the x(3872) at the tevatron ulrich kerzel, university of karlsruhe for the cdf and d0 collaborations...
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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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 3
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 4
)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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 5
)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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 6
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 7
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 8
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 9
) X(3872) behaves similarly to the (2S)
(with given uncertainties)
X(3872) production fraction from B
fraction from B decays:
2S): 28.3 § 1.0 (stat.) § 0.7 (syst.) %
X(3872): 16.1 § 4.9 (stat.) § 1.0 (syst.)%
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 10
Consistency check:overlay m(J/ + -) spectrumwith prediction from LogL) data is described well
N.B. almost no prompt signalfor c > 100 m
X(3872) production fraction from B
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 11
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
´
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 12
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 13
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 14
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 15
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)
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 16
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:
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 17
„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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 18
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)
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 19
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), ...
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 21
CDF D0
Tevatron
Main injectorand recycler
RunI: 1992 – 1996data taking period at
RunII: 2001 – 2009major upgrades tocollider anddetectors
ps :
The Tevatron
ps :
pp
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 22
Tevatron performance
Running well - both peak luminosity and integrated luminosityCurrently ~15 pb-1 / week delivered
1 fb-1 delivered in beginning of June .
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 23
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 24
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 25
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:
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 26
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:
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 27
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 28
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