The X(3872) at the Tevatron

The X(3872) at the Tevatron

Ulrich Kerzel, University of Karlsruhefor 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

p s :

• 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

andi

date

s / 1

0 M

eV/c

0

200

400

600

800 Dfl

(2S)

X(3872)

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

2C

andi

date

s / 1

0 M

eV/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 D0Original 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

D0D0: 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

Frac

tion

Dfl

p >

15

GeV

T

y <

1 (i

.e, c

entra

l)

xyL <

0.0

1 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¡ m½ m½ ½m¼¼

for broad resonances (kinematic factors vary across width)

form-factor

A! BC ;A! BCµ

k¤k¤

¶L µf k¤f k¤

¶ ³ mm

´


The m(+ -) mass spectrum2

Can

dida

tes

/ 5 M

eV/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(

3872

) yie

ld p

er 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¡ M ½ = £ 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)

0D¤ 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

p s :

The Tevatron

p s :

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 ¡ fSig

´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=¿Siglifetime 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¡ ¯xupx0 : turn-on valuexlow, xup : fit range

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The X(3872) at the Tevatron