at
least tw o b-quark je ts. T he d a ta used in th is L e tter were
collected by th e D0 experim ent from Ju n e 2002 th ro u g h
A ugust 2004 an d correspond to an in te g ra te d lum inosity
of 370 p b - 1 .
T h e D0 d etecto r includes a track in g system , calorim e­
ters, an d a m uon sp ectro m eter [4]. T he tracking sys­
tem is m ade u p of a silicon m icro strip track er (SM T)
an d a cen tral fiber tracker, located inside a 2 T su per­
conducting solenoid. T he SM T, w ith a typical strip
p itch of 50-80 um , allows a precise d eterm in atio n of
th e p rim ary in teractio n vertex (PV ) and an accurate
d eterm in atio n of th e im p act p a ram ete r of a track rela­
tive to th e P V [5]. T he tracker design provides efficient
charged-particle m easurem ents in th e pseu d o rap id ity re­
gion |n| < 3 [6 ]. T he calorim eter consists of a barrel
section covering |n| < 1 . 1 , and tw o end caps extending
to |n| « 4.2. T he m uon sp ectrom eter encapsulates the
calorim eter up to |n| = 2.0 and consists of th ree layers of
d rift cham bers and two or th ree layers of scintillators [7].
A 1.8 T iron toroidal m agnet is located outside th e in­
nerm ost layer of th e m uon detector.
We select d a ta sam ples in th e electron and m uon chan­
nels by requiring an electron w ith transverse m om entum
p T > 20 G eV an d |n| < 1.1, or a m uon w ith p T > 20 GeV
and |n| < 2.0. T he leptons are required to be isolated
from o ther particles using calorim eter and tracking in­
form ation. M ore details on th e lepton identification and
trigger requirem ents are given in Ref. [8 ]. W boson candi­
d ate events are th e n selected in b o th channels by requir­
ing m issing transverse energy, E t , in excess of 20 GeV
due to th e neutrino. To rem ove m ultijet background,
E T is required to be non-collinear w ith th e lepton di­
rection in th e transverse plane. Je ts are defined using
a cone algorithm [9] w ith radius A R = 0.5 [10]. These
events m ust be accom panied by four or m ore je ts w ith
p T > 15 G eV and ra p id ity |y| < 2.5. A fter all th e above
selection requirem ents are applied, we have a to ta l of 231
(277) events in th e m uon (electron) channel.
We use a secondary vertex tagging (SVT) algorithm
to reco n stru ct displaced vertices produced by th e decay
of B hadrons. Secondary vertices are reco n stru cted from
two or m ore tracks satisfying: p T > 1 GeV, > 1 hits
in th e SM T layers, and im pact p ara m e te r significance
dca/<rdca > 3.5. A je t is considered as SV T -tagged if
it contains a secondary vertex w ith a decay length sig­
nificance L xy/<TLxy > 7 [11]. T he d eterm in atio n of the
sam ple com position relies on b-tagging, c-tagging, and
light flavour tagging efficiencies and uses th e m eth o d de­
scribed in Ref. [12]. In order to increase th e p u rity of
th e sam ple we select only events w ith two or m ore SVTtagged jets. In th e selected sam ple of 21 events w ith two
SV T -tagged jets, th e largest (second largest) background
is Wbb (single to p q u ark [13]) pro d u ctio n w ith a contri­
b u tio n of « 5% ( « 1%) to th e num ber of selected events.
T he to p or a n ti-to p q u ark whose W boson decays
leptonically (hadronically) is refered to as th e leptonic
(hadronic) to p and th e associated b-quark is denoted b¿
(bh ). To com pute th e to p qu ark charge we need to i ) de-
5
cide which of th e tw o SV T -tagged je ts are bi and bh and
i i ) d eterm ine if bi an d bh are b- or b-quarks. T he detected
final sta te p a rto n s in th e t í can d id ate events com prise th e
bl an d bh quarks, tw o q u ark s from th e hadro nically de­
caying W boson, an d one m uon or one electron. T he four
highest-pT je ts can be assigned to th e set of final sta te
q u ark s according to m any p e rm u ta tio n s an d th ere are at
least tw o ways to assign th e SV T -tagged je ts to bi and
bh . For each p erm u tatio n , th e m easured four-vectors of
th e je ts an d lepton are fitted to th e t í event hyp o th e­
sis, tak in g into account th e ex perim ental resolutions and
constrain in g th e m ass of tw o W bosons to its m easured
value an d th e to p q u ark m ass to 175 GeV. We decide
which of th e SV T -tagged je ts are bl an d bh b y selecting
th e p e rm u ta tio n w ith th e highest p ro b ab ility of arising
from a t í event. S tudies on sim ulated t í show th a t this
gives th e correct assignm ent in a b o u t 84% of th e events.
We m easure th e absolute value of th e to p q u ark charge
on each side of th e event, given by Q 1 = |ql + qbl | on the
leptonic side an d Q 2 = | —ql + qbh | on th e hadronic side.
T he charge of th e lep to n is in d icated by ql , and qbl and
qbh are th e charges of th e SV T -tagged je ts on th e lep­
tonic an d h adronic side of th e event. T he charges qbl
and qbh are determ in ed by com bining th e p T and charge
of th e track s co ntained w ithin a cone of A R = 0 .5 around
th e SV T -tagged je t axis. B ased on an optim ization us­
ing sim ulated t í events g en erated w ith A L PG EN [14] and
G EA N T [15] for a full D0 d etecto r sim ulation, we define an
estim ato r for je t charge qjet = ( 2 i q¿ •pT.6) / ( 2 i pT.6)
w here th e su b scrip t i runs over all track s w ith p T >
0.5 G eV an d w ithin 0.1 cm of th e P V in th e direction
parallel to th e b eam axis.
To d eterm ine th e expected d istrib u tio n s for th e to p
q u ark charges Q 1 an d Q 2, it is crucial to determ ine the
expected d istrib u tio n s for qjet in th e case of a b-quark
or a b-quark je t. In « 5 % of th e t í events, one of the
SV T -tagged je ts is actu ally a c-quark je t arising from
W ^ c í (or its charge conjugate). Therefore we also
need to determ in e th e expected d istrib u tio n for qjet in
th e case of c- an d í-q u a rk jets.
We derive th e expected d istrib u tio n s of je t charge from
d ijet collider d a ta , enhanced in heavy flavor (b and c).
We select events w ith exactly tw o je ts, b o th S V T-tagged,
w ith p T > 15 G eV an d |y| < 2.5. T he m eth o d requires
th a t th e tw o je ts are of charge conjugate flavors. To
ensure this, we enhance bb an d c í p roduced by flavor cre­
atio n [16, 17, 18], by requiring th e azim uthal distance
betw een th e je ts to be larger th a n 3.0 an d one je t (des­
ig n ated as j j J to con tain a m uon w ith p T > 4 GeV. We
refer to th is sam ple as th e “tig h t dijet sam ple,” to j as
th e “ta g je t” an d to th e second je t j 2 as th e “probe je t.”
T he fraction of c í events in th e tig h t d ijet sam ple is
estim ated using th e d istrib u tio n of th e m uon transverse
m om entum w ith respect to th e ta g je t axis (p ^ 1). We
fit th e pTe1 d istrib u tio n w ith a sum of tw o p ^ 1 tem plates,
one for b-quark je ts (including b o th p ro m p t and cascade
decays) and one for sem i-m uonic decays inside c-quark
je ts. T his leads to a fraction x c of c í events of 1-1%
in th e tig h t dijet sam ple and since th e light flavor ta g ­
ging efficiency is « 1 5 tim es lower, we also conclude th a t
th e fraction of lighter flavor je ts is negligible. T he m uon
inside th e ta g je t comes either i) from a direct B m eson
decay, ii) a B ^ D m eson cascade decay, iii) an oscillated
n eu tral B meson, or iv) a direct D m eson decay. We find
th a t fu rther con trib u tio n from indirect D m eson decay
can be neglected. C harge flipping processes ii) and iii)
lead to a m uon of opposite charge to th a t of th e qu ark
in itiatin g th e ta g je t and therefore of sam e sign as the
q u ark in itiatin g th e probe je t. We find, w ith P Y TH IA [19]
sim ulated events and E V T G E N [20] for heavy flavor de­
cays, th a t charge flipping processes are x = (30 ± 1)%
of th e bb events in th e tig h t dijet sam ple. T his fraction
is experim entally confirm ed by studying charge correla­
tio n betw een m uons in back-to-back m uon-tagged dijet
events.
We denote th e charge d istrib u tio n s for th e probe je t
w hen th e m uon on th e ta g side is positive or negative as
P M+ and P M- . Sim ilarly we define P f to be th e charge
d istrib u tio n w hen th e je t is of flavor f = b, b, c, í. Given
th e fractions of c í events and of charge flipping processes
we can w rite
P M+ = 0.69Pb + 0.30Pb + 0.01P 5
P M-
= 0.30Pb + 0.69Pb + 0.01Pc.
(1)
P M+ and P M- are distrib u tio n s observed in d a ta and are
adm ixtures of th e qu ark charge d istributions. E q u a ­
tions 1 are n o t sufficient to ex tra c t th e four probabil­
ity density functions (p.d.f.’s) P f . Therefore we define
a “loose dijet sam ple,” where j is n o t required to be
SV T -tagged. U sing th e sam e techniques as for th e tig h t
dijet sam ple, we find th a t xc = (19 ± 2)% and th e sam e
fraction of charge flipping processes as for th e tig h t dijet
sam ple. We refer to P ^ + (P ^- ) as th e observed p .d .f.’s
for qjet on th e probe je t in th e loose dijet sam ple, when
th e ta g m uon is positive (negative). T hus we can w rite
P ¿ + = 0.567Pb + 0 .2 4 3 P + 0.19P5
P¿ -
= 0.243Pb + 0 .5 6 7 P + 0.19Pc.
(2)
We solve Eqs. 1 and 2 to o b tain th e P f for b-, b-, c-, and
í-q u a rk jets.
T he P f ’s are dependent on th e je t p T , since p T cor­
relates w ith trac k m ultiplicity in th e je t, and on the
je t y, since th e tracking efficiency is rapidity-dependent.
T herefore we m ust account for th e different je t p T and y
sp ec tra betw een th e probe je ts of th e dijet sam ples and
th e b-quark je ts in preselected t í events. T he P f ’s ob­
ta in ed above are corrected by w eighting th e d a ta events
to th e p T and y sp ec tra of S V T -tagged je ts in t í events.
F igure 1(a) shows th e resulting P b and P .
We derive th e expected distrib u tio n s for Q 1 and Q 2
by applying th e assignm ent procedure betw een th e SVT-
6
tagged je ts an d th e bh , bl q uarks on sim ulated t t events
using our calcu lated P f ’s. T he tru e flavor f of th e SVTtagged je ts is determ in ed from th e sim ulation inform a­
tion. T he values of qbh an d qbl are o b tain ed by random ly
sam pling th e d istrib u tio n of P f for th e corresponding fla­
vors. A bout 1% of t t can d id ate events contain a SVTtagged light-flavor je t. In th is case th e p.d.f. for qjet
is tak en from sim ulation. In th e case of a |q| = 4e/3
exotic q uark, th e expected d istrib u tio n s of exotic quark
charge are derived by com puting Q 1 = | — ql + qbl | and
Q 2 = |ql + qbh |, following th e sam e procedure as for the
SM to p quark. T he u n c e rta in ty on th e m ass of th e to p
qu ark [2 1 ] is p ro p a g a te d as a system atic uncertainty.
T h e expected d istrib u tio n s of Q 1 an d Q 2 for th e back­
ground are o b tain ed by i ) perform ing th e assignm ent pro­
cedure betw een S V T -tagged je ts an d th e bh, bl quarks on
Wbb sim ulated events, i i ) using th e tru e je t flavors f to
sam ple th e corresponding P f ’s. T he resu ltin g d istrib u ­
tions of Q 1 an d Q 2 for th e background are ad ded to the
to p charge d istrib u tio n s in th e SM an d exotic cases. We
denote Psm (P ex) th e p .d .f.’s for Q 1 an d Q 2 including the
background co n trib u tio n s in th e SM (exotic) case.
For 16 of th e 21 selected lepton-plus-jet events, the
kinem atic fit converges an d we can assign th e SVTtagged je ts to th e bl an d bh q uarks, th u s providing 32
m easurem ents of th e to p q u ark charge. Figure 1(b) shows
th e 32 observed values of Q 1 an d Q 2 overlaid w ith the
SM an d exotic charge distrib u tio n s.
To discrim inate betw een th e SM an d th e exotic hy­
potheses, we form th e ra tio of th e likelihood of th e ob­
served set of charges qi arising from a SM to p q u ark to
th e likelihood for th e set of qi arising from th e exotic
scenario, A = [ i PsM(qi)] / [n¿ Pex(qi)]. T he subscript
i ru n s over all 32 available m easurem ents. T he value of
th e ra tio is determ in ed in d a ta an d com pared w ith the
expected d istrib u tio n s for A in th e SM an d exotic scenar­
ios. We find th a t th e observed set of charges agrees well
w ith those of a SM to p quark. T he p ro b ab ility of our ob­
servation is 7.8% in th e case w here th e selected sam ple
contains only exotic q uarks w ith charge |q| = 4 e/3 , in­
cluding sy stem atic uncertain ties. T hus, we exclude a t the
92.2% C.L. th a t th e selected d a ta set is solely com posed
of an exotic q u ark w ith |q| = 4 e/3 . T he corresponding
expected C.L. is 91.2%. Table I sum m arizes th e dom i­
n a n t system atic u n certain ties an d th e ir cum ulative effect
on th e C.L.
It is n o t excluded th a t th e d a ta contain a m ix tu re of
two heavy quarks, one w ith |q| = 2 e/3 an d one w ith |q| =
4 e/3 . We perform an u nbinned m axim um likelihood fit
to th e observed set of qi in d a ta to d eterm ine th e fraction
p of exotic q u a rk pairs. T he likelihood of th e observed
set of qi can be expressed as a function of p by
N
L (pj q) =
data
]^[ (1 — p )P SM(qi ) + p P ex (qi )
i =1
(3)
S y ste m a tic
O bserv ed E x p e c te d
S ta tis tic a l u n c e rta in ty only
95.8
95.3
+ F ra c tio n of cc ev en ts
95.8
95.2
+ C h arg e-flip p in g processes
95.7
95.2
+ W eig h tin g w .r.t. p T a n d y s p e c tra
94.4
94.1
+ F ra c tio n of flavor c re a tio n
93.7
93.4
+ S ta tis tic a l e rro r o n P f
93.3
93.1
+ J e t en erg y c a lib ra tio n “
92.4
91.8
+ T op q u a rk m ass
92.2
91.2
“R eference [22].
T A B L E I: E x p e c te d an d observ ed confidence levels as func­
tio n of th e cu m u la te d sy ste m a tic u n c e rta in tie s.
F igure 1(c) shows —ln L as function of p. We fit p =
—0.13 ± 0 .6 6 (stat) ± 0.11(syst), consistent w ith th e SM.
Using a B ayesian p rio r equal to one in th e physically
allowed region 0 < p < 1 an d zero otherw ise, we o b tain
0 < p < 0.52 a t th e 6 8 % C.L. and 0 < p < 0.80 a t the
90% C.L.
In sum m ary, we present th e first experim ental discrim ­
in atio n betw een th e 2e/3 and 4 e /3 to p q u ark electric
charge scenarios. T he observed to p q u ark charge is con­
sistent w ith th e SM prediction. T he hypothesis th a t only
an exotic q u ark w ith charge |q| = 4 e /3 is produced has
been excluded a t th e 92% C.L. We also place an up p er
lim it of 0.80 a t th e 90% C.L. on th e fraction of exotic
q u ark pairs in th e double tagged lepton-plus-jets sam ple.
We th a n k th e staffs a t Ferm ilab and collaborating in­
stitu tio n s, and acknowledge su p p o rt from th e D O E and
NSF (USA); C E A and C N R S /IN 2 P 3 (France); FASI,
R osatom and R F B R (Russia); C A PE S, C N Pq, F A P E R J,
F A P E S P and FU N D U N E SP (Brazil); DAE and DST
(India); Colciencias (Colom bia); C O N A C yT (Mexico);
K R F and K O S E F (K orea); C O N IC E T and U B A C yT
(A rgentina); FO M (T he N etherlands); P PA R C (U nited
K ingdom ); M SM T (Czech R epublic); CRC P rogram ,
C FI, NSERC and W estG rid P ro je c t (C anada); B M B F
and D FG (G erm any); SFI (Ireland); T he Swedish Re­
search Council (Sweden); R esearch C orporation; A lexan­
der von H um boldt F oundation; and th e M arie C urie P ro ­
gram .
[*] O n leave from IE P SAS K osice, Slovakia.
[f] V isito r from H elsinki I n s titu te of P h y sics, H elsinki, F in ­
land.
[1] C D F C o lla b o ra tio n , F . A b e et al., P h y s. R ev. L e tt. 74,
2626 (1995); D 0 C o lla b o ra tio n , S. A b ach i et al., P hys.
R ev. L e tt. 7 4 , 2632 (1995).
[2] P. C. B h a t, H. P ro sp e r, a n d S. S. S n y d er, In t. J. M od.
P h y s. A 1 3 , 5113 (1998).
[3] D. C h an g , W . C h an g , a n d E. M a, P h y s. R ev. D 59,
091503 (1999); 6 1 , 037301 (2000); D . C h o u d h u ry , T . M.
T a it an d C. E. W ag n er, P h y s. R ev. D 6 5 (2002) 053002.
7
d 0.12 “ DO, 370pb"VL hH
¿ 0.1
T a
-P b
ù-“0.08
- Pb
¿
¥
0.06
0.04 h
V
y /
0.02 - 0
-1
-0.5
0.5
(a)
Jet charge [e]
(A 14
c 12
«
> 10
e
8
e 6
■Q 4
E 2
3
0
-t
■t
110 h ™
] DO, 370pb-1
- Stat. only
- Stat. + syst.
I
Physical region,.
108t
109t
107t
106
Top quark charge [e]
0.5
0
0.5
1
1.
Fraction of exotic quarks
F IG . 1: (a) b a n d b je t ch arg e d is trib u tio n s d eriv ed from d ije t d a ta , (b) th e 32 m easu red values o f th e to p q u a rk charge
co m p ared to th e e x p e c ted d is trib u tio n s in th e SM an d exotic cases, a n d (c) likelihood fit of th e fra c tio n of exotic q u a rk pairs
in th e selected d a ta sam ple.
[4] D 0 C o llab o ratio n , V. A bazo v et al., N ucl. In s tru m . M eth .
A 5 6 5 , 463 (2006).
[5] Im p a c t p a ra m e te r is defined as th e d ista n c e o f closest
a p p ro a c h (dca) o f th e tra c k to th e p rim a ry v e rte x in th e
p la n e tra n sv e rse to th e b eam lin e. Im p a c t p a ra m e te r sig­
nificance is defined as d ca/ a dca, w here o daa is th e u n c e r­
ta in ty on d ca.
[6] R a p id ity y a n d p se u d o ra p id ity n are defined as fu n c­
tio n s of th e p o la r angle 6 a n d p a ra m e te r ß as y ( 6 ,ß ) =
l+<3c
|l o g ( 1 —ß cos 9j)> a n d ??($) = y (6 ,1 ), w here ß is th e ra tio of
a p a rtic le ’s m o m e n tu m to its energy.
[7] D 0 C o llab o ratio n , V. A bazo v et al., N ucl. In s tru m . M eth .
A 5 5 2 , 372 (2005).
[8] D 0 C o llab o ratio n , V. A bazov et al., P h y s. L e tt. B 6 2 6 ,
45 (2005).
[9] W e use th e ite ra tiv e , seed -b ased cone a lg o rith m in clu d in g
m id p o in ts, as d esc rib e d o n p. 47 in G. C. B lazey et al.
in “Q C D and W eak B o so n P h ysics in R u n II, ” e d ite d by
U . B a u r, R. K . Ellis, a n d D . Z eppenfeld, F E R M IL A B P U B -00-297 (2000).
[10] A R is defined as a cone in p se u d o ra p id ity - a n d 0-sp ace,
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p rim a ry to th e seco n d ary v e rte x in th e p la n e tra n sv e rse
to th e beam lin e. D ecay le n g th significance is defined as
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