Transcript My decade working with Norman ~ 1973 – 2004 Mike Albrow (ex-RAL, now FNAL) ....

My decade working with Norman ~ 1973 – 2004
Mike Albrow (ex-RAL, now FNAL)
.... and some diffraction then and now.
From my occasional diary, Oct 2nd 1973: “Norman McCubbin joins the group, an
ex-Oxford man from Lancaster” [Group = CERN-Holland-Lancaster-Manchester,
on SAS = Small Angle Spectrometer on ISR ... discovered high mass diffraction.]
{Same day: “also Allen Sessoms appears again.” to Norman:
Allen became President of the Univ. of Delaware, now
President of the Univ. of D.C}
Hi Norman!
Oct 1974 (pre-J/ψ) Discussing making SAS+WAS a
2-arm spectrometer to search for charm (Kπ, Kp)
Nov 11th Revolution! J and ψ discovered!
Nov 16th “Finally got ~ 30 hours of SAS+WAS data”
Nov 29th Fri, “In at 5:30 a.m. with Norman to analyse 5 GeV SAS+WAS run.
Plotting effective masses of all combinations by 7:30. Hans (Sens) arrives at
8:30 and is mad that we do it without him. Interesting plots, no significant spikes,
but with 10x statistics as we hope ...”
Jan 2nd 1980: “John Thresher called with the great news that Norman will be offer
a permanent Ruth Lab post. We’ve been waiting a long time for that!”
p  p , n , K  ...
Single Diffractive Dissociation : at low energies
At ISR energies s = 22-63 GeV found scaling high xFeynman peak.
Diffractive excitation of high mass “states”
p ( xF )
t
What is this, carrying momentum?
“pomeron”
M
xF = xFeynman = pz/pbeam >~ 0.95
M2/s = 1-xF Mmax ~ √0.05 √s
Mmax ~ 0.22 √s
ln M X2  ln s  3
M e
2
X
2
(ln s 3)
eln s
s
 3 
e
20
M X2
 1  xF    0.05
s
184 citations
Diffractive masses scale with √s.
PS/AGS 1.6 GeV resonances,
at ISR to ~ 14 GeV,
at Tevatron to 400 GeV,
at LHC7 to 3000 GeV !
4 pages of these, + tables of course
Diffractive excitation range (“rule of thumb”)
M max ~ 0.22 s
(GeV)
s
M max
PS
7.4 --- 1.6 resonances
ISR
63 --- 14
Tevatron 1960 --- 400 Jets/W/Z
LHC7 10,000 --- 2200 top ??
ln M X2  ln s  3
M X2  e(ln s 3)
IP
p
p-IP total cross section
optical theorem :
p-IP elastic scattering
eln s
s
 3 
e
20
M X2
 1  xF    0.05
s
4
p
IP
IP
IP .. at high M
Central Diffractive Production or Double Pomeron Exchange
p p
IP
p
Double-triple-Regge
or Quintuple Regge:
Should happen &
rate calculable in Regge Th.
p
At ISR, Mmax ~ 3 GeV (+ 2 x 3 units y gaps)
or both x(p) > 0.95
X
Full range:
p
p
y ~ 3 units
y ~ 3 units
(better > 4) rapidity gaps = no hadrons
5
s
s
ln 2  2 ln
mp
mp
At LHC(10) Δy(p-p) = 18.5. 18.5-6=12.5 : Mmax(DPE) ~ 500 GeV ( > EWk)
SAS-WAS 1974-1976
Small Angle Spectrometer + Wide Angle Spectrometer combined
We were on SAS (low pT, diffraction), other Brit groups on WAS (high pT)
Idea to combine to look for narrow charm states.
Cool reception, then J/ψ discovered and we got together.
Common clock, event number and a hodoscope read to both tapes.
(Just did it. Cf now difficulties with TOTEM + CMS!)
Mass plots for 21 h1*h2 combinations,
with null distribution by mixing
events (N times!). Acceptance right.
Show χ for every bin, and plot χ2 cf
theoretical χ2 distribution.
Norman w/MGA did analysis.
Some excitement (which faded!)
Idea right, solid angles much too small
for open charm, Ds, but ~ no estimates then
Norman’s exemplary statistical analysis of 21 h1*h2 SAS-WAS mass plots
Less exciting, but correlations pbar(S)-p(W) not pbar(W)-p(S); also K+K-
1978+ : Axial Field Spectrometer (high pT)
Added forward p-tracking for DPE:
p + X + p. Maybe X = G = glueball?
ISR versatile: αα too!
Little (5cm x 5cm) drift chambers made at RAL (w/Janet and Tony Carter, Martin Evans +)
With elastic trigger t(drift) plot showed a dip, absent in pp running!
On shift with NAM: on-line discovery (bet??) from drift time distribution.
Also, α’s can collide and make ππ (same spectrum
as in pp) without breaking up:
coherent as expected for DPE
Happy after the annual round-CERN relay race
We came 3rd (?) ... had a ringer on 1st leg!
Group ski down Vallee Blanche to Chamonix: Norman, Martin Evans, DaveCockerill ...
Martin’s discovery !
ISR Experiment Selection
Phil Bryant interpretation
1976: NAM & MGA:
The Physics Possibilities of a Superconducting ISR upgrade, SCISR.
Paper to ISRC
Possibility of 120 GeV/beam with 5T superconducting magnets,
and up to 1033 cm-1s-1 luminosity.
Primary motivation: discover W and Z if in mass range < about 90 GeV
Two other simultaneous proposals to CERN:
Bjorn Wiik : Add e-ring in SPS tunnel for e + p collider
Carlo Rubbia: Convert SPS to pbar+p collider
Feb 1977
SCISR was designed by ISR staff, but it didn’t happen:
ISABELLE was being built (but would be later)
Mass reach more limited ... say M(Z) was 120 GeV?
SppS had more technical risks, but v. interesting
Carlo Rubbia was pushing SppS very hard!
But if built with 5T magnets
W, Z would be in reach
Axial Field Spectrometer AFS
Final config. :2π drift (jet) chamber, 2π Uranium – scintillator calorimeter – μ arm with PC’s and Cherenkovs
Earlier elements: L-Ar EM calo, transition radiation., Aerogel+HP+Atm Cherenkov arm for π/K/p in 45o
from Rutherford newsletter: ... Norman McCubbin (who really does have two heads !)
The Rutherford-built atmospheric gas Cherenkov array (η,ϕ cells)
at CERN, NAM+MGA, minus 2 with broken mirrors!
Earlier “Direct Evidence”paper submitted
to PL 25 Aug ‘82, same day as UA2 paper.
>> co-discovery, but σ(SppS) much larger, more
spectacular, stole our thunder!
High ET jets (co-)discovered in AFS. Set the ΣET threshold high enough and they nearly
all are picture postcard dijets, at rate ~ 1 Hz.
But had to share limelight (or partially eclipsed) by UA2 at SppS (1982)
Some of the AFS Collaboration, final configuration ~ 1981
The last store of the ISR, AFS Control Room night shift
Martin Evans, MGA, Norman hidden
The last ISR store: In the Main ISR control room about 5:00 am
In a bar in Oslo after 1980
Winter Scandinavian meeting
(“Spatind”)
NAM, MGA, DaveCockerill,
Cecilia Jarlskog
of “Jarlskog invariant” fame
I kept it, but we forgot to
check in 10 years.
Now it’s nearly 32 years!
At Collaboration dinners, made up many
bad limericks and other rhymes, e.g:
There once was a great ISR,
which collided both p and pbar
We all said to Schopper,
don’t be a beam stopper,
we might find the Z-triple-star!
It’s easy to count in octal, said Norman,draining his hock,
You stop it at seven, and start it at 10,
the rest comes at once in a block.
etc etc etc.
Put together with all who authored
papers.
Fast Forward about 25 years:
Diffraction has become a big deal at HERA, ep
Single diffractive excitation at Tevatron, p+pbar, to Jets, W, Z, charm etc.
Not much “double pomeron exchange” (a little in UA1 & UA6 (Schlein et al))
~ 2000 realization that Higgs boson might be produced exclusively p + H + p
at Tevatron even (?) MGA et al, arXiv: hep-ex/0511057 (2001)
but at LHC maybe. Higgs = vacuum, vacuum excitation.
If detectable this way, some unique possibilities:
Mass (σ ~ 2 GeV/event), J = 0, CP = ++, Width if Γ >~ 2 GeV, coupling Γ(Hgg).
Durham theory group Khoze, Martin, Ryskin, Stirling calculates several processes.
Brian Cox, Khoze et al develop “FP420”* project with Manchester meetings.
In CDF we start “Central Exclusive Production” studies
*Forward Protons 420m from Collision points ATLAS & CMS
From elastic scattering to exclusive γγ or H production
p
p
p
p
γγ or H
IP = {gg}
p
p
p
= gluon
p
About 25% of σTOT
About 10-11 – 10-13 of σTOT
These are related processes!
p  p  p    p
p p  pH  p
H
γ
γ
Color field;
shorted out by
another g exchange
Mike Albrow
Observation of Exclusive γγ Production in CDF
Fermilab Wine & Cheese, June 3rd 20ll
28
Exclusive Di-Jets
J
pbar
GAP
J
JET
JET
Observed in CDF, QCD tests
& related to p+H+p
“Almost” exclusive di-jet,
Two jets and nothing else
 (azimuth)
Transverse
Energy ET
 (~ polar angle)
M JJ
 0.8
M CEN
Interesting QCD: gap survival, Sudakov factor
Nearly all jets should be gg …. qq suppressed
by M(q)/M(JJ) (Jz=0 rule)
Gluon jet physics.
Mike Albrow
Diffraction in High Energy Collisions
CERN June09
29
CDF measured exclusive c  J/ψ + → μ+μ- 
μ+
J/ψ
c
μ-
c0
γ
& nothing else
in all CDF
-7.4 < |η| < + 7.4
Added to CDF: Beam Shower Counters BSC: 5.2 < |η| < 7.4
Scintillator paddles tightly wrapped around beam pipes.
Detect showers produced in beam pipes if p or p dissociate.
e.g. p  pππ
8 + 10 counters
If these are all empty, p and p did not dissociate
(or BSC inefficient, could estimate from data)
but went down beam pipe with small (<~ 1 GeV/c) transverse momentum.
- 50 m
CDF
central
BSC
Mike Albrow
Diffraction in High Energy Collisions
(size greatly exaggerated!)
CERN June09
30
p  p  p      p
402 events
Mike Albrow
Diffraction in High Energy Collisions
CERN June09
31
Photon “beams” radiated from electrons and protons
e,p
γ
LEP etc: e+e- (~ background free)
HERA: e p (more background, little done)
pp/ ppbar: Very high b/g … Seen in CDF
Tevatron as a  collider!
Phys.Rev.Lett 98,112001(2007)
μ μ 
ee
 
ee
μ μ 
M(μ μ  ) GeV/c2
Mike Albrow
Diffraction in High Energy Collisions
σ ~ 0.24 pb ~ 3 1012 σinel
CERN June09
32
Can be calculated in QCD, (Khoze et al)
but with uncertainties ~ x3
43 Candidates, πoπo b/g = 0, & < 15 events
Paper to be submitted to PRL this month
Mike Albrow
Diffraction in High Energy Collisions
CERN June09
33
Central Exclusive Production of Higgs ? Yes! If there is a Higgs!
Higgs has vacuum quantum numbers, vacuum has Higgs field.
So pp  p+H+p is possible in principle.
Allowed states:
I JPC = 0 0/2++
J >= 2 strongly suppressed at small |t|
t
Process is gg  H through t-loop as usual
with another g-exchange to cancel color
and even leave p’s in ground state.
If we measure p’s (4-vectors):
H
Mcen = √(p1 + p2 – p3 –p4)2
σ(MH) ~ 2 GeV per event
MGA+Rostovtsev: hep-ph/0009336
Even for H  WW  lν lν !
Mike Albrow
Diffraction in High Energy Collisions
CERN June09
34
Resolution
Rad hardness
Edgelessness
Speed, S/N
Availability
Enthusiasts!
FP420 = Forward Protons 420m : Stage I is 240m (220m in ATLAS)
Proposals in preparation
Best ever spectrometers!
~10μm origin (x,y), 1 μrad track
3D- silicon ~ 8 μm over 8m.
Fast timing P-U reduction factor ~ 25
Normal low-β, design for L = 1034
Moving beam pipe not Roman pots
Detector area
6mm x 24 mm
420m too far for L1 trigger
latency. 240m not, but > M.
6mm(y) x 24mm (x)
covers distribution
BPM
~ 8 layers
10um x-y
pixels
MCP
GASTOF
QUARTIC
p
3 mm
Mike Albrow
BPM
BEAM
~8m
Diffraction in High Energy Collisions
CERN June09
35
From observation of high mass (~ 14 GeV) diffraction at ISR
through p + G? + p at ISR (AFS) and SPS
NAM there in pioneering ISR days.
to p + H? + p at LHC, a long (and often slow) journey.
p+I+pp+Z+p?
The pomeron ???
QCD is still not a complete theory of strong interactions, only at high Q2.
At high Q2 = small distances p = {qqq, gluons, qqbar pairs)
Zoom out to lower Q2: gluon pairs of opposite colour (singlets) attract.
(also diquarks {gg} as colour triplets)
Cannot extract them (real glueballs) ... mass blows up, width high, decays inside.
But can exchange them, turn around L  R & R  L
Or one from each pair can transform  X and another cancels colour.
Also: Regge trajectory (continuous complex angular momentum transfer t-channel.)
Norman it was GREAT having you as a close collaborator and close friend.
Mike Albrow
Diffraction in High Energy Collisions
CERN June09
36