Transcript Diffraction and Central Exclusive Production in High Energy pp

Diffraction and Central Exclusive Production
in High Energy pp/ppbar Collisions
Mike Albrow (Fermilab)
LPC Topic of Week Lectures, April 2011
Lecture 2 : Central Exclusive Production:
p + p  p’ + X + p’
where + = rapidity gap Δy > 5 (to be definite), no hadrons
and X = “simple” system fully measured.
 
 
 
  ~~


Quantum
Numbers
restricted
 or IP
exchange
e e ,   ,  , l l ,W W
J / , (2S ),  ' s, Z
f 0 (600) /  , f 0 ( X ),  c / b , JJ , HIGGS
  IP
IP  IP
p’ = proton (best case),
or low mass state e.g. pππ when it doesn’t matter.
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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Why do I think CEP is interesting, even important?
These are the cleanest, simplest inelastic pp collisions.
Most collisions  lots of particles, cannot cope:
go to single particle inclusive e.g. pp → W + anything, t + anything, X + anything…
or 2-”particle” inclusive e.g. pp → WW + anything, seeking {H →WW} + …
In contrast, consider WW + nothing (p’s go down pipe, small pT)
H + nothing
No other tracks
on eμ vertex
μ-
Could be HWW.
Know M(WW) if
measure p’s
b-tagged jet
No tracks
on vertex
with large pT(rel)
or
e+
Missing ET
Ez too if measure p’s
Could be Hbb.
Know M(bb) if
measure p’s
b-tagged jet
Quantum numbers constrained: J=0,2, CP=++, M, Γ, Γgg
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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From elastic scattering to exclusive Higgs boson production
p
p
p
p
= gluon
H
IP = {gg}
p
p
p
p
About 1013 of σ(total)
But these are related processes!
About 25% of σ(total)
Space picture:
2 gluons “turn around”
H
Anyway these gluons are
wee and virtual and their
direction is frame-dependent
Mike Albrow
Diffraction and Central Exclusive Production
Color field;
shorted out by
another g exchange
CMS ToW April 20ll
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Central Exclusive Particle Production at High Energy Hadron Colliders
M.G.Albrow, T.D.Coughlin and J.R.Forshaw
Progress in Particle and Nuclear Physics 65 (20l0) l49-84
arXiv:l006.289[hep-ph]
How did we get here (Regge, triple…)
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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In QCD, serious calculations (don’t ask me):
H
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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ISR – Tevatron -- LHC
63 GeV
1960 GeV
p


G?
ISR
p
p
~ 7-14,000 GeV (CM)
p
W

p
H?
W-
p
p
p
(   , K  K  , pp)
Tevatron
ee , μ μ  , J/ψ/ ψ(2S), JJ, 
~~
LHC  , Z , h, H ,W W , l l , X ?


We are in R&D phase of high precision spectrometers HPS
to add to CMS to measure both protons (Monday’s lecture)
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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Remember, no absolute distinction experimentally.
Theoretically IP and IR terms, but interference.
Single diffractive
excitation (ISR)
CDF and D0 have observed
W, Z and high-ET jet pairs in
SDE at Tevatron.
Also heavy Q in jets.
W,Z : q/qbar play a role
In constituent models of IP g dominate
(cf p) but q evolve in (of course).
xFeynman 
M
pL
p beam
0.95
x > 0.95
p
M  0.05 s  0.22 s
Mike Albrow
M up to about 1.6 GeV at AGS/PS
14 GeV at ISR
440 GeV at Tevatron
3100 GeV at LHC
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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Central Diffractive Excitation
Regge theory: SDE implies
Δy > 3
Δy > 3
x > 0.95
… both protons coherently scattered
“Vacuum Excitation”
x > 0.95
M  0.05 s
M up to about 3 GeV at ISR –
s 63 GeV
100 GeV at Tevatron – 1960 GeV
350 GeV at LHC – 7,000 GeV
H,WW
If measure protons:
Missing mass to pp = MCEN
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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Low Mass Central Exclusive Production
ISR
p
Search for “Glueballs”
s = 63 GeV {gg} as distinct from {qq}

p

+ nothing else

Axial Field Spectrometer (R807)
Added very forward drift chambers
Central drift chamber half
U-Cal
U-Cal
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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Central Exclusive    Production (AFS)
No ρ
s  63 GeV, Δy  3
f 0 (980)
IG J PC =0+ even ++
G(1710)??
Also
Structures not well understood
beyond f(980). Not studied at higher
  , K K , pp, 4




s
M (   )
αα elastic scattering
on-line dip! Diffraction !
and αα→ α + ππ + α






In CDF/ CMS: KS0KS0 , D0 D0 , DSDS , c,b ,...ΛΛ, ΣΣ, ΩΩ,...!
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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Rates p + p  p + X + p, double pomeron exchange
with 2 gaps Δy > 5 (say) are very high…σ many μb.
Require no PU, e-<n>, good for low <n> stores/bunches
Need good trigger: forward gaps (or p’s)
In l0 hours of low-lumi CDF running collected 4 million events,
2 gaps Δy > 4 and central hadrons.
About l0,000 are exclusive h+h- also K0sK0s, hyperons etc
and M(X) up to ~ 80 GeV
Results not yet approved.
Comparison with LHC would be interesting and not very difficult
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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 
Interesting central states TeV, LHC (apart from multihadrons)
  IP
 
* p p  pe e  p
 
p

p

p


 p
*
p  p  p      p
p  p  p  W W   p
~ ~
p  p  p  l l   p
Quark pairs?
Go to e+e* Now measured in CDF
“Only” CMS can do, in some cases
needing forward p measurement
Mike Albrow
p
* p
p
p
p
p
p
p
p   p
p  J / , ' p
p   ,  ' ,  ' ' p
pZ  p
IP  IP
* p  p  p    p
* p  p  p  c  p
p  p  p  b  p
* p  p / p  p  JJ  p / p
p p pH  p
Diffraction and Central Exclusive Production
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CDF Exclusive charmonium: Phys.Rev.Lett 102,242001(2009)
Also in e+e- and e+p
Also in e+p
Only in hadron-hadron
Not essential to detect protons; can require all forward
detectors to be at noise levels, for ~3 < |η| < ~8.
Quasi-elastic protons inferred.
Implies no pile-up interactions allowed.
Or: Require pT(X) ~ 0 (<~ 1GeV for IP), Δφ ~ π, nass(tracks) = 0
Not sure if p → pππ (e.g.), but maybe don’t care. pT(X) helps
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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CDF
p  p  p      p
J/ψ
γγ → μ+μ-
Mike Albrow
Diffraction and Central Exclusive Production
ψ(2S)
CMS ToW April 20ll
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1
Exclusive Z photoproduction: SM process but small cross section:
Cisek, Schafer, Szczurek arXiv:0906. 1739
u+d+s+c+b
u+d+s
y(Z)
Test of BSM loops, with EW & strong couplings.
Must be done with P-U:
Nass(tracks) = 0, pT(Z) <~ 2 GeV/c
Both p-momenta known, seeing either confirms.
Not including BR
= 7% to ee,μμ
Value of high mass QED μ+μForward proton momenta are precisely known:
can calibrate momentum scale and resolution of
forward spectrometers for p + p  p + H + p at LHC .
Was advertised as LHC luminosity calibrator, but Van der Meer now 4%
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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J/ψ and Y photoproduction at LHC (14)
A. Szczurek: arXiv:0811.2488
J /
 ' (2S )
Simulation pre-data, 100/pb
 (1S )
~ 30 pb
 (2S )
Dashed: Born approximation;
solid: includes absorption corrections
BR (Y → μ+μ-) = 2.5%
30pb x 100/pb x Δy = 5 x 0.025 = 375 events x acceptance
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
16
High mass exclusive lepton pairs in CDF
CDF preliminary
One Z candidate, but very forward BSC
had hits: p dissociation.
Expect ~ 0.001 in SM, but
“one swallow does not make a Spring”
Keep an eye on CMS Z, nass = 0, small pT
High mass 2-photon collisions at LHC
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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Nicolas Schul &
40/pb: σ(pp→p + μμ + p) = 3.33/0.56/0. 14/0. 16 pb
Jonathan Hollar,DIS CMS data pT(μ) > 4 GeV, |η(μ)| < 2.1, M(μμ) >11.5GeV
Ratio to LPAIR = 0.82 +- 0.22
Muons are back-to-back
75 GeV
pT of dimuon is small
Mike Albrow
DiMuon mass distribution
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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1 Exclusive γγ Production is good test of theory
IP IP → γ γ
gg → γγ via q-loops is the easy part (pQCD)
or H
Need unintegrated gluon pdf g(x1).g(x2) … 4th power
No g-radiation (need at least 2) to make hadrons (Sudakov)
g-Loop integral … proton form factor …
No additional parton-parton interactions to make hadrons
(“gap survival probability” from diffractive cross sections)
Durham Group (KMR) claim factor 3 uncertainty in this calculation.
Others make very different estimates (for IP + IP → H), but leave γγ alone.
   & qq   much smaller
CDF published 3 candidates with ET(γ) > 5 GeV
cf KMR: 0.8 (~x 3)
Note :  MEAS  2 1012  INEL !
New CDF result coming soon, & search in CMS
(Wenbo Li, Yifei Guo & exclusive group)
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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KMR predictions:
0.6 pb for ET > 5 GeV, |η| < 2
Probably cannot
be done with P-U
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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Exclusive Di-Jets in CDF
JET
p
GAP
JET
JET
(p not seen)
JET
 (azimuth)
Transverse
Energy ET
 (~ polar angle)
IP + IP → J + J
>~ 99% pure gluon jets (unique)
What about 4J (double gg scattering)?
And high ΣET with no jets?
Mike Albrow
Diffraction and Central Exclusive Production
“Almost” exclusive di-jet,
Two jets and nothing else
M JJ
 0.8
M CEN
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Exclusive Dijets (2 central jets + “nothing”) : CDF
R JJ =
M JJ
 1.0
MX
MX = total central mass
MJJ  40 -150 GeV
Cross section agrees with ExHuME MC / 3
Durham (inside uncertainty)
DPEMC is IP + IP as “hadron-like”, excluded.
ExHuME: MC with
exclusive di-jets.
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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What is exclusive H cross section?
 [ pp  p  H  p](MH ), s = 14 TeV
H
u-loop : γγ c-loop : χ 0c
b-loop : χ 0b
t-loop: H
Related, so tests
σ ~ 3 fb (M(H)=125 GeV)
“factor ~ 3 uncertainty”
l00 fb-1  ~ 300 Ae events
(Ae = acceptance, efficiency)
Exclusive
X disfavored by CDF
X
X
Durham Gp: Khoze, Martin, Ryskin, Stirling
hep-ph/0505240 ++
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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A more recent calculation with
PDG g(x) dependence
Mike Albrow
Diffraction and Central Exclusive Production
HPS acceptance in M(H)
with 240m + 420m arms
(Monday)
CMS ToW April 20ll
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Determining Quantum Numbers of Central State (H?)
Is it J = 0, CP = ++?
In gg  X only CP = ++ is allowed.
(a CP –ve A (MSSM) is highly suppressed)
gg  vector (J = 1) forbidden, Landau-Yang theorem.
J = 0, 2 can be distinguished by angular distributions
partial wave analysis. Can even see states hidden in overall M distribution!
Of course this needs many events.
W+
“g”

“g”

IP


IP

W-
Moments H(LM) of the cos( ) distributions  M(J=0), M(J=2).
e.g. ISR/R807 glueball search in
Mike Albrow
pp  p      p NPB264 (1986) 154
Diffraction and Central Exclusive Production
CMS ToW April 20ll
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Summary
Any states with vacuum quantum numbers and strong or
electromagnetic couplings can be produced at LHC by
Central Exclusive Production
e e , μ μ , J/ψ/ ψ' (2S), χ c , Υ1,2(cand. ), JJ,  , WW, H
 


Cross section pp  p+SMH+p known to factor ~ 3 (~ 1-10 fb)
If protons well measured, can get mass of central state to
~ 2 GeV per event, Quantum numbers (J, CP) and couplings to gg.
In any case it is a glue-rich special strong interaction state.
Lecture #3 Monday 2 pm:
SUSY and other BSM physics, ++ ?
How we can do it by adding High Precision Spectrometers
How YOU (your students) can get into some cool detector
development : l0 ps timing counters, l μrad tracking, etc
Mike Albrow
Diffraction and Central Exclusive Production
CMS ToW April 20ll
26