The X(3872) at the Tevatron Ulrich Kerzel, University of Karlsruhe for the CDF and D0 collaborations Beauty 2005

The X(3872) at the Tevatron

Ulrich Kerzel, University of Karlsruhe

for the CDF and D0 collaborations

Beauty 2005

24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 2

• observe at• 1 fb-1 luminosity delivered early June• huge inelastic cross-section:

¼ 5000 times bigger than for) triggers are essential!

• events “polluted” by fragmentation tracks, underlying events ) need precise tracking and good

resolution

Physics at the Tevatronpp

ps :

• dedicated trigger for J/ ! + -

• trigger events where m(+-) around m(J/) ) high quality J/ events with large statistics

• channel J/ ! e+e- much more challenging in hadronic environment

bb


CDF:• precise tracking:

(silicon vertex detector and drift chamber)

• important for B physics:

direct trigger for displaced vertices

D0:• excellent muon system and coverage• large forward tracking coverage• new in RunII: magnetic field

) D0 has joined the field of B physics


)2

(GeV/c- - M-+-+M0.6 0.7 0.8 0.9 1

2C

and

idat

es /

10

MeV

/c

0

200

400

600

800 Dfl

(2S)

X(3872)

)2

(GeV/c-+M2.9 33 .1 3.2 3.3

2C

an

did

ate

s /

10

Me

V/c

0

10000

20000

J/

Observation of X(3872) at CDF and D0PRL 93,162002 (2004) hep-ex/0405004

)2

Mass (GeV/cJ/3.65 3.70 3.75 3.80 3.85 3.90 3.95 4.00

2C

andi

date

s/ 5

MeV

/c

1000

2000

3000

4000

5000

6000

-+J/

J/

3.80 3.85 3.90 3.951700

1800

1900

2000

2100

2200CDF IIPRL 93,072001 (2004)

reported widths are compatible with detector resolution

no signal in wrong-signcombination, i.e. X++, X--

M : § : stat § : syst:

¾ § M : § : stat § : syst

¾ : § :

hep-ex/0312021

D0


)2

Mass (GeV/c-+J/3.65 3.70 3.75 3.80 3.85 3.90 3.95 4.00

2C

andi

date

s/ 5

MeV

/c

0

500

1000

1500

2000

2500

3000

2) > 0.5 GeV/c-+M(

2) < 0.5 GeV/c-+M(

3.80 3.85 3.90 3.95

900

1000

1100

1200

1300

1400CDF II

Observation of X(3872) at CDF and D0

Original observation by Belle:m(+ -) clusters at large values

D0: demand m(+ -) > 0.52 GeV/c2 as default cut

CDF: separately plot m(J/ + -) for m(+ -) > 0.5 GeV/c2

and m(+ -) < 0.5 GeV/c2

) no apparent signal form(+ -) < 0.5 GeV/c2

PRL 93,072001 (2004) hep-ex/0312021


X(3872): central vs. forwardPRL 93,162002 (2004) hep-ex/0405004

D0

D0: large muon coverage

) reconstruct X(3872)in central and forward partof the detector

2S) and X(3872) behavevery similar in both rapidity ranges


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1(2S)

X(3872)

Comparison

Fra

ctio

n

Dfl

p >

15

GeV

T

y <

1 (

i.e, c

entr

al)

xyL

< 0

.01

cm

isol

ated

cos(

) <

0.4

cos(

) <

0.4

X(3872) properties

) X(3872) behaves similarly to the (2S)

compare fraction of yields w.r.t initial selection

isolation: p(X) / p(X + charged tracks in cone R = 0.5)

, : boost one of the pions (muons) in dipion (dimuon) rest-frame,

Lxy : distance (PV – decay vertex) * M/pt

PRL 93,162002 (2004) hep-ex/0405004

D0


X(3872) production fraction from B

Define pseudo-proper decay time:

L xy ~x ¡ ~x ¢~ptj~ptj

decay

PV

Unbinned LogL fit (simultaneously for c and M):• Mass:

• signal: Gaussian • BG : 2nd order polynomial for BG

• Proper time:• signal: exponential• BG : 2 pos., 1 neg. exponential all folded with Gaussian due to resolution

c¿ M J = ¼ ¼¡ pt J = ¼ ¼¡ L xy


) X(3872) behaves similarly to the (2S)

(with given uncertainties)


fraction from B decays:

2S): 28.3 § 1.0 (stat.) § 0.7 (syst.) %

X(3872): 16.1 § 4.9 (stat.) § 1.0 (syst.)%


Consistency check:overlay m(J/ + -) spectrumwith prediction from LogL) data is described well

N.B. almost no prompt signalfor c > 100 m



The m(+ -) mass spectrumDistribution of m(+ -) constrains quantum numbers JPC

shape depends on:• decay of (+ -) sub-system: (+ -) in s,p,d wave

(i.e. intermediate sub-resonances or not)• relative angular momentum between (+ -) and (+ -) • (and detector acceptance, efficiency, etc.)

e.g. for decay chain: X! J/ , ! + -

d Xdm¼¼

m¼¼ X ! J = ½m¼¼¢m½ ½! ¼¼m¼¼

m¼¼¡ m

½ m½

½m¼¼

for broad resonances (kinematic factors vary across width)

form-factor

A! BC ;A! BC

µk¤

k¤

¶L µf k¤f k¤

¶ ³mm

´


The m(+ -) mass spectrum2

Ca

nd

ida

tes

/ 5

Me

V/c

0

100

200

300

400

500

3.8 3.9

-1CDF II Preliminary, 360 pb

38 (stat.) X's102

2) < 650 MeV/c625 < M(

3.8 3.9 4

]2

Mass [GeV/cJ/

35 (stat.) X's165

2) < 710 MeV/c690 < M(

3.9 4

30 (stat.) X's182

2) < 765 MeV/c750 < M(

Challenge: Large background, rather low X(3872) yield) sideband-subtraction difficult, instead:

“slicing technique”• impose bin borders in m(+ -) as additional cuts• fit resulting (- + -) mass spectrum• obtained yield shows variation with m(+ -)

need to be careful at kinematic borders


The m(+ -) mass spectrum

0.4 0.6 0.8

2X

(38

72

) y

ield

pe

r 2

0 M

eV

/c-50

0

50

100

150

200

250

-1 CDF II Preliminary, 360 pb

]2

Mass [GeV/c

-+ J/X(3872) J/

Phase-SpaceJ/

1S3

x 51P1

JD3

:cMultipole Expansions for c

-1 CDF II Preliminary, 360 pb

d ½dm¼¼

/ m¼¼¡ M½ = £ P S

if (+-) in S-wave state: ) shape needs to be modelledcompare to multipole expansions

if (+-) form sub-resonance:) shape follows Breit-Wignere.g. decay via 0 ! + -

(no kinematics, form-factor here)

• m(+-) favours high end of mass spectrum ) compatible with intermediate 0 ! + - resonance

• also 3S1 multipole-expansion for charmonium possible• no charmonium candidate at that mass• 3S1 also has JPC = 1– ) non-observation by BES ((e+e-)B(+-J/) < 10 eV @90% C.L. )

notation: n2s+1LJ (JPC)

hep-ph/0310261


X(3872) with J/ ! e+ e-

Reconstruction of J/ ! e+e- very difficult in complex hadronic environment

• dedicated J/ ! e+e- trigger• use neural-network based approach to

identify soft e§ (pt > 2GeV/c)• reject e§ from conversions based on neural network approach• add at J/ vertex to accommodate Bremsstrahlung• X(3872) reconstructions follows

J/ + - case(replace cut on m(+-) by cut on Q = mX – mJ/ – m

) able to reconstruct X(3872) in this channel!

strong radiative tail


What is the X(3872) ?? Charmonium ?

2 1P1, i.e. h0c (1+-)

predicted at ¼ 3950 MeV/c2

why is the 1P1 hc not seen in J/ +- ?

Belle: |cosJ/| distribution does not fit

11D2 (2-+) pos. C-parity

1 3D2 (2--), 1 3D3(3--) then also decay: X! c1 , X! c

) if charmonium, very unusual properties!

charmed molecule? hybrid state, i.e. ? “Deuson” ?

ccg

(hep-ex/0408116)

notation: n2s+1LJ (JPC)


DeRujula, Georgi, Glashow (1977):Charmed molecules?

J/

X(3872) ??

D D;D D¤

D¤D¤

D D¤¤; D¤ D¤¤

J = ½ ; J = ´

possible formation of4q “molecules”:

decay via:


„Deuson“ model (Törnqvist)

0

D¤ DX(3872) similar to deuteron:• composed of two objects• bound by 0 exchange

Prediction:• JPC = 1++ or 0-+

(otherwise potential too weak or repulsive)• small binding energy:

• narrow resonance, big object• isospin breaking:

• X! J/ 0, 0 ! +- allowed• X! J/ forbidden for any isoscalar • X! J/ 0 0 forbidden


Further properties by B-factories

BaBar: search for charged partner X§ ! J/ §

expect twice the rate if X is part of iso-triplett

) no signal found

Belle: 4 evidence for decay X(3872) ! J/ evidence for decay X! J/ +

) Swanson: 1++

has contribution of X ! J/ , ! +

search for X! c1 , X!

) no signal found

C = +1

D D¤ (hep-ph/0311229)

(hep-ex/0505037)

(hep-ex/0408083)


Conclusions & Outlook X(3872) observed at CDF and D0 with high

statistical significance already many properties determined:

behaves similar to (2S): isolation, cos(,), rapidity y fraction from B decays + - mass distribution

experimental evidence seems to point to: X(3872) has positive C parity X(3872) compatible with ‘molecular’ interpretation + - spectrum compatible with intermediate 0 hypothesis

yet to come: determination of JPC (CDF), decay modes with photons (D0), ...


BACKUP


CDF D0

Tevatron

Main injectorand recycler

RunI: 1992 – 1996data taking period at

RunII: 2001 – 2009major upgrades tocollider anddetectors

ps :

The Tevatron

ps :

pp


Tevatron performance

Running well - both peak luminosity and integrated luminosityCurrently ~15 pb-1 / week delivered

1 fb-1 delivered in beginning of June .


CDF:• precise tracking:

(silicon vertex detector and drift chamber)

• important for B physics:

direct trigger for displaced vertices

D0:• excellent muon system and coverage• large forward tracking coverage• new in RunII: magnetic field

) D0 has joined the field of B physics


Physics at the Tevatron• large b production rates:

) 103 times bigger than !

• spectrum quickly falling with pt

• Heavy and excited states not produced at B factories:

• enormous inelastic cross-section:

) triggers are essential

• events “polluted” by fragmentation tracks, underlying events

) need precise tracking and good resolution!

S

Bc; Bs; B¤¤; b; b; : : :

¾pp;j´j < : ¼ ¹


Dedicated trigger J/ ! + -

trigger events where m(+ -) around m(J/) • high quality J/ events• large statistics available

N.B. channel J/ ! e+e- much more challenging in complex hadronic environment!

Evaluate muon chamber info on trigger level:


Likelihood function for measuring fraction from B

L Ni

hf Sig ¡ f LL L P f LLL LL

³ ¡ f Sig

´L B

idefine likelihood:

L i F i c¿ £ M im composed of lifetime and mass functions

M Sigm Gm ¡ m; ¾ Signal: Gaussian, m0, 0 from full fit

M B m a a m ¡ m a m ¡ m Background: 2nd degree polyn.

F c¿ Rc¿0¡ c¿; ¾¿ ¡ c¿0=¿Sig

lifetime component: exponential with Gaussian resolution

mass component:


Systematics for measuring fraction from B• mass window

• shift window at fixed width of 130 MeV/c2

• vary width of mass window: 50-250 MeV/c2

• fit model• vary parameterisations, e.g. 2 Gaussians instead of 1, etc. (negligible for X(3872))

• multiple candidates (Lxy dominated from J/ decay)• randomly select one candidate• take highest/lowest pt candidate• take candidate with largest m(+-)• take candidate with smallest error on Lxy

• take candidate with lowest 2 in vertex fit

• fit bias • generate many pseudo-experiments (Toy-MC) from original fit• define pulls and check for deviations from Gaussian at zero


Systematics for m(+-) measurement

• Yield systematics:• compare yield from Gaussian with counting bin entries• replace background parametrisation

with polynomial(n.b. special treatment for points at kinematic boundary)

• vary fit window size from 200 MeV/c2 to 150, 250 MeV/c2

• Efficiency systematics:• efficiency correction determined from MC• measure pt spectrum from data, vary parameters

A ® x¡ x ®

xup¡ xlow® ¢ ¯e¡ ¯x

e¡ ¯xlow¡ e¡ ¯xup

x0 : turn-on valuexlow, xup : fit range

Documents

The X(3872) at the Tevatron Ulrich Kerzel, University of Karlsruhe for the CDF and D0 collaborations Beauty 2005