The X(3872) at the Tevatron
description
Transcript of 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
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
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
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 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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 6
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
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
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
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¡ 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
´
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 12
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
24th June 2005 U.Kerzel, University of Karlsruhe Beauty2005 13
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
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)
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
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 20
BACKUP
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
p s :
The Tevatron
p s :
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 ¡ 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:
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¡ ¯xupx0 : turn-on valuexlow, xup : fit range