BSM searches at HERA John Martin University of Toronto / ZEUS for H1 and ZEUS.
Neutral Current Deep Inelastic Scattering in ZEUS The HERA collider NC Deep Inelastic Scattering at...
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Transcript of Neutral Current Deep Inelastic Scattering in ZEUS The HERA collider NC Deep Inelastic Scattering at...
Neutral Current Deep Inelastic Scattering in ZEUS
•The HERA collider
•NC Deep Inelastic Scattering at HERA
•The ZEUS detector
•Neutral current cross section measurement
•Some ZEUS structure functions results
•Conclusions and outlook
Ricardo Gonçalo
Imperial College
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
2
HERA and the ZEUS detector
1996-1997 running:
820 GeV protons
27.5 GeV positrons
Integrated luminosity 38.6 pb-1
1999-2000 running:
920 GeV protons
27.5 GeV positrons
Integrated luminosity 66.0 pb-1
Bunch crossings every 96ns
Centre of mass energy:
s = 318 GeV (98/00) 300 GeV (92/97)
1998-1999 running:
920 GeV protons
27.5 GeV electrons
Integrated luminosity 16.6 pb-1
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
3
Deep Inelastic Scattering at HERA
),(),(),(2
.
)( 2223
224
2
2
2
QxFyQxxFYQxFYxQdQdx
ped NCL
NCNCNCBorn
Leading order cross section:
2)1(1 yY
Kinematic variables:
Q² four momentum transfer
x Bjorken scaling variable
y inelasticity
Only 2 independent variables:
Q2 = x.y.s
(s is the c.m. energy)
with:
e (k)
p (P)X (P’)
e (k’)
,Z0 (Q2=-q2)
FL negligible at high Q2
Our aim: to determine the proton structure through the measurement of the proton structure functions
xF3 parity violating
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
4
Depleted uranium compensating calorimeter:
99.7% solid angle coverage
Timing resolution < 1ns (E>4.5 GeV)
Energy resolution (test beam)
HERA and the ZEUS detector
%18%35 .. EE
Eem
Ehad
Central Tracking Detector (CTD)
Angular acceptance 15o<<164o
r- resolution 230 m
Magnetic field of 1.43 T achieved with thin superconducting solenoid
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
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Neutral current cross section measurementOffline selection cuts:
Find the electron
•Vertex within: -50 < Zvtx < 50 cm
•Scattered electron cuts:
•Electron energy: Ee > 10 GeV
•Electron isolation
•Within CTD acceptance:
Electron track momentum > 5 GeV
Track and cluster matching
•Forward electrons: PT,e > 30 GeV
•Total transverse momentum should be small: PT,tot < 4ET,tot
•Background cut: 38 < < 65 GeV,
with: i
izi
ii pEE )()cos(
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
6
Neutral current cross section measurement
Low Q2:
exchange
similar cross sections for e-p and e+p
High Q2:
and Z0 exchange plus interference term
cross sections greater for
e-p (d/dQ2 xF3) than for
e+p (d/dQ2 -xF3)
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
7
F2 sensitive to valence and
sea quarks
All flavors contribute to F2
Why measure F2?
Gluon density can be extracted from d F2 /dlnQ2
))()((2 xqxqAxF qNC
),(),(),(2
.
)( 2223
224
2
2
2
QxFyQxxFYQxFYxQdQdx
ped NCL
NCNCNCBorn
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
8
How to measure F2em ?
)),(),((
)),(),((222
2
222
QxqQxqexF
QxqQxqAxF
qem
qNC
•Start by measuring Neutral Current reduced cross section
•Cross section has contributions from and Z0 exchange and their interference (at high Q2, reduced cross section falls for e+p data and rises for e-p data)
•Apply corrections to get F2 from R
)1)(1)(,(~32
22 radFxF
ewF
em
LQxF
Reduced cross section:
2
21
4
2 12~dxdQ
d
YxQ
NC
peNC
pe
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
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xF3 sensitive to valence
quarks only
Sea quarks created in pairs
=> (quark-antiquark)=0
))()((3 xqxqBxxF qNC
32
32
~
~
xFY
YF
xFY
YF
NC
pe
NC
pe
And How?
Why measure xF3?
),(),(),(2
.
)( 2223
224
2
2
2
QxFyQxxFYQxFYxQdQdx
ped NCL
NCNCNCBorn
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
10
),(),(),(2
.
)( 2223
224
2
2
2
QxFyQxxFYQxFYxQdQdx
ped NCL
NCNCNCBorn
First xF3 measurement from ZEUS
•First direct look at valence quarks at high Q2
•Yellow band is the calculated FL multiplied by 10
•Measurement used e+p data from 1996-97 (c.m. energy of 300 GeV) and e-p data from 1998-99 (c.m. energy of 318 GeV) => corrections necessary
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
11
Conclusions and outlook Present Neutral Current results from ZEUS are systematics limited up to Q2 800 GeV but there is room for improvement for higher Q2 using the currently available data.
Neutral current cross sections will be measured at high Q2 using data from 1998/99 (e-p) and 1999/00 (e+p) with s = 318 GeV.
Measurement of F2 and xF3 can be made with available data.
Outlook• Lepton beam polarization after the 2000/2001 shutdown and high luminosity expected (1 fb-1 until 2006).
•Improved tracking (new vertex detector and forward tracking)
•This will allow:
Setting limits for the mass of W-R, W+
L, using Charged Current measurements,
The direct measurement of weak couplings to quarks u and d.
Possibility of lower systematic errors for lepton tagging in fwd region.
Charm tagging.
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
12
My neutral current cross section measurement
•Only d/dQ2 so far
•Statistical errors only
•Analysis of 1998/99 e-p data and 1999/00 e+p data going in parallel
•Still a lot of work to be done...
R.Goncalo IoP HEPP Conference, Southampton, 3-5 April 2001
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Luminosity upgrade and polarisation
))(1(2
1.
)(
))(1(2
1.
)(
2
22
22
2
2
2
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22
2
2
bsdycuMQ
MGP
dQdx
ped
bsdycuMQ
MGP
dQdx
ped
W
WCC
W
WCC
PPNC
xFYFYPxFYFYxQdQdx
ped32
03
024
2
2
2 2
.
)(
Neutral current: 4 different x-sections will allow measurement of couplings au, vu, ad, and vd (HERA sensitive to u & d; LEP sensitive to c & b)
Charged Current: cross section linear on polarisation.
Limits or measurement of mass of W-R, W+
L