forward protons from the sps to the tevatron andrew brandt, university of texas at arlington physics...
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Forward Protons from the SPS to the Tevatron
Andrew Brandt, University of Texas at Arlington
Physics SeminarMay 17, 2006DESY
Thanks for slides: Koji Terashi, Dino Goulianos, Mike Albrow,Rainer Wallny Michele Arneodo, and othersDOE, NSF, UTA, Texas ARP for support
Elastic “dip” Structure fromPhys. Rev. Lett. 54, 2180 (1985).
Examples of Soft Diffraction
Modeled by Regge Theory Analysis of poles in the complex angular momentum plane give rise to trajectories
that describe particle exchange P.D.B. Collins, An Introduction to Regge Theory and High Energy Physics, Cambridge Univ. Press,
Cambridge 1977
Non-perturbative QCD
Elastic Single Diffraction
Priorto 1985
all diffractionwassoft
diffraction
Ingelman-Schlein Propose Hard Diffraction possibility in 1985 Factorization allows us to look at the diffractive reaction as a
two step process. Hadron A emits a Pomeron (pomeron flux) then partons in the Pomeron interact with hadron B in a standard QCD gg hard scattering. (basis of POMPYT, POMWIG MC’s)
The Pomeron to leading order is proposed to have a minimal structure of two gluons in order to have quantum numbers of the vacuum
AA*
BJ1
J2
P
X
G. Ingelman and P. Schlein, Phys. Lett. B 152, 256 (1985)
My first trip toDESY was April 1987
to meet Gunnar, begin work onPYTHIA 4.8X, precursor to POMPYT
UA8 Dijet Production in Diffraction
Hard Diffraction exists! Pomeron has a “super-hard” component.
A. Brandt et al., P.L. B 297(1992) 417 (196 citations!)
x(2-jet)
Diffractive Deep Inelastic Scattering
e
p
HERA
Proton energy = 920 GeVElectron energy = 27.5 GeVs=318 GeV
Q2 = virtuality of photon = = (4-momentum exchanged at e vertex)2
t = (4-momentum exchanged at p vertex)2
typically: |t|<1 GeV2
W = invariant mass of photon-proton system
xIP = fraction of proton’s momentum
taken by Pomeron = in Fermilab jargon = Bjorken’s variable for the Pomeron = fraction of Pomeron’s momentum carried by struck quark
LRGIP
Q2
t
W X
e’
p’
*e
p
920 GeV27.5 GeV
s 320 GeV
ZEUS
pe
X
e
p’p
e
e’
IP dPDF
1) Diffractive PDFs: probability to find a parton of given x in the proton under condition that proton stays intact – sensitive to low-x partons in proton, complementary to standard PDFs (ingredient for all inclusive diffractive processes at Tevatron and LHC)
2) Generalised Parton Distributions (GPD) quantify correlations between parton momenta in the proton; t-dependence sensitive to parton distribution in transverse plane• When x’=x, GPDs are proportional to the square of the usual PDFs (ingredient for all exclusive diffractive processes)
VM, exclusive dijets…Higgs
x’ x
p p
GPD
Two fundamental physics quantities can be accessed in diffractive DIS: dPDFs and GPDs
Rather than IP exchange: probe diffractive PDFs of proton
Applying dPDFs to FNAL/LHC Requires Care
CDF data
Extrapolationfrom HERA
F2D
GPDs and diffractive PDFs measured at HERA cannot be used blindly in pp (or ) interactions.
In addition to the hard diffractive scattering, there are soft interactions among spectator partons. They fill the rapidity gap and reduce the rate of diffractive events.
Multi-Pomeron-exchange effects (a.k.a. “renormalization”, “screening”,“shadowing”, “damping”, “absorption”)
pp
CDF Run 1-0 (1988-89)
Elastic, single diffractive, and total cross sections @ 546 and 1800 GeV
Roman Pot Spectrometers
Roman Pot Detectors Scintillation trigger counters Wire chamber Double-sided silicon strip detector
Results Total cross section tot ~ s Elastic cross section d/dt ~ exp[2’ lns] shrinking forward peak Single diffraction Breakdown of Regge factorization
Additional DetectorsTrackers up to || = 7
DESY seminar Oct. 1997 on DØ Hard
Diffraction leads to collaboration with young
Brian Cox
E
DØ Run I GapsDØ Run I Gaps
•Pioneered central gaps between jets: Color-Singlet fractions at s = 630 & 1800 GeV; Color-Singlet Dependence on , ET, s (parton-x). PRL 72, 2332(1994); PRL 76, 734 (1996);
PLB 440, 189 (1998)
•Observed forward gaps in jet events at s = 630 & 1800 GeV. Rates much smaller than expected from naïve Ingelman-Schlein model. Require a different normalization and significant soft component to describe data. Large fraction of proton momentum frequently involved in collision.PLB 531, 52 (2002)
•Observed W and Z boson events with gaps: measured fractions, properties first observation of diffractive Z. PLB 574, 169 (2003)
• Observed jet events with forward/backward gaps at s = 630 and 1800 GeV
Diffractive W Boson
Predicts15-20%
of W’s arediffractively
produced
CDF {PRL 78 2698 (1997)} measured RW = 1.15 ± 0.55%where RW = Ratio of diffractive/non-diffractive W
a significance of 3.8DIFFWsignal
DØ Observation of Diffractive W/Z
Observed clear Diffractively produced W and Z boson signals
Events have typical W/Z characteristics Background from fake W/Z gives negligible change in gap
fractions
Sample Diffractive Probability Background All Fluctuates to Data Central W (1.08 + 0.19 - 0.17)% 7.7Forward W (0.64 + 0.18 - 0.16)% 5.3All W (0.89 + 0.19 – 0.17)% 7.5All Z (1.44 + 0.61 - 0.52)% 4.4
ncalnL0
Diffractive W and Z Boson Signals
Central electron W Forward electron W
All Z
ncalnL0
ncal
nL0
•Phys. Lett. B 574, 169 (2003)
Soft Diffraction and Elastic Scattering: Inclusive Single Diffraction
Elastic scattering (t dependence)
Inclusive double pomeron
Search for glueballs/exotics
Hard Diffraction: Diffractive jet
Diffractive b,c ,t
Diffractive W/Z
Diffractive photon
Other hard diffractive topics
Double Pomeron + jets
Other Hard Double Pomeron topics
Exclusive Production of Dijets
DØ Run II Diffractive TopicsDØ Run II Diffractive Topics
Topics in RED were studied
with gaps only in Run I
Event Selection: Z→μ+μ- Events Two Good (PT > 15GeV) Oppositely Charged TracksBoth Identified as muonsBKGD Rejection: Min one muon Isolated in Tracker and Calorimeter (suppress Heavy Flavour BKGD), Cosmic Ray Rejection.
Diffractive Z Production
Demand Activity North and South Forward Gap (North or South)
Candidate Diffractive Z Events
DØ PrelimDØ Prelim
Forward Proton Detector
z [m]
Dipole Spectrometer Quadrupole Spectrometers
|t| ~ 0.0 GeV2 |t| > 0.8 GeV2
> 0.04> 0.0
18 Pots integrated into DØ readout and inserted every store since Jan 2004 Simultaneously tag/reconstruct protons and antiprotons
QuadrupoleMagnets
Separator
DipoleMagnets
Separator
PDOWN Spectrometer
DipoleSpectrometer
AUP Spectrometer
ADOWN Spectrometer
PUP Spectrometer
IP
Nine independent spectrometers each consisting of two detectors
Reconstruct particle tracks from detector (scintillating fiber) hits
Scattered antiprotons Scattered Protons
QuadrupoleMagnets
78 nsec109 nsec 78 nsec 109 nsec200 nsec
Elastics/Halo BackgroundA1U A2U
P2DP1D
P
Pbar
LM
VCElastic
78 nsec
109nsec
78 nsec
109nsec
A1U A2U
P2DP1D
LM
VCProton Halo
-78 nsec
-109nsec
In-time Bit set if pulse detected (above threshold) in in-time windowHalo Timing Bit set if pulse detected in early time window
double halo could be backgroundto elastics
p
Large * Store
Physics Goals:1. Low-t
elastic scattering
2. Low-t single diffractive and double pomeronscattering
Two day run of accelerator at injection tune *=1.6 m1x1 bunchLum=0.5E30
Estimatedt range accessible with injection tune
pot position
integrated luminosity
Hit Maps from 1x1 Store
Typical StoreLarge store (4647)(no low squeeze)
20 Million events; first results this summer/fall
potstypically
9-15from beam
CDF Exclusive Dijets in Run I
Exclusive dijet limit:
jj (excl.) < 3.7 nb (95% CL)
Expected shape of
signal events
Theoretical expectation (KMR) ~1 nb
PRL 85 (2000) 4215
Dijet Mass fraction X
jjjj M
MR
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